Climate change and latitudinal patterns of body temperature in rocky intertidal invertebrates

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Species inhabiting rocky intertidal environments are of marine origin, but must regularly contend with the terrestrial environment during low tide. As a result, these invertebrates and algae are thought to live very close to their thermal tolerance limits, and increases in thermal stress due to climate change could lead to changes in their growth, survival, and distribution patterns. Recent physiological studies have emphasized that thermal damage to many intertidal organisms occurs primarily during aerial exposure at low tide, when body temperatures are driven by multiple climatic factors. Temperatures experienced during aerial exposure far exceed those during submersion, and are often substantially different from air temperature. Our ability to extrapolate from physiological responses to temperature to community?scale processes is thus hampered by our limited knowledge of what body temperatures are under field conditions, how body temperatures change in space and time, and how patterns might vary between species.Dr. Helmuth's previous work has focused on latitudinal?scale patterns of body temperatures of the mussel Mytilus californianus, a competitive dominant in rocky intertidal ecosystems. Measurements in the northeast Pacific show that latitudinal patterns are highly complex, and that, because of consistent patterns in the timing of low tides, northern sites are often more likely to be thermally stressful than are southern sites. Furthermore, models of interannual variability in tidal regimes suggest that in the next 2?5 years levels of thermal stress at these northern "hot spots" may be approaching a 20?year maximum. These results have significant consequences for where and when we look for evidence of the effects of climate change in intertidal ecosystems, and suggest that impacts may potentially be observable in the near future at several sites.The project will extend on ongoing study of temperature patterns at 15 sites spanning a 160 range of latitude, and will produce a continuous 6+ year record of temperatures relevant to an ecologically important intertidal species. The study will address several explicit predictions stemming from my previous research, regarding spatial and temporal patterns of mussel body temperatures. As a means of assessing the ecological impacts of these changes in thermal stress, Dr. Helmuth will monitor zonation heights of mussels, and predict downward shifts in zonation at several northern "hot spots." Finally, he will apply biophysical techniques used for mussels to explore the thermal ecology of the gastropod Nucella, and important predator of Mytilus. The project has produced a unique data set of temperature patterns over a wide geographic scale, and is currently the best means available for monitoring and predicting the potential effects of climate change on intertidal body temperatures in the NE Pacific. Because exposure times at northern "hot spots" are predicted to reach a 20year maximum within the next 2?5 years, there is a critical need to maintain the continuity of the data stream that will be produced during the course of this study.Broader Impacts: As part of an ongoing collaboration, students in the Helmuth lab will work with a K?12 teacher to develop lesson plans based on their research, grading rubrics and assessment protocols. Specifically, they will create activities that allow students to investigate concepts related to climate change, the effects of temperature on organisms, species distribution patterns, and the dynamics of tidal cycles. Materials will be explicitly linked to state and national K?12 science and math standards, and will be posted on a outreach website. The teacher will work with the Helmuth lab in the field in year one to set up experiments, and will remain in contact with the group during the course of the study.