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1
Ridruejo, Carlos Mateo. "Isla del Rey : a marine biology center". Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/69353.
Testo completoAbstract (sommario):
Thesis (M. Arch.)--Massachusetts Institute of Technology, Dept. of Architecture, 1996.Includes bibliographical references (p. 78-79).
In our changing times many of our necessities have geared us to search for new spaces that can accommodate them. This thesis attempts to devise the use and expansion of a distinguished 18th Century building dominating a small island, Isla del Rey; in the deep sea port, Port de Mao, of Menorca. The task allows for the exploration of a specific type of intervention, which transforms both the isolated object of the historical building and the landscape of the site into a mutually dependent organization within the island a nd beyond. This design process considers the morphology of this extension (rather than addition) as an open system, so eloquently described in H. Wolfflin's Principle of Art History ...
Carlos Mateo Ridruejo.
M.Arch.
2
Klanjšček, Tin. "Dynamic energy budgets and bioaccumulation : a model for marine mammals and marine mammal populations". Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/34623.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 2006."June 2006."
Includes bibliographical references.
Energy intake of individuals affects growth of organisms and, therefore, populations. Persistent lipophilic toxicants acquired with the energy can bioaccumulate and harm individuals. Marine mammals are particularly vulnerable because of their large energy requirements, and transfer of energy and toxicants from mothers to their young during gestation and lactation. Dynamic energy budget (DEB) models for energy assimilation and utilization, coupled with pharmacokinetic models that calculate distribution of toxicants in individuals, can help investigate the vulnerability. In this dissertation I develop the first individual DEB model tailored specifically to marine mammals and couple it to a pharmacokinetic model for lipophilic toxicants. I adapt the individual model to the right whale and use it to analyze consequences of energy availability on individual growth, reproduction, bioaccumulation, and transfer of toxicants between generations. From the coupled model, I create an individual-based model (IBM) of a marine mammal population. I use it to investigate how interactions of food availability, exposure to toxicants, and maternal transfer of toxicants affect populations. I also present a method to create matrix population models from a general DEB model to alleviate some of the drawbacks of the IBM approach.
by Tin Klanjšček.
Ph.D.
3
Shoji, Akiko. "Incubation strategy in marine birds". Thesis, University of Ottawa (Canada), 2009. http://hdl.handle.net/10393/28466.
Testo completoAbstract (sommario):
The incubation shift length of the Ancient Murrelet ( Synthliboramphus antiquus), an exceptionally long and varied for an auk. I studied colonies of this species at East Limestone Island (1993-1995, 2002-2003: data collected by Laskeek Bay Conservation Society) and Reef Island (2007-2008), Haida Gwaii, British Columbia. Incubation shift length was correlated between pair members and my results show that maintaining incubation schedule was an essential component of reproductive success. Incubation shift length varied in response to prevailing local weather and sea conditions (e.g. wind speed, wave height), perhaps as a consequence of reduced foraging efficiency. Incubation shift length was longer in years when sea surface temperature in April was high. In years with longer shift, birds had lower reproductive success and chicks departed the nest with a lower body mass. My results explained if we assume that multi-day incubation shifts in Ancient Murrelets are the adaptively preferred strategy, through reduction in predation risk, but that actual shift lengths are modified by immediate weather and foraging constraints.
4
Jones, Angela M. "Aspects of the biology of some marine ascaridoid nematodes". Thesis, University of Stirling, 1994. http://hdl.handle.net/1893/1498.
Testo completoAbstract (sommario):
Larval Anisakis simplex, Pseudoterranova decipiens, Contracaecum osculatum and larvae and adults of Hysterothylacium aduncum were recovered from specimens of cod, haddock, blue whiting and bull rout; however, only A.simplex were retrieved from long rough dab. The epidemiology of infection by these four nematode species was examined both in whole fish, and in individual host tissues and organs. Frequency distributions of nematodes were found to be generally overdispersed in fish. Preliminary investigations revealed no strong evidence to suggest that competi tive interactions occurred between ascaridoid nematodes wi thin fish. Stomach lesions in gadoids were associated with single (partially penetrated) and mul tiple (throughout stomach wall) worm infections of larval A.simplex; such lesions were discrete and raised in appearance. Lesions associated with 1-3 larval P.decipiens in an open cavity within the stomach of angler fish were diffuse and not significantly raised. Histological examination of each form of ulcer revealed general similarities in pathology, with infil tration of inflamatory cells being the initial response to the nematode\s. Changes in the cephalic morphology of A.simplex, P.decip1ens, C.osculatum and H.aduncu were examined at different life cycle stages under scanning electron microscopy. Due to their small size, newly hatched third stage larvae of P .decip1ens were cultured in a bacterial mat prior to fixation for S.E.M., and the external ultrastructure of these larvae is described. The most prominent external feature at this stage is the cephalic boring tooth. Aspects of the internal ultrastructure of A. simplex, P.decipiens, C.osculatum and H.aduncu were examined using transmission electron microscopy. Newly hatched third stage larvae of P.decipiens show little differentiation of internal organs. The ultrastructure of sensory amphids in H.aduncum and A. simplex is cons i stent wi th that of a chemoreceptor, that of the single papilla in P.decipiens a mechanoreceptor. The ultrastructure of the digestive tract, excretory gland and body wall of marine ascaridoids were also examined.
5
Reyes, Nikolle Susanne. "Marine bacterial isolates utilize unique mercury resistance mechanisms". Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/25416.
Testo completo
6
Foor, Brandon. "The biology and macroparasites of the sixgill sawshark Pliotrema warreni". Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/25303.
Testo completoAbstract (sommario):
Thirty-two specimens of the sixgill sawshark, Pliotrema warreni, were trawled near Bird Island in Algoa Bay on the Eastern coast of South Africa in April and May 2015. The specimens were examined for anatomical proportions, reproductive characteristics, diet, and parasite assemblages. Several external measurements were collected including mass, total length, standard length, girth, rostrum length, interoccular to pre-caudal length, first dorsal origin to second dorsal origin, first dorsal origin to pre-caudal origin, and mouth width. The equation for mass (g) vs. total length (mm) was ln(Mass)=0.2997*ln(TL)+2.0383 for females and ln(Mass)=0.3321*ln(TL)+1.941 for males. 1st Dorsal to 2nd dorsal origin length (DD) to total length equations for females and males were DD=0.2451*TL-26.677 and DD=0.2598*TL-34.535, respectively. Mean lengths and masses were 11.5% greater and 50.3% heavier in females than males, respectively. Females were on average, 994 mm (759 mm – 1283 mm) in length while males were 891.8 mm (763 mm – 1015 mm). Average mass for females was 1702.5 g (602.5 g – 3478.5 g) whereas males it was 1132.6 g (687 g – 1593.5 g). Based on these data both sexes display isometric growth. Males were determined to reach sexually maturity around 850 mm which is similar to that reported by Ebert et al., (2013) around 830 mm. Females were found to reach sexual maturity at 1000 mm which is 100 mm smaller than what is reported by Ebert et al., (2013). Stomach mass increased with total mass and total length regardless of sex (female R² = 0.507; male R² = 0.213 for length and female R² = 0.6123; male R² = 0996 for mass). Females consumed larger prey items in terms of mass and length as well as a higher quantity of prey than males presumably because they are the larger sex and have an increased need for nourishment to provide for pregnancy. Prey items were redeye round herring, Etrumeus whiteheadi (64.96% of the diet), a benthic shrimp species not identified (7.69%), and Cape horse mackerel, Trachurus trachurus capensis (0.85%). Despite strict adherence to the guidelines for age determination for elasmobranchs provided in the literature, the conventional method used which involved extensive cleaning of the vertebral centra with an array of chemicals, setting and cutting in an epoxy resin, and staining for microscopy, did not yield readable results which could be used to determine the ages of these sharks. The highest abundance of parasites were found in the stomachs. Three specimens of a cymothoid isopod was found externally. Two specimens of Ascaris sp. nematode were found in the visceral cavity. The remaining 18 parasites consisted of three Neoechinorhynchidae sp. of acanthocephalan and 15 Proleptus obtusus nematodes all of which were found inside the stomachs. Given the results of the parasite survey, males and females do not have the same parasites as females have four different species while males only have one. More collections from other areas and times of year are necessary to obtain a better description of the species.
7
Pujade, Laura. "Development of a biomarker panel for identifying stressed marine mammals". Scholarly Commons, 2019. https://scholarlycommons.pacific.edu/uop_etds/3587.
Testo completoAbstract (sommario):
Increasing anthropogenic disturbance in marine ecosystems such as fishing, oil-drilling, and noise pollution can have detrimental effects on the reproduction and survival of apex predators such as marine mammals. Stress activates the hypothalamic-pituitary-adrenal (HPA) axis, resulting in increased circulating glucocorticoid (GCs) hormones, which alter expression of target genes encoding metabolic enzymes and other mediators of stress. Prolonged HPA axis stimulation may increase catabolism of nutrient stores and suppress immune and reproductive functions, impacting the fitness of marine mammals. GCs measurements are used to identify wild animals experiencing stress. However, these measurements may not be sensitive enough to distinguish between an acutely and a chronically stressed individuals. In this study, we present a new approach of assessing stress states in marine mammals, by measuring expression levels of gene markers in blubber. We previously characterized transcriptional and metabolic profiles and identified genes and metabolites that were differentially expressed in response to single and repeated adrenocorticotropic hormone (ACTH) administration in juvenile northern elephant seals. We then measured expression of these target genes in blubber tissue collected from juvenile northern elephant seals in their natural baseline stress states (n=30), and correlated their gene expression values with cortisol, aldosterone, total triiodothyronine (tT3), reverse triiodothyronine (rT3), and triglyceride levels, and body condition index. We found that blubber genes that were upregulated in response to repeated ACTH administration in the previous study were positively correlated with cortisol and inversely correlated with tT3 in the baseline sample set. These markers included genes that encode a lipid particle protein (PLIN1), an adipogenesis promoting transcription factor (DKK1), an oxidative stress enzyme (GPX3), and a lipid metabolism enzyme (AZGP1). Blubber genes differentially expressed in response to acute ACTH administration in the previous study included an adipokine (ADIPOQ) and a ketogenesis enzyme (HMGCS2), which were upregulated, and an adipogenesis inhibitor, TGFBI, which was downregulated. ADIPOQ and HMGCS2 were positively correlated with cortisol and negatively correlated with tT3 levels, while TGFBI was positively correlated with tT3 and body condition index, and negatively correlated with rT3 in the baseline sample set. These results provide insights into the molecular mediators of the physiological stress response and provide markers that can be used as a part of a potential diagnostic panel for differentiating between acute and prolonged stress states in marine mammals.
