The Temperate East Marine Region

In Part 6 of our coverage of Australian Marine Parks, Chris Whitelaw shines a light on the Temperate East Marine Region

The Temperate East Marine Region encompasses almost 1.5 million square kilometres of Commonwealth waters from the southern boundaries of the Great Barrier Reef and Coral Sea Marine Parks, 40km north of Bundaberg in Queensland to Bermagui in southern New South Wales. The Region borders shallow state waters 3NM from the coastal baseline and extends to deep ocean at the limit of Australia’s Exclusive Economic Zone (EEZ) 1000km offshore at its widest reach. It also joins state waters surrounding Lord Howe Island and rises to the high-water mark on Norfolk Island, which is a Commonwealth territory.

The Region contains eight marine parks — Gifford, Norfolk, Lord Howe, Central Eastern, Solitary Islands, Cod Grounds, Hunter, and Jervis — that collectively span 383,339 sqkm of spectacular subtropical and temperate environments.

THE PHYSICAL ENVIRONMENT

The Region’s submarine landscape was shaped during the last 110 million years by the rifting and separation of Australia’s eastern continental crust from the Lord Howe Rise, followed by periods of volcanic activity and subsidence. These tectonic forces forged a narrow continental shelf, beyond which the seafloor has a complex and varied topography: a shelf break incised by canyons; an expansive abyssal plain with basins, trenches and troughs; rocky reefs; deep-water terraces and plateaus linked by ridges and saddles, isolated guyots, and chains of conical seamounts. 

Most of the Region covers the continental slope where water depths range from 1000m to more than 5800m in holes and valleys between the mainland and Lord Howe Island. Through this expanse of ocean surge strong currents that greatly affect productivity and biological diversity. The East Australian Current (EAC) is the dominant influence, transporting warm waters from the Coral Sea down the outer edge of the continental shelf, nurturing both subtropical and temperate species. 

BIODIVERSITY

The combination of varied topography, ocean currents, and nutrient availability supports a rich diversity of species — particularly among corals, crustaceans, echinoderms, molluscs, sponges, and fish, of which about 34 per cent are endemic to the region. Temperate species are more prevalent in the southern waters, with subtropical species becoming progressively more common towards the north, sharing habitats in an overlapping zone. The region’s marine parks provide vital refuges for 106 species of marine life that are globally threatened, two of which are critically endangered — the grey nurse shark and black cod.

Lagoon habitat on Middleton Reef

CANYONS ON THE EASTERN CONTINENTAL SLOPE

Sonar surveys reveal a continental slope strongly dissected by numerous submarine canyons. Off northern New South Wales, two canyons are prominent. At depths of around 200m, the Tweed Canyon is 6.5km wide between exposed bedrock walls that rise to 480 metres; the Richmond Canyon is 13.5km wide and more than 800m deep, with a tributary canyon and several pinnacles. Four significant canyons occur along the slope north of Batemans Bay in depths between 300–750m, each with a V-shaped profile and up to 2km wide. A further ten canyons have been identified on the upper slope off the coast between Jervis Bay and Bermagui. 

The Jervis Marine Park has five notable intrusions — known collectively as the Shoalhaven Canyons — that cleave the upper slope, with at least one penetrating the continental shelf. V-shaped in their upper reaches and up to 200m deep, they become wider and more shallow further down the slope.  Although they have the appearance of river valleys, they are caused by the progressive collapse of sediments from the lower depths towards the canyon heads.

These canyon systems contribute significantly to biodiversity by providing steep, hard surfaces at depths where soft sediment habitats are more commonly found. Solid anchorage points, vertical relief, and increased availability of food in swirling currents favour communities of large filter-feeding species such as sponges, feather stars, and sea lilies. These habitats in turn attract a wide array of other marine life including crabs and lobsters, starfish, clams, octopuses, fish, and sharks.

