Status of fringing reefs in the Northumberland Islands, southern Great Barrier Reef

Brief description

Fringing reefs surrounding islands within the Northumberland Islands group were surveyed in September 2000. The Northumberland Islands occupy a relatively large area (approx 9000 km²). In order to get good geographic coverage of reefs, a sub-sample of islands was targeted within three distinct zones at various distances from Broad Sound and the coast.The study zones were:1. near-shore islands immediately adjacent to the coast (within 3km, Temple Island group and West Hill Island)2. mid-shore islands located approximately midway between the coast and the outer limit of the Northumberland Islands (Knight Island, Curlew Island and Poynter Island)3. offshore islands on the seaward side of the Northumberland Islands group bordering the lagoon of the GBR (Prudhoe Island, Pine Peak Island and South Percy Island).Surveys used one or more of the following techniques to gain a broadscale overview of reef habitat around island perimeters and to identify areas of fringing reef that would be suitable for long-term monitoring:1. Broadscale surveys used manta tow or, if visibility was less than 6m, spot checks. For manta tow surveys, the variables recorded included crown-of-thorns starfish counts, estimates of live coral, dead coral and soft coral cover, and the number of bleached corals. During spot checks, observers recorded substrate type and associated benthic organisms, but did not estimate coral cover.2. Detailed surveys were carried out along a series of 50m transects at each reef. Benthic organisms occurring along the transects were recorded on video for later analysis. Fish were also identified along each transect, however fish abundance was not recorded. The objectives of this research were:1. to provide an assessment of the status of coral and reef fish communities around a variety of islands within the Northumberland Islands group.2. To provide an interpretation of those data in terms of:a) how the Northumberland Islands reef biota compare with reef assemblages in other regions within the GBRb) the comparative biological/ecological value of the Northumberland Island's reefs c) historical comparisons of reef status (where data is available) to indicate current reef trajectoriesd) options for long-term monitoring of these reefs.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Statement: Broadscale surveys:Where underwater visibility permitted, manta tows were used to assess the benthic habitats surrounding the islands and to identify coral communities and fringing reefs for more detailed appraisal. A snorkelling observer holding on to a manta board was towed behind a small boat (3-5 km/h) parallel to the reef crest and close enough to see as much of the reef slope as possible. Two observers surveyed each island. From a designated start point, the observers were towed in opposite directions around the reef perimeter until they met. As the observers proceeded along the reef edge they scanned the benthos. The boat stopped briefly at two-minute intervals; allowing the observer to record data from the previous tow on waterproof paper mounted on the manta board. Crown-of-thorns starfish counts, estimates of live coral, dead coral and soft coral cover, and the number of bleached corals were recorded (see Bass and Miller 1996).Where visibility was less than 6m, spot checks were used. Two boats (each with a driver and an observer) worked their way around the perimeter of the island in opposite directions from a designated start point. At 200m intervals (estimated visually) the observer entered the water and swam to the bottom a number of times to make a visual assessment of the benthos. Observers recorded the type of substratum and associated benthic organisms. Hard and soft corals were identified to the level of genus. Coral cover was not estimated. On true fringing reefs, extra spot searches were conducted to determine the pattern and extent of the reefs.Detailed surveys:On fringing reefs suitable for long term monitoring, the fish and benthic communities were surveyed in detail using SCUBA. These surveys aimed to provide an overview of the habitat and associated biota (benthos and fish) along the full length of each fringing reef. To gain the widest coverage, five sites were positioned at regular intervals along the reef edge. At each site, two 50m transects were surveyed at two depth contours along a 50m fibreglass tape laid across the bottom. Typically there was a shallow transect laid on or just below the reef crest and a deeper transect on or near the bottom of the reef slope. Benthic organisms were surveyed on each 50m transect by recording a 25cm wide swathe of the bottom using a Sony DCR-TRV900E MiniDV digital video camera. Percent cover of corals and other benthic organisms were estimated from the video images using a point sampling technique, in which approximately 200 systematically dispersed points were sampled from each video transect. The organism beneath each point was identified to the most detailed taxonomic or descriptive classification possible, according to the resolution of the video image and the skill of the observer. Data was separated into three "levels of classification": benthic group, family group and genus. Each level is comprised of "categories" that may be formed by one or more species of benthic organism (see Table 1, Page et al. 2001). All hard and soft coral genera observed within five metres either side of each transect, were recorded on slates.Bass DK, Miller IR. 1996 Crown-of-thorns starfish and coral surveys using the manta tow and scuba search techniques. Long-Term Monitoring of the Great Barrier Reef, Standard Operational Procedure No.1, Australian Institute of Marine Science, Townsville, Queensland 38pp.Page C, Coleman G, Ninio R, Osborne K. 2001. Surveys of benthic reef communities using underwater video. Long-Term Monitoring of the Great Barrier Reef , Standard Operational Procedure No.7, Australian Institute of Marine Science, Townsville, Queensland 52pp.

Notes

Credit
Sweatman, Hugh PA, Dr (Custodian)