Coral early life history dynamics: conspecific facilitation or limitation are dependent on distinct life stage interactions

Abstract

Replenishment of species within a community is largely determined by early life history dynamics, yet the relative contributions of settlement versus post-settlement processes in establishing coral community structure are not well understood. Here, we examined the effect of larval density, number of settlers and presence of conspecific adults on settlement and post-settlement success for 3 broadcast-spawning scleractinian corals under aquarium conditions. We found that settlement and post-settlement survival are dependent on larval or settler densities but with contrasting effects among the studied coral species. Settlement of Anacropora spinosa larvae was inversely density-dependent, while settlement of Acropora gemmifera and Acropora digitifera larvae was density-independent. A. spinosa had high post-settlement survivorship, while A. digitifera underwent significant density-dependent post-settlement mortality within 14 d after settlement. A. gemmifera showed no significant trend in post-settlement survival by number of initial settlers, but had higher mortality in the second week than the first week, as did A. digitifera. For all species, settler spatial patterns were under-dispersed; the probability of contact between settlers positively correlated to initial settler numbers, and the extent of under-dispersion showed little change over time. The presence of conspecific adults led to a decrease in larval settlement of A. spinosa and A. gemmifera but had only a weak influence on settler survival for A. spinosa. These data indicate, in an experimental setting, that settlement success of larvae can be reduced when in close proximity to a conspecific adult and may be mediated by a waterborne agent. Overall, our results demonstrate the potential for self-limitation via conspecific larval-adult interactions and facilitation among early life stages of a cohort.