Tough love and resilience
The future of coral reefs is precarious and continues to look bleaker as more and more seas report bleaching and further losses of living cover on reefs due to pulses of warm water. This has sent coral reef scientists and managers searching for locations where corals thrive and that are cool and likely to stay cool as climate heats up in the coming decades. The hope is to insure that these cool spots will provide a refuge for corals and to give them the highest levels of protection, in order that at least some corals and living reefs survive climate change. Unfortunately, the number of such places are few and located in areas that often do not support flourishing coral reefs and their legendary biological diversity, resulting in a future that many informed marine biologists see as few scattered spots of uninspiring diversity in a sea of chalky reef skeletons. Not what they have come to expect from this underwater Eden.
But a recently published study documenting the change in coral reefs over the past 10 years in East Africa has considerably brightened this gloomy picture. The authors have identified another environment where high diversity corals may survive and possibly thrive. Ironically, these tropical seas are both warm and have among the fastest rising seawater temperatures, but what makes them different from many other reefs is that the temperature of the water is highly variable across seasons and years and this appears to give them the tough love that helps them survive the rare and deadly hot pulses that devastate their more pampered cousins. The study finds that these areas are often found around islands in the shadows of ocean currents where current speeds are slowed and where water temperatures fluctuate accordingly, but may also be found in subtropical locations that naturally fluctuate with seasons. This study and a companion study found that these reefs are among the most species diverse reefs, equally high in numbers of species to reefs found in environments with less seasonal and yearly fluctuations. This study shows that it is not just the high stability of tropical environments that creates high biological diversity but also fluctuations that prepare them for the unexpected and this may allow them to persist in what is becoming an increasingly hostile environment.
for further detail see: Effects of climate and seawater temperature variation on coral bleaching and mortality by T. R. McClanahan, M. Ateweberhan, C. Muhando, J. Maina, and S. M. Mohammed. Ecological Monographs, 74: 503- 525.