Short-term changes in reef fish community metrics correlate with variability in large shark occurrence

Abstract

Large predators exert control on lower trophic levels, often influencing long-term changes in community structure. Many large predators are highly mobile and occur in habitats along a continuum of presence and absence. In many natural systems, the movement of large predators through an area has been shown to lead to rapid changes in prey distribution through trait-mediated behavioral responses. To test whether a similar interaction also occurs for artificial habitats, we examined how reef fish community metrics (abundance, species richness, community composition) varied with the presence of a large coastal shark (sand tiger shark, Carcharias taurus). Remotely-operated vehicle surveys of large sharks and reef fishes on shipwrecks along the North Carolina, USA, continental shelf revealed that short-term shark presence correlated with changes in reef fish community metrics. Specifically, when sharks were present, fish species abundance and richness did not differ compared to when sharks were absent. Finer-scale analyses near sharks revealed similar abundance but elevated species richness proximate to sharks. We confirmed that this fine-scale pattern of similar abundance but higher richness near sharks held when the ROV was not in the water by repeating analyses using time-lapse videos from nearby shipwrecks. The detected differences in fish community metrics in the presence of sharks correlated with higher numbers of water-column associated species, such as jacks and barracuda, but lower numbers of benthic-associated species, including seabass and grouper. These findings suggest that the presence of large predators on artificial structures, as in natural systems, can drive short-term changes in community structure.