Early post-settlement mortality and the structure of coral assemblages

Abstract

Events occurring early in life history can have profound effects on the structure of populations and communities. In particular, susceptibility to predation is often highest early in life, and can greatly influence community structure. To better understand these events in reef-forming coral communities, we investigated how spatial variation in recruitment and early post-settlement predation influenced the spatial structure of a coral assemblage. Over a 5 yr period, we compared recruitment of corals and abundance of juveniles and adults at a combination of 3 locations and 3 depths in French Polynesia. We then measured mortality of recruits (< 3 mo old) and juveniles (about 1 to 4 yr old), and abundance of potential predators. Results demonstrate the crucial role of events occurring in the first weeks of the benthic stage. The abundance of scraping herbivorous parrotfishes explained substantial spatial variation in the mortality of recruits, but not juveniles, revealing a likely effect of incidental removal by grazing. Conversely, abundance of coral-feeding butterflyfishes explained substantial spatial variation in the mortality of juveniles. These findings underscore the importance of incidental mortality from grazing and specialized corallivory on coral populations. Moreover, these processes can play a key role in determining spatial patterns in coral assemblage structure.