Damage, scale and recovery in model coral communities: the importance of system state

Abstract

Spatial models indicate that recovery of coral cover after damage events depends on large-scale system-level properties as well as those that define parameters at much smaller scales. Monte Carlo simulation studies showed that recovery on individual reefs and in the system as a whole depended on the large-scale pattern of disturbance in the system, so that 2 systems of identical average reef state (- coral cover) but of different variance in reef state may demonstrate dissimilar abilities to recover. The models showed that the relationship between recovery rate and spatial extent of damage depends on (1) the effective connectivity of the system (a system-level property), which affects availability of larvae for recruitment, and the relative magnitudes of (2) larval retention (self-seeding) around individual reefs, (3) background mortality rates of coral and (4) the susceptibility of newly recruited corals to the disturbanse. Recovery rates may be highly dependent or largely independent of the spatial scale of damage depending on values of these parameters, and may vary with the intensity of damage. At high reef densities coral recovery rates are sensitive to survival of recent pre-damage recruits if coral life expectancy is relatively short (25 y), but the degree of self-seeding is relatively unimportant. In contrast, if the density of reefs is low and there is no self-seeding, coral does not recover at all but either stabilises at reduced cover or declines, depending on its life expectancy (i.e. background rate of mortality). If reef density is low and there is some larval retention (13% over 7 d), then recovery depends largely on survival of pre-damage recruits and the rate of background mortality is less important.