Planktivorous fishes withstand 20 years of major coral cover oscillations

Planktivorous fishes play a crucial role in coral reef ecosystems by converting pelagic planktonic resources into reef biomass. They serve as key vectors of energy transfer from the pelagic zone to the reef, thereby enhancing overall productivity. However, the habitats supporting planktivorous fishes are under unprecedented stress imposed by global changes, foremost of which widespread warming-induced coral mortality. We analyzed 20 years (2004–2024) of benthic and fish monitoring data around Mo’orea Island (French Polynesia, South Pacific) across three reef types (fringing reef, backreef, and forereef). Our results show that planktivorous fish density was positively but weakly correlated with coral cover. On the forereef, planktivorous fish communities were more responsive to disturbances affecting coral cover (e.g., heatwaves, cyclones, or Crown-of-Thorns starfish outbreaks). There, fishes responded by exhibiting relatively large fluctuations in density and community composition; the opposite was true for backreef and fringing reef. Indeed, zones characterized by low coral cover (< 25%) that initially supported few planktivorous fishes, showed a moderate but detectable increase in density after successive disturbances. Oscillations in coral cover driven by these disturbances have long-term cascading effects on associated fish assemblages, as evidenced by the gradual decline of Pycnochromis vanderbilti unveiled in our study. Collectively, our findings imply a relative resilience of planktivorous fishes facing repeated and severe coral cover decline and rebound.