A COMPARISON OF FISH ASSEMBLAGES FROM SEAGRASS AND UNVEGETATED AREAS OF A SOUTHERN AUSTRALIAN ESTUARY

Assemblages of small fish from eelgrass (mainly Zostera muelleri) and unvegetated patches in a shallow, marine-dominated estuary were compar ed over one year as a preliminary step towards finding the consequence s of eelgrass loss to small fish. There were more species and more ind ividuals 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 s ignificance of groupings was tested by using an analysis of similariti es (ANOSIM) randomization routine. The cryptic syngnathid Stigmatopora nigra and juvenile whiting, Sillaginodes punctata, the species of gre atest economic importance in the estuary, were predominantly over eelg rass, 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 cau sed by possible associations between the presence of vegetation and en vironmental factors have been partially offset by interspersion of sit es and by measurement of water temperature and salinity. Secondarily t o habitat differences, fish assemblages were weakly grouped according to distance of sites from open water.