Dissertations / Theses: 'Crabs'

1

Houser, Letise T. "The importance of horizontal swimming behavior in maintaining patches of larval crabs." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 1.34 Mb., 156 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3200543.

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2

Lai, Chi-sing. "The feeding ecology of Thalamita danae Stimpson 1858 (Brachyura:Portunidae), with a review of the genus Thalamita in Hong Kong /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B18933464.

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3

Yau, Po-ming. "Studies on the ecology, ecophysiology and ecotoxicology of three species of intertidal crabs in Hong Kong /." Hong Kong : [University of Hong Kong], 1991. http://sunzi.lib.hku.hk/hkuto/record.jsp?B1316661X.

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4

Lee, Ka-wai. "The impact of foraging by soldier crabs, Mictyris brevidactylus, on sandy shore communities." Click to view the E-thesis via HKUTO, 2007. http://sunzi.lib.hku.hk/HKUTO/record/B3955742X.

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5

Bellwood, O. "Systematics, biogeography and functional morphology of the box crabs (Family Calappidae) /." Connect to this title online, 2002. http://eprints.jcu.edu.au/1182/.

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6

Barbour, Russell W. "Patterns of larval distribution and settlement in a river-dominated estuary /." Electronic version (PDF), 2003. http://dl.uncw.edu/etd/2003/barbourr/russellbarbour.pdf.

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7

Kennedy, Patrick J. "Characterization of a gene family associated with calcified structures in the blue crab, Callinectes sapidus /." Electronic version (PDF), 2004. http://dl.uncw.edu/etd/2004/kennedyp/patrickkennedy.pdf.

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8

Buda, Elizabeth S. "Prophenoloxidase activating factor from the blue crab, Callinectes sapidus /." Electronic version (PDF), 2004. http://dl.uncw.edu/etd/2004/budae/elizabethbuda.pdf.

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9

Garrison, Lance Preston. "The influence of physical transport and nutritional stress on the zoeae of estuarine crabs." W&M ScholarWorks, 1997. http://web.vims.edu/library/Theses/Garrison97.pdf.

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10

Kennish, Robin. "Seasonal patterns of algal availability, influences on diet selection and fitness of the tropical crab grapsus albolineatus." Thesis, Hong Kong : University of Hong Kong, 1995. http://sunzi.lib.hku.hk/hkuto/record.jsp?B17591533.

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11

Connelly, Janet Hosier. "Horseshoe Crabs-Ancient Alien Protectors." Thesis, The George Washington University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10118697.

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Ancient Alien Protectors is an exhibition that tells the story of the wonders and benefits of horseshoe crabs. What are they and why should anyone care about them? Researching the topic revealed that more often than not an inhabitant of the Western Shore or any of the landlocked geographical locations in the United States has limited knowledge about horseshoe crabs. Their kind has inhabited our Earth for over 475 million years. They have outlasted over ninety-nine percent of all the species that ever swam or walked on the planet but are now in peril due to human activity. They have been harvested for farmers to make fertilizer for crops, chopped up as bait for fishermen, and captured and bled by biomedical companies. Their copper-based blue blood is used to produce a life-saving product that is hypersensitive to bacteria. The injectable drugs and medical devices that come in contact with our blood must be tested for the presence of toxins, horseshoe crabs have now become an invaluable commodity to modern medicine.

Horseshoe crab eggs are a food source for many crustaceans and fishes. Their eggs are an integral part of the diet of many shorebirds, allowing them to refuel and gain weight before continuing their journey northward to the Arctic. Disappearance of the horseshoe crab from the waters of the Atlantic Ocean would be a critical blow to the life-sustaining connection between members of local ecosystems.

The goal of this research is to create an exhibition that sparks an awareness about how we are an intrinsic part of the natural world. The exhibition is designed so that visitors will have an opportunity to enter a museum located in the Delaware Bay region, the natural setting where the largest population of horseshoe crabs are born, grow to maturity, and reproduce. Visitors can immerse themselves in an environment that will stimulate their senses as well as their mind and leave inspired to engage in the conservation and protection of this resilient species. The proposed site will also house a research facility collocated with the museum to foster cooperation and knowledge sharing among scientists. A partnership between the conservation and medical communities would strengthen the commitment to finding better ways to strategically manage and preserve this precious living resource.

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Suchanek, Jessica. "A Cast of White Crabs." ScholarWorks@UNO, 2011. http://scholarworks.uno.edu/td/1374.

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13

Johnson, Lisa K. "Metabolic influences of fiber size in aerobic and anaerobic muscles of the blue crab, Callinectes sapidus /." Electronic version (PDF), 2004. http://dl.uncw.edu/etd/2004/johnsonl/lisajohnson.pdf.

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14

Lee, Ka-wai, and 李嘉慧. "The impact of foraging by soldier crabs, Mictyris brevidactylus, on sandy shore communities." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2007. http://hub.hku.hk/bib/B3955742X.

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15

Kwok, Pik-wan. "The ecology of two sesarmine crabs, perisesarma bidens (de Haan) and parasesarma plicata (latreille) at the Mai Po Marshes nature reserve, Hong Kong /." Hong Kong : University of Hong Kong, 1995. http://sunzi.lib.hku.hk/hkuto/record.jsp?B14778348.

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16

Churchill, Giles John. "An investigation into the captive spawning, egg characteristics and egg quality of the mud crab (Scylla serrata) in South Africa." Thesis, Rhodes University, 2004. http://hdl.handle.net/10962/d1015963.

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The source of a reliable supply of seed is one of the most important factors determining the success of aquaculture. At present mud crab culture is reliant on wild caught juveniles, which limits the expansion of mud crab farming globally. This, coupled with the paucity of knowledge of the spawning and egg characteristics of mud crabs, prompted the investigation into the captive spawning, incubation and egg quality of Scylla serrata in South Africa. A total of 112 mature females were caught from three estuaries in northern KwaZulu Natal and acclimated to captive conditions. Mature females were present in the estuaries throughout the year and ranged from 90 to 200 mm carapace width. Except for 40 crabs all the females spawned in captivity. On average spawning took place 38 ± 23 days after capture but was not dependent on crab size. Fecundity was significantly correlated to crab size (p = 0.026), with larger females producing more eggs. The average fecundity per batch was 5.79 ± 2.07 million eggs. Hatch success rate for all egg batches was high averaging 84 ± 6 %. Egg dropping occurred in all egg batches during incubation. On average 6.5 % of the egg mass was dropped during incubation. At the average temperature of 27⁰C eggs in the incubation system hatched within 292 ± 12 hours after extrusion. In-vitro incubation of eggs proved to be an ineffective means of incubating Scylla serrata eggs with a hatch success rate of only 25 ± 5 %. Egg quality was assessed both directly, using variables such as hatch success rate and hatch synchronicity and retrospectively by using stress tests and comparing survival of larvae from different coloured egg batches. Lipid class composition and fatty acid methyl ester content for 28 batches of eggs and 16 batches of larvae were analyzed. The biochemical composition of the egg was correlated to survival of larvae in the stress tests to ascertain if the lipid content of the eggs determines their quality. Stress tests were used to retrospectively assess egg quality. Four stressors were administered to newly hatched larvae and the LD50 values recorded. An average LD50 of 64 hours was recorded for the starvation tests, 40% for the salinity tests, 37 ppm for the formalin tests and 39.7 mg/l NH3 for the ammonia stress tests was recorded. Egg colour ranged from pale yellow to orange-red. Egg colour was not influenced by female size or the time the females spent in captivity prior to spawning. Egg colour can therefore not be used as an indicator of quality. The lipid profiles of newly extruded eggs had no effect on hatch synchronicity or hatch success rate. However, the stress tests identified female size (p ≤ 0.02), DHA content of the egg (p ≤ 0.02), Σ omega-3 fatty acids of eggs (p ≤ 0.02) and EPA content of eggs (p ≤ 0.007) as possible determinants of egg quality. Larger crabs tended to produce poorer quality eggs. Egg quality also decreased as the amount of DHA, EPA and the Σ omega-3 fatty acids decreased in the eggs. To summarize, the results of this study indicated that the following parameters affect egg quality - crab size, DHA, EPA and Σ omega-3 fatty acid content of eggs.

