Biodiversity in saline coastal lagoons: patterns of distribution and human impacts on sponge and ascidian assemblages

Aim Estuaries are common focal points for industry and development, but often little is known of their biology or ecology, particularly for sessile taxa. We sought to examine how size and opening regime of shallow saline coastal lakes altered patterns of diversity and abundance for a suite of epifaunal invertebrates. We also sought to determine how these patterns were affected by the degree of lake modification by humans. Location We sampled 10 coastal barrier lakes of a range of sizes, opening regimes and degrees of modification in south-eastern Australia. Methods We quantified the diversity and abundance of sponges and ascidians in transects and undertook timed searches for these fauna at multiple locations within each coastal lake; placing the data in a hypothesis testing framework. Results Eighteen species of sponge, most of which appear to be new to science, and six species of ascidian were found among the 10 lakes we examined. All sponges and most ascidians were extremely patchily distributed among the lakes. Few species were widespread, with most restricted to one or two lakes. Diversity was largest in lakes mostly open to the sea and large in size. Diversity and abundance were smaller in highly modified lakes. Main Conclusions We suggest that sponge assemblages in these lakes consist of a combination of species largely restricted in distribution to lakes, and marine species that are at their limits of distribution. In contrast, ascidian assemblages were dominated by species that were more widespread. Conservation of biodiversity in these systems will rely heavily on effective management, which will in turn rely on a sound scientific understanding of natural processes; this will require the management of water quality through protection of catchments. The control of opening regimes should consider the ecological consequences rather than being purely based on ad hoc and reactive management