Academic literature on the topic 'Zostera muelleri'

Contemporary oceanic conditions and local dispersal of propagules influence the genetic diversity and connectivity among seagrass populations. The degree of connectivity between populations of Zostera muelleri in south-eastern Australia is unknown. In this study we examined genetic connectivity among 25 sites containing Z. muelleri using nine polymorphic microsatellite DNA loci. We hypothesised minimal sharing of genetic material between distant populations and a degree of connectivity between local populations. Genotypic diversity was high, with 64% of populations having unique multilocus genotypes (MLGs), indicating the importance of sexual reproduction. Two sites shared MLGs, which may be due to the dispersal and recruitment of vegetative propagules. Genetic differentiation was observed between most sites. With the exception of two outlying sites, two genetic population clusters were identified across the studied populations. Regionally, the populations have high clonal diversity, are strongly differentiated and generally exist in isolation from one another. However, non-significant within-estuary differentiation was observed for three estuaries, indicating a degree of connectivity. The results of this research improve our understanding of the connectivity of Z. muelleri populations in the region, an important process for managing this ecosystem engineer.

Seagrasses host an extremely diverse microbiome that plays fundamental roles in seagrass health and productivity but may be sensitive to shifts in host physiology. Here, we observed a leaf reddening phenomenon in Zostera muelleri and characterized bacterial assemblages associated with green and reddened leaves to determine whether this change in leaf pigmentation stimulates shifts in the seagrass microbiome. Using 16S rRNA gene amplicon sequencing, we observed that the microbiome associated with 4 different leaf pigmentation categories (i.e. green, white, purple and black) differed significantly, with substantial changes in microbiome composition when the tissue is whitened (non-pigmented). Actinobacteria, Rhodobacteraceae, Erythrobacter, Sulfitobacter and Granulosicoccus were enriched in black and/or purple tissues and discriminated these microbiomes from those associated with green leaves. Contrastingly, all ‘discriminatory’ zero-radius operational taxonomic units (zOTUs) were depleted within the communities associated with white samples. While 40% of the abundant zOTUs identified were exclusively associated with a single pigmentation category, only 3% were shared across all categories, indicating partitioning of the phyllosphere microbiome. However, a significant proportion of the ‘normal’ (green) leaf core microbiome was also retained in the core communities associated with black (70%) and purple (70%) tissues. Contrastingly, no core zOTUs were maintained in the white tissues. These results indicate that environmentally driven physiological shifts in seagrasses, such as leaf reddening expressed in response to high irradiance, can impact the seagrass leaf microbiome, resulting in significant shifts in the microbiome of reddened leaves with the most extreme expression (in white tissue of reddened leaves).

Seagrass wasting disease (SWD), an infection believed to be caused by Labyrinthula zosterae, has been linked to seagrass declines in several places around the world. However, there is uncertainty about the mechanisms of disease and the potential involvement of opportunistic colonising microorganisms. Using 16S rRNA gene amplicon sequencing, we compared the microbiome of SWD lesions in leaves of Zostera muelleri with communities in adjacent asymptomatic tissues and healthy leaves. The microbiome of healthy leaf tissues was dominated by Pseudomonas and Burkholderia, whereas the most predominant taxa within adjacent tissues were Pseudomonas and Rubidimonas. Members of the Saprospiraceae, potential macroalgal pathogens, were over-represented within SWD lesions. These pronounced changes in microbiome structure were also apparent when we examined the core microbiome of different tissue types. Although the core microbiome associated with healthy leaves included three operational taxonomic units (OTUs) classified as Burkholderia, Cryomorphaceae and the SAR11 clade, a single core OTU from the Arenicella was found within adjacent tissues. Burkholderia are diazotrophic microorganisms and may play an important role in seagrass nitrogen acquisition. In contrast, some members of the Arenicella have been implicated in necrotic disease in other benthic animals. Moreover, microbiome structure was maintained across sites within healthy tissues, but not within SWD lesions or the tissues immediately adjacent to lesions. Predicted functional profiles revealed increased photoautotrophic functions in SWD tissues relative to healthy leaves, but no increase in pathogenicity or virulence. Notably, we demonstrated the presence of L. zosterae in SWD lesions by polymerase chain reaction, but only in one of the two sampled locations, which indicates that other microbiological factors may be involved in the initiation or development of SWD-like symptoms. This study suggests that the dynamics of the seagrass microbiome should be considered within the diagnosis and management of SWD.

