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

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 conspicuous 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 (less than or equal to40 mm diameter, a size range that includes recruits) from the US Virgin Islands to demonstrate the subtle effects of an unusually rapid increase in seawater temperature (0.06degreesC per year since 1989) on coral community structure in shallow water (5 to 9 m depth). The analysis reveals that the density of juvenile corals is correlated 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 abundance. 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 ecological consequences for the survival of coral reefs.