An excursion to the Port Davey Estuarine System in April 1993 confIrmed earlier evidence of distinct horizontal and vertical zonation patterns within the invertebrate communities of Bathurst Channel. The fauna, with its dominance of deepwater species, is unique in both community structure and composition within the entire coastal zone of Australia The restriction of plant communities to near the surface, reflected by the low light penetration from dark tannin stained water, is an atypical situation within temperate Australian waters. The benthic invertebrate fauna is dominated t.y filter feeders such as corals, bryozoans, tube worms, ascidians and sponges. Marine groups, which are often dominant elsewhere in the sea, such as molluscs, crustaceans, and echinoderms, are relatively depauperate. The taxonomy of much of the fauna is still being resolved but initial indications are that it contains rare species, some of which may be endemic.
The communities contain many sedentary benthic species that are delicate and fragile. Many of these (eg bryozoans, corals, sea pens) are vulnerable to mechanical damage from divers or by nets and anchors. They also contain species that are not widely represented in adjacent inshore habitats and may be 'self-seeding' within the estuary. Many deepwater animals are habitat specifIc and may be vulnerable to environmental changes caused by pollutants, nutrient enrichment and other water quality factors. Gaining an understanding of water flow within the estuary is critical to evaluating the effects of such changes.
This study was little more than a pilot survey and generates more questions than it answers. The Channel harbours an extremely important but potentially vulnerable fauna which needs to be given high research and conservation priorities. While the basic structure of its communities have been identified, more subtle but yet undefined partitioning of zones appears to be evident. Resolution of these infrastructural elements awaits further collecting and identification of the spatial patterns. Future research should attempt to delimit potentially vulnerable communities and their distributions, and identify less vulnerable sites where ecotourism and other man-related activities could be permitted without causing environmental damage.