The seagrass Zostera muelleri Irmisch ex Asch. is abundant in estuaries in Australia and is under pressure from coastal developments. We studied sulfide intrusion in Z. muelleri along a gradient of anthropogenic impact at five stations in the Wallis Lake estuary, Australia. Results showed differences in sediment biogeochemical conditions, seagrass metrics as well as nutrient content and sulfide intrusion along the gradient from the lower estuary (affected) to the lagoon (unaffected). Sulfide intrusion was driven by complex interactions and related to changes in seagrass morphology and sediment biogeochemistry and was modified by the exposure to wind and wave action. The sediments in the lower estuary had high contributions from phytoplanktonic detritus, whereas the organic pools in the lagoon were dominated by seagrass detritus. Despite high concentrations of organic matter, sulfide intrusion was lower at stations dominated by seagrass detritus, probably because of lower sulfide pressure from the less labile nature of organic matter. Porewater diffusive gradients in thin-film (DGT) sulfide samplers showed efficient sulfide reoxidation in the rhizosphere, with high sulfur incorporation in the plants from sedimentary sulfides being likely due to sulfate uptake from reoxidised sulfide. This is a unique adaptation of Z. muelleri, which allows high productivity in estuarine sediments.

Zostera muelleri, the dominant seagrass species along the eastern coastline of Australia, has declined due to anthropogenic stressors, including reduced water clarity. Water quality has improved in recent years, but restoration efforts are hampered by limited knowledge of transplantation methods. To support future restoration efforts, we tested multiple techniques for transplanting mature seagrass shoots: (1) sediment cores with intact seagrass plants (plug); (2) individual shoots anchored on frames (frame); (3) frame methods combined with subsurface mats to exclude bioturbating animals (mat+frame); (4) above-ground cages to exclude grazing fish (cage+frame); and (5) combined treatment of above-ground cages and subsurface mats (cage+mat+frame). Transplant success over 10 months showed considerable variability among locations. At one site, seagrass persisted in all treatments, with highest growth in the mat+frame treatment. At two locations, uncaged shoots were lost within 6–35 days of transplanting, presumably due to grazing by fish. In treatments with cages, growth was again highest in the mat+frame treatment. At the fourth location, all seagrass was lost due to physical stress. Thus, we conclude that transplantation success is highest using the mat+frame technique, but overall success depends on careful assessment of biotic and abiotic stressors at the chosen locations.

In modifying the traits of producers, coastal development and latitude may influence the assimilation of organic matter resources by consumers. The aim of the present study was to assess spatial variation across gradients of latitude and diffuse nitrogen loading in: (1) the N content of the seagrass Zostera muelleri and the mangrove Avicennia marina; and (2) the ultimate organic matter sources (inferred from δ15N and δ13C signatures) of the detritivorous mud whelk Pyrazus ebeninus and the predatory polychaete Nephtys australiensis. It was hypothesised that the organic matter sources of each of the two consumers would vary spatially, following patterns of spatial variation in the N content of primary producers. Sampling in 12 estuaries of New South Wales, Australia, spanning 7° of latitude and variable nutrient loading revealed that the nitrogen content of Z. muelleri was negatively correlated with latitude and nitrogen loading, but the nitrogen content of A. marina leaves followed only latitude. Of the four organic matter sources considered by the present study, Z. muelleri was consistently the main source passed through the trophic chain to the detritivore P. ebeninus and the predator N. australiensis. Nevertheless, the proportionate contribution of Z. muelleri and microphytobenthos to the carbon sources of N. australiensis varied with latitude, the former negatively and the latter positively. These relationships suggest that latitude may influence carbon sources of consumers by modifying producer physicochemical traits.

