9781888569605-ch94

Benthic Habitats and the Effects of Fishing

Symposium Abstract: Community and Life History Divergence of Colonial Hydroids (Cnidaria, Hydrozoa) from Heavily Trawled Scallop Grounds in the Bay of Fundy, Eastern Canada

L. M. Henry

doi: https://doi.org/10.47886/9781888569605.ch94

Adverse effects of mobile bottom-fishing gear on communities of colonial invertebrates (sponges, anthozoans, hydrozoans and bryozoans) are rarely examined, and no studies have determined if sublethal damage caused by this gear impairs the life histories (e.g., sexual reproduction, growth competitive ability) of these animals. Colonial hydroids were used as a model group to investigate these issues at the community, population and colony-levels from heavily fished scallop grounds in the Bay of Fundy, eastern Canada. An MDS ordination of hydroid communities collected from the shells of 109 live scallops (Placopecten magellanicus) and 136 small boulders revealed a moderately strong divergence between these two assemblages: epilithic communities were comprised of more runner and vine-shaped annual species, while epizoic taxa typically had more arborescent morphologies with perennial lifespans. RAPD-PCR genetic techniques of 414 colonies revealed that epilithic populations of the upright macrobenthic hydroid Sertularia cupressina were dominated by fewer genotypes than those on live scallops. Epilithic colonies were damaged more often, less abundant, less often fertile and comprised of fewer, smaller and less fecund modular units than those on epizoic substrates. Field and lab experiments are planned to test the hypothesis that higher incidences of damage to colonies on small boulders versus live scallops explain community and life history divergence between epilithic and epizoic assemblages. The implications of divergent communities and impaired sexual reproduction will be discussed to emphasize the importance of considering ‘less obvious’ effects of bottom-fishing on marine benthos.