The Effect of Temporal Scale in Evaluating Physical Forcing of Shallow Coral Reef Communities

Globally, coral reefs have changed over the last half-century and are edging closer to functional extirpation. Understanding these changes requires time-series analyses of pertinent ecological and physical processes, and a growing number of these analyses now extend over decades. Using four decades of data from the shallow reefs of St. John, US Virgin Islands, to provide a model system, this study evaluates the roles of pulse and press disturbances in driving changes in coral reef community stucture. Since 1987, pulse disturbances (hurricanes and bleachings) have caused dramatic declines in coral cover, but the largest changes in benthic community structure reflect the temporal summation of numerous press disturbances. These effects are most strongly associated with annualized rainfall, which integrates the effects of multiple physical processes and captures land-sea interactions. Such decadal-scale data support tests of the roles of multiple physical and biological drivers in mediating retrospective changes in coral reef communities. Prospective analyses will need to interpret this emerging understanding through the prism of ecological memory vested in present-day reef communities, thus increasing the accuracy with which projections of future coral reef community structure can be made.