Seasonal Abundance, Spatial Distribution, Spawning and Growth of Astropecten irregularis (Echinodermata: Asteroidea)

Abstract

Seasonal trends in the abundance, spatial distribution, spawning and growth of a population ofAstropecten irregularis inhabiting the coastal waters of 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 strongly suggests that A. irregularis migrates offshore into deeper waters during the winter months probably to avoid strong onshore wave surges. High population densities of starfish which occur during the summer months may be associated with spawning aggregations or the availability of suitable prey species; a smaller peak in starfish abundance occurred during autumn 1997 coinciding with the settlement of the bivalve Spisula subtruncata and the cumaceanDiastylis rugosa , prey species which are readily consumed by A. irregularis. Astropecten irregularis spawned during late spring–early summer, but thereafter the gonad somatic index remained at a low level until late autumn; the index increased throughout winter and starfish attained peak reproductive condition by late spring. Small starfish (arm length <24mm), showed little evidence of reproductive development. Limited recruitment of A. irregularis (<8mm) occurred during October–November 1996, and the integration of this small cohort into the main population occurred within one year. Locomotory activity and burrowing depth of starfish maintained in laboratory aquaria correlated with changes in seawater temperature; activity was largely inhibited and burrowing depth significantly increased at temperatures <8°C. Seawater temperature is probably an important factor regulating the abundance and distribution of A. irregularis in coastal waters.