Habitats and benthic biodiversity across a tropical estuarine–marine gradient in the eastern Kimberley region of Australia

The Kimberley coast situated in north-western Australia has been recognised as one of the world’s least human-impacted coastal areas as well as being rich in wilderness and biodiversity values. However, the region is vast and patchily surveyed with many knowledge gaps remaining about the diversity and extent of marine life in nearshore habitats. The King George River, in the far north-east of the region is an area where knowledge is lacking and consequently, to fill these gaps, a multi-taxon biodiversity and habitat survey was conducted in 2014. The survey extended from the base of the King George River twin waterfalls, which mark the upstream limit of marine influence, to the mouth of the river and 15 km offshore into the Timor Sea. At least eleven habitat types were identified. These include extensive stands of mangroves, rocky shores and sandy beaches extending out through the estuary and along the coast. Offshore from the estuary, Lesueur Islet is a low, vegetated islet surrounded by a fringing coral reef that supports a diverse benthic invertebrate fauna and algal flora. Deep-water sedimentary and hard-bottom filter-feeder communities also occur between the estuary and Lesueur Islet and around it. A total of 1374 animal and plant lots were collected, comprising about 3500 specimens with 796 species recorded. There were at least nine new species discovered of which five have since been named. The new species included five crustaceans and four echinoderms. In addition, there were at least twelve new records for Australia (one cnidarian, two echinoderms, nine crustaceans and some molluscs). Eighteen new records of crustaceans were made for Western Australia. Species accumulation curve analyses suggest true species richness may be higher than observed here if greater sampling were conducted on deep hard-bottom substrates in the region. Nevertheless, these results confirm this region contains a highly diverse community of regional and national significance.