Canyons also interrupt the flow of water across the sea floor, generating turbulence and upwellings that transport nutrients over the shelf to the upper slope. These localised concentrations of food create foraging hotspots for a range of species like tuna, prawns, and squid supporting commercial shelf-based fisheries.

Common or weedy seadragon

ROCKY SHELF REEFS

Rocky shelf reefs occur in four Commonwealth marine parks along the New South Wales coast: Solitary Islands, Cod Grounds, Hunter and Jervis.

Along the continental shelf south of the Great Barrier Reef, marine life on rock outcrops and boulders shifts from algae-dominated communities to those in which attached invertebrates — large sponges, moss animals and soft corals — dominate. This shift generally occurs below wave-affected waters at depths of around 45m. These invertebrate communities create complex habitats for schools of bottom-dwelling fish such as morwong, barracouta, perch and warehou, and provide refuge to juvenile fish from sharks and rays prowling the gutters and caves among the reefs.

The Solitary Islands Marine Park is located 600km NNE of Sydney between Coffs Harbour and Plover Island, lying 5.5km offshore and adjoining a state marine park. Together, the two reserves cover almost 900sqkm at depths of 15–70m in a transition zone where the warm, subtropical EAC meets water from the cool, temperate south. Rocky reefs cover large areas of the seafloor within the parks in configurations that range from broad patches of low-relief platforms to linear ridges up to 2km long and 13m high. The most significant feature of the Commonwealth reserve is Pimpernel Rock, a submerged pinnacle rising 30m from the seabed to within a few metres of the surface. This popular scuba diving site is noted for the large numbers of grey nurse sharks that gather here. As many as 103 fish species have been recorded in the area, including many commercial and recreational target species such as yellowtail kingfish, pink snapper, Venus tuskfish, blue morwong and Maori wrasse.

Cod Grounds Marine Park lies about 7km offshore from Camden Haven 30km south of Port Macquarie. Covering only 4sqkm, it is the smallest marine park in the Temperate East Region and encloses a roughly circular rocky reef outcrop of 1000m radius. The reef is a group of jagged, steep-sided pinnacles that rise more than 20m from a relatively flat seabed, surrounded by fields of boulders and cobbles with shallow sandy gutters. These predominately rocky surfaces are encrusted with sponges, soft coral and seaweed communities that provide habitats for spiny sea urchins, feather stars, anemones, moss animals, and ascidians (sac-like filter-feeders). Sixty-nine species of fish inhabit these submarine gardens, the most abundant of which are mado, silver sweep and sea perch, together with pelagic species such as highfin amberjack, yellowtail kingfish and mulloway. Their main predator is the grey nurse shark, which the park was declared to protect.

A school of fish browses Middleton Reef

The Hunter Marine Park extends 6257sqkm and adjoins the NSW Port Stephens-Great Lakes Marine Park. Mapping of the park’s continental shelf less than 200m deep by research vessels Southern Surveyor and Investigator identified three areas of reef comprising fragmented outcrops of bedrock and boulders rising up to 7m above surrounding soft sediment. The reef is carpeted by a mosaic of sponges, branched soft corals and sea fans, above which 65 fish species are supported by upwellings of nutrient-rich water funneled by submarine canyons from the abyssal plain. The marine park also provides an important foraging habitat for seabirds and a waypoint for migratory humpback whales.

Covering almost 2500sqkm of shelf across depths ranging from 120 to 5000 metres, the Commonwealth Jervis Marine Park lies 20km offshore from Jervis Bay and adjoins the NSW marine park of the same name. Its rocky reefs provide a complex range of habitats for dense sponge gardens and fish communities like jackass morwong, butterfly perch and orange-spotted catshark. The park is also a biologically important area for white-faced storm-petrels that breed in burrows on nearby land and forage in these highly productive waters.

