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

Abstract

ABSTRACT Populations of botryllid ascidians (Botrylloides sp.) were investigated during October 1988-October 1990 along the subtidal of Akko (Acre) Bay, Israel. The studied area (600 m2) was visited every 1.5–2 months, and 50 stones per visit were randomly sampled. A total of 2,067 colonies were collected, of which 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 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 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 more colonies, compared to 50.5% of the summer stones. Reproductive activity was correlated with monthly mean wat...