Elucidating coral reef predator trophodynamics across an oceanic atoll

Abstract

Coral reef food webs are complex, vary spatially and temporally, and remain poorly understood. Predators on reefs may play major roles linking ecosystems and maintaining ecosystem integrity. In addition, there is increasing evidence of inter - and intra-specific variation in marine predator resource use. Given the high biomass and diversity of predator populations on coral reefs, sympatric predators may vary in their resource use to facilitate coexistence. Knowledge of predator trophodynamics and resource partitioning is important for predicting how reef communities will respond to environmental change and fluctuations in available prey. Using a combination of underwater visual census and baited remote underwater video survey methods, reef predator (e.g. Carangidae, Lutjanidae, Serranidae) populations were quantified across North Malé Atoll (Maldives), which includes outer edge forereefs as well as inner lagoonal reefs. Bulk δ13C, δ15N and δ34S stable isotopes revealed that predators’ isotopic niches varied substantially spatially and interspecifically, with minimal overlap in isotopic niches among species. Furthermore, within populations, there was evidence of intraspecific variation in resource use. Bayesian stable isotope mixing models revealed that all predators were heavily reliant on planktonic production sources, and this planktonic reliance extended to predators inside atoll lagoons. Compound-specific δ13C stable isotope analysis of essential amino acids further indicated that the planktonic subsidies that played an important role in sustaining both outer forereef and lagoonal reef grouper biomass likely originated from mesopelagic plankton communities rather than nearshore plankton communities. Various statistical modelling techniques (e.g. distance-based linear models and structural equation models) highlighted the importance of live coral and reef structural complexity in driving reef predator assemblages. Lagoonal and forereef predators are equally at risk from anthropogenic and climate-induced changes, which may impact the energetic linkages they construct. This highlights the need for management plans that employ a multiscale seascape approach by integrating findings and strategies across disciplines and ecosystem boundaries.