Six discrete marine regions have been identified under marine bioregional planning conducted in support of the EPBC Act: North, Coral Sea, Temperate East, South-east, South-west and North-west (Figure MAR2). Marine bioregional plans have been developed for 4 of the regions (North, Temperate East, South-west and North-west), and a marine regional profile has been developed for the South-east Marine Region. The plans and profile aim to improve decision-making processes under the EPBC Act, and to protect marine biodiversity and heritage values, while supporting the sustainable use of ocean resources by marine-based industries.

Designation of the 6 marine regions was informed by the provincial bioregions identified as part of the Integrated Marine and Coastal Regionalisation of Australia (IMCRA 4.0). The marine regions form the framework for the Commonwealth Marine Reserve Network (see also Effectiveness of marine management).

Assessments in this report consider each of the 6 recognised marine regions within the framework of a national overview of the marine environment, as well as relevant components within the area of the Great Barrier Reef Marine Park (Figure MAR2). Here, we provide an overview of the marine environment associated with each of the 6 regions. An overview of the marine environment within the Great Barrier Reef Marine Park can be found in GBRMPA (2014a) and will not be repeated here.

North Marine Region

The North Marine Region covers Australian waters from west of Cape York Peninsula to the Northern Territory – Western Australia border. The shelf west of Cape York Peninsula is overlain by mostly shallow, tropical waters of less than 70 metres depth, modified by complex tidal regimes and high cyclonic activity. A clockwise gyre in the Gulf of Carpentaria occurs during the summer monsoon and results from the net flow of the tides (Forbes & Church 1983). As a result of the gyre, the sea-floor basin in the centre of the Gulf receives low levels of sediment relative to sea-floor areas closer to shore. It tends to be flatter and less biologically diverse than nearshore environments (Long & Poiner 1994, Heap et al. 2004).

Further west, the Van Diemen Rise and Arafura Shelf contain complex sea-floor features such as canyons, shoals, banks, terraces and valleys. Oceanic currents across the marine region are driven largely by strong winds and tides, with minor influence from the Indonesian Throughflow and the South Equatorial Current to the north (Figure MAR3), which transfer water from the Pacific Ocean to the Indian Ocean. This seasonal circulation pattern broadly follows the contours of the Australian coastline and is known as the Holloway Current (Schiller 2011). The marine region is also one of the sources of the polewards-flowing Leeuwin Current, which flows along the west coast of Australia (Feng et al. 2003). Features such as the Arafura Sill and Torres Strait restrict water movement through the North Marine Region.

The North Marine Region borders the Coral Triangle, a marine biodiversity hot spot, which is known for its high biodiversity of tropical species, although endemism (species unique to the area and found nowhere else) is relatively low. One of the reasons for this low endemism is that there are no physical barriers to species dispersal, thereby facilitating species exchange with neighbouring regions. Food webs throughout the marine region are predominantly based on the large diatoms and zooplankton species that tend to be typical of warm, shallow coastal waters. Several protected, rare and endangered marine animals use the marine region for breeding and/or feeding, including marine turtles, sea snakes and marine mammals.

The marine region contains 4 provincial bioregions under IMCRA 4.0. Eight key ecological features have been identified across the region (DSEWPaC 2012a; see also Box MAR10):

• pinnacles of the Bonaparte Basin
• carbonate bank and terrace system of the Van Diemen Rise
• shelf break and slope of the Arafura Shelf
• tributary canyons of the Arafura Depression
• Gulf of Carpentaria Basin
• plateaus and saddle north-west of the Wellesley Islands
• submerged coral reefs of the Gulf of Carpentaria
• Gulf of Carpentaria coastal zone.

The North Marine Region supports several industries, including commercial fisheries managed by the Australian and Northern Territory governments, oil and gas exploration and production, commercial and recreational vessel activity, recreational fishing, Indigenous activities, and defence operations.