8
Stringer, Geraldine A. "The edge observed : island landscape for a marine biology facility". Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/78973.
Testo completoAbstract (sommario):
Thesis (M. Arch.)--Massachusetts Institute of Technology, Dept. of Architecture, 1987.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ROTCH.
Includes bibliographical references (p. 70).
This thesis explores the concept of edges through observation and design. The intent of the observation/design is to understand and to illustrate possibilities for design that will enrich the experience of the built environment. For a building to start having reciprocal relationships with inside and outside territories, its structure and skin configurations must not be only one sided containments, but begin to engage in two-sided dialogues between interior and exterior spaces. The possibility of overlap between individual parts, between the relationship of inside and outside and between the object and the ground it occupies is observed through Japanese vernacular buildings and their gardens and through the buildings and canals of Venice. Plans, sections and photo images are used as a way to become conscious of the characteristics that help make these places a total assemblage, with pieces in a coherent relationship to one another and to their site. The design of a Marine Biology Facility on an island affords an opportunity to test out and explore the observation studies. The island exists in a landscape context that has clearly defined edge conditions. A harmony is sought that interprets the natural landscape and transforms it in such a way that there is a reciprocity and interaction with the built. Orientation, views and landscape considerations all provide generators for an architectural response that engages the built world and the natural world in a tensioned relationship that defines the edge zones.
by Geraldine A. Stringer.
M.Arch.
9
Grange, Laura Joanne. "Reproductive success in Antarctic marine invertebrates". Thesis, University of Southampton, 2005. https://eprints.soton.ac.uk/41355/.
Testo completoAbstract (sommario):
The nearshore Antarctic marine environment is unique, characterised by low but constant temperatures that contrast with an intense peak in productivity. As a result of this stenothermal environment, energy input has a profound ecological effect. These conditions have developed over several millions of years and have resulted in an animal physiology that is highly stenothermal and sometimes closely coupled with the seasonal food supply, e.g. reproductive periodicity and food storage. Therefore, Antarctic marine animals are likely to be amongst the most vulnerable species worldwide to environmental modifications and can be regarded as highly sensitive barometers for change. Reproductive success is a vital characteristic in species survival and evaluation of change in reproductive condition with time key to identifying vulnerable taxa. Characterising reproductive success with time is a major requirement in predicting species response to change and the early stages of species loss. Some invertebrates are highly abundant in shallow water sites around the Antarctic and form conspicuous members of the Antarctic benthos. Three common echinoderms and one nemertean were sampled from sites adjacent to the British Antarctic Survey’s Rothera Research Station, Adelaide Island, on the West Antarctic Peninsula between 1997-2001. Reproductive patterns were determined by histological analyses of gonad tissue. This study provided further evidence for inter-annual variation in Antarctic gametogenic development, which appeared to be driven to some extent by trophic position and reliance on the seasonal phytoplankton bloom. The largest variation in reproductive condition was demonstrated for the detritivorous brittle star, Ophionotus victoriae. The seasonal tempos of this echinoderm have been attributed in part, to the seasonal sedimentation events common in the high Antarctic. The reproductive patterns in the scavenging starfish, Odontaster validus and the predatory nemertean, Parborlasia corrugatus showed less inter-annual variation. The de-coupling of these invertebrates from the intensely seasonal phytoplankton bloom appeared to partially account for the reproductive trends observed. The lack of inter-annual variation in the reproduction of the filter-feeding sea-cucumber, Heterocucumis steineni, was somewhat counterintuitive, although problems with sample processing probably accounted for the majority of this anomaly. Echinoderms were also collected during the Antarctic summer field seasons in 2003 and 2004. A series of fertilisation success studies were undertaken comparing the adaptations in an Antarctic and an equivalent temperate starfish to achieve optimal numbers of fertilised eggs, and elemental analyses were used to estimate the nutritional and energetic condition of the bodily and reproductive tissues in two Antarctic echinoderms. Fertilisation studies indicated that Antarctic invertebrates require 1-2 orders of magnitude more sperm to ensure optimal fertilisation success. These sperm tended to be long-lived and capable of fertilising eggs 24+ hours after release. The study suggested that synchronous spawning, aggregations and specific pre-spawning behaviour are employed to help counter the deleterious effects of sperm limitation. The Antarctic eggs and sperm were also highly sensitive to even small modifications in temperature and salinity, affecting the number of eggs fertilised. Such stenothermy is of particular relevance if the 1-2ºC rise in global temperature, predicted over the next century, is realised. Biochemical composition of body components of two species of Antarctic echinoderm indicated a significant difference in the composition between the male and female gonad, particularly in the Antarctic brittle star Ophionotus victoriae. The ovaries contained a much larger proportion of lipid compared to the testes, and demonstrated a distinct seasonality in composition. Higher levels of lipid were observed in the ovary during the austral winter coincident with a period of reproductive investment and maturing oocytes in the gonad. O. victoriae exhibited lower amounts of lipid in the late austral spring suggesting the removal of mature oocytes from the ovary through spawning. The seasonality in composition and the high levels of lipid and protein measured in the ophiuroid gut tissue, suggested the gut might play a role in providing material and energy for metabolic function and possibly gametogenesis; higher lipid levels were apparent during the period of seasonal phytodetrital flux. The role of the pyloric ceaca in asteroids as a nutrient storage organ was also evident in the high levels of both protein and lipid observed in this bodily component in the star fish, Odontaster validus.
10
Fullarton, J. Gregor. "Lipid biomarkers in marine symbiotic systems". Thesis, University of Stirling, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.384931.
Testo completo
11
Matich, Philip. "Environmental and Individual Factors Shaping the Habitat Use and Trophic Interactions of Juvenile Bull Sharks (Carcharhinus leucas) in a Subtropical Estuary". FIU Digital Commons, 2014. http://digitalcommons.fiu.edu/etd/1236.
Testo completoAbstract (sommario):
Top predators serve important roles within their respective ecosystem through top-down and bottom-up effects, yet understanding how these roles vary among individuals within predator populations is still in its early stages. Such individuality can have important implications for the functional roles predators play within their respective ecosystems. Therefore, elucidating the factors that drive persistent individual differences within populations is crucial for understanding how individuals, and in turn populations, will respond to environmental changes and anthropogenic stressors, and the implications of these responses for particular ecological functions. In this dissertation I investigated the movements, residency patterns, and trophic interactions of a juvenile bull shark (Carcharhinus leucas) population in a coastal estuary that serves as a nursery. I found that bull sharks undergo ontogenetic niche shifts in their diets and habitat use, with a gradual shift from using freshwater and estuarine resources to marine resources as sharks grew. This behavioral shift appeared to be driven by age-based differences in tradeoffs between safety from predators and availability of prey. Nested within population-level trends in behavior, there was considerable, and consistent, individual variation in both movements and trophic interactions suggesting individual specialization and divergent behavioral tactics within the population. Different behavioral types likely play different roles in food web connectivity and ecosystem dynamics, thus understanding the drivers and importance of phenotypic variability among species will be crucial for improving management strategies and predicting the responses of species and ecosystems to impending changes in environmental conditions and human impacts.
12
Bossart, Gregory D. "Immunocytes of the Atlantic bottlenose dolphin (Tursiops truncatus) and West Indian manatee (Trichechus manatus latirostris) : morphologic characterizations and correlations between healthy and disease states under free-ranging and captive conditions". FIU Digital Commons, 1995. http://digitalcommons.fiu.edu/etd/1772.
Testo completoAbstract (sommario):
Interest in the health of marine mammals has increased due, in part, to the attention given to human impact on the marine environment. Recent mass strandings of the Atlantic bottlenose dolphin (Tursiops truncatus) and rising mortalities of the endangered Florida manatee (Trichechus manatus latirostris) have raised questions on the extent to which pollution, infectious disease, "stress," and captivity influence the immune system of these animals. This study has provided the first in-depth characterization of immunocytes in the peripheral blood of dolphins (n=180) and manatees (n=56). Immunocyte morphology and baseline values were determined in clinically normal animals under free-ranging, stranded and captive living conditions as well as by age and sex. Additionally, immuocyte population dynamics were characterized in sick animals. This was accomplished with traditional cytochemical techniques and new lymphocyte phenotyping methodology which was validated in this study. Traditional cytochemical techniques demonstrated that blood immunocyte morphology and cell numbers are similar to terrestrial mammals with some notable exceptions. The manatee heterophilic granulocyte is a morphologically unique cell and probably functions similarly to the typical mammalian neutrophil. Eosinophils were rarely found in manatees but were uncommonly high in healthy and sick dolphins. Basophils were not identified. Manatees had higher total lymphocyte numbers compared to dolphins and most terrestrial mammals. Lymphocyte subsets identified in healthy animals included Th, Tes, B and NK cells. Dolphin and manatee T and B cell values were higher than those reported in man and most terrestrial mammals. The manatee has extraordinarily high absolute numbers of circulating Th cells which suggests an enhanced immunological response capability. With few exceptions, immunocyte types and absolute numbers were not significantly different between free-ranging, stranded and captive categories or between sex and age categories. The evaluation of immunocyte dynamics in various disease states demonstrated a wide variation in cellular responses which provided new insights into innate, humoral and cell-mediated immunity in these species. Additionally, this study demonstrated that lymphocyte phenotyping has diagnostic significance and could be developed into a potential indicator of immunocompetence in both free-ranging and captive dolphin and manatee populations.
