Fish movement drives spatial and temporal patterns of nutrient provisioning on coral reef patches

Abstract

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. However, aggregations of mobile animals might lead to temporal and spatial variability in local nutrient availability, which is not well understood. In this study, we quantified how patterns of fish movement 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 behavioral observations to compare reef nutrient budgets on diel, monthly, and annual time scales. Diel reef nitrogen provisioning by fishes varied greatly, with diurnal rates being on average four times greater than nocturnal rates. Diurnal rates were highly variable among reefs and were driven primarily by migratory grunts (Haemulidae) resting over reefs during the day but foraging off reefs at night. At the reef scale, overall nitrogen excretion rates were correlated with grunt abundance; however, grunt abundance could not be predicted by any reef physical characteristics. Within‐reef grunt excretion rates changed little across a 4‐month period but varied significantly over two years, indicating that nutrient supply on a patch reef is not stable over long periods of time. Quantifying how nutrient provisioning on patch reefs is linked to fish activity and movement patterns and how provisioning varies on different spatial and temporal scales is important for understanding overall patterns of primary productivity on reefs.

Nutrient limitation, bioenergetics and stoichiometry: A new model to predict elemental fluxes mediated by fishes

“…Specifically, based on simple census data of fish communities, our model can help decompose system-wide fluxes (cf. Allgeier et al, 2014;Burkepile et al, 2013;Francis & Côté, 2018). This is…”

“…Empirically measured excretion rates can considerably vary for similarly sized individuals of the same species (Allgeier, Wenger, Rosemond, Schindler, & Layman, 2015;Francis & Côté, 2018;Whiles, Huryn, Taylor, & Reeve, 2011). Yet, existing models that combine stoichiometry and bioenergetics do not account for this natural variability (e.g.…”

Global nutrient cycling by commercially-targeted marine fish

“…Moody et al, 2015;Pilati and Vanni, 2007;Nugraha et al, 2010) these were not included in our study apart from the uncertainty on zooplankton nutrient content (Table 1). Finally, fish movements also allow the transport of nutrients and constitute a sink of nutrients where the fish forage and a source of nutrients where the fish excrete, egest or die (Vanni et al, 2013;Francis and Côté, 2018), an effect we do not explicitly include here.…”

“…The amount of nutrient stored and cycled by fish can vary with different environmental and physiological factors, in space and time (e.g., Halvorson and Small, 2016;Prabhu et al, 2016;Francis and Côté, 2018;Czamanski et al, 2011;Allgeier et al, 2014). In addition to natural variations, anthropogenic activities, mostly fishing, modify the storage and cycling of nutrients by the icthyosphere.…”

Connectivity is Everything

“…Connectivity is all about flow: the rate and direction of that flow, and the distance over which it occurs. In the marine environment flow can be through the movements of currents transporting dissolved and particulate matter or passively drifting organisms, or through the active movement of swimming or crawling macrofauna (e.g., Francis and Côté 2018). Connectivity occurs across a broad expanse of spatial and temporal scales, connecting regions and local habitats.…”