Geographically specific recruitment and postsettlement mortality as influences on coral communities: The cross‐continental shelf transplant experiment

Abstract

The importance of geographic isolation in larval availability vs. postsettlement mortality as factors influencing coral community structure was examined. Coral recruitment and mortality patterns were assessed on the Great Barrier Reef (Australia) via settling plates implanted on three reefs located 16, 58, and 117 km from shore (across the continental shelf) at depths of 3 and 15 m. In a controlled experiment, plates were transplanted after 6 months of exposure to other reefs, covering all possible between‐reef combinations. Recruitment was higher on the outer half of the shelf and in deeper water. Acropora and Seriatopora were the major recruits on the mid‐ and outershelf reefs, where adult Acropora dominates. Porites and Alveopora dominated the inner‐shelf reef where Porites is a dominant adult. Mortality was lowest on the midshelf reef. Inshore recruits suffered greater losses in competition for space. Coral larvae settled cryptically, except in deeper inshore waters (low light). Taxonomic gradients occurred across the shelf, suggesting some geographic isolation, and implying that local larval pools differ. Spat transplanted from the midshelf reef to inshore or offshore reefs suffered higher mortality rates. Transplants from offshore survived better on the midshelf reef. Transplants from inshore to mid‐ or offshore reefs appeared to survive well. Larval availability, regional seeding of reefs, and postsettlement mortality may together play important roles in influencing coral community structure.