INFAUNAL BENTHIC COMMUNITY STRUCTURE AND FUNCTION IN THE GULF OF CARPENTARIA, NORTHERN AUSTRALIA

The infaunal benthos (>20 m) of the Gulf of Carpentaria was surveyed d uring November and December 1990. In all, 684 taxa were collected from 105 stations, each with three replicate 0.1-M2 grab samples (Smith-Mc Intyre grab). Trends in abundance and species richness were correlated with gulf-wide trends in sediment texture and depth. Highest abundanc e (20-153 individuals per 0.1 m2), wet-weight biomass (XBAR=7.6 g per 0.1 M2) and species density(XBAR=25.8 taxa per 0.1 M2) occurred in the sands and muddly sands along the eastern and south-eastern margins of the gulf. Lowest abundance (3.3-20.0 individuals per 0.1 m2) , biomas s (XBAR=3.0 g per 0.1 M2) and species density (XBAR = 9.5 taxa per 0.1 m2) occurred in the muds and sandy muds in the centra, western and no rth-western gulf. Infaunal abundance and biomass were similar to those of other tropical continental shelves but were lower than those pf so me temperate-region shelves and upwelling areas. Species richness was also lower than in temperate areas of upwelling or high production. Sc avengers/carnivores (44%) and deposit feeders (43%) numerically domina ted throughout the gulf. Suspension feeding was less prevalent (13%), and few herbivores were found (< 1%). There was a trend in the proport ion of deposit and suspension feeders that was related to sediment tex ture. Suspension feeding was highest in the muddy sands of the eastern and south-eastern gulf and lowest in the muds of the north-west. The proportion of deposit feeders was highest in muddy sediments and lowes t in sandy sediments. Small (<5 mm) surface deposit feeders numericall y dominated within this feeding mode. The 15 numerically dominant taxa were comprised mainly of opportunistic or second-stage colonizing tax a. Most had gulf-wide distribution patterns, but levels of abundance w ere correlated with sediment and depth. The infaunal benthic communiti es in the Gulf of Carpentaria appear to be regulated by physical facto rs of the environment that correlate with sediment grain size and dept h.