The awakening of invertebrates: The daily dynamics of fishes and mobile invertebrates at Rapa Nui's multiple use marine protected area

Abstract

1. On shallow reefs, day-night activity patterns between fishes and invertebrates are presumed to reflect trade-offs between feeding and predation; however, quantitative data on daily community dynamics are scarce. Moreover, night surveys may contribute important information for biodiversity inventories or baselines that normally are not considered. 2. This study used standardized day-night visual surveys of fishes and mobile invertebrates on the same transect lines in Rapa Nui (Easter Island) and investigated how diel patterns vary between taxonomic and trophic groups. 3. Distinct differences between taxonomic groups were observed, with fishes being more abundant during the day (>twice), whilst invertebrate abundance and richness showed an opposite trend with higher numbers at night (>three times). 4. Analysis of trophic groups showed that herbivorous and planktivorous fishes were more abundant during the day. Carnivorous fishes did not show any trends. Top predators (Apex) were observed only at very low abundances. However, a replacement amongst carnivorous fish species between day and night was found, where labridae fishes were practically absent during nights. 5. Most of the mobile invertebrates remained concealed during the day, probably due to the influence of predation risk (labrid fishes). The results emphasize the need for consideration of nocturnally active invertebrates in biodiversity inventories or baselines of reefs, which focus heavily only on diurnal surveys. 6. Day-night reef surveys should be included in marine protected area planning and monitoring as this provides a better understanding of shallow benthic communities and helps inform proper management decisions.