13
Dunphy-Daly, Meagan Mná. "Temporal variation in dwarf sperm whale (Kogia sima) habitat use and group size off Great Abaco Island, the Bahamas". FIU Digital Commons, 2008. http://digitalcommons.fiu.edu/etd/3101.
Testo completoAbstract (sommario):
Dwarf sperm whales, Kogia sima, are among the most commonly stranded yet least known pelagic cetaceans. I assessed seasonal and spatial variation in dwarf sperm whale group size and abundance off Great Abaco Island, the Bahamas. After correcting for survey effort and variation in sighting efficiency among sea states, I found that dwarf sperm whale group size and habitat use varied seasonally. In summer, dwarf sperm whale groups were small (median = 2.5, range = 1-8) and were found only in the two deep habitats within the study area (slope 400-900 m, deep 900-1600 in). In winter, group sizes increased (median = 4, range = 1-12) and sightings were almost six times higher in the slope habitat, where vertical relief is highest, than other habitats. My results suggest that studies of pelagic cetaceans and conservation plans must explicitly account for seasonal variation in group size and habitat use.
14
Cubillos-Ruiz, Andrés Fernando, Jessica Weidemier Thompson, Jamie William Becker, Sallie W. Chisholm, Yanxiang Shi, der Donk Wilfred A. Van e Audrey Olshefsky. "Ecology and evolution of lanthipeptides in marine picocyanobacteria". Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/101829.
Testo completoAbstract (sommario):
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, 2015.Cataloged from PDF version of thesis. Each chapter with its own abstract. Each appendix with its own summary.
Includes bibliographical references.
Microbial secondary metabolites are among the most structurally and functionally complex molecules in nature. Lanthipeptides are ribosomally derived peptide secondary metabolites that undergo extensive post-translational modification. Most lanthipeptides are bactericidal but they are also known to act as signaling molecules or morphogenetic peptides, nevertheless the function of many lanthipeptides remains unknown. Prochlorosins are a diverse group of lanthipeptides produced by strains of the ubiquitous marine picocyanobacteria Prochlorococcus and Synechococcus. Unlike other lanthipeptide-producing bacteria, picocyanobacteria utilize an unprecedented mechanism of catalytic promiscuity for the production multiple structurally diverse lanthipeptides using a single biosynthetic enzyme. Also unprecedented is the production of lanthipeptides by single celled, planktonic gram-negative bacteria in a dilute nutrient-limited habitat, which suggests that they may have an unconventional biological function. The overarching goal of this thesis is to further our understanding of the ecology and evolution of the prochlorosins, and provide insights into their biological role in the marine environment. Here, we demonstrate that the prochlorosin genes are widespread in the ocean and that globally distributed populations of marine picocyanobacteria have the genetic potential of producing thousands of different lanthipeptide structures. The diversity of prochlorosin structures provides an interesting model to study the evolutionary forces that drive the creation of new lanthipeptide structures. We present evidence that there is a unique evolutionary interplay between the components of prochlorosin biosynthesis pathway; while the peptide substrates independently expand and diversify within the genome, the catalytically promiscuous biosynthetic enzyme evolves under a strong purifying selection that maintains its substrate tolerant state. This relationship indicates that the lanthipeptide production trait in marine picocyanobacteria might find its evolutionary advantage in the plasticity of the production of multiple cyclic peptides with diverse ring topologies. The remarkable diversity of prochlorosins poses many questions regarding their biological role in the marine environment. In laboratory experiments, we explore of some of the potential bioactivity of the prochlorosins, namely their potential as signaling molecules, antimicrobials and nutrient sources. The results from this exploration open new perspectives for the role of the lanthipeptides in the natural environment - more specifically the oligotrophic ocean.
by Andrés Fernando Cubillos-Ruiz.
Chapter 1. Chapter 2. Chapter 3. Chapter 4. Chapter 5. Appendix A. Appendix B. Introduction -- Evolutionary radiation of lanthipeptides in natural populations of marine picocyanobacteria / Andres Cubillos-Ruiz ; Jessica W. Berta-Thompson ; Jamie Becker ; Sallie W. Chisholm -- Exploring the biological role of prochlorosins / Andres Cubillos-Ruiz ; Jamie Becker ; Yanxiang Shi ; Wilfred van der Donk ; Sallie W. Chisholm -- Amino acid toxicity and tolerance in prochlorococcus / Andres Cubillos-Ruiz ; Audrey Olshefsky ; Sallie W. Chisholm -- Conclusion and future directions -- Proposed molecular mechanism for the expansion and diversification of prochlorosins - Hawaii Ocean experiment : prochlorosin amendment.
Ph. D.
15
Thompson, Luke Richard. "Auxiliary metabolic genes in viruses infecting marine cyanobacteria". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/57562.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biology, 2010.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student submitted PDF version of thesis.
Includes bibliographical references (p. 281-293).
Marine viruses shape the diversity and biogeochemical role of their microbial hosts. Cyanophages that infect the cyanobacteria Prochlorococcus and Synechococcus often carry metabolic genes not found in other bacteriophages. The proteins encoded by these `auxiliary metabolic genes' (AMGs) are thought to increase phage fitness by altering host metabolism during infection. Dominant among the suite of AMGs carried by cyanophage are genes involved in photosynthesis and the pentose phosphate pathway (PPP). The overarching goal of this work is to understand the selective pressures driving the acquisition and maintenance of these particular AMGs by cyanophage. Transaldolase is thought to be a key step in the host PPP. The transaldolase encoded by phage shares less than 30% amino acid identity with that of the hosts and differs in tertiary and quaternary structure despite a conserved catalytic core. The phage transaldolase was functional in vitro, and a comparison of its kinetic parameters with those of the host enzyme revealed its turnover number to be one-third that of the host. We suggest that the selection pressures underlying maintenance of the phage protein could have their origins not in kinetic properties but in genome efficiency and regulation of protein levels in the host. Cyanophage genomes also contain genes for PPP enzymes glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase and an inhibitor of the Calvin cycle (CP12). These genes are also found in cyanophage genome fragments from the Global Ocean Sampling metagenome. Measuring their expression during infection in model phage{host pairs, we observed that phage-encoded PPP enzymes and CP12 were co-expressed with photosystem II genes while the NADPH/NADP ratio increased two-fold, consistent with increased activity of the NADPH-producing light reactions and PPP. Phage ribonucleotide reductase, which produces nucleotides using reducing equivalents from NADPH, was co-expressed with this set of genes. We propose, therefore, that phage carry these AMGs to boost the host PPP and light reactions to produce NADPH for phage genomic DNA production. No Calvin cycle AMGs have been found, supporting the hypothesis that the selection pressures molding phage genomes involve fitness advantages conferred through mobilization of host energy stores and not through carbon fixation.
by Luke Richard Thompson.
Ph.D.
16
Kruger, Lisa Maria. "Feeding biology of intertidal sea anemones in the south-western Cape". Master's thesis, University of Cape Town, 1995. http://hdl.handle.net/11427/19423.
Testo completoAbstract (sommario):
The species composition, abundance and distribution of intertidal sea anemone assemblages were investigated by means of line-transects at two sites on the Cape Peninsula - Wooley's Pool in False Bay and Blouberg in Table Bay. A single species, Bunodactis reynaudi dominated at Blouberg (average density 901 running m⁻¹). Juveniles < 35mm basal diameter) were particularly abundant in mussel beds. Seven species exhibiting clear vertical zonation were found at Wooley's Pool (average density 658 m⁻¹). High-shore species were Actinia equina and Anthothoe stimpsoni. A. stimpsoni was the smallest (9.1mm mean basal diameter) and most abundant (maximum density 1450. m⁻² ) anemone at Wooley's Pool. Three species were found at mid-shore: of these Anthopleura michaelseni and Bunodosoma capensis had the same vertical distribution and extended to higher tidal levels than Bunodactis reynaudi. Two species of Pseudactinia favoured the sheltered low-shore. P. flagellifera was confined to the subtidal zone and was the largest (60.2mm mean basal diameter) and least abundant of all the species (10. m⁻² ), while P. varia extended into the low intertidal. Although different anemone species exhibit distinct zonation on the shore, they show considerable overlap. Different morphological and behavioural characteristics facilitating this zonation are discussed. Bibliography: pages 86-98.
17
Miller, Robert J. "Ecological factors shaping subtidal rock wall communities in the Gulf of Maine". View this thesis online, 2005. http://libraries.maine.edu/gateway/oroauth.asp?file=orono/etheses/37803141.pdf.
Testo completoAbstract (sommario):
Thesis (Ph.D.)--University of Massachusetts Boston, 2005.Title from PDF title page. Available through UMI ProQuest Digital Dissertations. Includes bibliographical references (p. 82-102). Also issued in print.
18
Roel, Beatriz Adelaida. "Stock assessment of the Chokka Squid : Loligo vulgaris reynaudii". Doctoral thesis, University of Cape Town, 1998. http://hdl.handle.net/11427/19576.
Testo completoAbstract (sommario):
Summary in English.Bibliography: p. [199]-210.
