Fiji's Great Astrolabe Lagoon: baseline study and management issues for a pristine marine environment
Abstract The Great Astrolabe Lagoon ( 18°45′ S , 178°32′ E ), located some 70 km south of Suva, the capital of Fiji, is a marine environment in relatively pristine condition, impacted only by low human populations on small islands. The Great Astrolabe Reef which encloses the Lagoon is a barrier reef composed of oceanic ribbon reefs. A baseline study of the Lagoon was carried out in 1989–92 which consisted of two components: (1) biological monitoring of permanent reef transects, and (2) water and sediment quality monitoring. Twelve study sites encompassing different habitats were visited regularly during the study period. Substrate cover, hard coral cover, plant cover and counts of selected motile invertebrates were taken. Fish counts were also conducted. The water quality studies included temperature, dissolved oxygen and nutrients, trace metal analyses and microbiological examination of edible bivalves. Sediment samples were also analysed for a range of macro- and micro-elements. The reefs that were relatively inaccessible to the local villagers were found to be in a healthier state than those in close proximity to the islands. There were several problems encountered in the reef monitoring studies which exemplify the constraints of conducting research in a relatively isolated location. Water analyses indicated that the Lagoon is relatively free from pollution with pH, dissolved oxygen, temperature and salinity data close to open ocean values. Apart from nitrate, all nutrient values were below detection limits. Nitrate values averaged 0.74 μmol/L, but varied from 0.2 to 1.9 μmol/L. Data for trace metals in water were consistent with no contamination. Shellfish samples showed no contamination by trace metals and minimal faecal coliform contamination. Sediments showed no contamination by trace metals and were dominated by high magnesium calcite and aragonite, with minor amounts of low magnesium calcite. There are increasing pressures on this area, both from local residents who wish to move to a more cash oriented economy through increased fishing and tourism, and from external tourism interests. The Lagoon has also been suggested as a marine national park. Some of the management issues associated with these alternatives are discussed.