University of Technology Sydney. Faculty of Science.
Despite the vast research on the negative effects of anthropogenic pollution on marine organisms, little is known about the toxicity responses of seagrasses to such perturbations. Understanding seagrass responses at the molecular level will ensure adequate conservation strategies to mitigate the increasing decline rate of seagrasses as a result of climate change and anthropogenic driven disturbances. The meadows of the Southern hemisphere seagrass species, 𝘡𝘰𝘴𝘵𝘦𝘳𝘢 𝘮𝘶𝘦𝘭𝘭𝘦𝘳𝘪, encounter similar threats, which led to a significant loss along the Australia and New Zealand coasts. Trace metal pollution and most specifically copper (Cu), have been previously reported in industrial, agricultural and domestic run-off waste which often finds their way to the ocean and jeopardise the health of the seagrass meadows. Although we have a firm undersetting of the deleterious effect of Cu stress at the physiological and ecological level, no current knowledge exists on how 𝘡. 𝘮𝘶𝘦𝘭𝘭𝘦𝘳𝘪 responds to elevated levels of Cu at the molecular level. Upon our investigation of the physiological responses of 𝘡. 𝘮𝘶𝘦𝘭𝘭𝘦𝘳𝘪 to 250 μg Cu L⁻¹ and 500 μg Cu L⁻¹ over a 7 day period of exposure, the Cu accumulation in the leaves, the continual production of ROS and the decline of photosynthetic efficiency were observed in 𝘡. 𝘮𝘶𝘦𝘭𝘭𝘦𝘳𝘪 at both above mentioned Cu concentrations. However, the responses were concentration-dependent illustrating 250 μg Cu L⁻¹ and 500 μg Cu L⁻¹ as a tolerable and a toxic level for 𝘡. 𝘮𝘶𝘦𝘭𝘭𝘦𝘳𝘪, respectively. The results of our molecular investigations indicated regulation shifts in the expression of genes and the abundance of proteins mainly at 500 μg Cu L⁻¹ were associated with energy metabolism, carbon fixation, photosynthesis and defence mechanism. While the expression of genes (and the abundance of proteins) involved in energy metabolism (mainly glycolysis) and defence mechanism have been shown to be mainly increased, the opposite was observed in the photosynthetic process and carbon fixation. As a result, whilst these results offers a new level of understanding into the seagrass toxicity responses at transcriptomic and proteomic levels, it also provides candidate molecular markers for future toxicology studies and seagrass monitoring. This PhD thesis also evaluates a protein-centric and four peptide-centric proteomic methods and proposed an optimised peptide desalting protocol. Additionally, major alterations in photosynthesis process as a result of Cu stress has led us to report on an optimised intact chloroplast isolation method that can be used for future proteomic-based studies.

University of Technology Sydney. Faculty of Science.
Seagrasses are marine foundation species that have evolved to live in shallow coastal waters, an environment regularly subjected to changes through tidal patterns and anthropogenic activity. Global seagrass coverage is declining worldwide, mainly driven by decreasing water quality due to anthropogenic activity. Therefore, there is an urgent need to better understand seagrass biology, particularly the way their growth will be impacted by changing environments in order to assist their preservation. Through the use of emerging techniques such as gene expression analyses, the underlying mechanism driving photosynthesis can now be explored at the molecular level and is an emerging field in seagrass research. The overarching aim of my thesis was to identify the molecular mechanisms driving carbon metabolism in the seagrass 𝘡𝘰𝘴𝘵𝘦𝘳𝘢 𝘮𝘶𝘦𝘭𝘭𝘦𝘳𝘪. To accomplish this aim, a combination of physiological and molecular analytical tools were used to measure changes in photosynthesis in response to decreased O₂ concentrations in the water column, decreased irradiance and chemical inhibition of carbonic anhydrase (CA). The results presented in this thesis describe the ways in which genes associated with carbon metabolism were regulated in response to the different environmental factors as listed above. Specifically, we found that in low O₂ conditions, photosynthetic efficiency was enhanced while genes involved in the photorespiratory and recycling of TCA cycle intermediates were down-regulated. In addition, we found that under reduced irradiance conditions, ¹³C uptake was reduced and this correlated with a down-regulation of genes involved in photosynthetic, photorespiratory and recycling of TCA cycle intermediates pathways. Finally, when exposed to inhibition of CA, 𝘡. 𝘮𝘶𝘦𝘭𝘭𝘦𝘳𝘪 plants displayed a decrease in photosynthetic rate concomitant with up-regulation of photosynthetic and photorespiratory genes, suggesting the presence of a compensatory mechanism in this seagrass specie in order to overcome CA inhibition. In view of these results, we provide further details to the carbon metabolism pathways in 𝘡. 𝘮𝘶𝘦𝘭𝘭𝘦𝘳𝘪 and presents new techniques in molecular analysis that can be applied to different areas of seagrass research.

