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

Calpensia nobilis (Esper) is a bryozoan which grows on rhizomes of the seag rass Posidonia oceanica (L.) Delile. To assess the impact of the bryozoan o n the seagrass, at each of two localities, Tabarca Island and Cabo de Palos , two sites were sampled. The samples were subjected to a lepidochronologic al analysis in order to measure the differences in growth rate, weight/leng th ratio, rhizome production and number of leaves per year in rhizomes colo nised by C. nobilis Versus no colonised ones. A significant increase in rhi zome growth rate and a decrease in its weight/length ratio ocurred when C. nobilis was present. There were no significant differences in rhizome produ ction. The size of C. nobilis colonies was positively correlated with rhizo me growth rate and negatively correlated with its weight/length ratio. (C) 1999 Elsevier Science B.V. All sights reserved.