The effects of temperature on the composition of communities associated with Mytilus californianus

Mytilus californianus beds along the wave-exposed coast of the eastern North Pacific Ocean serve as an important habitat, harboring a high diversity of species due to their colonizable hard surfaces as well as through the creation of microhabitats within the mussel beds that may serve to diminish both the physical and biological stresses of the intertidal. Patterns of M. californianus body temperature during aerial exposure at low tide vary in physiologically meaningful and often counterintuitive ways: local "modifying factors," such as the timing of low tide in summer, can lead to large-scale geographic mosaics of body temperatures over this species' range. Previous studies doing long-term monitoring of mussel body temperatures have revealed two "hot spots" in a small range of the southern California coast, where body temperatures are warmer than expected based on latitude, each with a nearby site with more moderate, "normal" mussel body temperatures. This study was undertaken to determine how increasing mussel body temperatures affects their associated communities. The "hot spot" and "normal" M. californianus beds in southern California were sampled. Results highlighted the importance of site-specific characteristics in structuring the mussel bed community and the difficulty in predicting the effects of climate change in this complex habitat. Experimental manipulation of mussel body temperatures at a single site near Trinidad, CA, via the creation of artificial mussel beds of different colors, revealed changes in the epibiotic community: abundance and survival of several species decreased with increasing mussel body temperatures. Community composition within the beds, however, was not significantly different between temperature treatments. These data suggest that climate change-induced increases in aerial temperature and thus M. calfornianus body temperatures will most noticeably impact the surface community of mussel beds, yet mussel beds may, within the short term, effectively ameliorate the environment for the organisms living within them, thus sustaining the composition of these high diversity communities.