Reef biodiversity surveys of Australia’s Commonwealth Marine Reserve Network: An overview
Graham J Edgar, Daniela Ceccarelli, Rick D Stuart-Smith, Antonia T Cooper. Report to Parks Australia, Department of the Environment, 2017.
In Australia’s Commonwealth Waters, the broad areas used for marine planning include the South-east, Temperate East, Coral Sea, North, North-west and South-west regions.
Each region is recognised as hosting areas or features of conservation significance, and the Australian Commonwealth Marine Reserve (CMR) Network recognises the value of marine reserves in the protection of biodiversity, habitats, ecological processes and resources.
Shallow reefs occur in all the CMR Networks except the South-east, from coral reefs in the northern regions to a combination of rocky and limestone reefs in the temperate south.
Reef Life Survey (RLS) involves recreational divers trained to a scientific level of data-gathering to make it possible to conduct ecological surveys across broad geographic areas in a cost-effective manner.
Over the last decade, this has allowed coverage of a large geographic area, including reefs worldwide, and enabled, for the first time, comparisons of shallow reefs across all Commonwealth Waters.
The goal of this report is to compare ecological metrics from reefs in five CMR Network regions.
Data analysed and presented include the major macroscopic groups of species - fishes, mobile macroinvertebrates, and sessile benthic organisms. Comparisons were made between the CMR Network (both proposed and actively managed), existing State marine protected areas (MPAs) and areas outside any CMR boundaries (referred to here as “Open”); comparisons were also made between areas assigned to different IUCN categories within CMR networks, where applicable.
Fish species assemblages surveyed by RLS divers subdivide into three distinct groups: temperate fish species, fishes of the northern coastline, and tropical eastern and western offshore species.
Fish abundance, biomass and species richness (especially sharks and large fishes) were higher in CMRs across all ecoregions than either State MPAs or Open areas; biomass and species richness were higher in State MPAs than in Open areas. CMRs had almost double the biomass of large fishes than State MPAs and Open areas, and shark biomass was between four and five times higher.
Macroinvertebrate communities were more similar to each other across offshore coral reefs than across northern Australian or temperate ecoregions.
In many cases, CMRs appeared more unique than Open areas or State MPAs, especially in the coral reef provinces.
Across levels of protection (existing and proposed), macroinvertebrates were most abundant and diverse in State MPAs and Open areas, as well as Multiple Use areas (IUCN VI).
The cover of different benthic groups varied greatly between temperate sites, with less dissimilarity between tropical areas.
Southern and southwestern ecoregions were distinguished by a higher cover of macroalgae, and temperate eastern ecoregions had a greater diversity of sessile biota.
Tropical regions were distinguished by either a high cover of soft corals and turf, or hard corals and abiotic substrata.
Total live cover of sessile biota was slightly higher in CMRs than in State MPAs or Open areas.
The similarity between CMR and Open reefs varied between the different ecoregions.
One goal of establishing the CMR Networks was to ensure representation of the range of Australia’s marine flora and fauna in protected areas; this report provides insights into the extent that this has been achieved by the existing and proposed placement of CMRs for tropical, subtropical and temperate reefs.
A number of key patterns emerged:
- The former Coral Sea CMR had no Open sites, but the comparison between highly protected (I and II) and less protected (IV) zones showed that these all had similar community structure.
- The Bassian, Great Australian Bight, Houtman, Shark Bay, South Australian Gulfs, Ningaloo, Cape Howe and central/southern GBR ecoregions lacked shallow reef in CMRs; State MPA sites were similar to Open sites, but with lower macroalgal cover in the State MPAs of the Bassian ecoregion and more distinctive invertebrate and benthic assemblages in the State MPAs of the Houtman ecoregion.
- Within the Exmouth to Broome ecoregion, CMRs capture most of the biodiversity and community structure present on Open reefs. Most of the North Network’s reefs within CMR boundaries were also similar to the Open reefs; the largest difference was between Open reefs of the Torres Strait to northern GBR ecoregion and the West Cape York CMR. Together, however, the Northern CMR sites differed substantially from northwest and northeast tropical sites, with distinctive biota. However, no northern CMR is proposed to be IUCN I or II, hence none of these distinctive ecosystems will be fully protected from exploitation under the planned zoning arrangements.
- In the Manning-Hawkesbury ecoregion, the Cod Grounds CMR possesses a fish and benthic community different from State MPAs or Open sites, while the invertebrate assemblage is similar between the three levels of protection. This is most probably due to the unique geomorphic structure of the Cod Grounds. Similarly, the Solitary Islands CMR (Pimpernel Rock captures a unique pinnacle rising steeply from the seabed, a feature lacking in Open areas and State MPAs of the Tweed-Moreton ecoregion.
- Norfolk and Lord Howe CMRs were unique. These sites formed a distinct group rather than overlapping with other temperate sites. The Lord Howe CMRs and State MPAs together capture the biodiversity present within this group of islands and reefs. Norfolk Island, though somewhat similar to Lord Howe, has a distinctive flora and fauna again; a need exists to represent this unique environment through stronger protection, as the entire area of shallow reef is designated as a Multiple Use zone under planned zoning arrangements.
- In the Leeuwin ecoregion, the Geographe CMR had higher diversity of reef organisms than reference sites.
Observed ecological differences between CMR and Open reefs corresponded with expectations of the general objectives of marine protected areas, which is the protection of biodiversity and populations of exploited species.
In this study, the differences were especially recognisable in the biomass of sharks and large fishes, suggesting that the proposed CMR network encompasses a combination of areas that are presently successfully managed, and those which still support healthy populations of sharks and large fishes, possibly due to offshore and remote location.
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