Feeding ecology of whelks on an intertidal sand flat in north-eastern New Zealand

Abstract

The dispersion patterns and feeding behaviour of intertidal whelks were investigated in north-eastern New Zealand. Aggregations of whelks feeding on clams occurred regularly, with an average of 15-20 individuals per aggregation. Death of clams was attributable to predation in up to 50% of the aggregations, although scavenging of dead and moribund animals was the main activity of whelks. Laboratory and field studies showed that Lepsiella scobina (generally not considered a soft shore species) was the main whelk predator at Lews Bay, Whangateau Harbour, drilling a small neat hole through the clam shell. The distinction between Cominella spp. as predators or scavengers is not so clear. Reseeding of intertidal clams, Austrovenus stutchburyi, has been proposed as a technique for reestablishing populations in some degraded New Zealand estuaries. The impact of whelk predation has many implications for A. stutchburyi reseeding. Both L. scobina and Cominella adspersa may potentially prey on newly reseeded clams as they preferentially attacked small clams in the laboratory. On-growing to a larger size before reseeding may be advantageous although large size was not found to protect prey from predation. Additionally, no seasonal trend in whelk activity was found.