Climate change and the future for coral reef fishes: the potential for acclimation

Donelson, Jennifer Marie (2011) Climate change and the future for coral reef fishes: the potential for acclimation. PhD thesis, James Cook University.

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Abstract

Knowledge of the likely responses species to rapid climate change is important for effective future conservation and management. Critical to this is an understanding of the ability of species to cope with environmental alterations through acclimation (phenotypic changes) and/or adaptation (genetic changes through selection). The response of species to environmental change has generally been predicted by observing their current-day thermal sensitivity, yet this may not be sufficient to determine responses to climate change over the next 50-100 years. Tropical ectotherms are expected to be one of the most sensitive groups to climate change since they have evolved in relatively stable thermal conditions and do not physiologically regulate their internal body temperature. The lack of thermal variability experienced had led to the belief that tropical ectotherms will have limited ability to acclimate, however this hypothesis has not been rigorously tested. This study utilized a common coral reef fish Acanthochromis polyacanthus to investigate the potential for acclimation to future ocean conditions over multiple years and multiple generations.

To begin understanding the long-term impacts of climate change, knowledge of how current-day populations respond to the predicted environmental changes is required. This can serve as a baseline for testing the ability to acclimate over multiple years and multiple generations. The effects that elevations in sea water temperature and modifications to food availability have on coral reef fish were established by maintaining breeding pairs of A. polyacanthus in 3 water temperatures and 2 food levels crossed in a fully orthogonal design (Chapter 2). Water temperatures were the current-day average for the collection location (summer mean = 28.5°C) and temperatures predicted to become the average for this region over the next 50 to 100 years (+1.5°C = 30.0°C and +3.0°C = 31.5°C). Pairs were provided with either a high or low quantity diet based on average and minimum feeding rates in the wild. Both water temperature and food supply affected growth rate and reproductive ability including the quality and quantity of gametes produced. Reduced breeding at warmer temperatures may mean significant declines in A. polyacanthus populations as the ocean warms.

Variations in offspring quality due to parental effects are likely to affect their performance during early life, however, the importance of parentally sourced differences can depend on the environmental conditions juveniles experience. In highly competitive or stressful environments beneficial parental effects may be more important than when conditions are favourable. Offspring produced under future ocean conditions in Chapter 2 were reared under 3 levels of food availability to investigate differences in performance during early life (Chapter 3). The growth and survival of offspring depended on the combination of parental effects and juvenile environment quality. In poor environments offspring produced by elevated temperature parents had reduced survival. In contrast, in all food availabilities compensatory growth mediated the initial parental effects to the size, suggesting that parental effects induced by climate change may not be persistent. The benefits of compensatory growth can be short lived, however, this accelerated growth may trade-off with other important life history attributes.

Since a range of fish attributes were found to be influenced by sea water temperature, the potential for developmental acclimation to mediate the underlying driver of effects (metabolic rate differences) was investigated. Offspring produced by current-day adults were reared for their entire life-cycle at current-day and elevated (+1.5°C and +3.0°C) water temperatures (Chapter 4). Some evidence for metabolic acclimation was identified in fish reared at 3.0°C greater than the current-day average during summer, however no acclimation was exhibited by fish reared at 1.5°C above current-day temperatures. Fish possessing developmental acclimation at +3.0°C were smaller and in poorer condition than fish reared at current-day temperatures, suggesting that even with acclimation there may be significant consequences for future populations of tropical fishes caused by global warming.

Generally it is believed that the potential for thermal acclimation is influenced by the thermal variation experienced by a population. By comparing two geographically separated populations of A. polyacanthus (approximately 950km apart), which vary in average temperatures but not the seasonal or daily variation experienced, I found that acclimation ability differed regardless of thermal variability (Chapter 5). Specifically, fish from the higher-latitude location were able to fully acclimate resting metabolic rate (RMR) and aerobic scope, while the lower-latitude location could only partially compensate RMR at the warmest temperature. This indicates that acclimation capacity of populations may vary on relatively small scales (<800kms), and that understanding such variation will be critical for predicting the impacts of climate change.

Finally, this study investigated the potential for developmental acclimation to mediate the negative effects to reproduction and gametes produced at elevated water temperatures, as well as the potential for parents to produce offspring with enhanced performance in future ocean conditions (transgenerational acclimation; Chapter 6). With developmental acclimation reproductive ability was enhanced at +1.5°C, but limitations still existed for breeding pairs at +3.0°C. Evidence was found for transgenerational acclimation in both elevated temperature treatments, with offspring (F2) produced by +1.5 and +3.0°C breeding pairs (F1) exhibiting metabolic attributes equivalent to control fish at present-day average temperatures. Improvement in metabolic attributes is expected to lead to improvements in growth, condition and reproductive ability in this generation.

The present research showed that, contrary to expectations, the coral reef fish A. polyacanthus has a substantial potential to cope with alterations to the ocean environment predicted with climate change. Additionally, it provides the first evidence for rapid transgenerational thermal acclimation in reef fish. Such acclimation could reduce the impact of warming temperatures and allow populations to persist across their current range.

Item ID: 29799
Item Type: Thesis (PhD)
Keywords: Acanthochromis polyacanthus; climate change; coral reef fishes; acclimation; metabolism
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 2. Donelson, J.M., Munday, P.L., McCormick, M.I., Pankhurst, N.W., and Pankhurst, P.M. (2010) Effects of elevated water temperature and food availability on the reproductive performance of a coral reef fish. Marine Ecology Progress Series, 401 . pp. 233-243.

Chapter 3. Donelson, J.M., Munday, P.L., and McCormick, M.I. (2012) Climate change may affect fish through an interaction of parental and juvenile environments. Coral Reefs, 31 (3). pp. 753-762.

Chapter 4. Donelson, Jennifer M., Munday, Philip, Mccormick, Mark I., and Nilsson, Göran E. (2011) Acclimation to predicted ocean warming through developmental plasticity in a tropical reef fish. Global Change Biology, 17 (4). pp. 1712-1719.

Chapter 5. Donelson, Jennifer M., and Munday, Philip L. (2012) Thermal sensitivity does not determine acclimation capacity for a tropical reef fish. Journal of Animal Ecology, 81 (5). pp. 1126-1131.

Date Deposited: 14 Oct 2013 06:30
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0501 Ecological Applications > 050101 Ecological Impacts of Climate Change @ 34%
06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 33%
06 BIOLOGICAL SCIENCES > 0699 Other Biological Sciences > 069902 Global Change Biology @ 33%
SEO Codes: 96 ENVIRONMENT > 9603 Climate and Climate Change > 960399 Climate and Climate Change not elsewhere classified @ 50%
96 ENVIRONMENT > 9603 Climate and Climate Change > 960305 Ecosystem Adaptation to Climate Change @ 50%
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