Juvenile coral population dynamics track rising seawater temperature on a Caribbean reef

Abstract

There is now widespread consensus that climate change-related increases in seawater temperature have become a leading cause of coral mortality by bleaching. However, despite widely reported and geographically extensive coral-bleaching episodes, little is known about the less con- spicuous demographic consequences of elevated temperature for coral populations. Here, I use 12 yr of daily temperature records and 8 yr of annual surveys of juvenile corals (≤40 mm diameter, a size range that includes recruits) from the US Virgin Islands to demonstrate the subtle effects of an unusu- ally rapid increase in seawater temperature (0.06°C per year since 1989) on coral community struc- ture in shallow water (5 to 9 m depth). The analysis reveals that the density of juvenile corals is cor- related positively with mean seawater temperature, but concurrently, in warm years, juvenile corals tend to grow slowly and appear to die faster, in a pattern leading to changes in relative generic abun- dance. Although perturbations such as these appear minor against the backdrop of widespread reef degradation, summation of these subtle effects could result in major changes, with far-reaching eco- logical consequences for the survival of coral reefs.