Inter-relationships between benthic macroinvertebrates and habitat types in Broke Inlet, south-western Australia. Report to the Ernest Hodgkin Trust for Estuary Education and Research, September 2008

Abstract

The benthic macroinvertebrate fauna of Broke Inlet, a seasonally-open estuary located in the South coast of Western Australia was sampled seasonally between spring 2007 and autumn 2008 at 20 nearshore sites throughout the estuary. These sites were chosen to represent five of the twelve habitat types that were identified quantitatively on the basis of their differences in a suite of enduring environmental criteria that reflected either location within the estuary, exposure to wave activity or the amount of submerged aquatic vegetation. Sampling yielded 5,519 individuals that represented 25 species. Most of which belonged to the class Polychaeta (10 species and 63.5% of the individuals), followed by those representing the classes Amphipoda, Anthurida and Bivalvia contributed 14.8, 8.2 and 6.8% respectively to the total number of individuals. The number of species, density and Shannon diversity of the benthic macroinvertebrate fauna were found to be significantly influenced by both habitat type (p<0.001) and season (p<0.001), with the greatest values in the majority of habitat types occurring in spring and summer. The composition of benthic macroinvertebrate assemblages were significantly influenced both by habitat type (R=0.418) and season (R=0.304), with the greatest differences among habitat types occurring in spring (R=0.493). Furthermore the pattern of spatial differences among habitat types, as exhibited by the benthic macroinvertebrate fauna, statistically matched that among the suite of enduring environmental variables used to distinguish each of those habitat types in both spring 2007 (Rho=0.441) and summer 2008 (Rho=0.367). Possible reasons for the non significant matching between the benthic macroinvertebrate fauna in autumn 2008 and the enduring environmental variables are also discussed