Patterns and mechanisms of variable settlement and recruitment of a coral reef damselfish, Chromis cyanea

Distinguishing the relative contributions of various processes to variation in recruitment success is central to our understanding of patterns and rates of population replenishment in marine organisms. We monitored settlement and recruitment of a common Caribbean damselfish, the blue chromis Chromis cyanea, to ascertain the extent to which variation in recruitment reflected settlement dynamics. Daily settlement and weekly recruitment were censused on coral heads for 1.5 mo at each of 2 reefs separated by 7 km. We also conducted manipulations of resident conspecifics to test for intraspecific effects on patterns of settlement and recruitment. Temporal variation in settlement between the 2 reefs coincided with the new moon, but peak settlement at one reef lagged the other by 7 to 10 d over 2 settlement periods. Such variation may have been caused by longshore current flow delivering patches of larvae to the reefs in sequence or by high current velocities at one reef coinciding with the new moon that may inhibit and delay settlement. Weekly recruitment was marginally higher than but unrelated to cumulative daily settlement, indicating possible recruitment facilition. In subsequent experimental manipulations settlement occurred only where conspecifics were present and was inversely density-dependent. Observed early post-settlement mortality of C. cyanea on continuous fore-reef was density-dependent, which is consistent with patterns of mortality for this species previously reported on patch reefs. Combining rates of input (resident-facilitated settlement) with rates of output (density-dependent mortality) of C. cyanea suggests that both resident conspecifics and predators play a role in the abundance and regulation of local populations.