Remote video surveys unveil the diurnal variability of trophic-based processes by fishes on coral reefs

Feeding activities by fishes are among the key ecological processes that sustain coral reef functioning. Those trophic-based processes are known to vary across space and across seasons or years. However, there is still little knowledge about their variability within and between days as well as whether these processes are dominated by the same species across time. Using remote underwater cameras, we quantified rates of three feeding activities (corallivory, herbivory and invertivory) for three one-hour time slots (morning, midday, afternoon) over two days on two coral reefs around Mayotte Island (Western Indian Ocean). Feeding activities were highly variable at within and between-day scales and concentrated in a few pulses. Herbivory was the highest in the afternoon which aligns with previous findings regarding activity of herbivorous fishes. Corallivory was the highest in the morning, which highlights the advantage of long-duration benthic remote underwater videos to accurately assess all trophic activities. Trophic-related processes were dominated by the same few species in both sites and across time of the day. This study pinpoints the importance of including within-day and between-day variations when studying ecological processes, as neglecting these variations may introduce biases into our understanding of these processes.