Coral Sea Marine Region

The Coral Sea Marine Region covers Australian waters east of Cape York Peninsula, south to 24˚29′S. It is adjacent to, but does not include, the Great Barrier Reef Marine Park. The Coral Sea Marine Region and the Temperate East Marine Region previously comprised the East Marine Region. The Coral Sea Marine Region encompasses tropical to subtropical environments, and incorporates atoll reefs, reef complexes, coral cays, offshore islands, terraces, deepwater valleys and troughs, offshore plateaus, abyssal plains, and seamounts. High seasonal cyclonic activity is typical of the marine region. Oceanic currents reflect the bifurcation of the several currents and jets of the South Equatorial Current, and formation of the resulting northwards-flowing Hiri Current and the southwards-flowing East Australian Current (EAC; Figure MAR3). Surface currents associated with the Hiri Current form the quasi-stationary Coral Sea gyre in the Queensland Plateau area (Burrage 1993, Schiller et al. 2008), and the EAC forms a slow-moving clockwise eddy in the Marion Plateau area (Griffin et al. 1987).

Waters within the Coral Sea are influenced by the Western Pacific Warm Pool water mass. The warm pool is a water mass with a monsoonal and trade wind influence, and high interannual variability associated with the El Niño–Southern Oscillation (ENSO) (McPhaden & Picault 1990). Although Coral Sea waters are considered nutrient poor at the surface, a deep chlorophyll maximum layer, resulting from a nutricline at about 60–140 metres, has been observed, with chlorophyll levels (and primary production) peaking from June to August. This feature may be attributable to the increase in south-east trade winds at this time (Lyne & Hayes 2005).

Biological communities are poorly known, but are thought to reflect the high diversity of geomorphic features and habitats throughout the marine region. Food webs throughout the region are predominantly based on large diatoms, cyanobacteria and dinoflagellates, with the region supporting aggregations of prey species for apex predators, such as aggregations of lantern fish (Diaphus spp.; McPherson 1991). Several protected and migratory species use the marine region for breeding and/or feeding, including marine turtles, sea snakes and marine mammals. The marine region supports transient populations of highly mobile and migratory pelagic species (notably pelagic predators such as billfish, tuna and sharks), and is the only known spawning site for black marlin (Istiompax indica; Young et al. 2012).

Six IMCRA 4.0 provincial bioregions are contained within the region, and 3 key ecological features have been identified: the Tasmantid seamount chain; reefs, cays and herbivorous fish of the Queensland Plateau; and reefs, cays and herbivorous fish of the Marion Plateau (DSEWPaC 2011).

The marine region supports several industries, including commercial fisheries managed by the Australian Government, offshore tourism, commercial and recreational vessel activity, recreational fishing, Indigenous activities, and defence operations.

Temperate East Marine Region

The Temperate East Marine Region covers Australian waters from the southern boundary of the Great Barrier Reef Marine Park to Bermagui in southern New South Wales. It also includes the waters surrounding Lord Howe and Norfolk islands. The marine region encompasses subtropical and temperate environments, and incorporates the southernmost coral reefs, 3 seamount chains (Tasmantid and Lord Howe seamount chains, and Norfolk Ridge), the canyons of the eastern continental slope, shelf rocky reefs, offshore reefs and abyssal plains. Physical processes and ecosystems of the marine region are influenced by the EAC. Eddies separate from the main body of the EAC as it flows south along the continental shelf of Australia, forming areas of upwelling and downwelling. Once the EAC reaches around 33°S, the orientation of the coast changes and the EAC begins to separate from the continental shelf. This flow forms the Tasman Front (Figure MAR3), which plays a significant role in water mass transport through the Tasman Sea and out into the broader Pacific Ocean (Ridgway & Dunn 2003, Evans et al. 2016). A component of the EAC continues to flow south as the EAC extension.

Surface waters are generally of low to moderate productivity, and nutrient availability is strongly regulated by vertical mixing of the water column (Bax et al. 2001, Condie & Dunn 2006). Tropical species prevail in the north and are gradually replaced by temperate species in the south. Primary production is generally higher in the southernmost waters of the marine region because of greater vertical mixing associated with the Tasman Front and its eddies (Tilburg et al. 2002). High secondary productivity associated with areas of high eddy activity tends to aggregate species such as pelagic fish, invertebrates, seabirds and marine mammals (Young et al. 2010, 2011; Dambacher et al. 2011). Communities associated with the seamount chains in the marine region tend to have high endemism (de Forges et al. 2000).

