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Physiological response, nutrient allocation, and growth of seagrasses to varying levels of pCO2 along a latitudinal gradient in Western Australia
Western Australia (WA) harbours the most diverse and extensive seagrass meadows in the world, encompassing a number of tropical, subtropical and temperate species. In the advent of increasing partial pressure of carbon dioxide (pCO2) and decreasing pH in the seawater due to anthropogenic inputs, the physiological response of seagrasses and implications for their growth and abundance are still relatively unknown. Hence, the general objective of the study is to help improve our fundamental understanding of the physiological, nutrient allocation, and growth responses of key seagrass species along the latitudinal gradient, between 14 and 32oS, of WA under different environmental conditions (field) and pCO2 scenarios (mesocosm experiments). In particular, the study aims to evaluate the: (1) responses of tropical seagrasses to natural gradient of pCO2 in Kimberley region, (2) carbon-limitation of WA seagrasses and their mechanisms to counteract this limitation, (3) synergistic effects of increased pCO2 and nutrient addition to seagrasses, and (4) vulnerability of seedlings to higher concentrations of CO2 in seawater.
Seagrass meadows have been proposed as a potential global carbon sink as early as 1981 due to its high primary productivity and biomass per area basis, and slow-turnover rate. Three decades after, however, studies on the interaction between seagrasses and carbon dioxide are still very limited and mainly focused on particular seagrass species in temperate regions (Europe and USA). This study, therefore, is important because it covers larger spatial scale, 18 degrees latitude representing tropical, subtropical, and temperate regions of WA. It will also address the paucity of seagrass data in the Kimberley region, the least studied seagrass beds in Australia, perhaps due to extreme tidal regime of up to 11-m. Moreover, the study will elucidate the complexity of biological responses (from physiology to growth and species to community) and sensitivity of the developmental stages (seedling versus adult) of seagrasses to varying levels of pCO2. Key seagrass species in the three regions of WA will be selected for this study, e.g. Halophila ovalis which is the most widely-distributed species in the area. Finally, the implication of the results to seagrass conservation, management, coastal biogeochemistry, and restoration will be explored.