Space utilisation patterns of bryozoans on the Patagonian scallop Psychrochlamys patagonica

LÓPEZ GAPPA, J.; LANDONI, N.A.

SCIENTIA MARINA

Institut de Ciències del Mar de Barcelona (CSIC)

Lugar: Barcelona; Año: 2009 vol. 73 p. 161 - 171

0214-8358

The bryozoan assemblage encrusting valves of the Patagonian scallop, Psychrochlamys patagonica, was studied in 4 beds distributed along the continental shelf off Argentina to analyse (a) the distribution pattern of bryozoan colonies on different zones of the valves, (b) the influence of interspecific competition on assemblage composition, (c) whether encrusting species display different space utilization strategies, and (d) whether bryozoan species richness and number of colonies vary in relation to host size. The assemblage, composed by 22 taxa, was dominated by Arachnopusia monoceros and Osthimosia eatonensis, which were at least one order of magnitude more abundant than any other species. Multivariate analyses based on coverage data of multiserial bryozoans classified the beds by species richness rather than by geographic proximity and showed significant differences in assemblage structure between upper (left) and lower (right) valves and among beds. Competitive interactions occurred almost exclusively on lower valves, and more frequently on peripheral than on central zones of these valves. Correlations between valve area and number of bryozoan colonies, coverage and species richness were low but significant. Bryozoans were significantly more frequent, larger, and taxonomically diverse on lower than on upper valves. The uniserial colonies of Neothoa cf. chiloensis, the weakest bryozoan competitor, were as frequent on central as on peripheral zones, usually spreading out along channels on the scallop surface. This fugitive species was partially covered by multiserial colonies, but managed to persist even in peripheral areas of the lower valves.