Mesopredator trophodynamics on thermally stressed coral reefs
Ecosystems are becoming vastly modified through disturbance. In coral reef ecosystems, the differential susceptibility of coral taxa to climate-driven bleaching is predicted to shift coral assemblages towards reefs with an increased relative abundance of taxa with high thermal tolerance. Many thermally tolerant coral species are characterised by low structural complexity, with reduced habitat niche space for the small-bodied coral reef fishes on which piscivorous mesopredators feed. This study used a patch reef array to investigate the potential impacts of climate-driven shifts in coral assemblages on the trophodynamics of reef mesopredators and their prey communities. The ‘tolerant’ reef treatment consisted only of coral taxa of low susceptibility to bleaching, while ‘vulnerable’ reefs included species of moderate to high thermal vulnerability. ‘Vulnerable’ reefs had higher structural complexity, and the fish assemblages that established on these reefs over 18 months had higher species diversity, abundance and biomass than those on ‘tolerant’ reefs. Fish assemblages on ‘tolerant’ reefs were also more strongly influenced by the introduction of a mesopredator (Cephalopholis boenak). Mesopredators on ‘tolerant’ reefs had lower lipid content in their muscle tissue by the end of the 6-week experiment. Such sublethal energetic costs can compromise growth, fecundity, and survivorship, resulting in unexpected population declines in long-lived mesopredators. This study provides valuable insight into the altered trophodynamics of future coral reef ecosystems, highlighting the potentially increased vulnerability of reef fish assemblages to predation as reef structure declines, and the cost of changing prey availability on mesopredator condition.
KeywordsClimate change Coral bleaching Functional group Habitat degradation Mesopredator Trophic structure
The authors would like to thank the Lizard Island Research Station and its directors Lyle Vail and Anne Hoggett for all the logistical support and facilities they provided for the field component of this research. This research was conducted under animal ethics approval from James Cook University (Ethics approval number A1996). This research was supported by the Australian Research Council and the Australian Institute for Marine Science.
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