The primary aim of the study was to assess the status and productivity of chokka squid. Main hypotheses examined are the following: that the sharp decline in the trawl fishery catch per unit effort (CPUE) data in the early 1980s, reflects a real decline in the trawlers catch rate; that the decline in the trawl CPUE index is caused by the jig fishery removing the biomass that otherwise would be available to the trawl fishery; that the jig fishery "disturbs" the spawning process and causes a decline in subsequent recruitment. Catch and effort data from the two fisheries, as well as biomass estimates from spring and autumn research surveys, were used. The two main fisheries and the catch and effort data are described. General Linear Modelling (GLM) was performed on the CPUE data from the trawl fishery in order to obtain annual indices of abundance. Further, results from a GLM analysis on two years of monthly jig CPUE data are presented. The dynamics of the stock biomass on the spawning grounds were modelled in order to assess the effects of current levels of effort and the existing closed season on the resource. The dynamics of the stock and the fishery were captured by a simple biomass-based model. Two dynamic methods were used to estimate model parameters: 1. a process-error estimator; 2. an observation-error estimator. All model parameter were estimated by maximum likelihood, and the corresponding confidence intervals were estimated by bootstrapping.
19
Harington, Amy. "Trace metal effects on phytoplankton in subpolar seas with special emphasis on coccolithophores". Doctoral thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/27354.
Testo completoAbstract (sommario):
Coccolithophores are a biogeochemically important phytoplankton group, fulfilling an important role in the global carbon cycle through primary production and the formation and export of calcium carbonate. Despite this biogeochemical importance, relatively little is known about their ecophysiology, for example their response to nutrient availability in terms of both macronutrient (nitrate, phosphate) and micronutrient (trace metal) or how this impacts on their competition with other phytoplankton groups (e.g. diatoms, Synechococcus). Hence, this study investigated the response of coccolithophores to trace metal (iron, zinc and cobalt) additions in the high latitude North Atlantic (Iceland and Irminger basins) and the Southern Ocean (Great Calcite Belt, Scotia Sea). The response of coccolithophores to environmental conditions was investigated by examining distribution patterns in situ and in targeted bioassays where natural communities were incubated with elevated levels of trace metal concentration. The wide range of initial conditions for these bioassays (e.g. temperature, macro- and micro-nutrient availability and phytoplankton community composition), provided valuable insights into coccolithophore responses to trace metal addition across a range of different biogeographic regions. These responses were investigated in terms of coccolithophore cell abundances, species composition, calcite production and growth rates, and were contrasted with responses of the total phytoplankton community (chlorophyll α) and abundances of diatoms and other phytoplankton groups (e.g. Synechococcus). The major finding of this thesis is that iron addition positively enhances coccolithophore growth rates and calcite production in both the Northern and Southern subpolar oceans. Another significant finding was that zinc addition also positively enhanced growth rates of coccolithophores (and diatoms) in a number of bioassays across the Great Calcite Belt (Southern Ocean). Thus, the trace metals iron and zinc are important micronutrients to consider in regulating coccolithophore growth and calcite production. As climate change potentially altering the flux of such trace metals to the ocean it is therefore important to further investigate the role of these micronutrients in regulating coccolithophore communities and their biogeochemical impact.
20
Nibam, Abi Henry. "Reproductive biology and diet of the St. Joseph (Callorhinchus capensis) in South Africa". Master's thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/10791.
Testo completoAbstract (sommario):
Includes abstract.Includes bibliographical references (p. 72-84).
The reproductive biology of the commercially exploited fish St. Joseph or Cape Elephant fish Callorhinchus capensis, is described based on 173 fishes caught by gillnets in October 2010 from Velddrif along the west coast of South Africa. Segregation by sex was reflected by a difference in sex ratio from 1:1 for females to males fishes collected from the fishery (?2 = 16.23, d.f. = 1, p = 5.6 x 10-5).
21
Chien, Diana M. "Fine-scale ecological dynamics of closely related marine microbes". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/105636.
Testo completoAbstract (sommario):
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Biology, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references.
Microbial dynamics in the environment are major drivers of global biogeochemical cycles; hence there is great interest in characterizing their rates and causes. While dynamics are affected by processes across many spatiotemporal scales, and even closely related microbes are known to vary in their ecological distributions, most work has characterized dynamics at bulk scales and with low genetic resolution. Thus, little is known about the effects of finer structure. In this thesis, I show that characterizing the dynamics of environmental microbes with finer spatiotemporal and genetic resolution reveals otherwise concealed dynamics. I use the Vibrionaceae, an ecologically diverse family of marine heterotrophs, as a model system. First, I review past studies on environmental associations of the Vibrionaceae, showing that few abiotic parameters have consistent predictive value, and that observed patterns vary based on taxonomic resolution. Biotic associations, however, may represent more specific predictors for fine-scale Vibrionaceae taxa, reflecting their diverse lifestyles. I then characterize Vibrionaceae dynamics within a high-resolution environmental time-series, with three months of daily sampling across four habitat partitions, population-level resolution, and large datasets of potential biological correlates. These data reveal diverse and spatially structured population dynamics. Individual populations varied from consistently abundant generalists to rare populations that occasionally displayed brief but intense peaks of abundance. Free-living and particle-attached habitat partitions were distinct in terms of diversity, turnover, and biotic interactors. These results emphasize the ecological differentiation of the Vibrionaceae populations, and the extent to which spatial partitions can function as distinct ecological regimes. Finally, I use sequence data from the Vibrionaceae populations to investigate a methodological question relating to phylogenetic resolution: how well does the standard taxonomic marker gene, 16S rRNA, resolve populations known to have distinct ecological distributions and dynamics? The analysis shows that even full-length 16S rRNA sequences collapse the majority of populations into only 2-3 taxa, concealing the breadth of ecological behavior within the family. Altogether, this thesis demonstrates that high resolution sampling techniques reveal a wealth of otherwise unobserved ecological diversity even within one family of closely related microbes, and suggests that fine-scale turnover and structure may have an unappreciated impact on microbial dynamics.
by Diana M. Chien.
Ph. D.
22
Willey, Joanne M. "Characterization of swimming motility in a marine unicellular cyanobacterium". Thesis, Massachusetts Institute of Technology, 1988. http://hdl.handle.net/1721.1/14611.
Testo completo
23
Wänstrand, Ingrid. "Pigment and Thiamine Dynamics in Marine Phytoplankton and Copepods". Doctoral thesis, Uppsala universitet, Evolutionsbiologi, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-4560.
Testo completoAbstract (sommario):
Based on a field study and several mesocosm experiments, I evaluated the use of pigments as chemotaxonomical biomarkers for phytoplankton community composition in the Baltic Sea and I examined effects of inorganic nutrients on the dynamics of carotenoids and thiamine (vitamin B1) at the phytoplankton–copepod level in marine pelagic food webs. My results show that HPLC pigment analysis combined with CHEMTAX data processing was an accurate alternative to microscopic analysis of Baltic Sea phytoplankton. Experimental supply of N, P and Si affected copepod growth and biochemical status via changes in biomass and composition of their phytoplankton diet. Net population growth rates were generally higher when phytoflagellates dominated (low Si:N ratio) and lower when diatoms dominated (high Si:N ratio). Copepod body concentrations of astaxanthin decreased with fertilization. Correlations with reduced under-water irradiance were consistent with the photo-protective function of this antioxidant. Thiamine concentrations in phytoplankton also decreased with fertilization. In copepods, low Si:N ratios resulted in higher thiamine concentrations than high Si:N ratios. Thiamine concentration and degree of phosphorylation were useful as indicators of thiamine shortage both in phytoplankton and copepods. The concentrations of thiamine and astaxanthin in the copepod communities were positively correlated. As copepods constitute a major link between pelagic primary producers and higher trophic levels, fertilization effects may be responsible for astaxanthin and thiamine deficiencies in salmon suffering from the M74 syndrome, which appeared concurrently with large-scale eutrophication in the Baltic Sea. As both thiamine and astaxanthin are deficient in M74-affected salmon, there is a need for physiological and molecular investigations of possible interactions between the two compounds in living cells.
24
Kim, Jun-Woo. "Copper requirements of marine diatoms of the Thalassiosirales". Thesis, McGill University, 2012. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=106254.
Testo completoAbstract (sommario):
Copper (Cu), one of about seven essential metals used by photoautotrophs, is a limiting resource in some parts of the ocean because of its low and variable concentration. This thesis examined copper dependence of growth, Cu uptake and quotas of diatoms of the Thalassiosirales isolated from different ocean habitats. A major finding of the research was that Cu quotas of diatoms of the Thalassiosirales are dependent on the type of photosynthetic electron transport gene they contain viz. plastocyanin; encoding a Cu-dependent protein versus cytochrome c6; encoding a Fe-dependent protein. Increased Cu quotas of plastocyanin-containing species reduced the growth rates they attained in Cu-deplete seawater. Cytochrome c6-containing species required lower Cu concentrations to achieve maximum rates of growth and contained less cellular Cu than plastocyanin-containing species. Steady state uptake rate of Cu by T. oceanica (a plastocyanin-containing species) was a linear function of growth irradiance at low and high Cu concentration, suggesting that Cu uptake was light dependent. In Cu-deplete seawater, high light abolished the Cu-limited phenotype of this species by enabling it to acquire sufficient Cu for maximum growth.Le cuivre (Cu) est un des environs sept métaux essentiels utilisé par les photoautotrophes. De plus, cet élément est une ressource limitante dans certains endroits de l'océan car sa concentration est faible et variable. Cette thèse a pour but d'examiner la croissance, l'absorption et les quotas des diatomées Thalassiosirales en fonction du cuivre, isolées de différents habitats océaniques. Une des principales conclusions de cette recherche est que les quotas de Cu des diatomées Thalassiosirales sont dépendent du type de gêne présent pour le transport des électrons durant la photosynthèse viz. plastocyanine. Le gêne de la plastocyanine encode une protéine qui est dépendante sur le cuivre tandis que celle du cytochrome c6 encode une protéine dépendante sur le fer. L'augmentation des quotas de Cu des espèces qui contiennent la plastocyanine réduit le taux de croissance qu'elles atteignaient dans de l'eau de mer appauvrie en Cu. Les espèces qui contiennent le cytochrome c6 exigeaient des concentrations de Cu plus faibles pour atteindre des taux de croissance maximaux et contenaient moins de Cu dans leurs cellules que les espèces ayant la plastocyanine. Le taux d'absorption de Cu à l'état stationnaire par T. oceanica (une espèce contenant la plastocyanine) répondait de façon linéaire à l'irradiance lors de concentrations faibles et élevées de Cu. Ces résultats suggèrent que l'absorption du Cu est dépendent sur la lumière. Dans des eaux appauvries en Cu, des taux élevés de lumière ont supprimé le phénotype limité en Cu en permettant aux organismes d'acquérir une quantité suffisante de Cu pour la croissance maximale.
