In hot water: sustained ocean warming reduces survival of a low-latitude coral reef fish
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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 differ among populations and consequently low-latitude populations may respond differently to increased temperatures than higher latitude tropical populations. In this study, we investigate the long-term effects of climate change relevant temperature increases on commonly measured condition metrics for a low-latitude population of damselfish (Acanthochromis polyacanthus). Adult fish 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 fish from each treatment group and critical thermal limit (CTMax) was measured for a subset of fish 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 significant effect of temperature was observed on fish condition (Fulton’s K and hepatosomatic index); however, significant mortality was observed for fish maintained at 3 °C higher than current average temperatures. When a secondary exercise stressor was introduced, significant mortality was also observed at 1.5 °C higher than current average temperatures. Acute exposure to higher temperatures (CTMax) 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 fish condition may not be capable of detecting lethal and sub-lethal effects 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.
Australian Institute of Marine Science
Critical thermal maxima
Great Barrier Reef
Papua New Guinea
Sea surface temperature
Thank you to staff at JCU Research Aquarium Facility for logistical support. Thank you also to Sue-Ann Watson, Mike Emslie and Dave Williamson as well as the skipper and crew of the Kalinda for their aid in fish collection, and to Olivia Eisenbach for assistance in the lab. Appreciation is extended to Rhondda Jones for assistance with statistical analyses. Research funding was provided by an Australian Research Council Grant. Support was also provided by the ARC Centre of Excellence for Coral Reef Studies and the James Cook University Higher Degree Research Enhancement Funding Scheme. Appreciation is extended to three anonymous reviewers for their comprehensive feedback and valued suggestions throughout the review process.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All applicable institutional and/or national guidelines for the care and use of animals were followed. This project was completed under JCU Ethics A1737.
Availability of data and supporting materials
All data are available in the Tropical Data Hub (TDH) Research Data repository.
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