Although global warming is acknowledged as a primary threat to populations and communities, the impact of rising temperature on community structure remains poorly understood. In this study, we investigated the direct and indirect effects of temperature on epilithic primary producers (micro- and macroalgae) and an abundant consumer, the rough limpet Lottia scabra, in the rocky intertidal zone in central and northern California, USA. We factorially manipulated temperature and limpet abundance in the field to determine the effects of temperature on herbivore growth and mortality, algal abundance, and the strength of plant¿herbivore interactions. Microalgal growth was positively affected by shading at both locations, and negatively affected by limpet grazing at Pacific Grove but not at Bodega Bay. Macroalgae were only abundant at Bodega Bay, where changes in abundance were negatively related to grazing and independent of temperature. Despite temperature-related changes in microalgal food supply, there were no direct or indirect effects of temperature manipulation on L. scabra growth or mortality. Furthermore, temperature did not alter the importance of herbivory at either site. These results indicate that the influence of increasing temperature, as is predicted with climate change, will have differential effects on producers and consumers. However, thermal effects at one trophic level do not necessarily propagate through the food web to other trophic levels.
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