Natural Values of the Inshore Waters of Australia’s Indian Ocean Territories - Christmas & the Cocos (Keeling) Islands

Summary

Australia’s Indian Ocean Territories (IOTs), Christmas and Cocos (Keeling) Islands, are surrounded by important and unique marine environments. Of particular importance, are extensive areas of shallow-water habitat, including seagrass and diverse coral reef habitats, in the lagoon at South Keeling (Cocos) atoll. This large area and diversity of marine habitats support a wide range of marine species, including resident populations of green turtles (Chelonia mydas) and other important marine species (e.g., gong gong; Lambis lambis) that would not otherwise occur in the IOTs.

Six distinct Key Ecological Features (KEFs) are proposed for the IOTs, encompassing habitat areas and features that are nationally and regionally significant, and also recognising the ecological importance of a highly abundant endemic species that has a major influence on local productivity:

i) Extensive lagoon system at South Keeling (Cocos) Island; ii) Outer reef habitat at Cocos Keeling Islands; iii) Fringing coral reef at Christmas Island; iv) Areas of high productivity around Christmas Island v) Caves (including anchialine caves) at Christmas Island, and vi) Annual spawning migrations of land crabs at Christmas Island

Australia’s IOT waters also encompass many areas where species display biologically important behaviours, such as feeding, foraging, migrating or resting. A number of these areas, which relate to listed and threatened species, may qualify for more formal recognition as Biologically Important Areas (BIAs) within the framework of the Environment Protection and Biodiversity Conservation Act 1999. There are 11 species of sharks (including a seasonal aggregation of whale sharks; Rhincodon typus), five species of turtles, 10 cetacean species, a dugong, and both species of manta ray (Mobula birostris and M. alfredi), reported from waters of the IOTs. Importantly, many of the green turtles (C. mydas) that occur in the IOTs are part of a resident population that nest at North Keeling Island (NKI) and are critically dependant on seagrass habitats at the Southern Atoll of the Cocos (Keeling) Islands (SKI).

The diversity and abundance of land crabs at Christmas Island (CI) is the highest in the world, and although these crabs spend most of their life on land, they migrate to coastal habitats to reproduce and have a marine larval phase. The annual spawning migration of Christmas Island red crabs (Gecarcoidea natalis) is a globally recognised phenomena, resulting in large aggregations of crabs in coastal habitats both during spawning and also during the emergence of juveniles after they have completed larval development in waters surrounding CI. The marine larval phase of land crabs is short (weeks), but may have a significant influence on biological productivity and partly account for seasonal aggregations of pelagic species (e.g., whale sharks) near CI.

There are a wide range of specialist marine species (dependent on either corals reefs or seagrass habitats) that occur in the IOTs. Due to its unique biogeographic location, local assemblages of marine species contain a unique mix of Indian and Pacific Ocean species, including many Indian Ocean species that do not occur anywhere else within Australian territorial waters. The overlap between these major biographical provinces also gives rise to high incidence of hybridisation, and there are also a large number of endemic species that only occur within the IOTs.

While there has been significant and increasing research on shallow, nearshore marine systems within Australia’s IOTs (highlighting the unique and important marine species, environments and habitats within this region) further research is needed. Most critically, extensive and recurrent surveys across all major habitats are needed to establish status and trends in the abundance and composition of habitat-forming organisms (e.g., corals and seagrasses). Systematic and widespread sampling should also encompass the broad range of motile species (fishes and non-coral invertebrates) that might be sensitive to changes in habitat structure. Experimental studies are also warranted to better understand potential impacts of environmental change and other major disturbances on the demography and resilience of key habitat-forming organisms and other important species. There is also scope for extensive sampling and taxonomic research across poorly studied groups and habitats (including mesophotic reefs) to better understand the unique flora and fauna that exists within Australia’s IOTs.