Consequences of changing environmental variability on rocky shores: Effects of thermal variation on growth rates and energy flow

Background/Question/Methods

Increases in average air and sea temperatures are already implicated in alterations of species interactions, population dynamics, and community structure, but we know comparatively little about the potential effects of changing temperature variability. In rocky intertidal communities, an increase in temperature variation during low tide periods has the potential to impact the survival and productivity of many species, particularly those already living near their thermal tolerance limits. At a central California field site, we have implemented a novel field manipulation of temperature variability in the intertidal zone without altering mean temperature conditions, while also leaving solar and wave exposures unchanged. Our goal was measure how shifts in daily temperature variability affect herbivorous limpets (marine snails) and their microalgal food resources over multiple months.

Results/Conclusions

By manipulating thermal conductance between experimental plates and the substratum, we were able to raise or lower the intra-day temperature variation by 50% during low tide periods, thereby creating conditions that spanned a four-fold change in average daily temperature range. When freed from herbivory, the microalgal community responded with decreasing biomass as temperature variation increased, but when limpet grazers were present, the effects of temperature variability on microalgal communities disappeared. The response of limpets varied by species, with three species showing no strong pattern in growth with changing temperature variability, while Lottia scabra showed a negative response to increasing variability. Despite the fact that different grazers exhibit different responses to temperature variability, their interaction with the microalgal community is robust, as evidenced by the fact that microalgal biomass is constant across thermal variability treatments, independent of grazer species identity. Thus the details of species-specific differences in performance may be a key driver of consumer-resource interactions and ecological consequences of changing environmental variability.