Effects of Madagascar marine reserves on juvenile and adult coral abundance, and the implication for population regulation

Abstract

Recruitment is a critical component in the dynamics of coral assemblages, and a key question is to determine the degree to which spatial heterogeneity of adults is influenced by pre-vs. post-settlement processes. We analyzed the density of juvenile and adult corals among 18 stations located at three regions around Madagascar, and examined the effects of Marine Protected Areas (MPAs). Our survey did not detect a positive effect of MPAs on juveniles, except for Porites at the study scale. The MPA effect was more pronounced for adults, notably for Acropora, Montipora, Seriatopora, and Porites at the regional scale. For most dominant genera, densities of juveniles and adults were positively correlated at the study scale, and at least at one of the three regions. These outcomes suggest recruitment-limitation relationships for several coral taxa, although differences in post-settlement events may be sufficiently strong to distort the pattern established at settlement for other populations. The modest benefits of MPAs on the density of juvenile corals demonstrated here argue in favor of strengthening conservation measures more specifically focused to protect recruitment processes.