Coldwater corals in the Coral Sea
May 12, 2009

Coldwater corals occur globally in the deep ocean and are a diverse group of stony corals, soft corals, black corals and lace corals. These corals differ from tropical shallow-water corals because they lack symbiotic algae and typically exist in deeper waters below the sunlit zone. Like shallow-water corals, they can form reefs or mounds on the deep seafloor, which provide the complex habitat and variety of niches for a distinct and unique ecosystem.

coldwater gloriaknolls s3D view of the Gloria KnollsIn 2007, while on a research expedition using the Australian Marine National Facility vessel, RV Southern Surveyor, we discovered a cluster of eight knolls up to 2 km long and over 100 m high, in depths of about 1200 m in the Queensland Trough. These knolls are thought to be the debris block of a large undersea landslide that occurred on the continental slope of northeastern Australia.

A rock dredge sample taken from the top of the largest knoll in 1165 m recovered evidence of a coldwater coral community, comprising both live and dead stony (scleractinian) corals, soft (bamboo and sea whip) corals, goose barnacles and gastropod shells lying within a muddy sediment. Lithified (hard) calcareous nodules provided attachment surfaces for many of the fossil corals.

coldwater fossilcorals sfossil corals and nodulesAnother RV Southern Surveyor expedition to the Coral Sea in 2008 sampled the seawater over the knolls and expanded the seafloor mapping data over the knolls, which we have named the Gloria Knolls, after the Gloria deep-water sidescan imagery used to help locate these knolls.

The discovery is highly significant as little is known about coldwater coral ecosystems or even their distribution in Australian marine waters. This led to many questions, such as how old is the coldwater coral community? What is the geological origin of the knolls? What are the links between the coldwater corals and their physical habitat, which is vital for the ecosystem-based management of these sensitive areas.

To achieve these objectives, we are using a combination of radiocarbon ages on the coral, barnacle and shell samples, sediment analysis, and acoustic mapping data to provide the new maps and knowledge on the geographic distribution and possible connections to other coldwater coral communities in Australian waters.

The project will use a combination of radiocarbon and U/Th ages on the coral, barnacle and shell samples, sediment analysis of the muddy matrix, and acoustic mapping data to provide the new maps and knowledge on the ages, composition and geographic distribution of this fascinating coldwater coral community in Australia’s Coral Sea.

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