Competition in encrusting Antarctic bryozoan assemblages: Outcomes, influences and implications

Over 4000 bryozoan-bryozoan interactions were recorded from a total of 985 rocks from six locations at Signy Island in the maritime Antarctic. The majority of these interactions were interspecific meetings. The identity of the competitive species was a major influence on the outcome of encounters, whereas depth and surface area of rocks had little significant influence. The assemblage of bryozoans could be ranked into a clear hierarchy with a competitively dominant species. Zooidal height and colony growth morphology were found to be important factors in overall overgrowth rank. Few interspecific encounters resulted in indeterminate outcomes, but a tied outcome was found to be most likely between competitors of similar overgrowth rank. In contrast, intraspecific meetings mostly resulted in tied outcomes. Species with a higher proportion of colonies on the upper surfaces of rocks were found to have a lower incidence of tied outcomes. One explanation may be the potentially more successful larval dispersal on upper rock surfaces in higher water flow, and the resulting decreased likelihood of neighbours being related. Several incidences of homosyndrome were also observed in three bryozoan species.