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

Will  Figueira (1),    Riccardo    Cannas (2),    David    Booth (3)

1    University    of    Sydney,    School    of    Biological    Sciences,    Sydney,    NSW,    2006,    will.figueira@sydney.edu.au

2    Università    Politecnica    delle    Marche,    P.zza    Roma    22,    60121,    riccardo.cannas@hotmail.it

3    University    of    Technology,    Sydney,    School    of    Life    Sciences,    15    Broadway,    Ultimo,    NSW,    2007,    david.booth@uts.edu.au

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. 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.