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17

Bryant, Andrew D. "The life history patterns of brachyuran crabs." Thesis, University of Liverpool, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.316604.

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18

Do, Van Tu. "Freshwater crabs of Vietnam: diversity and conservation." Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-190347.

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The freshwater crab fauna of Vietnam has a high diversity and endemism, 49 species have been recorded and 42 of them are only known from this country. In addition, many species are undescribed or undiscovered while at least 10% of known species are facing extinction. Water pollution, urban, industrial and agricultural development, habitat loss and fragmentation, deforestation and overexploitation are the main threats to this fauna. The first conservation recommendation is keeping rain forest tracts large enough to maintain habitat and water quality for long-term survival of these crabs. More research on taxonomy, distribution, population dynamics, main pressures, conservation status are needed in order to assess conservation status and create efficient conservation actions for freshwater crabs in Vietnam
Khu hệ cua nước ngọt ở Việt Nam có mức độ đa dạng và đặc hữu cao với 49 loài đã được ghi nhận, trong đó có tới 42 loài chỉ được biết đến ở Việt Nam. Ngoài ra, nhiều loài cua nước ngọt còn chưa được mô tả hay chưa được khám phá, trong khi có tới 10% trong tổng số loài đã biết đang phải đối mặt với nguy cơ tuyệt chủng. Ô nhiễm môi trường nước, đô thị hóa, phát triển công nghiệp và nông nghiệp, nơi sống bị phân mảnh và mất, phá rừng cùng với khai thác quá mức là những mối đe dọa chính đối với khu hệ này. Công tác bảo tồn trước hết phải giữ cho diện tích rừng đủ lớn để duy trì chất lượng môi trường sống cho sự tồn tại lâu dài của các loài cua này. Các nghiên cứu về phân loại học, phân bố, động lực quần thể là rất cần thiết để đánh giá tình trạng bảo tồn và đưa ra những hành động bảo tồn hiệu quả cho các loài cua nước ngọt ở Việt Nam

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19

DeRivera, Catherine E. "Conflict over male searching in fiddler crabs /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9956458.

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20

Burch, Alexandra. "The foraging behaviour of shallow water crabs." Thesis, Bangor University, 1998. https://research.bangor.ac.uk/portal/en/theses/the-foraging-behaviour-of-shallow-water-crabs(0e293f58-80a5-466f-8d3a-90ac3c384b4c).html.

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This is a study of the foraging behaviour of Carcinus maenas on Mytilus edulis and of Thalamita danae on Perna viridis. Particular attention is given to differences arising in foraging behaviour as a result of intraspecific prey heterogeneity and experimental protocol. Intersite and temporal differences in the population density, shell morphology, biomass and byssal attachment strength of Mytilus edulis were found. Byssal attachment strength and shell strength were highly variable amongst individuals of a similar size. Carcinus maenas is strongly heterochelous. Intraspecific differences in the chelal mechanics, but not in the chelal geometry, were recorded; major chelae of large male crabs were significantly stronger than the major chelae of females and small males. Stomach content analyses showed that Carcinus maenas has a broad diet in which Mytilus edulis forms an important component. Intersite differences inMytilus edulis shell morphology altered the foraging behaviour of Carcinus maenas, and intersite and temporal variations in mussel flesh weight altered the prey value curves. Both C. maenas and Thalamita danae were highly prey size-selective when foraging on groups of different sized mussels, the size of prey most vulnerable to predation altering with the size composition of the group. The handling times of mussels for both species of crab were reduced when mussels were presented as part of a group as compared to when mussels were presented singly. For Carcinus maenas the reduced handling times resulted from the less extensive gleaning of mussel shells whilst for Thalamita danae reduced handling times appeared to result from the greater use of a more time efficient opening technique. When Carcinus maenas were presented with mussels of differing attachment strengths, crabs selected more weakly attached mussels over those with a more firm and rigid attachment. This selection did not appear to be based on prey value or prey length but rather on the resulting slight movement of weakly attached mussels whenever these were touched by a foraging crab.

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21

胡嘉麟 and Ka-lun Kelvin Wu. "Status, consumption and conservation of horseshoe crabs in Hong Kong." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B41549533.

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22

Wu, Ka-lun Kelvin. "Status, consumption and conservation of horseshoe crabs in Hong Kong." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B41549533.

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23

Thariyan, Sheeba K. "Size distribution and reproductive biology of the mud crab Scylla serrata at Cochin during monsoon period." Thesis, Central Marine Fisheries Research Institute, 1988. http://eprints.cmfri.org.in/11196/1/Sheeba%20K.%20Thariyan%20.pdf.

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The mud crab Scylla serrata Is the largest among edible crabs of India. Constituting a traditional fishery of sustenance level in the country, this crab has assumed considerable importance In recent years on account of Its growing popularity as a gourmet's favourite. It is also a good export commodity. At present the crab is underexploited in our waters and the catches could be increased many fold by improved devices and techniques of capture. In view of its euryhaline nature and many other favourable factors it Is also considered as a candidate species for coastal aquaculture. Realising the potentialities for Its culture, attempts are being made in many countries of the Indo-Pacific for commercial culture and propagation of this species.

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24

Zayasu, Yuna. "The cospeciation between massive corals and gall crabs." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188516.

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25

Withers, Patrick. "Hormonal control of growth and reproduction in crabs." Thesis, Bangor University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369443.

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26

Szebeni, Tommy. "Camouflage and associated adaptations in Manx spider crabs." Thesis, University of Liverpool, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396706.

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27

Warren, Janice H. (Janice Helene). "Behavioural ecology of crabs in temperate mangrove swamps." Thesis, The University of Sydney, 1987. https://hdl.handle.net/2123/26768.

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Patterns of distribution of crabs inhabiting burrows in three temperate mangrove swamps near Sydney, New South Wales, were described. Heloeoius cordiformis (an ocypodid) did not exhibit a consistent pattern of distribution among three tidal zones, but was always associated with well— drained mounds of substratum within zones. Paragrapsus laevis (a grapsid) tended to be most abundant in the lower two zones on the shore and usually inhabited burrows in the moist or submerged flats between mounds. Sesarma erythrodactyla (a grapsid) was distributed fairly evenly among the three tidal zones and also between mounds and flats. H. cordiformis hibernated in burrows from June through August or September. Overall abundances also varied seasonally, but trends were inconsistent among the three swamps sampled.

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Chan, Hing Man. "Aspects of the biology of zinc in crabs with particular emphasis on the shore crab Carcinus maenas (L.)." Thesis, Queen Mary, University of London, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389150.

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29

Yau, Po-ming, and 邱寶明. "Studies on the ecology, ecophysiology and ecotoxicology of three species of intertidal crabs in Hong Kong." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1991. http://hub.hku.hk/bib/B31232899.

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30

Lai, Chi-sing, and 黎志誠. "The feeding ecology of Thalamita danae Stimpson 1858 (Brachyura:Portunidae), with a review of the genus Thalamita in Hong Kong." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B31214204.

