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Research: Biogenic Calcification

Fig. 1. Coral colony transplanted onto a plastic disc, bolted to a cinderblock and fixed to the reef. [larger version] Fig. 2. Encrusting coralline algal community. [larger version]

Unappreciated until very recently, experimental work has demonstrated decreases in calcification rates of corals and other calcifying organisms under conditions simulating ocean acidification. If the experimental data are directly applicable to the field, we should already be seeing measurable declines in calcification rates of important reef-building organisms compared to during pre-industrial times, and some recent studies are starting to show this phenomenon on the Great Barrier Reef in Australia.

However, ocean acidification is occurring against a background of increases in sea surface temperature (SST). Experimental work has shown the relationship between temperature and coral calcification rates to be hyperbolic in nature, with modest increases in calcification with temperature up to a certain optimum temperature (around 27°C), followed by a decrease as temperature is increased further. It is critical to start measuring calcification rates in a systematic way now, particularly at subtropical latitudes where seawater conditions fluctuate seasonally, so that we can understand how changing ocean chemistry and temperatures are affecting calcifying organisms today and in the future.

This field study will provide baseline information on the latitudinal and seasonal variability in calcification rates for a species of reef-building coral and encrusting coralline algal communities. We will monitor calcification of coral by transplanting colonies onto plastic discs, which are then bolted to cinderblocks fixed to the reef (Fig. 1), so that they can be periodically weighed using a special method wherein the corals are kept submerged in seawater. Coral calcification monitoring stations will be co-located with the Sustained Ecological Research Related to the Management of the Florida Keys Seascape (SEAKEYS) oceanographic stations that record several oceanographic variables including SST, salinity, and underwater irradiance. This will allow us to correlate the calcification data with seawater chemistry and temperature data.

The Florida Keys represent a northerly position in latitudinal range for many tropical species. Because of the natural gradient and seasonal fluctuation in carbonate saturation state (largely driven by sea surface temperature), Florida's northern coral reefs and associated carbonate systems will likely be among the first to be impacted by changes in ocean pH and SST. Both corals themselves and encrusting coralline algal communities (Fig. 2) contribute to reef accretion. This study will contribute empirical data to make educated predictions about future reef accretion that will be essential to guiding national, state, and local resource managers and policy makers toward sound decisions regarding the management of carbonate ecosystems.