25
Porter, Donovan Stuart. "Isolation and characterisation of antibiotic-producing marine actinomycetes". Master's thesis, University of Cape Town, 2003. http://hdl.handle.net/11427/8591.
Testo completoAbstract (sommario):
Bibliography: leaves 94-102.Resistance to antibiotics poses a serious threat to healthcare and new drugs are needed. This is especially true for tuberculosis (TB), which is at epidemic levels in South Africa. Multidrug-resistance in Mycobacterium tuberculosis makes TB more difficult and expensive to treat and increases mortality rates. The surfaces of 12 seaweed species found in South African coastal waters were screened for the presence of antibiotic-producing actinomycetes. Of the 67 strains isolated, 26 exhibited antibacterial activity against Mycobacterium aurum A+ and for Enterococcus faecium VanA. These actinomycete strains were physiologically characterised. Three strains showing very strong antibacterial activity were further characterised by the use of chemical taxonomy, DNA sequencing and scanning electron microscopy and were shown to belong to the genus Streptomyces. A strain not showing activity was shown by the same methods to belong to the genus Micromonospora. Partial purification of the active compounds was carried out on the three strains exhibiting strong antibacterial activity. All were shown to produce moderately to highly polar compounds.
26
Johnston, Olivia Ruth. "Distribution and biology of the marine invasive bivalve Theora lubrica (Semelidae)". Thesis, University of Canterbury. School of Biological Sciences, 2005. http://hdl.handle.net/10092/2453.
Testo completoAbstract (sommario):
This study examined aspects of the biology and distribution of the marine invasive bivalve Theora lubrica in the Lyttelton Basin from two distinct sampling areas. Samples were collected monthly, over a 13 month period (January 2004 and January 2005), with particular emphasis on seasonal sedimentary characteristics and contamination. The sample sites consisted of five Port sites and five Harbour sites. They were sampled using a 20 litre anchor dredge. In winter and summer, core samples from each of the sample sites were collected, and the top 1.5cm of sediment was used to obtain sediment characteristics. Sediment characteristics indicated a depositional setting, with an average grain size (diameter) of 8-10 μm, which did not vary seasonally. Analysis indicated that the sediments naturally flocculated, to the 100μm size range and were platykurtic. Organic content (OC) in the sediment in Lyttelton Port showed significant seasonal variation. OC was highest during the winter period corresponding to an increase of T. lubrica abundance. There were noticeable seasonal changes in the abundance of T. lubrica, with high winter and low summer population densities. The period for recruitment coincided with high T. lubrica densities, and the greater frequency of juveniles with shell length below 4.33 mm. Histological sections showed that spawning occurred during the summer, confirmed by the presence of high percentages of ovigerous females and mature males. Community analyses distinguished four distinct seasonal and spatial benthic populations. The populations exhibited greater total species richness during the summer (compared to the winter). T. lubrica, maintained high abundance during periods of low total species richness. Furthermore, there was evidence of a predator prey relationship between the crab Macrophthalmus hirtipes and T. lubrica. Trace metals and hydrocarbons showed seasonal and spatial variation between the Port and Harbour sediments. Only the arsenic, nickel and copper in the Port location were at concentrations likely to be toxic to the biota. No trace metals exceeded threshold limits in the Harbour. Levels of arsenic and nickel were highest in the summer and copper was at its highest concentration in the winter. However, there was little evidence to suggest that the sediment contamination affects T. lubrica or the rest of the benthic community directly. Thus, the significantly lower species richness at the Port location may be due to other influences (i.e. sediment disturbance from shipping). In conclusion T lubrica is regarded as an opportunistic marine invasive species which can inhabit areas not occupied by other marine macro-biota. T lubrica did not appear to negatively impact the other benthic species at the Lyttelton Port or Harbour sites. It provided a plentiful food source and increased species diversity in sediments that are frequently disturbed (by shipping and wave action). Furthermore, T lubrica may help reestablish native species to the Port area by filtering and processing contaminated sediments (bioturbation), potentially pioneering the way for greater species diversity in Lyttelton Port and Harbour.
27
Carloni, Riccardo. "Electron paramagnetic resonance applications: from drug discovery to marine biology studies". Doctoral thesis, Urbino, 2021. http://hdl.handle.net/11576/2682203.
Testo completo
28
Ilikchyan, Irina N. "Phosphonates Utilization in Marine and Freshwater Picocyanobacteria". Bowling Green State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1229969527.
Testo completo
29
Cunniff, Kevin M. "Phenology, sexual reproduction, and the factors affecting sexual reproduction of the marine angiosperm, Thalassia testudinum, in the Florida Keys National Marine Sanctuary (FKNMS)". FIU Digital Commons, 2005. http://digitalcommons.fiu.edu/etd/2691.
Testo completoAbstract (sommario):
This study investigated phenology and the factors affecting sexual reproduction of Thalassia testudinum in the FKNMS. Flowering was assessed at 30 permanent monitoring sites via direct observation and age reconstruction techniques of seagrass cores in 2002. The mean flowering frequency was 1.49%, was spatially variable, and exhibited sex-specific timing in floral anthesis. Historical flowering reconstruction demonstrated that flowering frequencies are not temporally variable. Floral sex ratios were female-biased, spatially variable, and likely temporally variable. Relative nitrogen availability was most important in influencing flowering and was negatively correlated with flowering. Higher flowering occurred with low N availability and lower flowering occurred with high N availability. A 15 month in situ nutrient addition experiment conducted at 10 sites in the upper Florida Keys, where N + P were added at ecologically significant loading rates, significantly reduced flowering in the N + P treatment plots at all 10 sites.
30
Chon, Suet-ling, e 莊雪玲. "Remote sensing applications in studying marine biological processes". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2004. http://hub.hku.hk/bib/B31255826.
Testo completo
31
Gray, Victoria A. "Physiological consequences of temperature stress on the marine snail, Lottia gigantea". California State University, Long Beach, 2013.
Cerca il testo completo
32
Salter, Lesley. "Effects of Barotrauma on Four Species of Pacific Rockfishes (Sebastes spp.)". DigitalCommons@CalPoly, 2019. https://digitalcommons.calpoly.edu/theses/2007.
Testo completoAbstract (sommario):
Physoclistic fish, such as Pacific rockfishes (genus Sebastes), have closed swim bladders that help them regulate their buoyancy. When anglers catch these fish and reel them to the surface, gases within their swim bladder expand due to the decrease in pressure. This can cause their swim bladder to over inflate––a condition known as barotrauma. Overly buoyant fish experiencing barotrauma often struggle to swim back to dwelling depth if released at the ocean’s surface. These fish may experience high rates of mortality by thermal shock caused by the warmer surface temperatures, starvation, predation, or vision problems caused by barotrauma. Assisted release methods that recompress fish by returning them to depth prior to release may thus greatly improve survival of fish suffering from barotrauma.
In this study, I characterized species-specific responses of four species of nearshore Pacific rockfishes (Canary Rockfish, Sebastes pinniger; Gopher Rockfish, S. carnatus; Deacon Rockfish, S. diaconus; and Blue Rockfish, S. mystinus) to rapid ascent by hook-and-line fishing from shallow depths (<40 m). I videotaped their immediate responses upon recompression using a weighted inverted milk crate to transport fish back to their initial capture depth. Fish were videotaped during their descent, as well as their release from the crate. In some individuals, barotrauma symptoms were reversed and did not show behavioral impairment upon release, indicating that even a simple, inexpensive device can be effective in relieving barotrauma symptoms. Species differences were also observed in the severity of barotrauma observed following the collection of fish from depth. Capture depth was positively correlated with the occurrence of barotrauma for Blue Rockfish and Gopher Rockfish, but not for Canary Rockfish or Deacon Rockfishes.
I utilized data over an eight-year period from the California Collaborative Fisheries Research Project (CCFRP) to assess survivorship of rockfish experiencing barotrauma. A total of 20 rockfish (1 Black Rockfish, S. melanops; 2 Blue Rockfish; 12 Gopher Rockfish; 3 Copper Rockfish, S. caurinus; and 2 Kelp Rockfish, S. atrovirens) initially displaying barotrauma signs upon capture were tagged using a T-bar tag and released. It is unknown if these fish were recompressed because the CCFRP did not record this information. These 20 rockfish were recaptured days to 3 years later––indicating rockfish can survive long term after experiencing barotrauma. To minimize mortality of discarded fish in the fishery, fish recompression is recommended.
33
Shuuluka, Diina. "Ecophysiological studies of three South African Ulva species from integrated seaweed". Doctoral thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/10903.
