An Analysis of Marine Invertebrate Distributions in a Mangrove Swamp in Northwestern Australia

A detailed examination of the distribution of marine invertebrates in the Bay of Rest, North-West Cape, Western Australia, was conducted in September–October 1981. The bay has four intertidal habitats: an extensive mudflat (3.82 km²) in the lower intertidal, a band of mangroves in the middle intertidal composed of monospecific stands of Rhizophora stylosa (0.36 km²), and Avicennia marina (1.96 km²) and an upper intertidal flat (2.39 km²). A stratified random sampling technique was employed to collect marine invertebrates in all of these habitats. The richest area was the mudflat, which had a total of 112 species, a mean of 20.5 species per station, a mean density of 992/m², and a mean biomass of 4,056 mg/m² dry weight. Species diversity and animal densities in the two mangrove zones were lower: a total of 31 species in R. stylosa, a mean of 5.1 species per station and a density of 473/m²; 59 species in A. marina, a mean of 7.3 species per station, and a density of 257/m². Biomass was high in A. marina, 4,594 mg/m², but was only 1,088 mg/m² in R. stylosa. The fauna of the backflat was impoverished; only five species of crustaceans were collected, with a mean of 0.3 species per station, a density of 1.0/m² and a biomass of 193 mg/m². The faunas of the mudflat and mangrove zones were dominated by molluscs, crustaceans and polychaetes. In all 163 species were collected. It is suggested that the marine invertebrates of the Bay of Rest constitute a community dependent on detritus resulting from a breakdown of the primary production of the mangrove trees.