Fine-scale spatial distribution of the temperate infaunal bivalve Tapes (= Ruditapes) philippinarum (Adams and Reeve) on fished and unfished intertidal mudflats

Abstract

Temperate intertidal mudflats are important to both human and nonhuman foragers, the former for professional and recreational clam fishing, and the latter for food, especially for migratory shorebirds. Foraging strategy and success will depend to a large degree on the spatial distribution of the infaunal prey, which is very poorly-known at the scale at which these foragers exploit the resources. We characterized the fine-scale spatial distribution of the bivalve Tapes philippinarum on a chronically-fished and on an unfished (reference) mudflat, using autocorrelation, variogram, and fractal analyses. Two cohorts were identified at each site: one sub-legal and one legal size. Although both cohorts were clearly aggregated at the scale of ≤130m, this aggregation was greatly attenuated at the fishing-impacted site, and most severely for the fished-size cohort. The fractal dimensions of the cohorts at the two sites corroborated the decreased spatial structure at the fishing — impacted site, and in particular for the fished-size cohort. Together with similar observations for other components of this mudflat ecosystem, these results underscore the need to incorporate the spatial aspect in assessments of both organism (prey or resource) distribution, its relationship to foraging strategies, and the effect of intertidal fishing on these processes.