OFFSHORE SEAMOUNT CHAINS

Three parallel seamount chains extend north-south across the Temperate East Marine Region between 24–34 degrees south: the Tasmantid and Lord Howe chains and Norfolk Ridge. These submerged mountain ranges and guyots were formed by volcanic activity about 24 million years ago as the Australian Plate moved northward over a ‘hotspot’ in the mantle. Although some pinnacles may reach high above the seabed, they rarely break the surface. Where they do, they form islands that have become rookeries for oceanic seabirds and marine turtles for which the surrounding waters are feeding grounds. 

These prominent submarine features profoundly influence biological productivity around them, altering the circulation of deep ocean currents and creating localised eddies that concentrate nutrients to feed abundant marine life. Seamount habitats support deep-sea coral gardens and sponge fields inhabited by fauna that is often unique to the area. Their isolation also makes them refuges for species such as black cod that were once common along the New South Wales coast but are now rare in those zones. Resident communities associated with seamounts are typically slow-growing species with remarkably long life spans, while pelagic fish, squid and crustaceans brought in by the currents are prey for high-order predators such as yellowfin tuna, swordfish and sharks.

Australian gannets

The Tasmantid seamount chain is a series of extinct submarine volcanoes running along the 155 degrees east meridian into the Tasman Basin. They vary in size and complexity, including flat-topped guyots, plateaus and terraces. Taupo Seamount is the largest at 60km in diameter and rising from the seabed at 4800m to a summit only 120m below sea level. Their flanks are commonly steep with rocky outcrops of boulders and subsidiary cones.

The Lord Howe chain lies 300km to the east of the Tasmantid chain. It runs for about 1000km along the western margin of the Lord Howe Rise, from Nova Bank in the north to the Lord Howe Island complex in the south, and incorporates Elizabeth and Middleton Reefs and Gifford Guyot.

Lord Howe Island, 550km north-east of Sydney, is the largest seamount in the chain with a base about 40km wide by 80km long, rising steeply from depths of 3500m to a terrestrial peak of 875m at Mt Gower. The spire of Balls Pyramid lies 4km south-east of the island and is linked to it by a sill 500m deep. The broad shelf around the island supports the most southerly coral reef in the world. The complex is surrounded by state and Commonwealth marine parks covering more than 110,000sqkm and is World Heritage Listed by UNESCO thanks to its outstanding natural and geological values. 

The Commonwealth marine park also includes the Elizabeth and Middleton Reefs 200km north of Lord Howe Island. These two small coral atolls occupy platforms atop volcanic seamounts separated from each other by 45km of deep ocean. Both roughly circular and of similar size, the reefs enclose 30m-deep lagoons that are submerged at high tide, save for a small sand cay at Elizabeth Reef. Straddling the boundary of the Coral and Tasman Seas, the reefs lie at the convergence of tropical and temperate currents that produce a unique and unusually diverse assembly of marine species from both bioregions. As well as hosting 122 kinds of coral and 324 species of fish, the atolls are listed as a Ramsar wetland of international significance providing open-ocean platforms for large populations of seabirds.

Islands of the Lord Howe Marine Park

Three hundred kilometres to the north, the Gifford Guyot is a 2000m-high flat-topped tablemount bearing fossil evidence of shallow-water corals that encrusted the peaks before erosion and subsidence submerged them to their present levels. This unusual guyot structure is contained within the Gifford Marine Park which covers almost 6000sqkm of important foraging habitats for migratory seabirds and humpback whales.

CURRENTS, FRONTS AND EDDIES

The South Equatorial Current flows east-to-west between the equator and about 20 degrees south as part of a large-scale subtropical gyre driven by the trade winds. Its surface waters are warm at 27 degrees celcius and generally low in nutrients. After passing through the Coral Sea, it meets the Australian mainland between Cairns and Townsville and bifurcates, flowing north as the Hiri Current towards Papua New Guinea and south with the EAC.

The EAC is the largest ocean current close to Australia’s east coast. Moving up to 30 million cubic metres per second in a swathe 100km wide and 500m deep, it is strongest in summer and weakest in winter. It is the principal driver of all ecological processes in the Temperate East Marine Region, exerting its influence deep into the Tasman Sea before dissipating east of Tasmania.