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31

au, kdsmith@fish wa gov, and Kimberley Dale Smith. "Distributions, relative abundances and reproductive biology of the deep-water crabs Hypothalassia acerba and Chaceon bicolor in southwestern Australia." Murdoch University, 2006. http://wwwlib.murdoch.edu.au/adt/browse/view/adt-MU20061129.142618.

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Three species of large crab are found in Western Australian waters, namely the champagne crab Hypothalassia acerba, the crystal crab Chaceon bicolor and the giant crab Pseudocarcinus gigas, all of which are fished commercially in these waters. This thesis reports the results of studies carried out on the biology of the first two species, for which there were previously very little information. The results increase our knowledge of the benthic fauna in deeper waters off the southwestern Australian coast and provide data that can be used by fisheries managers to develop plans for conserving the stocks of H. acerba and C. bicolor. The champagne crab Hypothalassia acerba is found southwards of Kalbarri at ~ 27aS, 114aE on the west coast and eastwards to Eucla at ~ 32aS, 129aE on the south coast. There is a small commercial trap fishery for H. acerba on both the lower west and south coasts of Western Australia. However, on the west coast, H. acerba is managed as a single species fishery, whereas on the south coast it is a component of a multi-species fishery, which also includes the southern rock lobster Jasus edwardsii and P. gigas. On the west coast, the commercial catches of H. acerba increased sharply from ~ 1,500 kg in 1989 to reach maximum levels of 30-46,000 kg in 1997-99, reflecting a marked increase in fishing effort. However, it subsequently declined to essentially zero after 2000 due to effort shifting towards fishing for C. bicolor. Catches of H. acerba on the south coast peaked at 26-27,000 kg in 1997-98 but, in contrast to those on the west coast, remained relatively high in 2001 to 2003. The crystal crab Chaceon bicolor occurs in water depths of ~ 450 to 1220 m around Australia and New Zealand. However the commercial fishery is almost entirely located between Carnarvon on the north-west coast at ~ 25aS, 113aE to approximately Windy Harbor at ~ 35aS, 116aE on the south coast. Commercial catches of C. bicolor in southwestern Australia, which came almost entirely from the lower west coast, rose from very low levels in 1997 to ~ 222,000 kg in 2001 and then remained close to this level in 2002 and 2003. These trends largely reflect an increase in fishing effort. Hypothalassia acerba was sampled seasonally by setting traps at depths of 35, 90, 145, 200, 255, 310 and 365 m on the west and south coasts of Western Australia. Catch rates on the west and south coasts peaked sharply at depths of 200 and 145 m, respectively, but at similar temperatures of 16 - 17¢XC. The catches on those coasts contained 69 and 84% males, respectively. The carapace length of H. acerba declined significantly by 4 mm for each 100 m increase in depth. Males attained a greater maximum carapace length than females on both the west coast, i.e. 135 vs 113 mm, and south coast, i.e. 138 vs 120 mm. Furthermore, after adjustment to a common depth of 200 m, the mean carapace length of males was greater than females on both the west coast (96.6 vs 94.6 mm) and south coast (101.5 and 91.4 mm) and the latter difference was significant (p < 0.001). These results thus show that, for H. acerba, (1) the distribution is related to depth and temperature, (2) body size is inversely related to water depth and (3) males grow to a larger size and are more prevalent in catches than females. There was also evidence that the distribution of H. acerba changed slightly with season and that there was spatial partitioning by this species and other large deep water invertebrate predators. The trends exhibited by reproductive variables demonstrate that H. acerba reproduces seasonally on the lower west coast, with ovaries maturing progressively between July and December and oviposition occurring between January and March. The characteristics of H. acerba on the south coast differed in the following ways from those on the lower west coast. (i) No ovigerous females and only two females with egg remnants were caught. (ii) Ovaries did not develop late yolk granule oocytes until females had reached a larger size. (iii) Investment in gonadal development was less. These results strongly suggest that conditions on the south coast are not as conducive for ovarian development and reproduction and indicate that females migrate from the south to lower west coast for spawning. In contrast to H. acerba, C. bicolor reproduces throughout much or all of the year on the lower west coast, presumably reflecting its occupancy of far deeper waters where environmental conditions vary less during the year. Although the mean weights of ovigerous females of H. acerba and C. bicolor were not significantly different (p > 0.05), the mean fecundity of the former species (356,210) was significantly greater (p < 0.001) than that of the latter species (192,070). The relatively high fecundity of H. acerba may reflect adaptations by this species to optimise egg production during its relatively short breeding season. The size at onset of sexual maturity (SOM) of the females of crustacean species, which is often used by fisheries managers for developing management plans for such species, is typically estimated using logistic regression analysis of the proportions of mature females in sequential size classes. The validity of this approach depends on the composition of the samples reflecting accurately that present in the environment. However, catches obtained by traps, a passive fishing method, typically contain disproportionately greater numbers of large crabs, whereas those obtained using active fishing methods, such as seine netting and otter trawling, will presumably represent far better the size composition of the population. Since H. acerba and C. bicolor could be caught in numbers only by using traps, comparisons between the influence of passive and active fishing methods were explored using the extensive data previously collected for Portunus pelagicus employing different sampling methods (de Lestang et al. 2003a,b). These data are analysed in order to demonstrate that the females of P. pelagicus caught by trapping were predominantly mature, whereas those obtained by seining and trawling contained numerous immature as well as mature females. The samples of females collected by trap are, therefore, clearly biased towards mature crabs. Consequently, for any size class, it would be predicted that the proportion of mature females in trap catches will be overestimated, thus shifting the logistic curve fitted to the proportions of mature crabs at each size to the left, and thereby yielding an underestimate of the SOM. This conclusion is substantiated by the fact that the carapace width of female P. pelagicus, at which 50% of individuals reach maturity (SOM50), was estimated to be markedly greater when using the proportion of mature females obtained by seine-netting and otter trawling collectively, i.e. 101.1 mm, than by trapping, i.e. 86.1 mm. From the above data for P. pelagicus, it is considered likely that, through a greater vulnerability of mature females of these species to capture by traps, the respective SOM50s derived for female H. acerba and C. bicolor from trap samples (i.e. carapace lengths of 69.7 and 90.5 mm) will represent considerable underestimates of the true SOM50s. Many workers have assumed that the chelae of male crabs undergo a change in allometry at the pubertal moult and that this could thus be used as the basis for determining the size of those crabs at morphometric maturity. Since initial plots of the logarithms of propodus length and carapace width (CW) of the males of P. pelagicus and carapace length (CL) of the males of H. acerba and C. bicolor revealed no conspicuous change in allometry, the question of whether the chelae of these species undergo such an allometric change was explored statistically. The Akaike and Bayesian Information Criteria were thus used to ascertain whether a linear, quadratic, broken stick or overlapping-lines model best represented the above logarithmic size data. Since the broken stick model provided the best fit for P. pelagicus, the chelae of this species does undergo allometric change. This occurred at 80.0 mm CW, which is ~ 8 mm less than the CW at physiological maturity. In contrast, my analyses provided no evidence that the chelae of either H. acerba or C. bicolor exhibited an inflection and thus morphometric maturity could not be determined for these two species from chela length. Thus, mangers will have to use the SOM50 for physiological maturity, which was estimated to be 68.1 and 94.3 mm CL for H. acerba and C. bicolor, respectively.

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32

Percival, Scott R. "Feeding and substrate preferences of the Japanese shore crab, hemigrapsus sanguineus /." View abstract, 2002. http://library.ccsu.edu/ccsu%5Ftheses/showit.php3?id=1662.

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Thesis (M.S.)--Central Connecticut State University, 2002.
Thesis advisor: Kim Wilson. " ... in partial fulfillment of the requirements for the degree of Master of Science in Biology." Includes bibliographical references (leaves 54-58). Also available via the World Wide Web.

