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Crown-of-Thorns Starfish
A log of crown of thorns starfish (COTS) observations has been kept at the Research Station since October 1993. It was started at that time because the number of COTS at Lizard Island and other reefs in the vicinity had increased noticeably over that year. In 1992, COTS were rarely seen around Lizard Island at all. This log cannot be used to calculate densities because it is based on casual observations of the number of COTS noticed by research divers as they conduct their other activities. The only estimate of area is whether or not the divers swam more than 50 metres. Despite these limitations, the log does provide many observations over a long period of time and shows distinct trends. According to these observations, the recent COTS outbreak at Lizard Island first became noticeable in 1993, reached its peak in 1996 but it had not declined to 1993 levels by 1998. Considering only those dives where observers swam more than 50m, the following mean numbers of COTS were seen per dive:
A similar pattern is seen for the proportion of dives on which no COTS were seen during dives that covered more than 50 m:
Areas that have suffered severe coral mortality due to the COTS outbreak, such as Mermaid Cove, are now showing signs of recovery due to recolonisation by corals. The outbreak of COTS in the vicinity of Lizard Island between 1993 and 1998 appears to be common to all mid-shelf reefs in the area, but the outer reefs escaped this impact. During the five year period, only seven COTS were recorded during 386 dives on the outer barrier reefs stretching from Hicks Reef to Ribbon Reef Number 10. Of these, six were observed in 1994 and one in 1995. In addition, the Lizard Island Lodge recorded only one COTS during 523 visits to the Cod Hole on Ribbon Reef Number 10 between April 1992 and April 1997. Relevant links
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