O’DONNELL, M.J.; MILLER, L.P.; , ; , ; , ; , ; Hopkins Marine Station; Hopkins Marine Station: Field measurements of mussel feeding time in the surf zone

Organisms living in the intertidal zone must contend with both terrestrial and aquatic environments, frequently twice each day. Despite the fact that they must survive the stresses of both air and water, certain life processes, such as feeding, are only available during one of the phases (usually aquatic). While tides appear on charts as simple sinusoids, on wave-swept shores, wave splash makes the transition from air to water a difficult thing to know precisely. In order to determine the part of the tide at which mussels (Mytilus californianus) experience the transition from air to water, we attached sensors to measure submersion. To ascertain the biological relevance of various levels of submersion (infrequent splash versus total inundation), we simultaneously measured the position of the valves as a proxy for feeding opportunity. In this study, we show that brief immersion is not enough to incite feeding, but that wave splash provides considerably more feeding time than simple tidal height would suggest. Additionally, certain elements of shoreline topography may create microhabitats that extend mussel feeding opportunities, either by trapping receding water or by throwing splash up the shoreline.