CORALS, COASTS, AND CARBON: THE CONTINENTAL SHELF, CLIMATE CHANGE, AND A DYNAMICALLY-COUPLED ECOSYSTEM

Corals are important recorders of paleoenvironments, and coral reef ecosystems contribute to the earth’s CO2 feedback processes – their calcification is enhanced by the high surface ocean carbonate mineral supersaturation that typically accompanies low atmospheric CO2 concentrations. However, their calcification liberates CO2 from the marine bicarbonate pool into the surface ocean and atmosphere, providing negative feedback to the calcification process. Coral distributions and productivity are sensitive to other climatic factors, including temperature, water quality, and salinity. Because reef-building corals contain algae as obligate endosymbionts, they require light, and therefore relatively shallow water.

Depth restrictions mean that most suitable coral habitat is close to land, and that the bottom area within a suitable depth range changes dramatically between glacial and interglacial conditions. Changes in potential benthic habitat over sea level cycles interact with changes not only in temperature and carbonate saturation state, but also with hydrologic variations – freshwater runoff and suspended sediment tend to make coastal habitats less suitable for coral reef development. Together with the circulation and erosion changes associated with shelf flooding, reproduction mechanisms and the distribution of coral population centers at lowstands will influence the rates at which the ecosytems shift in both location and function as climate changes.

Modern reef ecosystems have been shaped by a protracted highstand, culminating in a period of often devastating human alteration of the coastal environment. Reconstructing the history and causation of coral and reef variations under conditions of natural environmental forcing represents an interdisciplinary challenge, but one with payoffs in terms of better understanding both past shelf and coast dynamics and the probable future of coastal habitats and ecosystems under conditions of anthropogenic climate change.