GREAT BARRIER REEF
// Outlook Report 2014
Great Barrier Reef shelf edge 91,92 and may add substantially to the known coral reef area in the Region. In fact, about 60 per cent (25,600 square kilometres) of the seabed where coral reefs are likely to grow is deep-water habitat.93 Cold water coral reefs (below 150 metres) typically occur in depths where light does not penetrate and temperatures are between four and 14 degrees Celsius.94 They can form reefs or knolls and be hotspots of biodiversity on the deep seabed.95 Although no cold water coral reefs have been identified within the Region, there are locations potentially suitable for them.96 There is no long-term data on the condition of deeper reefs; for most of the Region, it is unlikely there has been recent physical damage.92,95 However, the substantial damage recorded at Myrmidon Reef offshore from Townsville, as a result of the category 5 cyclone Yasi in 201197,98, indicates that deeper reefs can also be affected by the physical damage of intense cyclones.
There are few indications of recent damage to deeper reefs.
The lagoon floor makes up about 210,000 square kilometres, approximately 61 per cent of the Region.99 It includes the non-reefal seafloor inside the outer barrier reefs, typically at depths of between 20 and 40 metres.34 The lagoon floor habitat is variable and includes some marine life that rises above the seafloor with sponges, sea-whips, gorgonians (sea fans) and interreefal gardens.100 The lagoon floor supports many species, such as nematodes and microbial communities, which are important elements of a healthy functioning ecosystem101. Larger organisms use the lagoon floor for food and shelter and as a nursery habitat. These include shellfish, crabs, prawns, sea urchins, sea stars, sea cucumbers, sponges, worms, fishes (including sharks and rays) and some marine turtles. The ecological importance of interreefal areas is recognised in the Reef’s world heritage listing. While a large-scale study of the Region’s lagoon floor provided a comprehensive and extensive snapshot of the habitat13, there is no long-term monitoring. In recent years, the area affected by trawling has decreased (Section 5.4.1).9,102 On a more local scale close to the coast, the lagoon floor is affected by dredging, disposal and resuspension of dredge material, land-based run-off and anchoring.
Reduced trawling effort and better management have reduced the area of lagoon floor being affected.
The lagoon floor and shoals are not well studied
Shoals are submerged features on the seafloor away from obvious emergent coral reefs.103 They include continental rock, and Pleistocene reef edges.103 They are diverse and variable and attract and support many fishes and other species, such as gorgonians, sponges, algae, macroalgae and seagrasses.104,105,106 Based on limited studies to date13,104,107, shoals are likely to be affected by physical damage from fishing activities, anchoring, vessel groundings and storms; however, there is no ongoing monitoring of shoals in the Region.
Shoals are likely to be affected by physical damage from fishing activities, anchoring, vessel groundings and storms.