Naticid snail predation on early post-settlement surfclams (Spisula solidissima) on the inner continental shelf of New Jersey, USA

Naticid gastropod predators leave characteristic boreholes in the shells of their bivalve prey that allow the evaluation of spatial differences in occurrence and intensity of predation. This approach, extensively used in paleobiological research, was used to compare spatial variation in predation by moonsnails (Euspira heros Say) on initial recruits of the Atlantic surfclam (Spisula solidissima Dillwyn). A four-year sampling at two 12-m deep stations on either flank of Beach Haven Ridge on the inner continental shelf detected temporal and spatial differences in surfclam densities following a large settlement pulse in early July. Between-station density differences were large during the first peak in surfclam density, but decreased in August-September, when densities at both stations also decreased. Surfclam seasonal peaks were followed by peaks in density of articulated shells (recent mortality due to non-crustacean predators and/or intrinsic mortality) and surfclams with boreholes (mortality due to naticids). The proportion of surfclams with boreholes was consistently higher (more than twice, on average) at the station where the highest densities of surfclams were also detected. These spatial differences are interpreted as differences in predation intensity resulting from a corresponding higher abundance of moonsnails at the same station. Although naticid predation is not the primary source of surfclam mortality, it consistently contributes to the reduction of spatial differences in density initially created by dissimilar levels of larval surfclam settlement.