Coldwater coral ecosystems on the Great Barrier Reef margin
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 and three dimensional mounds (or knolls) on the deep seafloor, which provide the complex habitat and variety of niches for a distinct and unique ecosystem.
Coldwater coral reefs are known as biodiversity hotspots on the flat muddy seabed for a wide variety of deep marine life, including commercial fish species. Studies of coldwater coral reefs show that they are very slow growing, taking 1000s of years to develop in areas with stable conditions. However, they are quite vulnerable to physical damage from deep-sea trawling and the effects of climate change through variation in ocean chemistry.
Figure 1. 3D view of the Gloria Knolls
Then in 2007, we were on a research expedition along the Great Barrier Reef margin using the Australian research vessel, RV Southern Surveyor. We discovered a cluster of eight knolls up to 2 km long and over 100 m high, in depths of 1100 m along the edge of the Great Barrier Reef margin (Figure 1 & Map below). A rock dredge sample taken from the top of a knoll recovered evidence of a coldwater coral community, comprising live and dead stony corals, soft corals, barnacles and shells within a muddy sediment (Figure 2). Another RV Southern Surveyor expedition to the Coral Sea in 2008 sampled the seawater over the knolls (Movie below).
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? And what are the links between the coldwater corals and their habitat, which is vital for the ecosystem-based management of these sensitive areas.
Figure 2. Coral community samples
The objectives of the Coldwater coral ecosystems on the GBR project are:
To study the origin and biodiversity of the cold-water corals; and
To understand the role of the submarine landscape in defining the boundaries of the coldwater coral habitat.
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.
Figure 3. Live coral pieces
We applied for grant funding at the Australian Nuclear Science and Technology Organisation (ANSTO) based in Sydney, to conduct radiocarbon age dating on the coral and shell samples brought up in the rock dredge. The ages will tell us how old these corals are and provide clues as to their origin. Also, deep-water taxonomy specialists are providing information on the species names of these animals (Figure 3).
A major finding of the expedition was that the knolls appear to be huge blocks that have broken off the continental slope and slid down into the basin where they have formed a high-relief habitat for the coldwater coral community. This project will use the extensive 3D maps collected during the expedition to test the hypothesis that the knolls were originally derived from the Great Barrier Reef margin.
Overall, the project will use advanced 3D visualisation and GIS (digital mapping) software to analyse all the geographic data. The combination of the digital maps, radiocarbon ages on the coral samples, and sediment analysis data, will provide the vital new information to help understand the relationship between the coldwater corals and their physical environment on the Great Barrier Reef margin.
