Water temperature and fish growth: otoliths predict growth patterns of a marine fish in a changing climate ADAM N. ROUNTREY 1 , PETER G. COULSON 1,2 , JESSICA J. MEEUWIG 1,3 and MARK MEEKAN 4 1 Centre for Marine Futures, Oceans Institute, University of Western Australia, Crawley, WA, Australia, 2 Centre for Fish and Fisheries Research, School of Veterinary and Life Sciences, Murdoch University, Murdoch, WA, Australia, 3 School of Animal Biology, University of Western Australia, Crawley, WA, Australia, 4 Australian Institute of Marine Science, Crawley, WA, Australia Abstract Ecological modeling shows that even small, gradual changes in body size in a fish population can have large effects on natural mortality, biomass, and catch. However, efforts to model the impact of climate change on fish growth have been hampered by a lack of long-term (multidecadal) data needed to understand the effects of temperature on growth rates in natural environments. We used a combination of dendrochronology techniques and additive mixed-effects modeling to examine the sensitivity of growth in a long-lived (up to 70 years), endemic marine fish, the western blue groper (Achoerodus gouldii), to changes in water temperature. A multi-decadal biochronology (1952–2003) of growth was constructed from the otoliths of 56 fish collected off the southwestern coast of Western Australia, and we tested for correlations between the mean index chronology and a range of potential environmental drivers. The chronology was significantly correlated with sea surface temperature in the region, but common variance among individuals was low. This suggests that this species has been relatively insensitive to past variations in climate. Growth increment and age data were also used in an additive mixed model to predict otolith growth and body size later this century. Although growth was relatively insensitive to changes in temperature, the model results suggested that a fish aged 20 in 2099 would have an otolith about 10% larger and a body size about 5% larger than a fish aged 20 in 1977. Our study shows that species or populations regarded as relatively insensitive to climate change could still undergo sig- nificant changes in growth rate and body size that are likely to have important effects on the productivity and yield of fisheries. Keywords: Achoerodus gouldii, additive mixed models, Australia, climate change, fish growth, otolith, sclerochronology, sea sur- face temperature Received 21 July 2013; revised version received 13 March 2014 and accepted 17 March 2014 Introduction Determining the sensitivity of marine species to climate change is an important part of the development of miti- gation and adaptation strategies for the management of marine ecosystems (Rowland et al., 2011), and to date, sensitivity has largely been defined in terms of changes in species distributions. When the rate of climate change exceeds the rate at which a species can adapt to the changing environment, distribution change is a likely response (VanDerWal et al., 2013). If new suitable habitats are unavailable or unreachable for a species, then it may be at higher risk of extinction, and thus, it could be characterized as sensitive. Niche modeling has often been used to predict changes in distributions under future conditions (based on some assumptions; Garc  ıa-Vald es et al., 2013), and predicted range loss has been used as an indicator of sensitivity (Thuiller et al., 2005). However, species that appear robust using this criterion may still be strongly affected by changing cli- mate conditions. The distributions of organisms are determined by habitat preferences (physical parameters and biotic interactions), dispersal ability, and history (Pearson & Dawson, 2003; Ara ujo & Pearson, 2005). The relative importance of these factors can vary spatially and tem- porally, and it is possible that large parts of a range could be suboptimal (e.g. for growth) in one or more parameters due to other more limiting factors such as dispersal barriers or human exploitation. In these cases, a shift toward the optimal value of an environmental parameter, such as temperature, may or may not cause changes in distribution. However, it could influence Correspondence: Present address: Adam N. Rountrey, Museum of Paleontology, University of Michigan, Ann Arbor MI, USA, tel. +1 734 936 1385, fax +1 734 936 1380 , e-mail: arountre@umich.edu 1 © 2014 John Wiley & Sons Ltd Global Change Biology (2014), doi: 10.1111/gcb.12617 Global Change Biology