1. Distribution over Space and Time in Epizoobiontic North Sea Bryozoans

The epizoobiontic bryozoan-community on fronds of Flustra foliacea from 51 stations kept in four German museums was analysed. Sampling covers the entire North Sea and different time periods (1776–2008). Cluster analysis based on presence/absence shows a differentiation into a northern and a southern North Sea assemblage separated along the 50 m depth contour. The northern assemblage is characterized by Amphiblestrum flemingii (Busk), Callopora dumerilii (Audouin) and Tricellaria ternata (Ellis and Solander), while the southern North Sea is characterized by two cyclostome species – Crisia eburnea (Linnaeus), and Plagioecia patina (Lamarck) – and a cheilostome – Electra pilosa (Linnaeus). In the Helgoland Deep Trench (HTR), the occurrence of cyclostomes is more conspicuous than elsewhere, judging from the studied material. The occurrence of erect growth forms increases from the northern to the southern North Sea.