The Temperate East Marine Region contains 10 IMCRA 4.0 provincial bioregions and 8 key ecological features (DSEWPaC 2012b):

• shelf rocky reefs
• canyons on the eastern continental slope
• Tasman Front and eddy field
• upwelling off Fraser Island
• Tasmantid seamount chain
• Lord Howe seamount chain
• Norfolk Ridge
• Elizabeth and Middleton reefs.

The marine region supports several industries, including commercial fisheries managed by the Australian, Queensland and New South Wales governments; commercial and recreational vessel activity; recreational fishing; Indigenous activities; and defence operations.

South-east Marine Region

The South-east Marine Region covers Australian waters from the southern boundary of the Temperate East Marine Region, around Tasmania and west to Kangaroo Island in South Australia. It also includes the waters surrounding Macquarie Island (included in the Antarctic environment report). The marine region includes a wide range of temperate habitats, including the vast shallow expanse of Bass Strait, shelf rocky reefs, continental margin canyons, groups of seamounts and abyssal plains. Eastern parts of the marine region are dominated oceanographically by the southward extension of the EAC and associated eddy fields (Figure MAR3), which move warm subtropical waters along the east coast of Tasmania during summer. This flow reverses during the winter months, with cool subantarctic waters moving up from the south (Ridgway 2007). To the west, the Leeuwin Current travels seasonally eastwards along the shelf edge east of the Great Australian Bight as the South Australian Current and then south along the west coast of Tasmania as the Zeehan Current (Ridgway & Condie 2004). The continental shelf is relatively narrow throughout most of the marine region. The shelf break intensifies currents, eddies and upwelling, particularly in the areas east of Bass Strait and along the shelf edge from King Island to Kangaroo Island, where it is known as the Bonney Upwelling.

Overall, the South-east Marine Region is relatively low in nutrients and primary productivity (the rate at which new organic matter is developed at the base of the food web), although seasonally enhanced areas of biological productivity, such as the Bonney Upwelling, drive aggregations of pelagic marine life (Figure MAR3; see also Box MAR10). Plant and animal communities in the region are highly diverse, and many endemic species occur throughout the marine region (Wernberg et al. 2011). Several protected and migratory species use the marine region for breeding and/or feeding, including marine mammals, seabirds, tunas and sharks.

The marine region contains 11 IMCRA 4.0 provincial bioregions and 8 key ecological features (DoE 2015a):

• Bonney Upwelling
• East Tasmania subtropical convergence zone
• Bass Cascade
• upwelling east of Eden
• Big Horseshoe Canyon
• West Tasmania canyons
• seamounts south and east of Tasmania
• shelf rocky reefs and hard substrates.

The marine region supports several industries, including commercial fisheries managed by the Australian, New South Wales, Victorian, Tasmanian and South Australian governments; oil and gas exploration and production; small-scale renewable energy; commercial and recreational vessel activity; recreational fishing; Indigenous activities; and defence operations.

South-west Marine Region

The South-west Marine Region comprises Australian waters from the eastern end of Kangaroo Island, South Australia, to Shark Bay, Western Australia. The marine region includes both temperate and subtropical habitats. It incorporates the wide continental shelf of the Great Australian Bight; significant canyon features such as the Perth Canyon, the Albany canyon group and canyons near Kangaroo Island; subtropical and temperate islands and reefs; fracture zones; deepwater plateaus; and abyssal plains.

The marine region is an area of complex oceanography, which is largely driven by the eastern boundary current, the Leeuwin Current (Figure MAR3). The Leeuwin Current transports warm nutrient-depleted water along the shelf break and outer parts of the shelf, seasonally extending across the entire region during the winter months when it is the strongest (Ridgway & Condie 2004). Interactions with the equatorial-flowing Leeuwin Undercurrent and regional topography result in the formation of mesoscale eddies, particularly near the Houtman Abrolhos Islands, the Perth Canyon and Cape Naturaliste (Rennie et al. 2007). Two other current systems contribute to the marine region (Middleton & Cirano 2002):

• The Capes Current—a seasonal equatorial-flowing current, driven by southerly wind stress along the Western Australian shelf—upwells colder water onto the shelf in summer.
• The Flinders Current—an upwelling favourable current—transports water from east to west along Australia’s southern shelves.

