Evaluating thermal performance reactions norms as a predictor of vagrant tropical fish success in temperate waters

The recruitment of tropical fishes to temperate waters during warm summer months is a common occurrence where western boundary currents provide a larval transport mechanism. While survival and growth during the summer months... [ view full abstract ]

The recruitment of tropical fishes to temperate waters during warm summer months is a common occurrence where western boundary currents provide a larval transport mechanism. While survival and growth during the summer months is often quite high, survival over the winter period is low, thus creating a significant hurdle to the range expansion of tropical fishes into temperate habitats. Previous work has highlighted the interactive roles of thermal physiology and ecology in this overwinter survival barrier and in particular, the important role which thermal performance reaction norms can play in predicting outcomes of ecological interactions in variable thermal environments. Here we generate thermal reaction norms across 8°C for metabolic rates (resting and active oxygen consumption) and burst swimming performance for three tropical and two temperate reef fish species found in the temperate waters of Sydney Australia. We evaluate the ability of these curves to reflect the life history and predict the relative establishment success of these tropical species. Overall we found reaction norms accurately reflected the life history of the species but were much broader than anticipated. We also found general support for the prediction that the more commonly occurring tropical species exhibited generally greater performance across the thermal range of the study. While it will also be important to consider processes such as acclimation and adaption to these novel environments, this work highlights the utility of establishing thermal performance reaction norms as a means to evaluate the relative likelihood and possibly speed with which tropical fish species may permanently establish themselves in temperate habitats as global ocean temperatures continue to increase.