Testo completoAbstract (sommario):
Includes bibliographical references (leaves 210-273).In South Africa, Ulva cultivation is of paramount importance to the marine aquaculture industry. Three local Ulva species (Ulva lactuca Linnaeus, Ulva rigida C. Agardh and Ulva capensis Areschoug) were selected for this research. The first two are currently cultivated on abalone farms for abalone feed and for use as bio-filters, and Ulva capensis was included because it is morphologically and biogeographically distinct from Ulva rigida in nature, despite the inability of molecular methods to separate them. Ulva rigida was collected at I & J farm and from nature at Kommetjie on the southwest of the Cape Peninsula, and U. lactuca was exclusively collected from I & J farm because it could not be found at sites where it had previously been recorded. Ulva capensis was exclusively collected from Kommetjie as this morphological species has not been recorded on abalone farms. The research also aimed to compare U. capensis with U. rigida on a variety of different measures, as molecular studies have suggested that they may represent a single polymorphic species.
34
Mead, Angela. "Climate and Bioinvasives drivers of change on South African Rocky shores?" Doctoral thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/11308.
Testo completoAbstract (sommario):
Includes abstract.Includes bibliographical references.
The overall aims of the thesis were to assess spatio-temporal change in macro species assemblages at sites located around the South African coast. Detected changes were considered in parallel with regional patterns of bioinvasion and climate change driven shifts in temperature trends over comparable time scales.
35
Sankar, Kishan. "Life on a gradient : activity levels of the seastar Patiriella exigua in different abiotic conditions". Bachelor's thesis, University of Cape Town, 2005. http://hdl.handle.net/11427/26051.
Testo completoAbstract (sommario):
Two morphs of Patiriella exigua occur in South Africa. These morphs occur on opposite sides of a temperature divide present at Cape Point. The green morph occurring on the West Coast (cold temperate) and the mottled morph occurring on the South Coast (warm temperate). In a previous study by Katherine Dunbar these two morphs were shown to be the same species. This project tests if there is a physiological difference between the two morphs of P. exigua. This was achieved by observing the activity coefficient of righting response of the two morphs of P. exigua under different temperatures and dissolved oxygen concentrations. The green morph was collected from Green Point (West Coast) and the mottled morph from Kalk Bay (South Coast). The results of a general linear model indicated that temperature and dissolved oxygen were significant factors determining righting time of P. exigua with P-values of less than 0.05. AT-test indicated that there was a significant difference between the righting times of the two morphs of P. exigua with the green morph turning at a faster rate than the mottled morph when placed under similar conditions.
36
Innes, Sheona. "Tropical intertidal seaweed turf communities of Jesser Point, Sodwana Bay, South Africa". Bachelor's thesis, University of Cape Town, 2010. http://hdl.handle.net/11427/26378.
Testo completoAbstract (sommario):
Algal turfs play an important role in both tropical and temperate reef ecology, supporting a diverse array of macrofauna as well as being primary producers within both intertidal and subtidal ecosystems. Biodiversity and biomass patterns of the intertidal algal turfs at Sodwana Bay, South Africa have not yet been established so this study was undertaken to investigate these. It was hypothesised that both biodiversity and biomass would decrease with increasing height along the shore, as well as that sediment would have an effect on the community composition of the turfs. The community was sampled over a vertical range of 1.2 m and found to be dominated by the red alga Jania intermedia (24.21 % of total algal coverage) followed by Tolypiocladia glomerulata (18.05 %), Dictyota sp. (13.39 %), Jania adhaerens (12.32 %) and Sphacelaria tribuloides. (5.83 %). No significant vertical zonation patterns were found, though certain species showed vertical trends such as Asparagopsis taxiformis and Sphacelaria tribuloides, which occurred in greatest biomass lower down on the shore, while Tolypiocladia glomerulata occurred higher up on the shore. Sand was found to affect certain species more than others, with Tolypiocladia glomerulata, Jania adhaerens and Asparagopsis taxiformis occurring in greatest biomass when the amount of sediment found in the quadrat was low, while Sphacelaria tribuloides. showed the opposite pattern and Jania intermedia showed no distinct pattern. Sampling took place over 1.2 m vertical height along the shore at spring low tide therefore covering 60 % of the intertidal zone vertically (maximum tidal range in South Africa is 2 m). It is therefore possible that the turfs are the cause of a decline in zonation by remaining damp and decreasing desiccation gradients vertically along the shore.
37
Olivieri, Emilia T. "Phytoplankton growth and zooplankton grazing in the southern Benguela current". Doctoral thesis, University of Cape Town, 1985. http://hdl.handle.net/11427/22590.
Testo completoAbstract (sommario):
Bibliography: pages 135-146.The development and production of several phytoplankton communities and the consumption of these communities plankton were investigated in newly by herbivorous mesozooupwelled waters of the southern Benguela Current by means of an electronic counting and sizing technique (Coulter counter). A feasibility study was initiated to test the accuracy of the Coulter counter (Model TAII) in estimating phytoplankton size and biomass in fresh and preserved samples from the Benguela current. Counting phytoplankton using this method gave a higher degree of reproducibility than the inverted microscope method. Certain recommendations as to the counting procedures were made. The counting of preserved samples was shown to introduce artefacts, resulting in a 77 per cent reduction in particle volume after a year of preservation. Correlations of particle volume with chorophyll a, carbon and nitrogen were calculated, with highest correlations occurring between particle volume and chlorophyll a. Particle volume was shown to represent biomass as accurately as any of the other methods.
38
Levy, Sarah Bernadette. "How reliable is morphological species delimitation in kelp? : a study of two closely related South African Ecklonia species". Bachelor's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/12923.
Testo completoAbstract (sommario):
Includes bibliographical references.Ecklonia maxima and Ecklonia radiata are both kelp bed forming macroalgae along the South African coast, and the latter is also found in considerable abundance in Australia and New Zealand. Genetically they exist as two distinct species and can usually be differentiated morphologically, especially when occurring as geographically separate entities. However, they do appear to intergrade when growing together, where plants of apparent intermediate and indeterminate morphology have been observed. This study tested the reliability of morphology in separating these two Ecklonia species across their intraspecific range of morphological variation, from locations where the species co-occur, as well as where they appear in isolation in South Africa (both species) and Australia (E. radiata only). No individual characters reliably separated between species, yet overall size distinctions as well as the morphometric separation of hollow and solid-stiped sporophytes provide good evidence for morphological differentiation of E. radiata and E. maxima. While E. radiata clusters morphometrically, a distinction between Australian and South Africa specimens is observed. In localities where the two species are reported to co-exist morphological distinction is less clear, particularly in deep water at Buffels Bay. The blade morphology of these deep water sporophytes is distinct from both E. radiata and E. maxima across all locations, while overall size distinctions contribute most prominently to the morphological separation of E. radiata and E. maxima at De Hoop. Environmental data in combination with more detailed genetic analyses, especially those aimed at hybrid identification, are necessary to resolve the nature of these subtidal plants as well as to investigate the relationship between genetic differentiation and overlapping morphology in plants at De Hoop.
39
Szeinfeld, Edy Sylvia Valdes. "Abundance and mortality of anchovy eggs caused by cannibalism and intraguild predation, and the potential effect on anchovy recruitment and clupeoid fluctuations". Doctoral thesis, University of Cape Town, 1991. http://hdl.handle.net/11427/26106.
Testo completoAbstract (sommario):
This thesis is structured in the form of five main chapters, each written in the form of an independent paper and supported by a general conclusion and one previously published paper on the same general theme. The central theme is the dynamics, ecology and evolution of intraspecific and intraguild predation - specifically the determination of an interacting mechanism between the guild fish species Engraulis capensis and Sardinops ocellatus and its significance for future fisheries management.
40
Raw, Robert Nicolas Vause. "Population structure, site fidelity, and fine-scale habitat use of the broadnose sevengill shark, Notorynchus cepedianusat Pyramid rock, False Bay, South Africa". Master's thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/11312.
Testo completoAbstract (sommario):
Includes bibliographical references.The aims of this study were to investigate elements of the demographics, fine-scale habitat use and site fidelity of sevengill sharks. The study was conducted at an aggregation hotspot within a Marine Protected Area, near Miller’s Point in False Bay, South Africa.
41
Shannon, Lynne Jane. "Modelling the oceanographic transport of young Cape anchovy Engraulis capensis by advective processes off South Africa". Master's thesis, University of Cape Town, 1995. http://hdl.handle.net/11427/21784.
Testo completoAbstract (sommario):
Bibliography: pages 107-121.A Monte-Carlo type model has been developed to investigate the importance of passive transport by currents above the thermocline for anchovy recruitment off South Africa. Simulation studies indicate that mean year-class strength of Cape anchovy is relatively robust to altered advective processes off South Africa. This occurs despite the fact that changed flow alters the likelihood of offshore advection and hence losses of anchovy from the system. Two different approaches have been taken to address the effects of altered advection, and the applicability of each is discussed. One approach involves altering westward advection in proportion to the mean current field (derived from Acoustic Doppler Current Profiler measurements), and the other, altering westward and northward advection by the addition of fixed offshore current velocities. The proportional approach did not affect year-class strength significantly, whereas the other approach, which incorporated large changes in the flow field, yielded statistically significant differences in predicted year-class strengths between advection scenarios. Reduced flow in the latter approach led to a mean year-class strength 2.7 times stronger than a proposed base flow scenario (which incorporated westward and northward drift in addition to the ADCP currents), whereas enhanced flow resulted in a mean year-class strength of similar magnitude to that of the base flow scenario. Changed flow may alter the geographic distribution of eggs and larvae, which might in turn influence recruitment of young-of-the-year anchovy to the South African purse-seine fishery. The north-flowing shelf-edge jet current plays an important role in transporting anchovy eggs and larvae from spawning grounds in the south to nursery areas frn1her north along the west coast of South Africa. Enhanced model advection westward and norward from the spawning grounds in the south serves to transport anchovy into the region of the jet current. However, advection into unproductive waters offshore is also enhanced and prevents good recruitment under these flow conditions. On the other hand, reduced westward and northward advection in the model, shown through wind records to characterise El-Nino years in coastal areas of South Africa, serves to retain anchovy reproductive products and often transports young anchovy into coastal areas, preventing offshore loss. Therefore the advection model suggests that good year-class strengths (in terms of numbers) are likely to be supported in years when westward and northward advection are reduced. A further reduction in westward advection may be less favourable by causing advective losses offshore along the south coast of South Africa. This may be viewed in terms of an "optimal environmental window" hypothesis, where reduced westward advection is favourable for anchovy survival off South Africa, but further reduction of westward advection as well as enhanced westward advection appear unfavourable. It is concluded that although passive transport, of anchovy in South African waters is relatively robust, it may account for a substantial proportion of recruitment variability.
