Biodiversity Survey of the Temperate East Coast Commonwealth Marine Reserve Network: Elizabeth & Middleton Reefs, Lord Howe Island & Norfolk Island
Graham J Edgar, Daniela Ceccarelli, Rick D Stuart-Smith, Antonia T Cooper. Report to Parks Australia, Department of the Environment, 2017.
- Biodiversity Survey of the Temperate East Coast Commonwealth Marine Reserve Network: Elizabeth & Middleton Reefs, Lord Howe Island & Norfolk Island
The Temperate East Commonwealth Marine Reserve (CMR) Network includes Commonwealth waters between the southern limit of the Great Barrier Reef to the southern coast of New South Wales, eastward to Lord Howe Island, and includes the Commonwealth waters surrounding Norfolk Island further east.
Eight CMRs have been established in this CMR Network, four of which are known to support prominent reef systems: the Cod Grounds and Solitary Islands CMRs, the Lord Howe CMR and the Norfolk CMR.
This report focuses on the latter two.
Field surveys in the Temperate East were conducted between 2009 and 2013 by a team of skilled divers from the Reef Life Survey program (www.reeflifesurvey.com) and the University of Tasmania.
Ecological surveys were conducted at varying depths along 173 transects at 53 sites across the East CMR Network.
The reefs of the Temperate East CMR Network have developed on the latitudinal boundary of coral reef formation, between tropical, subtropical and temperate influences.
Reef communities are further structured according to their isolation and the dominant habitat.
Elizabeth and Middleton Reefs had broadly similar reef communities that differed from those at Lord Howe Island and Norfolk Island; the two islands often also differed from each other.
Elizabeth and Middleton Reefs had more tropical species commonly found on the Great Barrier Reef, Lord Howe Island hosted a mix of tropical, subtropical and temperate species and Norfolk Island was dominated by subtropical and temperate species.
The isolation of these reefs from each other and from the surrounding reef bioregions has also contributed to the presence of endemic fauna, and the high abundance of populations that may be rare or unusual elsewhere.
Despite the abundance of some tropical reef fishes, some key factors distinguish Elizabeth and Middleton low latitude reefs:
- a lack of high-intensity pulse disturbances typical in the tropics (e.g. cyclones and bleaching events)
- a high abundance of scraping and excavating fishes at Elizabeth and Middleton Reefs, whose effects on coral are both beneficial (by removing algal biomass) and detrimental (by removing live coral and coral recruits)
- a historically low cover of live hard corals.
Functionally-important fishes were recorded in high densities, including excavating and scraping parrotfishes and large browsing herbivorous fishes.
Middleton Reef in particular had very high fish biomass, likely driven by a high abundance of toporder piscivores such as the Galapagos shark and black cod.
Grazers contributed to high biomass in all areas except Norfolk Island.
To some degree this is reflected in the benthic communities, as macroalgal cover was highest at Norfolk Island, which had the lowest biomass of grazers.
Biogeographically, Elizabeth and Middleton Reefs appear to have some connectivity to Lord Howe Island, but less than would be expected given their geographic proximity.
The Lord Howe Island reef fauna probably has relatively low genetic diversity; populations of corals, for example, are genetically isolated and likely derived from few colonists.
Norfolk Island is the most isolated of the locations studied, with expected high levels of self-replenishment and peripheral populations that are highly vulnerable to extinction.
Differences in fish community structure may also have been driven by underlying reef geomorphology and exposure to prevailing wind and swell.
This was certainly reflected in the benthic community composition, with low-lying turfs and encrusting corals dominating the oceanic platform reefs, and a wider variety of sessile biota recorded on the fringing reefs of Lord Howe and Norfolk Islands.
Erect and tabular corals, and calcified algae (e.g. Halimeda spp.) rather than crustose coralline algae, are often typical of sheltered habitats, as is a high cover of fleshy macroalgae.
Elizabeth and Middleton appear to have the typical lowrelief structure of highly exposed reef fronts, with more delicate sessile biota restricted to the lagoons.
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