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33

Bell, Karen Lennox. "Studies on phagocytosis in the shore crab Carcinus maenas (Crustacea, Decapoda)." Thesis, University of St Andrews, 1994. http://hdl.handle.net/10023/14845.

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Phagocytosis by hyaline cells of the shore crab, Carcinus maenas, was investigated in vitro. In particular, the project examined the role of the prophenoloxidase activating system (proPO) in opsonisation, the metabolic requirements of the cells during phagocytosis and the extent of intracellular bacterial killing. Related work investigated the mechanism and regulation of bacterial killing. Uptake was assessed using monolayers of separated hyaline cells challenged with the bacterium, Psychrobacter iminobilis. The bacteria were pretreated with haemocyte lysate supernatant (HLS) to enhance uptake. The opsonic factor(s) were found to be freeze stable and to be generated during serine protease activation of the proPO system. Phagocytosis was also found to depend upon electron transfer and oxidative phosphorylation and to require an intact cytoskeleton for engulfment. Following ingestion, ca 84% of the bacteria were found to be killed within 3h. Experiments designed to investigate the mechanism of killing showed that treatment of the hyaline cells with phorbol 12-myristate 13-acetate, lipopolysaccharide, phytohaemagglutinin or concanavalin A, but not laminarin, sdmulates the production of superoxide ions (O2-). The semi-granular and granular cells did not produce O2- following stimulation. Incubation of the cells with superoxide dismutase (SOD) confirmed that O2- was produced. Parallel experiments were conducted on a range of marine invertebrates. In all cases O2- production was observed, showing that O2- production is a general phenomenon for invertebrate phagocytes. However, quantification of hydrogen peroxide (H2O2) production, using a H2O2 assay, showed that crab phagocytes produced more H2O2 than tunicate phagocytes indicating that the kinetics of the response varies between species. Using immunocytochemistry, the antioxidant enzymes, catalase, glutathione peroxidase and SOD were found to be located within the haemocytes and plasma of C. maenas. These enzymes may minimise the risk of damage to the host tissues by the O2- and H2O2 produced by the hyaline cells.

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34

Phiri, Ethel Emmarantia. "Molecular phylogeny and biogeography of the Afrotropical freshwater crab fauna." Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86312.

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Thesis (PhD)--Stellenbosch University, 2014.
ENGLISH ABSTRACT: Freshwater organisms, such as crabs (Crustacea: Decapoda: Brachyura), are useful in studies examining inland historical biogeographic patterns and speciation because they are isolated to specific drainage systems, which often serve as barriers to gene flow. The Afrotropical freshwater crab fauna (Potamonautidae) present ideal organisms for investigating hypothesis relating to evolutionary histories because they occur on continental Africa (sub-Sahara) and islands. However, there is a great deal of undiscovered freshwater crab diversity, especially with the prevalence of undiscovered cryptic lineages, which are poorly studied among freshwater crabs, leading to uncertain regional diversity. In this research, multiple genetic (mt- and nuDNA) markers were used to infer the phylogenetic relationships and the biogeographical histories of the Afrotropical freshwater crab superfamily, Potamonautidae. Divergence time estimations were used to infer biogeographic histories, to ascertain whether speciation could be linked to past geologic and / or climatic events. Two widely distributed Potamonautes species complexes were targeted for the investigation of regional cryptic species diversity. In Chapter 2, the intraspecific phylogenetic variability within Potamonautes perlatus sensu lato occurring on the Cape Fold Mountain range (South Africa) was examined, with sampling localities occurring in western- and southern flowing drainages. Previous research suggested possible cryptic speciation within this species complex; however, no tangible inferences could be made because of analytical constraints. Two major clades were recovered: one corresponding to western flowing drainages and another to southern flowing drainages. Moreover, three cryptic lineages were recovered: P. perlatus sensu stricto, restricted to western flowing drainages, and two geographically discrete novel cryptic lineages from the southern flowing drainages, described as P. barbarai sp. nov and P. barnardi sp. nov., with divergence (±2.61 Mya) linked to Pleistocene climatic events. Subsequent to the recovery of the two novel lineages from the Cape Fold Mountain range, the Pleistocene climatic events. Subsequent to the recovery of the two novel lineages from the Cape Fold Mountain range, the revision of the P. clarus / P. depressus species complex from the Tugela and uMkomazi drainages (Drakensberg Mountain range, South Africa) was conducted. This species complex was previously found to comprise at least five cryptic lineages (Chapter 3). A coalescent multilocus (three mt- and three nuDNA) Bayesian species delimitation method was used, and an additional three cryptic lineages were recovered, bringing the total to eight species (two already described as P. clarus and P. depressus), with divergence having occurred approximately 10.3 Mya. Following the recent discovery of novel freshwater crab lineages in the mountainous areas of Mozambique and Malawi, a sampling trip to the Zimbabwean Highlands was undertaken, where a novel freshwater crab species was discovered and described as P. mutareensis, highlighting the need to sample high-lying regions (Chapter 4). Furthermore, two additional novel lineages from Mozambique (P. bellarussus sp. nov.) and the Mpumalanga Province in South Africa (P. flavusjo sp. nov) were described (Chapter 5). In Chapter 6, increased taxon sampling, with additional specimens acquired from various museums and personal collections was used to obtain a better resolution of the phylogeny of the Afrotropical Potamonautidae and to infer the ancestral affinities of the two sub-families, Deckeniinae and Potamonautinae. The Potamonautidae were found to have speciated eastward from West Africa, with a late Cretaceous divergence (±107 – 96.04 Mya). The Potamonautinae originated in West Africa (three genera), while the paraphyletic Potamonautes and Platythelphusa had East African affinities. Potamonautes was not monophyletic, comprising several fragmented geographic clades, which may suggest that this genus requires revision. Nevertheless, the overall speciation within the Potamonautidae reflects past geological and climatic events, such as rifting and uplift episodes and the contraction of forests, which occurred from the Tertiary onwards.

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35

Colavite, Jéssica. "Phylogenetic relationships and taxonomic revision of the genus Macrocoeloma Miers, 1879 (Crustacea Decapoda: Brachyura) /." Botucatu, 2020. http://hdl.handle.net/11449/192314.

