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EXTENT OF ACTIVITY AND EFFECTS OF THE CROWN-OF-THORNS STARFISH ON THE GREAT BARRIER REEF
37. How much of the Great Barrier Reef has been affected in recent times? This is a very difficult question to answer because no one has been able to survey the entire Great Barrier Reef. This would be an almost impossible task given that the Reef comprises approximately 2,900 individual reefs, it covers a distance of more than 2,300 km and it has an area of 349,000 square kilometres (see Fig. 14). Despite the problems involved some attempts have been made to answer this question. Up until 1985 all surveys had been concentrated in specific areas of the reef in a year. In 1985 the Australian Institute of Marine Science initiated a large-scale survey program in conjunction with the Commonwealth Community Employment Program. Its objective was to survey 228 reefs throughout the length and breadth of the Great Barrier Reef within 1 year. The results of this survey provided the most accurate account of the effects of recent outbreaks of crown-of-thorns starfish. In essence they revealed that the central third of the Great Barrier Reef (between Lizard Island and Townsville, see Fig. 14) had been affected by outbreaks within the previous 6 years. Within this region approximately 65% of all reefs surveyed were considered to have experienced a recent outbreak of starfish. This figure increased to almost 80% for reefs in the vicinity of Townsville. The effects of outbreaks on individual reefs were found to vary. Almost 86% of reefs that had experienced a recent outbreak had moderate to high coral mortality over at least a third of their perimeters. About 10% of reefs had high coral mortality over most of their perimeters. These surveys are continuing.
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