Role of early post-settlement mortality in setting the upper depth limit of ascidians in Florida epifaunal communities

Abstract

At three sites in Florida, the communities of marine sessile invertebrates are dominated by oysters Crassostrea virginica in the mid-intertidal zone, and by ascidians (several species) in the low intertidal and subtidal zones. In "fixed' experiments, recruitment of all ascidian species was confined to the ascidian zone. In "floating' experiments, the number of recruits of Diplosoma glandulosum did not differ between shallow and deep plates, and recruitment of Styela plicata was confined to shallow plates. Thus early post-settlement mortality is a major factor setting the upper depth limit of these species. The authors vertically transplanted S. plicata and Botryllus planus; survivorship of both was greater in the ascidian zone than in the oyster zone. Further support was thus gained for the post-settlement mortality hypothesis. -from Authors