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Orientador: William Ricardo Amancio Santana
Resumo: O gênero anfi-americano Macrocoeloma Miers, 1879 é composto por caranguejos decoradores de habitats tropicais e subtropicais. Esses caranguejos são encontrados em substratos distintos, incluindo principalmente recifes de corais e rochas. Esse gênero passou por várias alterações sistemáticas em seu status de família, desde sua descrição original até a sua recente exclusão de Mithracidae. No início deste estudo Macrocoeloma era considerado incertae sedis, devido ao pouco conhecimento das relações entre as espécies do gênero e outros gêneros relacionados, sendo sua revisão taxonômica sugerida diversas vezes na literatura. Assim, com o objetivo de suprir essas lacunas taxonômicas e filogenéticas, este estudo empregou abordagens morfológicas e moleculares para reconstruir as relações filogenéticas de Macrocoeloma. Para isso, utilizamos um conjunto de dados moleculares combinados de um gene nuclear (18S) e três mitocondriais (12S, 16S, COI), usando máxima verossimilhança e inferência bayesiana. Além disso, uma inferência de delimitação de espécies foi realizada com o modelo de Poisson tree processes (PTP), usando a filogenia de máxima verossimilhança do gene mitocondrial COI. Foi realizada a revisão taxonômica de Macrocoeloma, com diagnóstico elaborado, descrições detalhadas e mapas de distribuição geográfica com base no material examinado. A monofilia de Macrocoeloma foi demonstrada, após exclusão de Pericera heptacantha Bell, 1836 e P. septemspinosa Stimpson, 1871. O gênero monot... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The amphi-American genus, Macrocoeloma Miers, 1879, is composed of decorator crabs from tropical and subtropical regions. These crabs are found on distinct substrates, including mainly coral reefs and rock. Macrocoeloma has undergone several systematic changes in its family status, since the original description until its recent exclusion of Mithracidae. Prior to this study, Macrocoeloma was considered incertae sedis, due to little knowledge of the relationships between species of the genus and related genera, and its taxonomic revision has been suggested several times in the literature. Thus, in order to address these taxonomic and phylogenetics gaps, this study employed morphological and molecular approaches to reconstruct the phylogenetic relationships of Macrocoeloma. We used a combined molecular dataset of a nuclear (18S) and three mitochondrial genes (12S, 16S, COI) using Maximum Likelihood and Bayesian Inference. In addition, the inference of species delimitation was performed with the Poisson tree processes model (PTP), using Maximum Likelihood phylogeny of the mitochondrial COI gene. The taxonomic revision of Macrocoeloma was provided with elaborated diagnosis, detailed descriptions and maps of geographic distribution based on examined material. The monophyly of Macrocoeloma was demonstrated after exclusion of Pericera heptacantha and P. septemspinosa. The monotypic genus Thersandrus Rathbun, 1897 is a sister group of Macrocoeloma, followed by the new genus proposed ... (Complete abstract click electronic access below)
Doutor

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36

Do, Van Tu. "Freshwater crabs of Vietnam: diversity and conservation: Review paper." Technische Universität Dresden, 2014. https://tud.qucosa.de/id/qucosa%3A29079.

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The freshwater crab fauna of Vietnam has a high diversity and endemism, 49 species have been recorded and 42 of them are only known from this country. In addition, many species are undescribed or undiscovered while at least 10% of known species are facing extinction. Water pollution, urban, industrial and agricultural development, habitat loss and fragmentation, deforestation and overexploitation are the main threats to this fauna. The first conservation recommendation is keeping rain forest tracts large enough to maintain habitat and water quality for long-term survival of these crabs. More research on taxonomy, distribution, population dynamics, main pressures, conservation status are needed in order to assess conservation status and create efficient conservation actions for freshwater crabs in Vietnam.
Khu hệ cua nước ngọt ở Việt Nam có mức độ đa dạng và đặc hữu cao với 49 loài đã được ghi nhận, trong đó có tới 42 loài chỉ được biết đến ở Việt Nam. Ngoài ra, nhiều loài cua nước ngọt còn chưa được mô tả hay chưa được khám phá, trong khi có tới 10% trong tổng số loài đã biết đang phải đối mặt với nguy cơ tuyệt chủng. Ô nhiễm môi trường nước, đô thị hóa, phát triển công nghiệp và nông nghiệp, nơi sống bị phân mảnh và mất, phá rừng cùng với khai thác quá mức là những mối đe dọa chính đối với khu hệ này. Công tác bảo tồn trước hết phải giữ cho diện tích rừng đủ lớn để duy trì chất lượng môi trường sống cho sự tồn tại lâu dài của các loài cua này. Các nghiên cứu về phân loại học, phân bố, động lực quần thể là rất cần thiết để đánh giá tình trạng bảo tồn và đưa ra những hành động bảo tồn hiệu quả cho các loài cua nước ngọt ở Việt Nam.

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Marijnissen, S. A. E. "Lake Tanganyika crabs evolution, ecology, and implications for conservation /." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2007. http://dare.uva.nl/document/54978.

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38

Baker, Patrick. "Predation on an introduced marine snail by native crabs." Thesis, Thesis (M.S.)--University of Oregon, 1988, 1988. http://hdl.handle.net/1794/9843.

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Typescript. Includes vita and abstract. Bibliography: Includes bibliographical references (leaves 55-58).
Ceratostoma ioornatum is an introduced marine snail in Puget Sound, Washington. Two of five native species tested as possible predators ate Ceratostoma. These two species, the crabs Cancer gracilis and Lopbppaoopeys bellys, did not eat native snails similar to Ceratpstpma, but ate native and introduced bivalves more than Ceratpstpma. The reasons for the differences in predation seemed to be explained by shell strength of the prey species. The presence of Ceratpstpma adds a new type of prey to the menu of the two crab species at the sites studied.

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39

Bui, Thi Hong Hanh. "Detritivory in the Mangrove Sesarmid Crab Parasesarma Erythodactyla." Thesis, Griffith University, 2015. http://hdl.handle.net/10072/366242.

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Sesarmid crabs have important ecological roles in the mangroves of the Indo-west-Pacific biogeographic region. By processing large amount of leaf litter, these crabs retain organic matter in the mangroves, increase the rate of mineralisation, and fuel additional trophic links with the processed material. However, the dietary composition of the mangrove sesarmids is still a controversy. Gut content analyses suggest a dominant contribution of mangrove leaf litter in the crab diet but stable isotope data seem to support the assimilation of organic matter derived from the microphytobenthos but not mangrove litter. In addition, ability of the sesarmid crabs to obtain sufficient nutrition from mangrove litter, which is rich in structural carbon (cellulose) but poor in other nutrients such as nitrogen, has been questioned. The over-arching goal of this thesis was to fill these gaps of knowledge in detritivory of the mangrove sesarmids, using Parasesarma erythodactyla (Hess, 1865), the dominant shredder in sub-tropical Australian mangroves, as an animal model.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
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40

Kennelly, Steven James. "The Empirical Study of Marine Biological Resources." University of Sydney, Marine Studies Centre, 1999. http://hdl.handle.net/2123/390.

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The papers presented in this thesis represent my contributions to the empirical study of marine biological resources. This research has adopted the same experimental approach to: (i) develop scientifically validated techniques to solve specific problems; (ii) use these techniques to detect patterns and form conceptual models about the processes that may have caused them; (iii) do manipulative field experiments to support or refute hypotheses derived from these models; (iv) use these results to develop new models and hypotheses and to test them in new experiments; and (v) recommend, where appropriate, changes to the management of the resources examined. A rigorous, empirical approach is the common feature throughout my research (in its overall direction and subject-to-subject execution) and represents one of the few attempts to adopt such an approach across the three fields in which I have worked: (1) the ecology of underwater kelp systems; (2) the biology of and fishery for a commercially exploited crab; and (3) solving by-catch problems in commercial trawl fisheries.

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How, Martin J. "The fiddler crab claw-waving display : an analysis of the structure and function of a movement-based visual signal /." View thesis entry in Australian Digital Theses Program, 2007. http://thesis.anu.edu.au/public/adt-ANU20081001.111333/index.html.

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Peura, Jennifer Frances. "HERMIT CRAB POPULATION STRUCTURE AND ASSOCIATION WITH GASTROPOD SHELLS IN THE NORTHERN BERING SEA." OpenSIUC, 2013. https://opensiuc.lib.siu.edu/theses/1281.

