Distribution patterns of mobile epifauna associated with rope fibre habitats within the Bathurst Harbour estuary, south-western Tasmania

Abstract

The mobile epifaunal community within the Bathurst Harbour estuary, southwestern Tasmania, was surveyed by placing standardized rope fibre habitats at 1, 4 and 8 m depths at various sites along the estuary, and retrieving these habitats with associated animals after approximately 3 months submergence during each of the four seasons. Discrete assemblages of mobile epifauna were found in the eastern (Bathurst Harbour), central (Bathurst Channel), and western (Port Davey and the western entrance to Bathurst Channel) sections of the estuary. Each of these assemblages showed a high fidelity to site; there was no indication of a seasonal migration up or down the estuary in response to changes in the hydrological environment. The species richness of the macrofauna associated with rope fibre habitats was influenced by distance from the estuary mouth, water depth, season and also by factor interactions. Most of the total variance (69%) in the species richness of rope fibre habitat assemblages was, however, attributable to location along the estuary. Mobile invertebrates were most abundant in the upstream sections of the estuary in November, and in the marine section in February. Estimated epifaunal production showed consistent seasonal patterns throughout the estuary, decreasing to lowest levels in the cooler months. Epifaunal production decreased very rapidly with depth in the upper but not in the lower sections of the estuary. The patterns of faunal production were thus closely related to ambient light levels and water temperatures—these two factors explaining 54% of total variance in log production. The production of faunas associated with rope fibre habitats is postulated to be primarily a function of microalgal production, which in turn is dependent on light.