Variability in larval settlement of abalone on artificial collectors

Abstract

The spatial and temporal variability in settlement of greenlip abalone, H. laevigata on artificial settlement collectors was examined over three years. Pairs of the collectors of an improved design were deployed on the sea bed at six sites over a number of different spatial scales. A period of peak settlement occurred between October and December in each of the three years at all sites. The similarity in size frequencies between sites at the settlement peaks demonstrated that spawning was epidemic, occurring over a period of 2–3 days. The synchronous timing and intensity of peaks at four sites within 2 krn of each other contrasted with that of a site 8 km distant. Adult densities between sites during the spawning season ranged from 0.0 m-2 to 1.2 mm-2. Over this range of densities, numbers of larval settlers were independent of local adult abundance. Collectors are a useful tool in examining inter-annual variability in the timing and synchrony of spawning and in measuring the relative abundance of abalone larvae. Growth rates inferred from "cohorts" followed at two week intervals allowed settlement/spawning times to be more accurately estimated than with previous methods such as gonad indices.