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Most models of the impacts of climate change on the distributions of animals have focused on limits to thermal tolerances of individual species. Such "bioclimatic envelope" models do not consider the importance of interactions among species, each of which may respond to climate change in its own way. Hermit crabs (Paguridae) cannot exist without shells produced by gastropods. Thus, their ranges are expected to depend not only on their own physiological tolerances, but also on tolerances of gastropod species that produce shells of suitable sizes for growing crabs that use successively larger shells. To assess their potential importance to range shifts of hermit crabs, I characterized these commensal relationships over a large area of the northern Bering Sea in May to early June. Of 1539 hermit crabs collected, Pagurus rathbuni comprised 55%, P. trigonocheirus 44%, and Labidochirus splendescens 1%, with only four individuals of three other Pagurus species. Species richness for all living gastropods in my study area was 26 species, of which 18 were used by hermit crabs. P. rathbuni used shells of mostly moon snails (Naticidae); only 7 to 19% used whelk shells (Buccinidae) in the first four size classes, and 34% in the largest size class. P. trigonocheirus also used shells of mainly moon snails, but its use of whelk shells ranged from 18 to 44% in the first four size classes, and 70% in the largest size class. Densities of P. rathbuni and P. trigonocheirus varied independently of each other (r2 = 0.08, p = 0.09, N = 36 stations). Other studies suggest that hermit crabs obtain most of their shells from gastropods that have recently died, and that such empty shells are available for a relatively short period before being buried in sediments; thus, available shells should resemble the local pool among living gastropods. Correlation of P. rathbuni densities with densities of living gastropods with suitable shells was weak (r2 = 0.18, p < 0.01, N = 36 stations), while there was no correlation for P. trigonocheirus (r2 < 0.01, p = 0.59). Density patterns of hermit crabs within the five size classes did not correspond to those of living gastropods with suitable shells (randomization tests of independence, all p < 0.002). These results suggest that in the northern Bering Sea, initial effects of climate change on hermit crab distributions will depend more strongly on factors other than concurrent effects on dispersion of gastropods.

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43

Hill, Jennifer Marie. "Predator biomass and habitat characteristics affect the magnitude of consumptive and non-consumptive effects (NCEs): experiments between blue crabs, mud crabs, and oyster prey." Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41172.

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Recent research has focused on the non-lethal effects of predator intimidation and fear, dubbed non-consumptive effects (NCEs), in which prey actively change their behavior and habitat use in response to predator chemical cues. Although NCEs can have large impacts on community structure, many studies have ignored differences in predator population structure and properties of the natural environment that may modify the magnitude and importance of NCEs. Here, I investigated the roles of predator size and density (i.e. biomass), as well as habitat characteristics, on predator risk assessment and the magnitude of consumptive and NCEs using blue crabs, mud crabs, and oyster prey as a model system. Predation experiments between blue crabs and mud crabs demonstrated that blue crabs consume mud crabs; however, the consumptive effects were dependent upon blue crab body size and habitat type. When mud crabs were exposed to chemical cues from differing biomasses of blue crabs in laboratory mesocosms, mud crab activity and predation on oysters was decreased in response to high biomass treatments (i.e. large and multiple small blue crabs), but not to low biomass predators (i.e single small blue crab), suggesting that risk associated with predator size is perceptible via chemical cues and is based on predator biomass. Further experiments showed that the perception of risk and the magnitude of the NCEs were affected by the sensory cues available and the diet of the blue crab predator. The NCE based on blue crab biomass was also demonstrated in the field where water flow can disperse cues necessary for propagating NCEs. Properties of water flow were measured within the experimental design and during the experiment and confirmed cage environments were representative of natural conditions and that patterns in NCEs were not associated with flow characteristics. These results affect species conservation and commercial fisheries management and demonstrate that we cannot successfully predict NCEs without considering predator size structure and the contexts under which we determine predator risk.

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44

Ferreira, Da Silva Ana Catarina. "Predation by crabs on rocky shores in north-east Atlantic." Thesis, University of Plymouth, 2008. http://hdl.handle.net/10026.1/1993.

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Highly mobile predators are known to have an important influence on shallow-water habitats. There is, however, little information about the role of crabs on the ecology of rocky shores. Here I examine the extent and consequences of predation by crabs on shores in the North-East Atlantic. The specific aims of this thesis are to: investigate spatial variation in use of the intertidal by crabs along a horizontal gradient of exposure to wave action and a vertical gradient of tidal elevation; assess their use of the intertidal as a feeding area by examining stomach content composition; examine the extent of connectivity between the subtidal and intertidal habitats as a consequence of predation by crabs, investigate the ecological role of crabs as predators in the intertidal, and to assess the importance of behavioral and morphological factors in determining the outcomes of these predator-prey interactions. Field sampling showed that on shores in southwest Britain, the abundance of Carcinus maenas, Necora puber and Cancer pagurus varied between high and low-tide, with the vertical gradient of tidal height and horizontal gradient of exposure to wave action. Crabs were typically more abundant on the lower shore than on the upper shore. C. maenas and N. puber were more abundant on sheltered shores than on exposed shores, while C. pagurus showed the opposite pattern. Individuals captured at high-tide were on average larger than those captured at low-tide. Stomach content analysis of individuals captured with traps at high-tide showed that all three crabs feed on intertidal prey including limpets, chitons and algae. In a mark-recapture field experiment, I demonstrate the migration of sublittoral crabs into the intertidal during high-tide. Subsequent manipulative field experiments showed that predation by crabs can have a considerable effect on abundance of limpets. Laboratory experiments showed that Necora puber has a preference for smaller limpets, indicating that the population structure of these grazers may also be modulated by predation. On shores of differing exposure in Portugal I examine cheliped morphological variation of Eriphia verrucosa in response to variation in prey abundance. Chelipeds were typically larger on exposed shores, where hard shelled prey such as mussels were more abundant than they were on sheltered shores, which were dominated by chitons and algae. Predation by crabs therefore appears to have an important ecological role in shallow-water habitats by influencing intertidal prey populations and establishing an important trophic link between intertidal and subtidal habitats. The implication of predation by crabs on the ecology of rocky shores is discussed.

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Pearson, Timothy. "Adaptive responses to temperature in homogeneously and heterogeneously acclimated crabs." Thesis, Durham University, 1998. http://etheses.dur.ac.uk/4822/.

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Walking leg closer muscle neuromuscular parameters were recorded electrophysiologically from homothermally and heterothermally acclimated Carcinus maenas (eurythermic) and Cancer pagurus (stenothermic). Homothermal (and immobilised) crabs of both species were acclimated to either 8 C or 22 C, whereas heterothermally acclimated crabs were acclimated to 8 C and 22 C coincidentally, exposing the animal's central nervous system (CNS) to either the warm (22 C) or cold (8 C) acclimation temperature. Thus, heterothermal acclimation exposes the CNS/endocrine system and one set of walking legs at one acclimation temperature, the contralateral walking legs are acclimated to the other acclimation temperature. This allowed an investigation into the CNS influence on the attainment of acclimation by walking legs. Comparisons of acclimation responses of the neuromuscular function of isolated walking legs from the same animal were done with respect to the walking leg and CNS acclimation temperatures experienced. Animals were acclimated for two weeks, recordings were taken of excitatory junctional potentials (EJP) etc., from dactylopodite closer muscle fibres when stimulated by the tonic motor axon over an experimental temperature range (6-26 C).The acclimation responses in homothermally exposed crabs of both species resulted in partial (Precht, type III) responses in resting potential, single and double pulse stimulated excitatory junctional potential amplitudes, these were interpreted as responses that allowed the maintenance of muscle function in the new thermal condition. With respect to long term thermal acclimation other electrophysiological parameters gave equivocal compensatory responses. Capacity acclimation responses were more complete in C.pagurus than C.maenas. In heterothermally acclimated animals resting potentials and EJP amplitudes revealed partial acclimation responses in a compensatory manner. Acclimation of heterothermally acclimated C.maenas and C.pagurus was determined to be independent of a CNS influence, indicating thermal acclimation was in response to the local tissue acclimation temperature.

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Ralph, Gina M. "Quantification of Nursery Habitats for Blue Crabs in Chesapeake Bay." W&M ScholarWorks, 2014. https://scholarworks.wm.edu/etd/1539616819.

