Seasonal abundance, spatial distribution, spawning and growth of Astropecten irregularis (Echinodermata : asteroidea)

Seasonal trends in the abundance, spatial distribution, spawning and growth of a population of Astropecten irregularis inhabiting the coastal waters o f North Wales are described. Population densities of A. irregularis varied seasonally with starfish attaining their maximum and minimum abundances in summer and winter respectively. Changes in their spatial distribution stron gly suggests that A. irregularis migrates offshore into deeper waters durin g the winter months probably to avoid strong onshore wave surges. High popu lation densities of starfish which occur during the summer months may be as sociated with spawning aggregations or the availability of suitable prey sp ecies; a smaller peak in starfish abundance occurred during autumn 1997 coi nciding with the settlement of the bivalve Spisula subtruncata and the cuma cean Diastylis rugosa, prey species which are readily consumed by A. irregu laris. Astropecten irregularis spawned during late spring-early summer, but thereafter the gonad somatic index remained at a low level until late autu mn; the index increased throughout winter and starfish attained peak reprod uctive condition by late spring. Small starfish (arm length < 24 mm), showe d little evidence of reproductive development. Limited recruitment of A. ir regularis (<8 mm) occurred during October-November 1996, and the integratio n of this small cohort into the main population occurred within one year. L ocomotory activity and burrowing depth of starfish maintained in laboratory aquaria correlated with changes in seawater temperature; activity was larg ely inhibited and burrowing depth significantly increased at temperatures < 8 <degrees>C. Seawater temperature is probably an important factor regulati ng the abundance and distribution of A. irregularis in coastal waters. (C) 2001 Academic Press.