Patterns of coral community structure of subtropical reefs in the Solitary Islands Marine Reserve, Eastern Australia

Although the Solitary Islands Manne Reserve lies at latitude 30" S on the east coast of Australia, over 700 km south of the Great Barrier Reef it contains benthic communities dominated by extensive areas of scleractinian corals. A qualitative survey published In 1974 reported a total of 34 coral species in the region and more recent records Include a total of 55 coral species. Here, we present the results of the first quantitative benthic surveys for 7 sites in the Solitary Islands Marine Reserve. As a result of these surveys an additional 35 species of scleractinian coral have been recorded from the region bringing the total to 90 coral species, in 28 genera from 11 families. However 21 of the 55 coral species previously recorded were not found during this study.These results indicate that a dynamic temporal pattern of species recruitment and replacement is occurring within these subtropical coral communities. Scleractinian coral cover ranged from a low of 8 5% at Muttonbird Island, the reef closest to the coastline, to 50 9% at SW Solitary Island. These values are within the range of coral cover reported for tropical fringing reefs. Multidimensional scaling (MDS) analysis indicated 4 major site groupings the 2 sites closest to shore, the most northern offshore site; which was different from all other sites; South Solitary Island; and the other 3 island sites which showed some similarity to one another. The major differences among sites were higher coral species richness and the relative importance of Acropora specles on the more northern and offshore reefs, and higher abundance of large macroalgae close to the coastline.The Solitary Islands coral communities contain a unique association of tropical species near their southern latitudinal range, and subtropical scleractinian species which are rare or absent from the Great Barrier Reef region. Although coral cover is high at the Solitary Islands, these high-latitudinal sites are less diverse than tropical fringing reefs, with respect to both total number of coral species and the number of species per sampling unit. Furthermore, the primary substratum is formed by rock rather than limestone, so the extensive coral communities fall to form coral reefs at this latitude.