Vol.:(0123456789) 1 3 Marine Biology (2018) 165:73 https://doi.org/10.1007/s00227-018-3333-z ORIGINAL PAPER In hot water: sustained ocean warming reduces survival of a low‑latitude coral reef fsh G. G. Rodgers 1,2  · J. M. Donelson 2,3  · M. I. McCormick 1,2  · P. L. Munday 2 Received: 3 August 2017 / Accepted: 23 March 2018 © Springer-Verlag GmbH Germany, part of Springer Nature 2018 Abstract Tropical species are predicted to be particularly vulnerable to the impacts of climate change given the relatively narrow thermal range they naturally experience. Within the tropics, average temperature and thermal variation can difer among populations and consequently low-latitude populations may respond diferently to increased temperatures than higher latitude tropical populations. In this study, we investigate the long-term efects of climate change relevant temperature increases on commonly measured condition metrics for a low-latitude population of damselfsh (Acanthochromis polyacanthus). Adult fsh were randomly assigned to one of the three seasonally cycling treatments: (1) current average ocean temperatures for the collection locations, (2) 1.5 °C, or (3) 3 °C higher than current average temperatures. Treatments were maintained for approximately 10 months. At the end of the experimental period, Fulton’s K and hepatosomatic index were calculated for fsh from each treatment group and critical thermal limit (CT Max ) was measured for a subset of fsh at control temperatures. Fish mortality was recorded throughout the experimental period, as well as at the end of the experimental period after the introduction of a secondary exercise stressor. No signifcant efect of temperature was observed on fsh condition (Fulton’s K and hepatosomatic index); however, signifcant mortality was observed for fsh maintained at 3 °C higher than current average temperatures. When a secondary exercise stressor was introduced, signifcant mortality was also observed at 1.5 °C higher than current average temperatures. Acute exposure to higher temperatures (CT Max ) suggested a much higher thermal tolerance for this population than long-term mortality, producing a thermal limit of 37.1 °C compared with a chronic thermal limit of 33 °C. Our results show that some basic measures of fsh condition may not be capable of detecting lethal and sub- lethal efects of increased temperature. The results of this study are consistent with the hypothesis that low-latitude species are already living close to their thermal maximum. Abbreviations AIMS Australian Institute of Marine Science CO 2 Carbon dioxide CT Max Critical thermal maxima GBR Great Barrier Reef PNG Papua New Guinea SST Sea surface temperature Introduction Tropical species are expected to be especially sensitive to projected future environmental warming, because they have evolved in a relatively stable thermal environment that now faces a high trajectory for temperature change when compared with other regions (Janzen 1967; Deutsch et al. 2008; Tewksbury et al. 2008; Burrows et al. 2011). An organism’s physiological performance is often plotted as a function of temperature in what is commonly known as a thermal reaction norm (Angilletta 2009). The thermal reaction norm of species from tropical environments is generally observed to be narrower than for temperate spe- cies (Deutsch et al. 2008; Tewksbury et al. 2008; Sunday et al. 2011). Furthermore, numerous tropical organisms Responsible Editor: A. E. Todgham. Reviewed by Undisclosed experts. * G. G. Rodgers giverny.rodgers@my.jcu.edu.au 1 Department of Marine Biology and Aquaculture, College of Science and Engineering, James Cook University, Townsville, QLD 4811, Australia 2 ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD 4811, Australia 3 School of Life Sciences, University of Technology Sydney, P.O. Box 123, Broadway, NSW 2007, Australia