The low-nutrient environment of the South-west Marine Region results in clear waters and high levels of light penetration, giving rise to a continental shelf characterised by high diversity of algal species and benthic communities. These, in turn, provide habitats for a large variety of species, contributing to high species diversity and endemism in the region. Several protected and migratory species use the region for breeding and/or feeding, including marine mammals, seabirds, tunas and sharks.

The marine region contains 7 IMCRA 4.0 provincial bioregions and 16 key ecological features (DSEWPaC 2012c):

• marine environment surrounding the Houtman Abrolhos Islands
• Perth Canyon and adjacent shelf break, and other west-coast canyons
• marine environment within and adjacent to the west-coast inshore lagoons
• marine environment within and adjacent to Geographe Bay
• Cape Mentelle upwelling
• Naturaliste Plateau
• Diamantina Fracture Zone
• Albany canyon group and adjacent shelf break
• marine environment surrounding the Recherche Archipelago
• ancient coastline at a depth of 90–120 metres
• Kangaroo Island Pool, canyons and adjacent shelf break, and Eyre Peninsula upwellings
• mesoscale eddies (several locations)
• demersal slope and associated fish communities of the Central Western Province
• western rock lobster
• benthic invertebrate communities of the eastern Great Australian Bight
• small pelagic fish of the South-West Marine Region.

The marine region supports several industries, including commercial fisheries managed by the Australian, South Australian and Western Australian governments; oil and gas exploration and production; small-scale renewable energy; commercial and recreational vessel activity; recreational fishing; Indigenous activities; and defence operations.

North-west Marine Region

The North-west Marine Region includes Australian marine waters from Kalbarri, south of Shark Bay, to the Western Australia – Northern Territory border. The marine region includes subtropical and tropical habitats, with extensive areas of continental shelf and slope, plateaus, terraces, coralline algal reefs, pinnacles, shoals, offshore reefs, canyons and abyssal plains. The oceanography of the marine region is subject to the Indonesian Throughflow (Figure MAR3), which brings warm, low-nutrient, low-salinity water from the western Pacific Ocean through the Indonesian archipelago to the Indian Ocean (Schiller 2011). The Indonesian Throughflow also contributes to the Leeuwin Current (Feng et al. 2003). Seasonal fluxes in water transport by the Indonesian Throughflow are associated with the annual monsoon cycle and influence the Leeuwin Current (Schiller 2011). The weakening of the Indonesian Throughflow and Leeuwin Current during the summer months, along with seasonal changes in wind and cyclone activity throughout the marine region, increase mixing of the deeper, cold, nutrient-rich waters with surface waters, increasing biological productivity in what is overall a low-productivity environment. Internal waves resulting from interactions within vertical gradients in water temperature, currents, extreme tidal regimes and the sea floor also increase biological productivity.

The marine region’s range of geomorphic features and habitats is reflected in high species diversity, which is predominantly tropical and typical of the Indo–Pacific area. Several protected and migratory species use the marine region for breeding and/or feeding, including marine mammals, marine turtles, seabirds, tunas and sharks—particularly aggregations of whale sharks (Rhincodon typus).

The North-west Marine Region contains 8 IMCRA 4.0 provincial bioregions and 13 key ecological features (DSEWPaC 2012d):

• carbonate bank and terrace system of the Sahul Shelf
• pinnacles of the Bonaparte Basin
• Ashmore Reef, Cartier Island and surrounding waters
• Seringapatam Reef and the waters in the Scott Reef complex
• continental-slope demersal fish communities
• canyons linking the Argo Abyssal Plain and Scott Plateau
• ancient coastline at the 125 metre depth contour
• Glomar Shoals
• Mermaid Reef and the waters surrounding Rowley Shoals
• Exmouth Plateau
• canyons linking the Cuvier Abyssal Plain and the Cape Range Peninsula
• waters adjacent to Ningaloo Reef
• Wallaby Saddle.

The marine region supports several industries, including commercial fisheries, shipping, oil and gas exploration and production, commercial and recreational vessel activity, recreational fishing, Indigenous activities, and defence operations.