Behavioural, physiological, and biochemical responses of two species of scleractinian coral to butterflyfish predation

The negative effects of coral loss on fish assemblages are well established, particularly for obligate corallivores. In contrast, the impacts of corallivorous fish on corals themselves have received less attention, though chronic predation is expected to impose sublethal costs. This study examined how two scleractinian corals, Acropora samoensis and Pocillopora damicornis , responded to varying levels of predation by the polyp-feeding butterflyfish, Chaetodon rainfordi , in a 17-day tank experiment. We assessed the effects of predation on behaviour (polyp withdrawal), physiology (growth, ash-free dry weight, photosynthetic efficiency), and biochemistry (fatty acid content) of coral colonies; with fatty acid profiles further providing insight into energy balance (structural vs. storage lipids), trophic strategy, and coral health. The two species showed contrasting responses. A. samoensis withdrew most polyps even at low predation (88% withdrawn at 0.5 bites min -1 colony -1 ), likely suppressing heterotrophy and leading to reduced growth, although other physiological and biochemical traits remained unaffected. In contrast, P. damicornis , a relatively heterotrophic species, maintained ∼71% of polyps extended under the same intensity, sustaining feeding but incurring greater tissue loss and declining health condition. Nevertheless, growth and ash-free dry weight were maintained, likely through mobilization of storage fatty acids derived from both autotrophic and heterotrophic sources. These results highlight the resilience of corals to chronic butterflyfish predation, as most colonies maintained positive growth even under relatively high per-colony bite rates. However, the observed energy trade-offs suggest potential consequences for reproduction and susceptibility to environmental stress, indicating that chronic predation by non-skeletal feeding corallivores may subtly shape coral performance and persistence.