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The blue crab is an iconic species in Chesapeake Bay, supporting important commercial and recreational fisheries and functioning as a critical link in the food web. Structurally complex habitats are often cited as nurseries for the blue crab, and other commercially important fish and crustacean species, by providing enhanced growth and survival for juveniles. I quantified the value of shallow habitats as nurseries for blue crabs through field studies and a demographic model. In Chapter 2, I utilized a two-year juvenile survey in vegetated habitats of the lower Bay to examine the effect of habitat complexity on the density of juvenile blue crabs. The functional relationship between seagrass cover and juvenile density was exponential, such that there were proportionally more crabs per unit increase in cover of vegetated habitat at high percent cover than at low percent cover. The relationship varied spatially, with higher densities on the eastern shore, and between the two years. The high spatial and annual variability led to questions about how habitat utilization varied throughout the recruitment season. I addressed the timing of recruitment and migration between habitats in Chapter 3 through the development of a survey of shallow habitats in the York River with high temporal and spatial resolution. The study provided evidence for a carrying capacity of juvenile blue crabs in vegetated habitats at 10-15 crabs m2. I found substantially higher densities of small juveniles in shallow unvegetated habitats than previously documented, which suggested that the current paradigm for blue crab recruitment requires modification to include the importance of shallow unvegetated habitats for small juveniles. In Chapter 4, I examined the effect of habitat utilization patterns as a function of age or ontogeny on the blue crab stock assessment by comparing juvenile density and abundance estimates from shallow vegetated and unvegetated habitats to estimates from deep habitats sampled by the primary survey for the stock assessment. Juvenile abundance was very high in both shallow habitats despite the relatively smaller area, thus suggesting that the winter dredge survey substantially underestimated the abundance of juvenile crabs. If this bias is inconsistent inter-annually, potentially as a function of temperature, then stock assessments may be producing biased reference points. Finally, I developed an exploratory habitat-specific demographic model to quantify the effects of habitat on population fitness in Chapter 5. Under all fishing mortality rates, including a complete fishing moratorium, the population growth rate was less than 1 when only unvegetated habitat was present; the increased survival of age-0 crabs provided by vegetated habitats led to increases in the population growth rates. The vegetated habitats provided a buffer from fishing mortality; that is, as the survival of juveniles increased in vegetated habitats, the population could sustain higher fishing mortality rates while still remaining stable or even increasing. Shallow vegetated habitats substantially influence juvenile blue crabs and the overall population growth rate. It is essential that these habitats be considered in future explorations of the dynamics of blue crabs, as well as other species that exhibit ontogenetic shifts in habitat utilization.

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De, Bruyn Colin. "Modalités fonctionnelles et évolutives des parasitoses développées par les crabes Pinnotheridae aux dépens des échinides fouisseurs." Doctoral thesis, Universite Libre de Bruxelles, 2011. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209978.

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Ce travail s’est intéressé aux liens existant entre la stratégie d’exploitation développée par un crustacé ectoparasite et son comportement reproductif. Le crabe Pinnotheridae Dissodactylus

primitivus exploite deux espèces Spatangidae vivant dans la Mer des Caraïbes, Meoma

ventricosa et Plagiobrissus grandis. Des approches comportementales, démographiques et

génétiques ont été adoptées afin de mettre en lumière le fonctionnement et la biologie de cette

symbiose. Par son comportement alimentaire, le crabe occasionne des lésions tégumentaires

sur ses hôtes. Celles-ci affectent la fitness de M. ventricosa, au travers de son développement

gonadique. Dissodactylus primitivus exploite ses deux espèces hôtes de façon asymétrique. La

reproduction des parasites se déroule sur les deux hôtes, alors que le recrutement ne s’effectue

que sur M. ventricosa. Ce cycle vital asymétrique du crabe serait stabilisé par la qualité et la

rareté de P. grandis. En outre, Le comportement sexuel du crabe sur M. ventricosa répondrait

aux critères de la polygynandrie à femelles mobiles. Selon ce modèle, les mâles et les

femelles se déplacent entre les hôtes à la recherche de partenaires multiples. Lors de ces

déplacements, le crabe s’aiderait de son aptitude à localiser chimiquement ses hôtes.

Néanmoins, ce mécanisme s’avère plastique et pourrait refléter l’asymétrie du cycle vital. En

effet, cette différence n’a pas d’origine génétique, car les crabes vivant au sein du site d’étude constituent la même population quelle que soit l’espèce hôte considérée. Les marqueurs

moléculaires microsatellites mis au point dans ce travail permettront lors de futurs travaux

d’affiner les observations sur les modalités d’accouplement du crabe et d’estimer sa capacité

de dispersion.

This work aimed to highlight the relationships between the host exploitation strategy of an

ectoparasite crustacean and its mating system. The pea crab Dissodactylus primitivus exploits

two Spatangidae species living in the Caribbean Sea, Meoma ventricosa and Plagiobrissus

grandis. Behavioural, demographic and genetic approaches have been conducted to examine

the functioning and biology of this symbiosis. Owing to its feeding behaviour, the crab

wounds the host tegument. The wounds negatively affect M. ventricosa's fitness through its

gonadic development. Dissodactylus primitivus asymmetrically exploits its two host species.

The reproduction of the parasites happens on each host, but the recruitment only takes place

on M. ventricosa. The asymmetrical life cycle would be stabilised par the quality and the

scarcity of P. grandis. The mating system of crabs living on M. ventricosa would correspond

to the Pure-search polygynandry of mobile females criteria. According to this model, the

males and the females practice the host switching behaviour to find several sexual partners.

During these movements, the crab could use its chemodetection ability to locate its hosts.

However, this mechanism is plastic and presumably reflects the asymmetrical life cycle of the

crab. This difference has indeed not a genetic cause because the crabs living inside the

investigated region belong to the same population, whatever the regarded host species. In

future studies, the microsatellites markers developed for this work could be used to test the

mating system of D. primitivus and to estimate its dispersion ability.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

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Choi, Kwong-chuen. "The ecology of fiddler crabs (Crustacea: Ocypodidae) at the Mai Po Marshes Nature Reserve, Hong Kong /." [Hong Kong : University of Hong Kong], 1991. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12971820.

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Leelapiyanart, Nongnud. "Ecophysiological studies on developing eggs and ovigerous females of intertidal crabs." Thesis, University of Canterbury. Zoology, 1996. http://hdl.handle.net/10092/5533.

