Spatial competition between colonial ascidians: the importance of stand-off

Abstract

The outcome of 925 encounters between colonies of 4 species of compound ascidians growing on perspex panels were recorded. Of encounters involving Diplosoma listerianum, 61 % resulted in stand-off, and almost all the rest in overgrowth by D. listerianum. Of encounters involving any two of Trididemnum tenerum, Botryllus schlosseri and Botrylloides leachii, 82 % resulted in stand off, and the rest in overgrowth by either one of the adjacent pair. These 3 species were competitively equivalent, but subordinate to D. listerianum. The very high proportion of stand-offs recorded between these ascidians contrasts sharply with the low proportions previously reported for other taxa.