The aim of the research was to ascertain whether the locally predominant seagrass species, Zostera muelleri, could be a potential TE bioindicator. This is was achieved by conducting two multi-factor laboratory Cu and environmental experiments and spatial and temporal field assessments. Results has shown that the seagrasses life cycle and the part of the seagrass analysed can influence the metal concentrations, which is important for interpretation of results.

The role of seagrass systems, including those of Zostera muelleri, in providing critical ecosystem services including provision of nursery habitat for economically important fish species and significant nutrient cycling services are well known (Orth et al., 2006). The current understanding of the population ecology of the species is however lacking, potentially leading to management decisions that fail to incorporate the ability of Z. muelleri to disperse, recruit and grow as well as the role the species plays in the development of microphytobenthic communities within seagrass systems. Important abiotic (non-living) variables that influence the growth and survival of Z. muelleri within the marine environment include near-shore and oceanic currents, light availability, nutrients, temperature and salinity levels, with the latter being predominantly driven by changes in freshwater inputs (Kaldy et al., 2015). Biotic factors include herbivorous predation which may assist in propagule release, competition and potential facillitatory roles of existing seagrasses that may aid in the ongoing productivity of populations (Holmgren et al., 1997).

Coastal zones are complex and highly productive social-ecological systems (SES), but their resilience is increasingly threatened by a range of human activities including land use change and the expansion of port infrastructure associated with the global movement of minerals, petroleum products and other commodities. Over the last decade, the gas industry has emerged as a key driver of port development as it seeks to rapidly develop unconventional resources such as Coal Seam Gas (CSG). In many cases, unconventional gas developments are accompanied by the construction of coastal infrastructure including gas processing and liquefaction plants, pipelines and shipping facilities, used for export and import of refined gas products. This brings the gas industry into increasingly close contact with marine and coastal ecosystems. Seagrasses (marine flowering plants) are among the habitats most at risk of disturbance associated with port development. Seagrass meadows are critical to the health of marine ecosystems, playing an important role as a coastal filter for sediment and nutrients, acting as foraging and nursery habitats for wildlife, and storing carbon and other greenhouse gases (GHGs) in the oceans. The loss of seagrass meadows can therefore have secondary impacts on the broader ecosystem, including on the wildlife that depend on them for habitat, including fish, benthic invertebrates, marine turtles and sirenians (dugongs and manatees). Many of these fauna species are facing localised declines across the world as a result of multiple pressures including loss of foraging and breeding habitat, an increase in marine pollutants and fishing pressure. Adding to this complexity, infrastructure developments along the coastline are embedded within complex networks of human-environment interactions and as such, their ecological and social impacts are intimately linked. Human communities are affected by the environmental, social and economic changes that are associated with large-scale industrial developments, including a deterioration in ecosystem services, higher living costs, increased burden on healthcare and other community services and public safety concerns, in addition to economic benefits. Because coastal counities are intimately connected to the environment through the exchange of material inputs and ecosystem services, degradation of the local environment also has ramifications for local livelihoods and quality of life. Australia is currently the world’s leading exporter of coal, and is expected to become the largest global exporter of Liquefied Natural Gas (LNG) by 2018-19. Six LNG facilities are currently in operation or development around the country, three of which are located inshore of the Great Barrier Reef (GBR) on the north-eastern coast of Queensland. The GBR is perhaps best known for the natural values that make it one of the great wonders of the world, but it is also home to a number of large industrial ports and the subject of ongoing port development proposals. The proposed expansion of port development in the Great Barrier Reef World Heritage Area (GBRWHA) to support growth in the LNG and coal sectors prompted the World Heritage Council to review Australia’s management of the GBRWHA in 2012, placing the World Heritage status of the GBR in question. The review expressed