THE ROLE OF THERMAL STRATIFICATION ON THE POPULATION-DYNAMICS OF SAGITTA ELEGANS VERRILL IN THE WESTERN IRISH SEA

Temperature and prey availability have a marked effect on the developm ent and growth of Sagitta elegans. This study addresses the effects of thermal stratification on the growth and size of adult S.elegans in t he western Irish Sea. It shows that in stratified waters, bottom water temperature had a greater effect on the development of mature adults than surface water temperature. Whilst the length of mature individual s caught in 1992 and 1994 decreased with increasing temperature, they did not conform to the models of McLaren (1963) and Sameoto (1971), as the animals were larger than pre dieted. The long breeding period fou nd in the stratified region, suggests that previous reports of one or two generations per year in the western Irish Sea do not account for t he likely mix of generations that occur from February through to Septe mber.