Stress, ontogeny, and movement determine the relative importance of facilitation for juvenile mussels

A number of ecological factors have been shown to influence the importance of positive interactions (i.e., facilitation) in nature, including environmental stress and ontogenetic effects, and many more are likely to emerge as facilitation research expands to new ecosystems and taxa. In this study, I used a combination of field surveys and experiments to explore the roles of stress, ontogeny, and organismal movement in determining the importance of mussel ( Mytilus californianus ) recruit facilitation in central California. Results indicate that interactions between mussel recruits (shell length <20 mm) and habitat ameliorating neighbors shift from neutral to positive from the low to high mussel zone. I also observed ontogenetic shifts in recruit survival and growth in the upper mussel zone that suggest mussel recruits migrate from algal substrate to adult mussel beds. This type of habitat shift, where an organism moves sequentially from one facilitator to another, may be common in nature and presents an exciting new area for research.