LIFE-HISTORY CHARACTERISTICS OF BOTRYLLOIDES (TUNICATA) POPULATIONS IN AKKO BAY, MEDITERRANEAN COAST OF ISRAEL

Populations of botryllid ascidians (Botrylloides sp.) were investigate d during October 1988-october 1990 along the subtidal of Akko (Acre) B ay, Israel. The studied area (600 m(2)) was visited every 1.5-2 months , and 50 stones per visit were randomly sampled. A total of 2,067 colo nies were collected, of which 2.0% were found in a state of zooid regr ession. All colonies were found on the lower surface of stones. They w ere recorded year-round but showed marked seasonal fluctuations, from as many as 410 colonies per visit in the summer months to 13 colonies per visit in the winter. Botrylloides coverage area varied from 4.4% ( summer) to 0.9% (winter) of total stone undersurface area. During the autumn and winter months, 49.2-63.2% of the stones were free of Botryl loides colonies, compared to 4.5% of the summer collections. Only 2-2. 7% of the stones collected in winter were populated by 6 or more colon ies, compared to 50.5 % of the summer stones. Reproductive activity wa s correlated with monthly mean water temperatures and colony size. Dur ing January-April, only a few colonies were fertile, while in August m ore than half were sexually mature. Examinations of all studied coloni es revealed the existence of three distinctive morphs (subpopulations) which differ in their colors, system organization, zooid orientation, relative abundance, and reproductive seasons. The possible existence of only one Botrylloides species (probably B. leachi) in this area or of three different species is discussed. The taxonomic difficulties in distinguishing between closely related species of botryllid ascidians prevent final conclusions.