ADULT RAFTING VERSUS LARVAL SWIMMING - DISPERSAL AND RECRUITMENT OF ABOTRYLLID ASCIDIAN ON EELGRASS

The importance of larval dispersal in determining the distribution and abundance of benthic marine organisms is well recognized; however, th e contribution of post-larval dispersal has not been measured. I compa red the dispersal of swimming larvae with that of rafting colonies in a population of compound ascidians, Botrylloides sp., living attached to leaves of the eelgrass Zostera marina in Tomales Bay, California, U SA in 1990-1992. Colonies rafting on broken eelgrass traveled over 200 times farther and had comparable recruitment success relative to swim ming larvae. The recruitment of rafting colonies into new habitats was facilitated by the ability of these colonial animals to grow asexuall y onto surrounding substrata. Rafting colonies brooded larvae that wer e subsequently released after the colony settled into a new habitat. T hese results suggest that colonization of new habitats can occur by po st-larvae as well as larvae, and that long-range dispersal by species with short-lived larvae may occur by post-larval rafting.