A comparison of fish assemblages from seagrass and unvegetated areas of a southern Australian estuary

Abstract

Assemblages of small fish from eelgrass (mainly Zostera muelleri) and unvegetated patches in a shallow, marine-dominated estuary were compared over one year as a preliminary step towards finding the consequences of eelgrass loss to small fish. There were more species and more individuals at eelgrass sites than at unvegetated sites at every sampling period. Multivariate analysis (MDS ordination) of assemblages showed distinct grouping of eelgrass and unvegetated sites. The statistical significance of groupings was tested by using an analysis of similarities (ANOSIM) randomization routine. The cryptic syngnathid Stigmatopora nigra and juvenile whiting, Sillaginodes punctata, the species of greatest economic importance in the estuary, were predominantly over eelgrass, whereas the flounder Rhombosolea tapirina was usually caught at unvegetated sites. Atherinosoma microstoma, the most abundant species, was more common over eelgrass at two dates but had similar abundances over both habitats at other dates. The limitations of survey work caused by possible associations between the presence of vegetation and environmental factors have been partially offset by interspersion of sites and by measurement of water temperature and salinity. Secondarily to habitat differences, fish assemblages were weakly grouped according to distance of sites from open water.