Natural values of the Solitary Islands Marine Park - Marine Parks ...

4 Ocean ecosystemsConsolidated areas consisting of bedrock identified above the seabed, andunconsolidated areas primarily consisting of sand, have been identified. Theseareas have been further divided in order to better reflect the spatial patterns ofbiodiversity in the marine park. As depth is an important determinant of the dominantassemblages on rocky reefs (Edgar 1984, Barrett et al 2001), it is important that depthis considered in the classification of habitats. As there is a lack of detailed biologicaldata about ocean ecosystems, the continental shelf has been divided into three depthzones: shallow (0–25 metres), intermediate (25–60 metres) and deep (over 60 metres)for marine park planning purposes.These depth zones were applied to reef habitats defined through the swath-mappingto assess the distribution of shallow, intermediate and deep rocky reef throughout themarine park. The division at 25 metres is based primarily on changes in the dominantreef assemblages at this depth (e.g. from coral to sponge-dominated assemblages),and data showing a regular change in sea temperature at around 25 metres deep.4.1 Subtidal rocky reef habitatThere are extensive subtidal rocky reefs throughout the marine park, and while manyof these are adjacent to the mainland and the offshore islands, other reefs are presentas discrete subtidal features (Figure 13). While the swath-mapping has revealedconsiderably more rocky reef throughout the marine park than was defined from thebroad-scale bathymetry, the location and extent of all subtidal reefs has not beenmapped, particularly those in depths greater than 20 metres.In many areas, the swath-mapping identified reef located considerable distancesoffshore. This is particularly evident on the eastern and southern sides of SouthSolitary Island, where reef extends several kilometres offshore of the island, muchof it being at depths of 25–60 metres (Figure 13). There is also extensive reef offthe coastline between Corindi and Wooli Wooli rivers. Reefs in the Minnie Water toSandon area are also more extensive and complex than previously identified.The high resolution of the swath bathymetric data has also revealed considerablevariations in the geomorphic structure (e.g. in boulders, gutters, walls and pinnacles)and patchiness of reefs, often within the same continuous reef system (Figs. 14 and15). This variability in reef complexity is likely to influence the diversity of species inthe region, as reef complexity can significantly influence diversity and assemblages(Harman et al 2003).Overall, the rocky reefs throughout the marine park contain a mix of tropical,subtropical and temperate benthic assemblages, reflecting latitudinal and cross-shelfgradients of water temperatures and ocean currents (Zann 2000a). From reef-fishdiversity surveys carried out across the marine park (Malcolm unpubl. data), and basedon surveys and observations of benthic communities (e.g. Harriott et al 1994, Mau1997, Mau et al 1998, Smith and Edgar 1999), rocky reefs in the marine park can beseparated into three groups based on general distance offshore, depth and dominantbenthic community. These are:• inshore reefs – those less than 1.5 kilometres from the shore, containing shallow reefsless than 25 metres deep;• mid-shelf reefs – those around 1.5 to 6 kilometres offshore, containing shallow andintermediate reefs less than 60 metres deep;• offshore reefs – those more than 6 kilometres offshore containing shallow andintermediate reefs, and deep reefs over 60 metres deep.