COMPETITIVE INTERACTIONS AMONG SESSILE ORGANISMS IN TOMIOKA BAY, SOUTH JAPAN - IMPORTANCE OF LIGHT CONDITIONS ON THE PANEL SURFACE

Interspecific competitive interactions among sessile epibenthos were s tudied by suspending PVC panels at Tomioka Bay, south Japan, for a max imum period of 16 mo. Interactions were monitored from photographs of a fixed area of the panels. Four panels were suspended during two diff erent months in autumn 1991, and the development of the community was followed until December 1992. Altogether, 6511 interspecific overgrowt h interactions were recorded, of which 37 resulted in standoffs and th e rest in overgrowths. The competitive relationship observed in this s essile assemblage followed the pattern of a hierarchy with numerous ba ckloops. Among the 36 species, belonging to the seven taxonomic groups encountered during the study, the colonial ascidian Didemnum moseleyi was recorded as the dominant species (with respect to competitive abi lity) while the barnacle Balanus trigonus was the weakest species. The month of panel exposure and whether or not the panel surface was shad ed had a significant influence on the competitive ability of the sessi le organisms. The order of hierarchy of the most dominant species chan ged with the month of panel submersion and its light conditions. Among the several abundant species tested, longer residence times were reco rded for serpulid worms than for the colonial species. A significant, positive relationship was obtained between the areal cover of competit ively dominant sessile organisms and the number of their interspecific interactions. From the short residence time of sessile organisms and the significant relationship between their areal cover and number of i nterspecific interactions, it is concluded that the interspecific inte ractions played important role in the species succession.