Foraging plasticity in obligate corallivorous Melon butterflyfish across three recently bleached reefs

Abstract

Because obligate corallivorous butterflyfish feed exclusively on coral polyps, they are particularly sensitive to changes in coral cover and its spatial distribution. To understand how such differences in coral cover influence obligate corallivores, we examined the densities and foraging behavior of Melon butterflyfish Chaetodon trifasciatus across three reefs in the Lakshadweep archipelago. These reefs suffered differential bleaching mortality after the 2010 El Niño Southern Oscillation, resulting in wide variation in coral cover and community composition. Despite these differences, C. trifasciatus were able to persist at similar densities across reefs. However, our analysis of high‐resolution video recordings of multiple focal fish revealed that time budgets, bite rates, and diet selectivity differed significantly. Fish in resource‐poor reefs spent more time moving between coral patches and less time foraging than ones in relatively resource‐rich reefs. We also found that fish in resource‐poor reefs had higher bite rates and were less selective in their foraging. Our results provide novel insights into how obligate corallivores cope with even large differences in resource availability. At a time when we are rapidly losing corals to repeated climate‐induced bleaching events, this flexibility may represent a critical mechanism that enables persistence of obligate corallivores in resource‐poor reefs, even if it does not guarantee longer‐term survival.

Wave exposure reduces herbivory in post-disturbed reefs by filtering species composition, abundance and behaviour of key fish herbivores

“…1). The atolls have distinct windward (west, exposed) and leeward (east, sheltered) aspects in relation to the south-west monsoon 30 , which plays a strong role in shaping coral and fish assemblages 24,29,[31][32][33] . Given these clear differences, we expected fish herbivore composition, biomass, density, herbivore activity and function (algal control) to differ between reef exposures.…”

Corallivory in the Anthropocene: Interactive Effects of Anthropogenic Stressors and Corallivory on Coral Reefs

“…If preferred corals become rare then specialized corallivores (e.g., butterflyfishes) often increase feeding on remaining healthy conspecifics (Cole et al, 2009). Conversely, generalist predators (e.g., wrasses and muricid snails) tend to prey more intensely on bleached colonies (Cole et al, 2009;Tsang and Ang, 2014) or other healthy coral species (Pratchett et al, 2004;Hoeksema et al, 2013;Zambre and Arthur, 2018). These alterations to feeding behavior have indirect effects on corallivorous fish populations.…”

“…For instance, specialized butterflyfishes are projected to disappear from reefs as preferred prey species decline in response to bleaching whilst generalist butterflyfish populations are expected to remain stable (Berumen and Pratchett, 2006;Graham, 2007;Graham et al, 2009;Emslie et al, 2011;Wilson et al, 2014). However, diet plasticity in some specialized corallivores (e.g., Chaetodon trifasciatus) in response to bleaching may allow local populations to persist (Zambre and Arthur, 2018). Altogether, these data suggest that bleaching events can reduce population sizes of specialized corallivorous fishes but also concentrate corallivory on the remaining corals after a bleaching event, potentially slowing coral recovery.…”

Foraging in nature: Contrasting responses to resource heterogeneity at small‐ and large‐spatial scales

“…Additionally, animals should spend more time feeding in resource-poor environments as the rate of energy gain is also slower (Charnov, 1976). A study of butterflyfish similarly reports that individuals modify their foraging behavior to compensate for low resources (Zambre & Arthur, 2018).…”