The feeding, moving and cryptic behaviours of 5749 crown-of-thorns starfish, Acanthaster
planci (L.), were studied on 15 reefs of the Great Barrier Reef between June 1986 and December
1987. Log-linear analyses of field data showed that these behaviours were influenced by complex
interactions between a number of important physical and biological factors including the size of
starfish, their depth and physical condition, time of day, and substratum type. For most of these
factors, the patterns of behaviour were shown to be consistent across reefs. Irrespective of their
size, starfish spent on average about 45% of their time feeding. However, there were strong diurnal
effects with smaller starfish (,20 cm) strongly favouring nocturnal feeding. For larger starfish
(.40 cm) this pattern was reversed, though the diurnal effects were not as strong. Diurnal
variation was greater at shallower depths (,3 m). Larger starfish spent more time moving
(| 20%), particularly during the day, compared to smaller starfish (| 5%), with the latter moving
mainly at night. Motion increased with depth for all starfish. The density and degree of
aggregation of starfish had no effect on behaviour. The cryptic behaviour of starfish decreased
with size, from | 60% for small starfish to less than 10% for large starfish. For starfish ,30 cm
in size, there were strong diurnal effects on cryptic behaviour, with smaller starfish being almost
exclusively cryptic during the day. Cryptic behaviour was also influenced by the condition of
starfish. Those in poor condition were 5 times more likely to be moving than those in good
condition. Cryptic starfish were 10 times more likely to be in good condition than non-cryptic
starfish. This may partly explain the relatively rapid breakdown in starfish aggregations which has
been observed at the ends of outbreaks. Ó 1998 Elsevier Science B.V.
The feeding, moving and cryptic behaviours of 5749 crown-of-thorns starfish, Acanthasterplanci (L.), were studied on 15 reefs of the Great Barrier Reef between June 1986 and December1987. Log-linear analyses of field data showed that these behaviours were influenced by complexinteractions between a number of important physical and biological factors including the size ofstarfish, their depth and physical condition, time of day, and substratum type. For most of thesefactors, the patterns of behaviour were shown to be consistent across reefs. Irrespective of theirsize, starfish spent on average about 45% of their time feeding. However, there were strong diurnaleffects with smaller starfish (,20 cm) strongly favouring nocturnal feeding. For larger starfish(.40 cm) this pattern was reversed, though the diurnal effects were not as strong. Diurnalvariation was greater at shallower depths (,3 m). Larger starfish spent more time moving(| 20%), particularly during the day, compared to smaller starfish (| 5%), with the latter movingmainly at night. Motion increased with depth for all starfish. The density and degree ofaggregation of starfish had no effect on behaviour. The cryptic behaviour of starfish decreasedwith size, from | 60% for small starfish to less than 10% for large starfish. For starfish ,30 cmin size, there were strong diurnal effects on cryptic behaviour, with smaller starfish being almostexclusively cryptic during the day. Cryptic behaviour was also influenced by the condition ofstarfish. Those in poor condition were 5 times more likely to be moving than those in goodcondition. Cryptic starfish were 10 times more likely to be in good condition than non-crypticstarfish. This may partly explain the relatively rapid breakdown in starfish aggregations which hasbeen observed at the ends of outbreaks. Ó 1998 Elsevier Science B.V.
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