Coast Care

2001 - A baseline assessment of the flora and fauna of North Stradbroke Island dive sites, Queensland

Executive summary of final project.

Unidive, The University of Queensland Underwater Club, was awarded funding by Coastcare to map and conduct a biological survey of popular North Stradbroke Island SCUBA dive sites in 2000-2002, using the local dive operator Point Lookout Scuba, Ken Holzheimer. Involvement in the project was voluntary. Members of Unidive who were marine experts,conducted training for the rest of the group who had no experience in identifying marine organisms and mapping habitats.

The mapping and biological surveys were conducted over 6 weekends between June 2001 and April 2002, with the local dive operator Point Look Out SCUBA, Ken Holzheimer. One weekend (June 2001) was for training, another (August 2001) for mapping and 3 weekends (October 2001, December 2001 and March 2002) for conducting biological surveys. An additional weekend (April 2002) was used exclusively to monitor the extent of coral bleaching.

No baseline information was available about the area despite it being a Conservation Zone in the Moreton Bay Marine Park, an important region for commercial and recreational activities and also a critical habitat for endangered species such as the Grey Nurse Shark.

Methodology comparable to the Reef Check voluntary program was used to monitor organisms growing on the substrate (algae, coral and other organisms), invertebrates and fish and additional analysis was conducted with video. Two reefs were surveyed, Flat Rock and Shag Rock, with two permanent transects at each reef. Each transect was sampled once every weekend. Additional sites, Mantaray Bommie and Mid Reef, were sampled opportunistically. It was not possible to define a control site in this study region, making conclusive statements about impacts to the area impossible.

At least 50 species of algae, 1 species of seagrass, 120 species of invertebrates, including 42 species of hard coral and 173 species of fish were identified at the reefs of Flat Rock and Shag Rock. The diversity of species observed at North Stradbroke Island indicates a complex, productive community.

The most abundant group of organisms growing on the rocky reefs was algae. Algal cover was 40 to 80%, comprising mostly small turf algae and larger macroalgae. The most commonly observed macroalgae was Asparagopsis.

Cover of hard and soft corals totalled 15%. The common families of hard coral were Faviidae, Acroporidae and Pocilloporidaea and the common genera of soft coral were Sarcophyton (Leather coral) and Dendronepthya (Prickly red tree coral).

Other invertebrates observed included sponges, ascidians, sea cucumbers, anemones, sea stars, feather stars, sea urchins, nudibranchs and worms. The rapid assessment of invertebrates found less diversity at Shag Rock compared to Flat Rock. However, the long spined sea urchin was more abundant at Shag Rock.

Nineteen out of the 22 indicator fish families and 15 out of the 20 target fish species were observed at Flat and Shag Rock. The surveys indicated no differences between Flat and Shag Rock and no differences over the sampling period. Many of the fish targeted for human consumption were not found in great abundance. The most abundant fish were territorial fish (eg. Damselfish). The next most abundant groups were invertebrate feeding fish, and the least abundant, coralivore, herbivorous and piscivorous fish. It is not clear whether the lower abundance of piscivorous fish is related to either the availability of food resources or fishing pressure.

Indicators of ecosystem health suggest the North Stradbroke Island reefs are in generally good health. This includes no evidence of nutrient enrichment, recovery from coral bleaching and low levels of coral predators. A lack of large fish, which are targeted for human consumption, may be of concern.

This is the first biological assessment of North Stradbroke Island dive sites. The survey has demonstrated the diversity and complexity of these rocky reef systems and certainly some impacts from humans through rubbish and potentially, fishing pressure. This information will be useful to the community and managers in the future to determine if any changes have occurred at these sites.