Seminar

Coral reefs and rhodolith beds are both calcium carbonate-based ecosystems that are biodiversity hotspots, provide numerous ecosystem services and play a significant role in several biogeochemical cycles. However, they are under threat from anthropogenic global warming, ocean acidification and nitrogen pollution. While the effect of these stressors on certain aspects of coral and coralline algae physiology have been well studied, e.g., calcification, their effect on the nitrogen cycle and microbiome has received less attention. Both the nitrogen cycle and microbiome are critical to the health of corals and coralline algae. Therefore, I investigated the effects of global warming and ocean acidification on the nitrogen cycle in corals and coralline algae, as well as the effect of global warming, ocean acidification and nitrogen pollution on the coral microbiome. Simulated ocean acidification resulted in significantly greater uptake rates of dissolved organic nitrogen and isotopic data suggested nitrogen fixation rates may have been suppressed in corals. The bacterial community composition was significantly different between low CO₂ and high CO₂ conditions, including a reduction in beneficial bacteria and increase in bacteria associated with disease in the high CO₂ treatment. Elevated temperature and nitrate also had a significant effect on bacterial community composition, particularly elevated nitrate which appeared to drive the coral microbiome towards a stressed state. Coralline algae exposed to elevated temperature and CO₂ showed significantly greater DIN uptake rates. These results suggest anthropogenic stressors will have a significant effect on the nitrogen cycle within corals and coralline algae and the ecosystems they form the basis of. While changes in the bacterial community composition suggest the health of corals could be impaired under future scenarios.

Additional information: u3005348@connect.hku.hk