Nutrient provisioning by animals can be a major driver of primary productivity in ecosystems. Animal-mediated nutrient sources are particularly important in nutrient poor systems such as coral reefs where nutrient levels are low. While aggregations of animals can create large nutrient pools, the mobile nature of animals often leads to temporal and spatial variability in the availability of these nutrients to an area. In this study we quantified how patterns of fish behaviour and abundance influence the stability of nitrogen provisioning on Bahamian coral reefs. We empirically measured and modeled nitrogen excretion estimates for 16 coral reef fish communities and combined these measurements with fish abundance and behavioural observations to compare reef nutrient budgets on diel, monthly, and annual time scales.
Diel reef nitrogen provisioning varied greatly with diurnal rates being on average four times greater than nocturnal rates. Diurnal rates were highly variable between reefs and were driven primarily by migratory grunts (Hamulidae) resting over reefs during the day. Overall reef excretion rates were highly correlated with grunt abundance, however, grunt abundance could not be predicted by any reef physical characteristics. Variation in grunt excretion rates on a reef was similar across a 4-month period but varied significantly over a 24-month period indicating that nutrient supply on a given reef is not stable over long periods of time. These results suggest that nutrient provisioning on reefs is closely linked to fish behavioural patterns, and that understanding the spatial and temporal patterns of fish movement can help predict patterns of overall primary productivity on reefs.