Populations of botryllid ascidians (Botrylloides sp.) were investigated duringOctober 1988-0ctober 1990 along the subtidal of Akk:o (Acre) Bay, Israel.The studied area (600m2) was visited every 1.5-2 months, and 50 stones pervisit were randomly sampled. A total of 2,067 colonies were collected, ofwhich 2.0% were found in a state of zooid regression. All colonies were found on the lower surface of stones. They were recorded year-round but showedmarked seasonal fluctuations, from as many as 410 colonies per visit in thesummer months to 13 colonies per visit in the winter. Botrylloides coveragearea varied from 4.4% (summer) to 0.9% (winter) of total stone undersurfacearea. During the autumn and winter months, 49.2-63.2% of the stones werefree of Botrylloides colonies, compared to 4.5% of the summer collections.Only 2-2.7% of the stones collected in winter were populated by 6 or morecolonies, compared to 50.5% of the summer stones. Reproductive activity wascorrelated with monthly mean water temperatures and colony size. DuringJanuary-April, only a few colonies were fertile, while in August more than halfwere sexually mature. Examinations of all studied colonies revealed the existence of three distinctive morphs (subpopulations) which differ in their colors, system organization, zooid orientation, relative abundance, and reproductiveseasons. The possible existence of only one Botrylloides species(probably B. leachi) in this area or of three different species is discussed. Thetaxonomic difficulties in distinguishing between closely related species ofbotryllid ascidians prevent fmal conclusions.