Marine bioregional plan for the North Marine Region prepared under the

2.2 Conservation values—the Commonwealth marine environment

By global standards, the marine environment of the North Marine Region is known for its high diversity of tropical species but relatively low endemism (i.e. species that are found nowhere else in the world) in contrast with the relatively isolated southern Australian marine fauna, which has high species endemism. Regions particularly rich in biodiversity include the Gulf of Carpentaria coastal zone, plateaux and saddle north-west of the Wellesley Islands, and the submerged coral reefs of the Gulf of Carpentaria.

Several factors contribute to the high level of biodiversity and low endemism in the region. These factors include the vast species-rich biogeographic ocean zone stretching from the western Pacific to the east coast of Africa where, apart from small stretches of deep ocean in the Arafura and Timor seas, there are thought to be few physical barriers to species dispersal. Most species endemic to the region lack a long-lived pelagic (open sea) larval stage that enables them to cross deeper waters.

The North Marine Region is increasingly recognised as an area of global conservation significance for marine species and as an aggregation area and staging point for migratory birds. Waters in and/or adjacent to the region provide important bird, marine turtle and dugong breeding, feeding and nursery sites. Six of the world’s seven species of marine turtle are found in the region and all are listed as endangered or vulnerable under the EPBC Act. The Australian snubfin dolphin, a resident in the region, is endemic to the Australian continental shelf and is found along the Northern Territory coastline. Other protected species known to occur in the region include sawfish, 28 of the 35 known Australian species of sea snakes, the saltwater crocodile, and a vast array of seahorse and pipefish species. The coral reef systems of the region support some endemic species, however, flora and fauna are generally typical of oceanic reefs in the Indo–west Pacific region. Coral, invertebrates and phytoplankton are all highly diverse, while fish such as snapper, emperor and grouper are common higher-order predators of coral and rocky reef habitats.

The most significant known influence on ecosystem structure and function in the North Marine Region is the sea level across the region, which has periodically oscillated during recent geological times. Around 20 000 years ago much of the Gulf of Carpentaria was a shallow brackish lake. Present ocean levels became relatively stable only in the past 6000 years. As a consequence, the region is a relatively new marine environment and many species may still be colonising it. Today, the Gulf of Carpentaria is a semi-enclosed sea bordered by the Torres Strait to the east and by a sill extending from the Wessel Islands in the west to Papua New Guinea in the north, both of which limit the movement of water between the Gulf and the neighbouring Coral and Arafura seas. The Gulf of Carpentaria seabed is mostly flat with waters increasing in depth gradually by about one metre every kilometre, creating a shallow coastal zone up to 20 kilometres wide. Other factors that influence the ecosystems in the Gulf of Carpentaria include complex and varied winds and tides and striking seasonal weather patterns.

The North Marine Region is influenced primarily by tidal flows and less by ocean currents. The net tidal flows that occur over time drive longer-term transport patterns through the region. The movement of tidal waters across the northern Australian marine environment is complex due to the barrier of islands and submerged reefs in the Torres Strait that hinder tidal energy entering from the Coral Sea. Currents that have some minor influence in the region include the Indonesian Throughflow and the South Equatorial Current. The Indonesian Throughflow brings warm water of lower salinity from the tropical western Pacific Ocean between the Indonesian islands to the Indo-Australian basin in the north-west of the region. The influence of the South Equatorial Current in the region is marginal, although the strength of its influence varies with the season.

Key ecological features (KEFs) are elements of the Commonwealth marine environment in the North Marine Region that, based on current scientific understanding, are considered to be of regional importance for either the region’s biodiversity or ecosystem function and integrity.

The criteria used to identify KEFs in the region are:

a species, group of species or community with a regionally important ecological role, where there is specific knowledge about why the species or species group is important to the ecology of the region, and the spatial and temporal occurrence of the species or species group is known

a species, group of species or community that is nationally or regionally important for biodiversity, where there is specific knowledge about why the species or species group is regionally or nationally important for biodiversity, and the spatial and temporal occurrence of the species or species group is known

an area or habitat that is nationally or regionally important for

enhanced or high biological productivity

aggregations of marine life

biodiversity and endemism

unique seafloor feature with ecological properties of regional significance.

KEFs were first described in the bioregional profile for each region and have since been modified as a result of further analysis and review by scientific experts.

Eight key ecological features have been identified in the North Marine Region (see Figure 2.1 and Table 2.1). Further information on the KEFs can be found in the Commonwealth marine environment report card (www.environment.gov.au/marineplans/north). Understanding of KEFs may evolve as new scientific information emerges.