Corresponding planktivore and predator spatial distributions in an oceanic coral reef system

Abstract

Understanding the drivers of food web community structure is a fundamental goal in ecology. While studies indicate that many coral reef predators depend on pelagic subsidies, the mechanism through which this occurs remains elusive. As many of these species are important fishery targets, a better understanding of their trophodynamics is needed. To address these gaps, we employed a comprehensive structural equation modelling approach using extensive surveys of the reef community to explore relationships between groupers and snappers, their prey, and the surrounding habitat in an oceanic coral reef system. There were significant positive relationships between site-attached and transient planktivores and grouper and snapper biomass, respectively, indicating that pelagic subsidies are transferred to upper trophic levels through planktivores. Contrary to previous studies, habitat complexity and depth were not important for predators or prey. Instead, corallivores and site-attached and transient planktivores were primarily associated with live habitat and coral cover. This indicates that a decline in coral cover could have severe direct and indirect impacts on the structure and functioning of multiple levels of the reef food web. While pelagic reliance may suggest that predators are resilient to bleaching-related habitat loss, the associations of their planktivorous prey with live coral suggest that both benthic and pelagic pathways should be preserved for continued resilience of these food webs and their fisheries. By considering direct and indirect relationships, our study generated insights not only on the complex dynamics of coral reef ecosystems, but also on how they may respond to environmental change.