THERMAL REGIME OF AN INTER-TIDAL MYTILUS-CALIFORNIANUS CONRAD POPULATION ON THE CENTRAL OREGON COAST

Data describing the thermal environment of an intertidal population of Mytilus californianus Conrad were collected over a four-year period. A formula estimating tissue temperature during exposure to air was established and used to calculate the internal temperature of mussels each hour of the day in a mussel bed located at +3 ft above mean low low water level. The resulting thermal regime was then discussed in terms of average temperature, daily extremes, and periods of heating and cooling. From experiments using radioactive labelled Isochrysis it was found that periods of exposure lead to increased assimilation efficiency. The thermal regime was used to calculate scope for growth by incorporating both its acute and acclimatizing effects on oxygen consumption, filtration rate, and assimilation. Particulate food levels had a greater effect upon seasonal values for scope for growth than temperatures within the normal environmental range. An energy budget was established for animals at various heights in the intertidal to produce a quantitative picture of the decrease in scope for growth with height. An exposure period may lead to slight increases in energy available for growth during winter. Maximum temperature changes may induce spawning at advantageous times. The implications for reconstructing and predicting thermal regimes of intertidal animals are discussed. © 1979.