ECOLOGICAL AND LIFE-HISTORY CHARACTERISTICS OF BOTRYLLUS-SCHLOSSERI (TUNICATA) POPULATIONS INHABITING UNDERSURFACE SHALLOW-WATER STONES

Populations of Botryllus schlosseri (PALLAS 1772), a cosmopolitan colo nial ascidian, were examined on the undersurface of stones for the fir st time in three adjoining localities along the Israeli Mediterranean coast. A two-year study of 1589 stones which were inhabited by 1345 co lonies, revealed that colony coverage was <1.5 % of the total availabl e substrate area; values were highest in spring, Lowest in winter. The two years differed significantly in the number of colonies . m(-2), a nd these numbers were correlated with mean seawater temperatures. Most of the stones contained 1-5 Botryllus colonies year-round; no signifi cant correlation was found between number and stone size. The brown mo rph was dominant (80 %) at all three localities. The distribution of o ther colour morphs differed between localities. Reproductive colonies were either hermaphroditic or contained male gonads only. Peak reprodu ction was in the spring, but did not correlate with seawater temperatu res. While colony size ranged between 1 and 1155 zooids, sexually matu re colonies consisted of 171-273 zooids on the average, compared with 37-90 zooids for sterile colonies. The three populations differed sign ificantly in several ecological and life history characteristics. This further confirmed past studies indicating that Botryllus populations are characteristically divided into local subpopulations exhibiting mi crogeographic differences in life history patterns. The results are co mpared with the accumulated data on other world-wide Botryllus populat ions residing in other habitats.