Infaunal bivalve molluscs on the flood tidal delta of Tauranga Harbour, north-eastern New Zealand, were surveyed twice over a 6-month period, with the aim of assessing shellfish resources, assessing the magnitudes of temporal and spatial variability in abundances, and identifying potentially important processes. The surveys identified a total of 31 bivalve taxa from 27 sites. Species richness per site ranged between 0 and 9, and varied greatly in space and time, as did two other measures of diversity. Extremely high densities of bivalves (>20 000 m -2 ) were encountered at several sites. Densities of several abundant species varied greatly in time, as a result of recruitment pulses. The abundances of the three species that dominated the fauna (Paphies australis, Tawera spissa, and Ruditapes largillierti) had characteristic spatial scales on the order of 200 m. Comparisons of size frequency distributions for individual sites suggested that mortality or emigration in the first year of benthic life was high. Substantial populations of bivalves occur on Centre Bank, and the most abundant of these are greatly influenced by events early in their lives. M99018

Laboratory and field experiments examining the burrowing behaviour of the estuarine infaunal bivalve Paphies australis (Bivalvia: Mesodesmatidae) were conducted in two areas of northeastern New Zealand. Field experiments examining reburial showed that when exposed on the sediment surface most P. australis were able to bury within 40 min. Slightly fewer pipi buried during high-tide trials than during mid-tide trials. Laboratory experiments established the ability of P. australis of various sizes to burrow up to the sediment surface after being inundated with sediment to a depth of up to 40 cm. P. australis buried under 10 cm of sediment burrowed to the surface at a slower mean rate than those buried under lesser depths of sediment, and variability in ascension rates increased with increasing burial depth. P. australis with an initial upright orientation burrowed and ascended at a greater rate than P. australis placed laterally or inverted. Though capable of ascending through as much as 50 cm of sand in laboratory experiments, there was evidence of decreased ability to respond to repeated burials over 5 and 8 day periods. P. australis is an active burrower which is capable of responding rapidly to inundations and uncoverings by sediments.