NATURAL AND ANTHROPOGENIC DISPERSAL MECHANISMS IN THE MARINE-ENVIRONMENT - A STUDY USING CHEILOSTOME BRYOZOA

The global geographic ranges occupied by 197 species of cheilostomate Bryozoa found in British waters were obtained by a literature survey. Morphological grade, larval mode, environmental tolerance, species abu ndance and the ability to raft and to foul shipping were all investiga ted as traits potentially able to affect the geographic ranges of thes e bryozoan species. When considered independently all variables except larval mode had a significant correlation with the geographic range o ccupied by a species. However, when controlling for the potentially co nfounding effects of the other covariates, only the ability to foul or raft and species abundance had a significant effect on median geograp hic range and only fouling and abundance had a significant effect over global ranges. The strength of the association between fouling abilit y and range suggests that transport upon the hulls of ships is a very important dispersal mechanism for bryozoans, as it is thought to be al so for various other marine taxa. Potential long-term (evolutionary) c onsequences of increased ranges brought about by anthropogenic mechani sms are discussed.