Infaunal benthic community structure and function in the Gulf of Carpentaria, northern Australia

Abstract

The infaunal benthos (>20 m) of the Gulf of Carpentaria was surveyed during November and December 1990. In all, 684 taxa were collected from 105 stations, each with three replicate 0.1-m² grab samples (Smith-McIntyre grab). Trends in abundance and species richness were correlated with gulf-wide trends in sediment texture and depth. Highest abundance (20-153 individuals per 0.1 m²), wet-weight biomass (X=7.6 g per 0.1 m²) and species density (X=25.8 taxa per 0.1 m²) occurred in the sands and muddy sands along the eastern and south-eastern margins of the gulf. Lowest abundance (3.3-20.0 individuals per 0.1 m²), biomass (X=3.0 g per 0.1 m²) and species density (X=9.5 taxa per 0.1 m²) occurred in the muds and sandy muds in the centra, western and north-western gulf. Infaunal abundance and biomass were similar to those of other tropical continental shelves but were lower than those of some temperate-region shelves and upwelling areas. Species richness was also lower than in temperate areas of upwelling or high production.

Scavengers/carnivores (44%) and deposit feeders (43%) numerically dominated throughout the gulf. Suspension feeding was less prevalent (13%), and few herbivores were found (< 1%). There was a trend in the proportion of deposit and suspension feeders that was related to sediment texture. 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 lowest in sandy sediments. Small (<5 mm) surface deposit feeders numerically dominated within this feeding mode.

The 15 numerically dominant taxa were comprised mainly of opportunistic or second-stage colonizing taxa. Most had gulf-wide distribution patterns, but levels of abundance were correlated with sediment and depth.

The infaunal benthic communities in the Gulf of Carpentaria appear to be regulated by physical factors of the environment that correlate with sediment grain size and depth.