Dynamics of external brooding in the sea anemone Epictis Epiactis prolifera

Abstract

The sexually produced young of the externally brooding actinian Epiactis prolifera Verrill, 1869 are attached to the parent's column just above the base. A transitory “brood groove” may be formed around the limbus when the parent contracts. In the population studied on the coast of Sonoma County, California, USA, from 27 to 49% of the adult anemones were brooding at any time, the proportion being inversely related to seawater temperature and directly related to size of the anemones. A brood usually consisted of young of various sizes. Overall, number of young being brooded was directly related to parent size and inversely related to size of the brooded juveniles. The growth rate of juvenile anemones was inferred to average about a millimeter in pedal disc diameter per month. Juveniles dislodged from the parent when smaller than 4 mm in basal diameter apparently cannot survive in the intertidal zone. Juveniles which successfully make the transition to adulthood have, therefore, been brooded for at least 3 months. Fewer than 50% of the smallest juveniles survived to a size at which they could live independently. The transition to adulthood was accompanied by a mortality of 80%. The survival rate, from egg to adult, was calculated to be about 1% per season.