Ectotherms generally shrink under experimental warming, but whether this pattern extends to wild populations is uncertain. We analysed ten million visual survey records, spanning the Australian continent and multiple decades and comprising the most common coastal reef fishes (335 species). We found that temperature indeed drives spatial and temporal changes in fish body size, but not consistently in the negative fashion expected. Around 55% of species were smaller in warmer waters (especially among small-bodied species), while 45% were bigger. The direction of a species’ response to temperature through space was generally consistent with its response to temperature increase through time at any given location, suggesting that spatial trends could help forecast fish responses to long-term warming. However, temporal changes were about ten times faster than spatial trends (~4% versus ~40% body size change per 1 °C change through space and time, respectively). The rapid and variable responses of fish size to warming may herald unexpected impacts on ecosystem restructuring, with potentially greater consequences than if all species were shrinking.
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All codes used in this analysis are available at https://github.com/astaaudzi/RLSfishSize.
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We acknowledge all divers and support personnel who contributed to the data collection and repository, especially A. Cooper, J. Berkhout, E. Oh, J. Stuart-Smith, J. Hulls and E. Clausius. We also thank M. Sumner for help with the SST data, F. Heather for help with figures, J. Berkhout for help with parallel computing, and A. Bates and C. Waldock for thermal distribution information. This research used the NCRIS-enabled Integrated Marine Observing System (IMOS) infrastructure for database support and storage. This study was supported by the ARC Discovery grant DP170104240 (to J.L.B., G.P. and R.D.S.-S.), UTAS visiting scholars fellowship (to A.A. for N.P. visit to IMAS), ARC Future Fellowship to G.P., and the Marine Biodiversity Hub, a collaborative partnership supported through the Australian Government’s National Environmental Science Programme (NESP).
The authors declare no competing interests.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Extended Data Fig. 1 Spatial distribution of Australian fish survey data used, coloured according to the mean annual sea surface temperature.
All sites are grouped onto 0.5 degree grid cells. Colours represent mean annual SST over the entire sampling period in that cell (ranging from 12 °C for yellow to 29 °C for red) and circle size is proportional to the total number of species used for the analyses in the cell (determined by species richness and number of surveys in the cell). Black stars indicate the nine long-term monitoring locations. The Australian coastline shapefile was downloaded from the Australian Natural Resources Data Library website (Commonwealth of Australia).
Extended Data Fig. 2 Correlation between species body size – SST slopes and abundance – SST slopes from literature.
Species-specific slopes between body size and mean annual SST through space (β1, on y axis) are compared with the species specific abundance and mean annual SST slopes estimated in Waldock et al. (2019). Data on both slopes was available for 300 species. If abundance was a major driver of average body size, we could expect an overall negative correlation between size-temperature and abundance-temperature slopes, such as mean body size is smaller at sites with higher abundances. Alternatively, larger average body sizes might have positive effects on abundance through e.g. improved recruitment or inter-specific effects. In this case we could expect a positive correlation between size-temperature and abundance-temperature slopes. The correlation between body size slopes and abundances was close to zero (r = 0.09, P = 0.14), suggesting that abundance is unlikely to be a major driver of body sizes and vice versa.
Extended Data Fig. 3 Species-specific body length changes at nine long-term monitored and warming locations.
Location and species specific temporal responses, represented by slopes of body length change in 105 coastal fish species in nine warming and long-term monitored locations. Each dot represents a species, arranged according to the temperature at the centre of their distribution area (temperature midpoint). Blue and red colours indicate species for which 90% of the posterior probability density range for the slope of the annual body length change (on y axis) was above or below zero, respectively. For the map of the nine locations see Extended Data Fig. 1.
Supplementary Tables 2 and 3, and Figs. 1–4.
List of Bayesian estimates of body size–SST slopes through space for each of the 335 individual species used in the analyses (Supplementary Table 1) and Bayesian estimates of annual changes in body lengths (slopes of size versus year) in nine long-term locations (Supplementary Table 4).
Filtered and final datasets used in the analyses.
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Audzijonyte, A., Richards, S.A., Stuart-Smith, R.D. et al. Fish body sizes change with temperature but not all species shrink with warming. Nat Ecol Evol 4, 809–814 (2020). https://doi.org/10.1038/s41559-020-1171-0