Geographic variation in the abundance and morphology of the bryozoan Alcyonidium diaphanum (Ctenostomata : Alcyonidiidae) in UK coastal waters

The ctenostome byrozoan Alcyonidium diaphanum is widespread and abundant in the coastal waters of England and Wales. It was recorded in 77-90% of beam trawl catches in the eastern English Channel and southern North Sea, and in 53-73% of catches in the Bristol Channel and Irish Sea. The maximum catch rates in these two study areas were 1410 and 731 kg h(-1) respectively. Alcyonidium diaphanum was most abundant in the greater Thames Estuary. Additional data from the North Sea indicated that A. diaphanum is widely distributed throughout the southern North Sea. Alcyonidium diaphanum was found intertidally in only seven of 99 locations sampled. Several different morphotypes were observed, ranging from cylindrical to lobate forms. The distribution patterns of various morphotypes are discussed.