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Morphological, ecological and physiological adaptations of ovigerous crabs and their developing eggs to conditions on shore were compared in two species of New Zealand intertidal crabs. Newly-laid eggs of both Heterozius rotundifrons and Cyclograpsus lavauxi are ellipsoidal, with initial mean volume of 204 and 10 nL respectively, increasing to 360 and 19 nL respectively before hatching. The incubation periods of eggs of H. rotundifrons and C. lavauxi were 194±3 and 56±1 days respectively at constant 15°C. Morphological criteria and timing of the 5 major developmental stages are reported: (1) Newly laid egg stage (2) Blastula stage (3) Gastrula stage (4) Eyespot and pigmentation stage and (5) Heart-beating stage. Two major membranes surround developing eggs at both early and late stages of H. rotundifrons. The thickness of the outer and inner membranes are approximately 3.4-4.8 and 0.6-0.9 µm respectively and are separated by a perivitelline space. The timing of larval release was examined during continuous immersion (and continuing light/dark cycle) in ovigerous H. rotundifrons and C. lavauxi entrained to experimental tidal and light/dark cycles. For H. rotundifrons, larval release occurred over 4-6 consecutive days only during the dark phase at times related to both the light/dark and tidal cycles. For C. lavauxi, larval release was a single event occurring during high tide period at both light and dark phases. Detached eggs of both crab species were able to hatch into larvae independently of the female although the percentage hatching was low. In H rotundifrons, at 15°C, resting mass-specific Mo2 of non-ovigerous and ovigerous crabs was of similar magnitude in air and water but for C. lavauxi, M02 was about two times higher in air. In both species, in air and in water, the mass-specific Mo2 of ovigerous crabs (adults and eggs combined) was higher than in non-ovigerous crabs, the difference being greatest in crabs with late stage eggs. Mo2 of developing eggs of H. rotundifrons and C. lavauxi was measured in seawater at 15°C. In both species, Mo2 of eggs increased 10-12 times, the major increase being toward the end of their development. The cost of development, estimated from total O2 consumption of single eggs of H. rotundifrons and C. lavauxi, was 1.517 and 0.077 µmol O2 respectively. The 20-fold ratio is approximately equal to the ratio of their masses (about 19 times). The elevated metabolic rates of ovigerous crabs can largely be accounted for by the increased metabolism of the eggs. However, a significant unexplained component of the elevation in H rotundifrons suggests a small metabolic cost of bearing eggs. In response to declining oxygen tension, eggs of H rotundifrons and C. lavauxi exhibited characteristics of oxygen conformers and regulators respectively. The Pcrit value for eggs at stage 5D of C. lavauxi was approximately 45 mmHg. The lactate concentration in eggs of H rotundifrons increased from about 0.602 mmol.L-1 in normoxic eggs to about 10.20 mmol.L-1 after 3 hours hypoxic exposure. The rate of lactate accumulation during hypoxia suggests that the eggs are not sustaining metabolism by anaerobiosis, but are allowing metabolic depression. In H rotundifrons, no specific respiratory behaviour was associated with egg-bearing. Upon exposure to hypoxia, non-ovigerous and ovigerous crabs showed similar "emersion behaviour" (initial agitation, followed by leg extension and abdominal elevation and later quiescence). There was no difference in heart rates and scaphognathite activities between non-ovigerous and ovigerous H rotundifrons. Both non-ovigerous and ovigerous crabs of this species showed decreased heart and ventilation rates in response to hypoxia which is similar to the behaviour found in other shore crabs. Both early and late stage eggs of H rotundifrons and C. lavauxi survived 24 hours exposure to dilute seawater and fresh water. Late stage eggs were more tolerant of reduced salinity than early stage eggs. Similar relationships existed when these eggs were acclimated for 96 hours to 50% seawater. In both species, eggs were hyperosmotic to the external medium in all salinities. The osmolalities of eggs were relatively insensitive to the external salinity and, even in fresh water,' maintained osmolality equivalent to 70% seawater. Eggs exhibited remarkably little volume change over the same range of ambient salinities. Measurements of four cations (Na+, K+, Ca2+, Mg2+) in eggs at different stages after 24 hours exposure to a range of salinities, at 15°C, demonstrated that internal ions are retained and regulated differently at different egg stages. The overall concentrations of all four cations increased during development and decreased as salinities decreased. Sodium and potassium are the main cations in the eggs. Sodium was consistently hypo-ionic and potassium hyper-ionic compared with seawater. Sodium and magnesium concentrations changed at a proportionally greater rate with dilution than did potassium and calcium. These observations are consistent with location for most of the sodium and magnesium in a small compartment between the permeable outer egg membrane and the embryo itself and with an embryonic (in the cells, blastocoel or yolk) location for most of the potassium and calcium. Water and sodium influx studies suggested that egg membranes of H. rotundifrons are very permeable to water and salt throughout their development. Eggs at the early stage are more permeable to water but less permeable to sodium than eggs at the late stage. There are two components of water and sodium exchange in all egg stages of H. rotundifrons: a small rapidly exchanging or "fast pool" (outer pool) and a much larger, slowly exchanging or "slow pool" (inner pool). The outer pool is thought to represent the perivitelline space of eggs (4-8% of volume throughout development). The volume of exchangeable water in the inner pool increased with egg development. Eggs at stage 2 and 5D acclimated to 50% seawater showed a permeability to water and sodium less than eggs acclimated to 100% seawater. Such a mechanism would be advantageous in an intertidal environment by limiting the work required to balance the osmotic influx of water and the loss of sodium. The results of this study provided information on the ecology and physiology of ovigerous crabs and developing eggs and suggested that the eggs of both H. Rotundifrons and C. lavauxi could survive periods of hypoxia that might be encountered when the female is partially buried at low tide or in shallow pools. Additionally, the eggs could cope physiologically with periods of dilution of the surface water by precipitation or freshwater seepage. Measurements of sodium and water fluxes indicated that, contrary to earlier suggestions, the eggs are highly permeable and are in dynamic exchange with the seawater at all stages.

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50

Spencer, David. "The Effects of Oceanographic Drivers on the Catchability of Spanner Crabs." Thesis, Griffith University, 2018. http://hdl.handle.net/10072/380993.

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The world’s largest commercial spanner crab (Ranina ranina) fishery, situated on the east coast of Australia, is showing signs of a fishery-wide population decline. This trend has become ubiquitous in many global fishery stocks and is most commonly attributed to anthropogenic pressure and the rapidly changing climate. Thus, the importance of better understanding how commercially-important fishery species thrive in their immediate and surrounding environment is imperative. Catchability is an important parameter used to describe the relationship between catch rates and the abundance of the target species. Variations in catchability are often attributed to fluctuations in environmental and oceanographic conditions in the species’ preferred habitat. Earlier research had suggested several hydrodynamic and hydrographic parameters affect the catchability of spanner crabs. However, a review of the literature (thesis chapter 2) indicated the need for further investigations, particularly on the specific oceanographic processes responsible for these effects. This thesis examines the effects of several oceanographic parameters on spanner crab catch rates at a range of spatiotemporal scales. At large spatial scales (100:500 km) over several years, higher surface chlorophyll-a concentrations, relative to the range of chlorophyll-a observed in each management region, were correlated with lower catch rates in fishing grounds close to the coast and bays. Additionally, region-specific processes responsible for bringing oceanic waters into spanner crab fishing grounds were associated with an increase in catch rates. The link between oceanic water and increased catch rates was further supported by a more localised study (~100 km) that showed cooler ambient temperatures, occasionally attributed to wind-driven upwelling, increased catch rates of spanner crabs at both seasonal and shorter (days-months) temporal scales. At various fishing locations off the Gold Coast, Australia, the effects of current speed, direction and turbidity were examined to determine how specific conditions (day to day) and changes in conditions during soak times (hours) affected catch rates. The most significant finding from this work suggests that catch rates of spanner crabs benefit from a specific range of current speeds (~0.07-0.12 m.s-1), and current speeds exhibiting a large amount of variability may trigger a spike in catch rates over a period of hours. Results from this work show current speed can help explain short-term catch rate anomalies that are currently deemed “random” in stock assessment models. Incorporating environmental and oceanographic parameters into stock assessment models has been an ever-evolving challenge for fishery management. Depending on the region-specific oceanographic and coastal processes, various remotely-sensed oceanographic parameters are also useful in explaining catch rates. The most significant outcomes from this thesis indicate bottom temperature, alongshore wind stress, and bottom current speed are suitable in explaining variability in spanner crab catch rates. A coupled hydrodynamic and biogeochemical model capable of resolving and predicting fluctuations in these oceanographic parameters will help support studies in other areas of the Australian fishery and smaller fisheries in the Indo-Pacific, help improve the accuracy of stock assessment models, and greatly benefit the economic efficiency of commercial crabbing operations.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
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Dissertations / Theses on the topic 'Crabs'

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