42
Wright, Amy Grace. "Deep water parapagurid hermit crabs: their distribution, abundance, population structure and associations in the Southern Benguela". Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/25650.
Testo completoAbstract (sommario):
The parapagurids Sympagurus dimorphus (Studer, 1883) and Parapagurus bouvieri (Stebbing, 1910) dominate South African deeper-water benthic invertebrate communities. Samples from the 2016 DAFF bi-annual hake demersal research trawl surveys provided data on population structure and morphology. Since these species forego the use of "traditional" gastropod shells in favour of symbiotically-associated Epizoanthus pseudoshells, these data were also used to investigate parameters of pseudoshell association. S. dimorphus to have a female-biased sex ratio of 1:1.5, and P. bouvieri of 1:1. The proportion of males in both species increased with cephalothoracic shield (CL) length. S. dimorphus males had positive allometric major right chelipeds, while P. bouvieri cheliped lengths were positively allometric in males, and negatively allometric in females. All collected P. bouvieri occurred in pseudoshells, but S. dimorphus showed a real shell occupancy rate of 3.39% (n = 38). A positive relationship was found between CL size and real shell occupation frequency (r2 = 0.96). S. dimorphus pseudoshell zoanthid polyps increased in number as a function of both total shell volume (R2 = 0.73) and colony height (R2 = 0.61), with polyps present on every available part of the shell. No such relationship was found for P. bouvieri, presumably because the polyps are distributed in a linear pattern around the back and outside of the pseudoshell. Juvenile parapagurids appear to select for Naticidae original shells, with Euspira napus being the dominant original shell species for both S. dimorphus (45.45 %) and P. bouvieri (39.00 %). Questions are raised about whether these hermits exist along an evolutionary continuum of traditional shell reliance, whereby the species utilise their pseudoshells differently - P. bouvieri appears to show a stronger mutualistic symbiosis with its exclusive pseudoshell species than S. dimorphus, and may have lost the ability to change shelters entirely, utilising the pseudoshell as a brood pouch covering only the abdomen, rather than as a shell in which to retract to escape predation. Data from 1987 - 2014 surveys were used to map the distribution patterns and densities of these species in the southern Benguela, and to investigate changes in the populations over time. As it stands, no correction factor need be applied to South African parapagurid catches as a result of the 2003-2004 change in survey gear. However, further work is needed. S. dimorphus occurred at a significantly greater mean sample mass (287.88 kg.km⁻²) than P. bouvieri (31.37 kg.km⁻²). The bulk of sample mass occurred within the West Coast Benguela upwelling region, with very few parapagurids caught over the Agulhas Bank, which may be too shallow for either species, given that S. dimorphus showed a preferential depth range of 200 - 299 m (range 30 - 814 m) and P. bouvieri of 400 - 499 m (range 62 - 700 m). The highest mean sample masses occurred on muddy sand (61.00 kg.km⁻²) and sandy sediments (45.68 kg.km⁻²). Overall catchability (mean = 43.35%) has remained constant over the 23 years (R2 = 0.13) with a slight trend towards increasing catchability over time, which may correspond to a change in survey design.
43
Pasnin, Charles Olivier Arvin. "A marine systematic conservation plan for Rodrigues Island, Western Indian Ocean". Master's thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/11054.
Testo completoAbstract (sommario):
Includes abstract.Includes bibliographical references (p. 53-59).
In 2007 the local government of Rodrigues gazetted four marine reserves in the north of the island based on knowledge and insights from stakeholders, mainly from the fishing community. In order to verify the stakeholder-based design, a marine reserve network was designed using Marxan, a systematic conservation planning programme.
44
Loosen, Kristina. "Predictors of white shark Carcharodon carcharias presence at two recreational beaches in a major metropole". Master's thesis, University of Cape Town, 2017. http://hdl.handle.net/11427/27493.
Testo completoAbstract (sommario):
The presence of white sharks Carcharodon carcharias in False Bay, South Africa follows a clear seasonal cycle. In the austral winter months, white sharks aggregate around Seal Island with female sharks in particular moving to the inshore areas in summer. What triggers these fine scale migrations at one of the largest white shark aggregation sites in the world remains a subject of debate. Previous research identified the environmental variables, water temperature and lunar phase, as significant influences on white shark presence inshore. In this study, I attempt to investigate the influence of prey fish availability on the presence of white sharks at two inshore areas of False Bay, namely Muizenberg and Fish Hoek. In addition, I explored the influence of sea surface temperature (SST), El Niño/Southern Oscillation (ENSO), dolphin presence, diatom patch presence and the occurrence of purse-seine fishing (treknetting) on shark presence. A total of 1209 shark sightings were recorded from 1 January 2006 - 31 December 2015 with 742 sightings at Muizenberg and 467 at Fish Hoek. I used randomization tests to determine whether the occurrence of shark sightings was randomly distributed across the environmental and biological variables and determined the dependencies between the predictor variables. I confirmed that shark sightings were clearly seasonal and sightings peaked between 17.49 - 18.57°C. Fish presence revealed a similar peak at 17.94°C. Randomization tests indicate that a spotter is 66% more likely to detect a shark when fish are present, which supports my prediction of a prey mediated cue. The occurrence of treknetting was also found to be non-randomly linked to white shark presence, increasing the probability to spot a shark to 38% instead of 20% at random. The presence of diatom patches was found to be negatively correlated with SST; with numbers increasing in colder waters. The presence of dolphins, as other predators in False Bay, didn't show a significant pattern with any of the analysed variables. The influence of ENSO on the presence of white sharks was also hypothesized and the data revealed that there was a significant influence of weak negative ENSO values on their inshore occurrence. In addition to providing a better understanding of the ecology of white sharks in False Bay, my results can also be used in shark safety and education programs to reduce the risk of shark human conflict.
45
Gersun, Leanne. "The abundance and diversity patterns of seaweed communities on natural and artificial substrata at Sodwana Bay, South Africa". Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/13051.
Testo completoAbstract (sommario):
Includes bibliographical references.The high latitude coral communities of southern Africa suffered minimal impacts during mass bleaching events in the recent past. However, during the 2005 warm-water anomaly in the southern Indian Ocean, coral bleaching reached unprecedented levels. There is surprisingly little known about the fate of bleached corals, which may either regain their zooxanthellae and recover, or may die, in which case they generally become overgrown by macroalgae. The nature and dynamics of this algal overgrowth are not well understood. This study was done on Two-Mile Reef, Sodwana Bay, located in the iSimangaliso Wetland Park, a World Heritage Site. The first aim was to investigate the abundance and diversity of benthic algal communities colonising different hard substrata (comprising bleached digitate, brain and plate coral assemblages, and beach rock). The second was to compare the algal communities colonising various artificial hard substrata. The third was to document the species of non-geniculate coralline red algae found on the natural hard substrata during sampling. Fieldwork was carried out during the marine autumn (March) and spring (September) of 2010 using SCUBA. A total of 90 quadrats (10 cm x 10 cm) were sampled and the underlying substratum was recorded and classified. A Braun-Blanquet scale was used to assign cover-abundance values to each species within each quadrat. Additionally, the relative cover of different types of substrata was estimated using line-point intercept methods. Multivariate analysis (detrended correspondence analysis) and cluster analysis (complete linkage Bray-Curtis) were used to show how substrata and season relate with respect to their seaweed flora. Additionally, Kruskal-Wallis nonparametric tests with pairwise Mann-WhitneyU-tests were used to examine differences in macroalgal assemblages among substratum types.
46
Winckler, Heidi. "The application of univariate and distributional analyses to assess the impacts of diamond mining on marine macrofauna off the Namibian Coast". Master's thesis, University of Cape Town, 1999. http://hdl.handle.net/11427/17969.
Testo completoAbstract (sommario):
Bibliography: pages 114-116.This study is one of three based on grab samples of macrobenthos obtained before and at different times after mining for diamonds off the coast of Namibia. The first study dealt with multivariate clustering analysis of the first samples before and after mining. The second study focused on recovery times after mining and this study is aimed at estimating the amount of stress encountered by benthic communities, for comparision with the descriptive multivariate approach. Two research areas, classified as 'northern' and 'southern' were investigated. Data were aggregated and analysed at the genus level. Graphical and statistical analyses were conducted on the data which was classified in three ways. First, on all unmined sites from the two research areas together to test for natural site-to-site variability. Secondly and thirdly, each research area (north and south) was analysed separately to test for differences between unmined and mined sites at each area. Stress levels in the community were assessed by Caswell's neutral model (the Vstatistic) and by interpretation of the value of the W-statistic (a summary statistic of the ABC curves). Correlation techniques were applied to assess if there was any relationship between the diversity indices (as indicators of the influence of disturbance on community structure) on the one hand, and the environmental indicators of disturbance (percentage gravel, sand, mud) on the other.
47
Plagányi, Éva Elizabeth. "A model of copepod population dynamics in the southern Benguela upwelling region". Master's thesis, University of Cape Town, 1995. http://hdl.handle.net/11427/14969.
