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OCCURRENCE IN THE PAST
17. Have outbreaks of crown-of-thorns starfish occurred in the past? The first records of outbreaks date back to the late 1950's when large numbers of starfish were observed in the Ryukyu Islands (see Fig. 3). Not long after, in the early 1960's, outbreaks were reported on Green Island, and several reefs nearby, on the Great Barrier Reef. Since then outbreaks of crown-of-thorns starfish have been observed in other parts of the Ryukyu Islands and the Great Barrier Reef, as well as other regions in the Indo-Pacific (see 11). The reports of early biologists and the information from Pacific Island cultures and other historical records are insufficient to show that outbreaks have occurred in the past. Recent studies on the Great Barrier Reef have demonstrated that crown-of-thorns starfish were well known to trochus divers before 1960. Some even had specific names and cures for the starfish. Such information, whilst of interest, does not provide indisputable evidence of past outbreaks rather only evidence of the past occurrence of starfish. It should be recognised that crown-of-thorns starfish may be prominent in the memories and cultures of indigenous peoples not because they have occurred in large numbers in the past but because they are conspicuous and venomous. Geological studies (conducted in the 1970's) of the skeletal remains of crown-of-thorns starfish in sediments also have been unable to conclusively demonstrate that outbreaks have occurred in the past. Fragments of starfish skeleton as old as 3,355 years BP (Before Present/were recovered from sediment cores taken from a number of reefs on the Great Barrier Reef. Again, it is difficult to interpret the significance of these results because it is not known whether finding several fragments (or just one/constitutes a past outbreak or a "normal" (low density) population. Furthermore, it is not known whether the amount of skeletal material incorporated into the sediments increases in proportion to the number of starfish in the population. At present it is assumed that outbreaks produce much larger amounts of skeletal material since many more starfish are presumed to die on the reef. However, the fate of starfish in outbreaks is still unknown. Do they die in large numbers on reefs or do they move off in search of more food (see 15)? Further research is needed before these questions can be answered with any degree of confidence. New geological studies (using the latest dating and sampling techniques) are being conducted at James Cook University of North Queensland which seek to provide a greater understanding of the occurrence of outbreaks in the distant past.
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