OPTIMIZING THE SUCCESS OF AUSTROVENUS STUTCHBURYI RESTORATION: PRELIMINARY INVESTIGATIONS IN A NEW ZEALAND ESTUARY

Abstract

Degradation of coastal habitats can result in loss or depletion of valued vegetation, fish, and shellfish stocks. Consequently, there are many initiatives to protect and restore these areas or populations to their previous state. Here we describe a study designed to provide necessary information on dispersal, mortality and growth rates of transplanted adult (25–32-mm shell length) cockles, Austrovenus stutchburyi (Gray) with which to evaluate the density of transplants and need for predation protection that should be used in larger-scale projects. Marked Austrovenus were transplanted at high (75 ind) and low (20 ind) densities, at two sites on an intertidal sandflat. To distinguish between epibenthic predator-associated mortality, other mortality and natural dispersal, caged and uncaged plots (30 × 30 cm) were used. Around 30% of the adult Austrovenus transplanted remained in the plots 12 mo later, and abundances were enhanced relative to pretransplant ambient densities. Death rates increased in later months and were significantly higher for Austrovenus kept at high densities in cages. There was no effect of caging on plot sediment characteristics, no obvious targeting of the plots by predators and no size-dependency of the deaths. However, being caged at high densities appeared to act as a stressor that rendered Austrovenus less able to cope with the extreme environmental conditions that occurred in later months. Growth rates were low over the 12-mo trial (<0.2 cm mo−1), did not differ significantly with site, transplant density, or the presence/absence of cages. Results indicate adult Austrovenus should be transplanted at densities intermediate between those used here and that caging is unnecessary. Our observations of dispersal of cockles out of the uncaged plots suggest that future trials should investigate transplanting cockles in patches within larger areas than the plots used here.