Where Y is the yield coefficient, μmax is the maximum growth rate (day−1), Ks is the half-saturation coefficient (mg L−1), S is the substrate concentration (mg L−1) and X is the biomass concentration (mg L−1). Temperate sea waters are thought to be dominated by mesophilic bacteria, which have a minimum growth temperature of around 5 °C, and also inhabited by cold-adapted bacteria (psychrophilic and psychrotolerant), which grow below 5 °C ( Morita, 1975). At the incubation temperature of 0.5 °C, cold-adapted species would be expected to grow and become dominant in temperate sea water ( Brakstad and Bonaunet, 2006). If these cold-adapted species are in low abundance, then biomass limitation could be the reason for Q10 values being higher than expected below 5 °C. This can be more clearly seen if one expresses the k1 values from Equation (5), taking into account the assumptions that the first order interpretation of the Monod model requires, i.e. substrate concentration is much lower than the half-saturation coefficient (S