Comparison of Fish Assemblages Associated with Seagrass and Adjacent Unvegetated Habitats of Port Phillip Bay and Corner Inlet, Victoria, Australia, with Emphasis on Commercial Species

Species richness, abundance and biomass of fishes from seagrass and unvegetated habitats were analysed for sites in the Swan Bay region of Port Phillip Bay, and Corner Inlet, Victoria, Australia. Fish assemblages from intertidalZostera muellerisites showed greater similarity with a number of shallower unvegetated sites than to subtidalHeterozostera tasmanica. Similarly, subtidal, unvegetated sites in Swan Bay were more similar to subtidalHeterozosterasites than to other, generally shallower, unvegetated sites. Species richness was significantly higher in seagrass beds and showed an increase over the warmer months of the year. Differences in abundance and biomass of fishes between vegetated and unvegetated habitats depended on the location of sampling. In general, abundance and biomass of fish in the deeper subtidal seagrass were significantly higher than in unvegetated habitats of the same depth. In contrast, abundance and biomass were not significantly different between seagrass and unvegetated habitats of the intertidal and shallow subtidal zones when significant abundances of the long-finned goby,Favonigobius lateralis, occurred on unvegetated habitats. As a consequence, species richness would be expected to decrease with any seagrass loss; however, decreases in abundance and biomass of fishes would be greatest with loss of deeper subtidalHeterozosterahabitats. Although juveniles of a number of commercially important species were associated with subtidalHeterozosterahabitats, juveniles of other species of commercial significance were found on shallow, unvegetated habitats. Newly settled juveniles of the King George whiting,Sillaginodes punctata, were associated with unvegetated patches amongst subtidal seagrass in Swan Bay, in contrast with a direct association with seagrass reported from other areas.