Lack of coherence in the warming responses of marine crustaceans
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1. Understanding the extent to which organisms are affected by climate change and are capable of adapting to warming is essential for managing biodiversity. Recent macrophysiological analyses suggest that range-related responses to warming may be more coherent (less variable) and predictable in marine than in terrestrial systems. 2. To examine this generalization, we investigate basal upper thermal tolerances (measured as CTmax), the extent of their phenotypic plasticity and the impacts of different rates of temperature change on these tolerances, in five species of intertidal crustaceans from three distinct thermal regimes, incorporating South African (RSA) shores and sub-Antarctic Marion Island (MI). 3. For all species, lower rates of change resulted in lower CTmax, while acclimation resulted in varied responses depending on the rate of temperature change. At fast rates of temperature change, higher temperature acclimation resulted in elevated CTmax, while at slow rates of change, acclimation had no effect or resulted in a decline in CTmax. 4. Maximum habitat temperatures recorded at the organisms’ microsites were lower than the CTmax for the MI populations but were above CTmax at slow rates of change for RSA populations. Thus, populations from more equatorward locations have a lower tolerance of extremes than those from cooler regions. In addition to reduced warming tolerance, RSA populations had a lower acclimation capacity than their sub-Antarctic counterparts. 5. We find substantial differences in long-term responses among groups in different areas as a consequence of spatial variation in the interactions among basal tolerance, phenotypic plasticity and thermal environments. These outcomes emphasize the significance of examining forecasts using a range of data and approaches so that their certainty can be established to inform key policy decisions in a spatially appropriate context.