Seawater chemistry of CO2 system and nutrients as drivers of benthic community structure and carbon metabolism of coral reef ecosystems of different trophic status in the Caribbean

We will study the combined effects of ocean acidification and eutrophication on (1) net ecosystem calcification (NEC) of coral reef ecosystems of different trophic status in the Caribbean (Saba Bank, St Eustatius, Bonaire) and on (2) dissolution of CaCO3 and consequent bioerosion by common excavating sponges on these reef systems. 

Acidification and eutrophication

Ongoing ocean acidification reduces the ability of many marine calcifiers to produce CaCO3, while rates of bioerosion increase. Bioerosion may be further enhanced by the positive effect of eutrophication on growth of bioeroders that cause further loss of coral reef functioning. Transition from net accretion to net dissolution of CaCO3 in Caribbean coral reefs due to ocean acidification and eutrophication will have negative consequences for coral reef ecosystem services. We will quantify the impacts of ocean acidification and eutrophication on bio-erosion in field studies (subproject 1) in combination with experiments with coral excavating sponges (subproject 2).

Impact of bioeroding sponges

These results will be upscaled to reef-wide erosion estimates by mapping seawater chemistry (DIC, Alkalinity, pCO2, pH), nutrients, metabolic activity as well as benthic community composition over several coral reefs in oligotrophic versus eutrophic environments (subproject 1). Subproject 2 will target the physiological basis of CaCO3 dissolution by excavating sponges and assess in situ variations in bioerosion by grafting pieces of Iceland spar calcite and aragonite with these sponges and quantify dissolution under natural conditions. Overall this will allow a better understanding of Carbon metabolism of reef ecosystems and the role of bioeroding sponges in dissolution of CaCO3 in relation to ocean acidification and eutrophication.