Testo completoAbstract (sommario):
Bibliography: leaves 190-216.A simple population dynamics model is constructed to simulate temporal variability in the biomass of a dominant copepod Calanoides carinatus (Copepoda: Calanoida) along the West Coast region of South Africa. C. carinatus is extensively preyed upon by the commercially important anchovy Engraulis capensis and variability in zooplankton production may serve as an useful predictor of variability in anchovy recruitment levels. The model developed here circumvents the need to include a large number of parameters because it uses satellite-derived estimates of chlorophyll a concentration and sea surface temperature as primary inputs. Abundance estimates necessary to initialise the model are readily obtainable from biannual research cruises. The model successfully simulates observed features of a copepod population's response to pulses of upwelling and results obtained are consistent with data from field studies. The model is robust with respect to most of its parameters because minor changes in their values result in predictable changes in model output. The effect on model predictions of errors in field estimates is quantified. The model showed greatest sensitivity to parameters which are difficult to determine empirically, such as predator-induced mortality rates. Gaps in our present understanding of the nature and scale of processes affecting copepod egg abundance, survival and viability in the Southern Benguela system, were identified as the dominant impediment to attempts to simulate copepod population dynamics in the region. The Southern Benguela system is patchy on a range of different space and time scales. The effect of fine-scale distributional heterogeneity on mesoscale patterns of copepod productivity was investigated by assuming that spatial patchiness affected the degree of overlap between zooplankton and phytoplankton populations. The effect of spatial patchiness is particularly prevalent under poor feeding conditions, and may result in predictions based on average feeding conditions underestimating zooplankton production by as much as 30% in some circumstances. Estimates of zooplankton production are sensitive to both the spatial arrangement and intensity of food patches in a heterogeneous environment. There is a need to isolate the essential mechanisms causing distributional heterogeneity and to quantify the effect of spatial patchiness on model predictions to permit the correct averaging of model results over broad horizontal areas. Because of the model's sensitivity to the predator-induced mortality rate, a temporally and spatially integrated system is used to quantify this parameter as a function of varying patterns of predator and prey abundance. Shoals of anchovy recruits are explicitly modelled feeding on patches of C. carinatus prey, and the fish's performance is quantified through temporal and spatial integration of periods and patches of prey abundance and shortage. Constant high fish densities dampen the spatial variability in copepod abundance, whereas a pulsed predation pressure permits locally depleted copepod populations a short respite in which to recover some growth, thereby allowing the persistence of a few good prey patches which offer favourable energy returns for foraging fish. The model suggested that at high densities of anchovy recruits, predicted growth rates are strongly density-dependent and predation rates may exceed copepod production rates. Absolute measures of prey availability are sometimes unable to predict anchovy feeding success as mechanisms permitting temporal and spatial segregation play a vital role in synchronizing the relationship between fish predation pressure and prey turnover rates. The model emulates observed variability in anchovy growth rates and analysis of the output indicates that the availability of high sustained abundances of food along the West Coast may be a critical "bottleneck" contributing to the strength of recruitment to the pelagic puseseine fishery in South African waters. Observed chlorophyll a concentration and sea surface temperature data in 1971 and 1972 were used as inputs into an annual version of the basic model, and model-predicted patterns of copepod biomass were compared with observed patterns of zooplankton biomass in the two years. The ability of the model to simulate major differences in the general features observed in the two years supports its use as a tool to describe net patterns of zooplankton productivity over large horizontal areas. The model · identified the need to quantify the role of major size-class groups, such as the microzooplankton and macrozooplankton, in mediating the flow of energy from phytoplankton to fish.
48
Baker, Shirley Marie. "Oyster (Crassostrea virginica) metamorphosis: Effects of low oxygen". W&M ScholarWorks, 1994. https://scholarworks.wm.edu/etd/1539616556.
Testo completoAbstract (sommario):
The objective of my research was to examine the physiology and behavior of metamorphosing oysters, Crassostrea virginica, and to investigate the effects of low oxygen stress on metamorphic processes. Specifically, I examined the effects of hypoxia (20% of air saturation) and microxia (&<&1% of air saturation) on settlement, survival, growth, morphology, metabolic rate and feeding on post-settlement oysters. All of the functions I measured were adversely affected by hypoxia and microxia, compared to normoxic controls. Survival times indicate that, like larvae and adults, post-settlement oysters are capable of anaerobic metabolism. The 2 week period following settlement is especially critical to recruitment. Low oxygen conditions increases mortality and have detrimental effects on the development and growth of post-settlement oysters. Oysters have the ability to feed at nearly all stages of settlement and metamorphosis. While hypoxic conditions reduce feeding only in the youngest metamorphosing oysters, microxic conditions affect all ages. Not only does weight-specific metabolism decrease as the oysters grow, but metabolic responses to low oxygen change from relatively oxygen independent to oxygen dependent. I conclude that oyster distribution may be influenced by low oxygen, especially in those areas that experience prolonged (24-48 h) hypoxia or severe microxic events. Low oxygen events may control recruitment into the adult population directly, because of larval settlement failure and post-settlement mortality, and indirectly, because of reduction in feeding, development rate, and growth of post-settlement oysters.
49
Brylawski, Bryce J. "Cultural eutrophication and the clam Macoma balthica: Evidence for trophic disruption and effects on blue crabs". W&M ScholarWorks, 2009. https://scholarworks.wm.edu/etd/1539616585.
Testo completoAbstract (sommario):
Cultural eutrophication (CE) is the allochthonous input introduction of a quantity of matter, such as sediments, organic material, or nutrients, into a water body over the pre-anthropogenic (natural) levels. In most coastal estuaries CE has come to refer primarily to an increase in the concentration of phyto-nutrients. CE has been identified as the cause of very graphic phenomena such as hypoxia and fish kills. In this work I examine the potential for CE to alter the composition of the primary producer community and potentially alter or disrupt the benthic food web, using Macoma balthica as an indicator species. A series of surveys and experiments identified that clams in areas with greater than average nutrient concentrations had lower health, slower growth, and greater non-predatory mortality than clams in less eutrophic areas. Primary production, as estimated from chlorophyll a concentration, was greater at higher nutrient locations while the health and growth of clams was lower. The phytoplankton community in the more eutrophic areas had a lower proportion of diatoms relative to dinoflagellates. A biochemical analysis of clam tissue indicated that the clams from the less nutrient rich sites had a greater proportion of Eicosapentaenoic acid (EPA) relative to other fatty acids. Diatoms are rich in EPA compared to dinoflagellates. Thus, we hypothesize that CE induced shifts from diatom based production toward dinoflagellates may be limiting trophic transfer due to a lack of EPA. Using a series of models we were able to predict that trophic disruption could significantly reduce the scope for growth of the blue crab, Callenecties sapidus . Thus it is possible that the CE induced changes to primary producer community could disrupt the food web creating a trophic bottleneck.
50
Robison, Clara L. "Impacts of Margalefidinium polykrikoides and Alexandrium monilatum on Oysters Cultured in Lower Chesapeake Bay". W&M ScholarWorks, 2019. https://scholarworks.wm.edu/etd/1593092072.
Testo completoAbstract (sommario):
Harmful algal blooms (HABs) are expanding globally and are anticipated to continue increasing with climate change. Two dinoflagellate species, Margalefidinium polykrikoides and Alexandrium monilatum, form extensive and dense blooms most summers in the lower Chesapeake Bay. Alexandrium monilatum, which produces the toxin goniodomin A, tends to bloom soon after M. polykrikoides, for which a toxin has not yet been identified. Previous laboratory studies and a more limited number of field studies indicate mortality and pathology in multiple shellfish species associated with exposure to M. polykrikoides and A. monilatum. However, the impacts of sequential exposure to both HAB species on marine organisms in the natural environment are less well understood. Local aquaculturists grow oysters under a variety of conditions that may be differentially impacted by HAB exposure. No extensive and controlled studies have been carried out in lower Chesapeake Bay assessing impacts of sequential exposure to M. polykrikoides and A. monilatum blooms on oysters cultured using different aquaculture strategies. The two main objectives of this study were to: 1) investigate M. polykrikoides and A. monilatum as a potential threat to cultured oysters, and 2) inform mitigation strategies to minimize HAB impacts based on current grow-out methods. To address these objectives, oysters were grown in 2017 and 2018 at sites characterized by differing water energetics and HAB dynamics. At all sites during both summers, oysters were grown intertidally and subtidally, and in 2018 were also grown in floating cages at one site. Water quality parameters were monitored, including cell concentrations of M. polykrikoides, A. monilatum, and two other local HAB species known to negatively impact oysters, Karlodinium veneficum and Prorocentrum minimum, along with oyster health and survival. Blooms of M. polykrikoides and A. monilatum occurred at the study sites, but not the reference site, in summer 2017 with cell concentrations that were lower than those quantified in some previous years. In summer 2018, neither species bloomed, providing the opportunity to assess oysters during both a bloom and a non-bloom year. Overall oyster mortality in both summers was relatively low compared to mortality often seen associated with other oyster stressors such as disease. Results indicated oyster health and survival were more impacted by factors indirectly related to HABs, specifically location factors (i.e. site and placement location), temperature, and DO. In both summers, mortality was significantly higher for intertidal oysters, compared to subtidal oysters, suggesting intertidal placement may incur stress in summer. It is unknown whether this intertidal stress may be further compounded during more HAB-intensive years. The results of this study suggest M. polykrikoides and A. monilatum had little impact on the health and survival of oysters cultured in the lower Chesapeake Bay in the summers of 2017 and 2018. More than one year of bloom data is likely necessary, however, to fully evaluate the impacts of M. polykrikoides and A. monilatum as potential stressors to cultured oysters in the context of inter-annual variability and the expanding distribution of these two HABs in the Chesapeake Bay.