Effect of colony size on the competitive outcome of encrusting colonial organisms

Abstract

AbstractThe relative importance of colony size ratio of interacting species was studied in Tomioka Bay, Japan. Six encrusting colonial species belonging to the following three different taxonomic groups were tested: Ascidia (three species), Bryozoa (two) and Porifera (one). Colonies of these organisms were grown in the community of sessile organisms developed on plastic panels. Logistic regression analysis was carried out to determine the effect of size ratio on the competitive outcome of interacting colonies. The results between all possible combinations among these six species did not show a significant size effect in competitive outcome (i.e. a larger colony size did not always prove important in the success of a competitive interaction with smaller colonies of other species). On the contrary, competitive success depends on the types of species interacting. Certain species such as Didemnum moseleyi (ascidian) and Haliclona sp. (sponge), in spite of being smaller in colony size, won in competitive interactions with larger colonies of other species such as Diplosoma mitsukurii (ascidian) and Watersipora subovoidea (bryozoan). These results contradict the one reported earlier: that the larger the colony size, the more chance the colony will have to win in competitive interactions.