Environmental factors and plant-animal interactions on rocky shores along the Oregon coast

Graduation date: 1995Presentation date: 1994-08-19Factors affecting the persistence of mussels (Mytilus californianus) and their associated epibiont species were studied along the central Oregon coast. Interactions between mussels and their algal epibionts (Endocladia\ud muricata) varied in sign and strength with environmental conditions. In extreme temperatures mussel—epibiont interactions determined survival of individual mussels,\ud and persistence of the mussel—bed assemblage.\ud Under normal conditions Endocladia had weak negative effects on mussels. Mussels colonized by Endocladia had lower body weight, produced more byssal threads, and\ud experienced increased drag. However, in the field, dislodgment of mussels with Endocladia epibionts was higher only when mortality in the mussel bed was >25%. By contrast under freezing conditions, Endocladia appeared to\ud insulate mussels, and protect them from freeze—induced mortality. Historical temperature records suggested that freezing temperatures may be important in the ecology of mussel—epibiont interactions. Short—term negative interactions between mussels and algal epibionts are balanced by occasional, but important positive interactions which affect the persistence of mussels and\ud their associated assemblage. Factors affecting the development of the epibiont\ud community on mussels were experimentally studied. The epibiont assemblage on mussels consisted primarily of barnacles, and the alga E. muricata. Barnacles colonized\ud mussels, but no algal species successfully recruited directly onto mussels. Barnacles facilitated Endocladia. Limpets reduced diatom and algal abundance, except for\ud Endocladia, and reduced barnacle abundance at low and moderate recruitment intensity only.\ud The effect of human trampling on mussels, and the uppershore barnacle—algal assemblage was experimentally studied. Trampling reduced the abundance of canopy-forming algae, and mussels, and their epibionts. Continued\ud trampling inhibited succession. After trampling stoppep, the algal assemblage recovered within a year, but mussels loss continued in previously trampled plots. This suggests that trampling may increase susceptibility to natural disturbance