FACTORS AFFECTING THE BEHAVIOR OF CROWN-OF-THORNS STARFISH (ACANTHASTER-PLANCI L.) ON THE GREAT-BARRIER-REEF - 1 - PATTERNS OF ACTIVITY

The feeding, moving and cryptic behaviours of 5749 crown-of-thorns sta rfish, 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 fac tors including the size of starfish, their depth and physical conditio n, time of day, and substratum type. For most of these factors, the pa tterns of behaviour were shown to be consistent across reefs. Irrespec tive of their size, starfish spent on average about 45% of their time feeding. However, there were strong diurnal effects with smaller starf ish (<20 cm) strongly favouring nocturnal feeding. For larger starfish (>40 cm) this pattern was reversed, though the diurnal effects were n ot as strong. Diurnal variation was greater at shallower depths (<3 m) . Larger starfish spent more time moving (similar to 20%), particularl y during the day, compared to smaller starfish (similar to 5%), with t he latter moving mainly at night. Motion increased with depth for all starfish. The density and degree of aggregation of starfish had no eff ect on behaviour. The cryptic behaviour of starfish decreased with siz e, from similar to 60% for small starfish to less than 10% for large s tarfish. For starfish <30 cm in size, there were strong diurnal effect s 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 likel y to be moving than those in good condition. Cryptic starfish were 10 times more likely to be in good condition than non-cryptic starfish. T his may partly explain the relatively rapid breakdown in starfish aggr egations which has been observed at the ends of outbreaks. (C) 1998 El sevier Science B.V.