On its southward journey, the current frequently criss-crosses the continental shelf, deflected offshore by major headlands and sweeping close inshore again. These fluctuations generate large anti-clockwise eddies that can be 200km across and more than 1km deep.The eddies draw up nutrients from the deep in upwellings that flood across the shelf to enrich coastal waters and promote biological productivity in concentrated ‘hotspots’. One of these occurs off Fraser Island and supports spawning grounds for many important commercial species. 

Grey nurse shark

At about 33 degrees south, a large part of the EAC separates from its coastal trajectory and veers east, leaving a much weaker current to continue south in a series of eddies that eventually peter out in the southern Tasman Sea. This partial separation of the current from the coast and its eastward flow into the South Pacific has created one of the most complicated and dynamic areas of ocean in the world.

After leaving the coast, the east-flowing current forms the Tasman Front, following a path that meanders between 32 and 36 degrees south, shifting to the north in winter and southward in summer. As the Front flows toward New Zealand it crosses the northern edge of the Tasman Sea, separating those cooler waters from the warmer Coral Sea. The Front is greatly influenced by seafloor topography, which is dominated by seamount chains between broad basins, and other deep-sea currents that steer the Front from below.

Along its winding passage, the Front generates a series of large, semi-permanent eddies that migrate eastwards, trapping plankton in concentrations that attract schools of pelagic fish and, in turn, their predators. As well as enhancing productivity, the Front and its associated eddies increase biodiversity by transporting and dispersing tropical and temperate species from Australian coastal waters across the Norfolk Ridge towards New Zealand and the South Pacific.

NORFOLK RIDGE AND ISLANDS

Norfolk Island lies in the south-eastern Coral Sea, 1400km due east of Evans Head in New South Wales. Together with neighbouring Phillip and Nepean Islands, the group forms the Territory of Norfolk Island administered by the Australian Government. Norfolk has an area of 34sqkm and is surrounded by a 200NM Exclusive Economic Zone. Within the EEZ, the Commonwealth Norfolk Marine Park spans 188,444sqkm from the islands’ high-water line to a seafloor depth of 5000 metres.

The coral grouper is found on Elizabeth and Middleton Reefs

The islands are the only exposed parts of the Norfolk Ridge — a narrow, steep-sided range of seamounts and pinnacles running 1600km from the northern tip of New Zealand to New Caledonia. The Ridge lies along the eastern margin of continental crust that separated from the Australian plate about 65 million years ago. Since then, a complex series of tectonic forces has buckled the crust beneath the ridge and generated volcanic eruptions that forged the mountain range as it is today. Submerged at depths of between 1000 and 2000 metres, it is flanked by the deeper New Caledonia Basin to the east and the Norfolk Basin to the west.

The Norfolk Islands are strongly impacted by the east-flowing Tasman Front and associated eddies, crossing the Norfolk Basin at around 31 degrees south before encountering the Norfolk Ridge. Here the two interact to blend warm water from the Coral Sea with colder Tasman water, concentrating nutrients and plankton that create productivity hotspots over the ridge. The currents transport species from the west and assemble on the ridge to enhance local biodiversity. Norfolk’s islands and seamounts also act as stepping stones for the dispersal of species to and from New Caledonia and New Zealand, provide habitats for migratory whales, sharks, and seabirds.

The result of these ecological processes is a mixture of tropical and temperate species that include 32 kinds of coral, 546 macro-invertebrates, and 251 fishes, many of which are new to science and possibly unique to the Norfolk Ridge. 61 of these species are protected under Australian law as being vulnerable or endangered. Commercial and recreational pelagic species include billfish, tuna, seabass, kingfish, snapper, and trevally.

For more information about the marine parks in the Temperate East Marine Region visit parksaustralia.gov.au/marine/parks/temperate-east.