strong concerns about the capacity of current governance structures to protect the ecosystems of the GBR, given the unprecedented scale and speed of industrial development along its margins, and highlighted the need to better understand the impacts of such developments on the ecology of the GBR and the local communities whose wellbeing and livelihoods depend on its resources. Although there has been much research on the social, economic and environmental impacts of inland CSG infrastructure, this has not been the case for coastal LNG plants and associated port developments. With this in mind, this thesis sought to understand how recent forms of industrial development affect complex SES in the GBRWHA through an in-depth case study of the Port of Gladstone, where recent LNG development has led to concerns over port impacts to the marine environment and social wellbeing among the local community. In so doing, I employed a trandisciplinary methodology comprising a suite of ecological and social research methods, which was subsequently developed into a broader framework for application to other contexts. The first phase of the research involved a survey of local residents in the Gladstone Region, which revealed that impacts of port development on water quality, fish health and seagrass meadows, and the socio-economic impacts associated with rapid LNG development, were of highest concern to local residents. Short-term declines in seagrass cover have been observed in a number of areas of the GBR since 2011, and these are attributed to the interaction of multiple processes including dredging, flooding and cyclones (Great Barrier Reef Marine Park Authority, 2014; McKenna et al., 2015). The research also included a component of ecological field- and laboratory-based research that examined the interactions between elevated event-based sedimentation rates and seagrasses in the Port of Gladstone. Lastly, the research drew together these two components through a critical assessement of the processes of Environmental Impact Assessment (EIA) and Social Impact Assessment (SIA) for the Gladstone LNG projects. These twin processes are designed to predict and provide a framework for managing the impacts of developments at the local scale. The findings of this research relate both to the ecology of seagrass meadows in the port of Gladstone and to the socio-economic changes that are intimately linked to environmental change. The research demonstrates that local attitudes towards LNG development in the GBR are closely linked to perceptions of environmental health before and after port development, as well as the values that local residents associate with the marine environment. The importance of coastal ecosystems to local livelihoods, lifestyles and sense of place, and their vulnerability to port-related disturbance emphasises the need to protect them into the future. Seagrasses in the Port of Gladstone demonstrate resistance to sedimentation, but growth declines significantly when these species are shaded or buried for prolonged periods, such as may occur after flood events or dredging. Additionally, the research found that the coastal setting and specific characteristics of the LNG industry – including the speed and unprecedented scale of development – have led to highly specific, and often cumulative, social and economic impacts that are difficult to predict and manage through current project-based impact assessment processes. Finally, although it is widely acknowledged that both scientific and local knowledges, including the knowledge of local indigenous peoples, play an important role in governance processes, current governance arrangements inhibit effective knowledge sharing and adaptive governance throughout the project lifecycle. This thesis provides evidence for the benefits of a more inclusive, adaptive approach to impact assessment, and also highlights the ways in which transdisciplinary research may be used to improve our understanding of complex social-ecological systems.

The article presents data on biotechnology for manufacture of feed for different stages of development sea cucumber in the factory conditions. The regime of multi-cycle cultivation of three species of microalgae Isochrisys galbana, Dunaliella salina, Chaetoceros muelleri, Phaeodactylum tricornutum with sequential start of cycles is used for continuous provision of live food for larvae trepang. A fermented mixture consisting of red algae Ahnfeltia tobuchiensis, brown algae Saccharina japonica and the sea grass Zostera marina is recommended as the basis for starter and production feeds for juvenile trepang. Use of starter feed of fermented mixtures in industrial conditions increases mass of young trepang by 5,4 times, producton – by 5,9 times. Recommendations have been developed on the use of feeds based on fermented macrophytes for the industrial cultivation of juvenile sea cucumber of different stages of development.