Global analysis of fish growth rates shows weaker responses to temperature than metabolic predictions

Aim Higher temperatures increase the metabolic rate of ectothermic organisms up to a certain level and make them grow faster. This temperature-sensitivity of growth is frequently used to predict the long-term effects of climate warming on ectotherms. Yet, realized growth also depends on ecological factors and evolutionary adaptation. Here we study whether faster growth is observed along temperature clines within and between marine fish species from polar to tropical regions. Location Global. Time period The sampling or publication year is for 718 observations before 1980, 1,073 observations between 1980 and 2000, and 390 observations after 2000 (for 336 observations no year was recorded). Major taxa studied Marine teleost fish and elasmobranchs. Methods The effects of temperature on fish growth are studied using 2,517 growth observations, representing 771 species in 165 marine ecoregions. The effects of temperature are presented with aQ(10), describing relative increase in the rate of growth for each 10 degrees C increase. Results We find weak within- and between-species effects of temperature on growth. The typical within-species effect of temperature has aQ(10)of 1.1. The between-species effect is a little higher (Q(10) = 1.4, orQ(10) = 1.2 when corrected for phylogenetic relationships). When analysed per fish guild, growth responses vary from nearly independent of temperature in large demersals (Q(10) = 1.1) to positive in small pelagics (Q(10) = 1.6) and elasmobranchs (Q(10) = 2.3). Average growth is higher in ecoregions with high primary production. Main conclusion The change in average growth along temperature clines is weaker than predicted by metabolic theory, suggesting that the metabolic predictions are not sustainable in an ecosystem context. The long-term response of fish to the increase in temperature associated with climate change may hence be shaped more by local environmental and ecological dynamics than by the physiological temperature response of the species currently present.