Environmental limits to coral reef development: Where do we draw the line?

Understanding how reefs vary over the present ranges of environmental condi tions is key to understanding how coral reefs will adapt to a changing envi ronment. Global environmental data of temperature, salinity, light, carbona te saturation state, and nutrients were recently compiled for nearly 1,000 reef locations, These data were statistically analyzed to (1) re-define env ironmental limits over which reefs exist today, (2) identify "marginal" ree fs; i.e., those that exist near or beyond "normal" environmental limits of reef distribution, and (3) broadly classify reefs based on these major envi ronmental variables. Temperature and salinity limits to coral reefs, as det ermined by this analysis, are very near those determined by previous resear chers; but precise nutrient levels that could be considered limiting to cor al reefs were not obvious at the scale of this analysis. However, in contra st to many previous studies that invoke low temperature as the reef-limitin g factor at higher latitudes, this study indicates that reduced aragonite s aturation and light penetration, both of which covary with temperature, may also be limiting, Identification of "marginal" reef environments, and a ne w classification of reefs based on suites of environmental conditions, prov ide an improved global perspective toward predicting how reefs will respond to changing environmental conditions.