Effects of Calpensia nobilis (Esper 1796) (Bryozoa: Cheilostomida) on the seagrass Posidonia oceanica (L.) Delile

Calpensia nobilis ( Esper) is a bryozoan which grows on rhizomes of the seagrass Posidonia oceanica (L.) Delile. To assess the impact of the bryozoan on the seagrass, at each of two localities, Tabarca Island and Cabo de Palos, two sites were sampled. The samples were subjected to a lepidochronological analysis in order to measure the differences in growth rate, weight/length ratio, rhizorne production and number of leaves per year in rhizomes colonised by C. nobilis versus no colonised ones. A significant increase in rhizome growth rate and a decrease in its weight/length ratio ocurred when C. nobilis was present. There were no significant differences in rhizome production. The size of C. nohilis colonies was positively correlated with rhizome growth rate and negatively correlated with its weight/length ratio.