Emiliania huxleyi population growth rate response to light and temperature: a synthesis

The relationship between the maximum specific growth rate (mu, d(-1)) of the coccolithophore Emiliania huxleyi and photon flux density (PFD, mu mol photons m(-2) s(-1)) was quantified using a combination of quantile regression and culture experiment data from the literature (n = 1387). This relationship, used in ecosystem models incorporating E. huxleyi or coccolithophores as a functional group, is often assumed to follow a Monod function although values for the model parameters vary greatly. In this analysis, a Monod function was compared with other models to determine the model which best fit E. huxleyi growth rate data. Analysis showed that a Monod model of mu = 1.858 [PFD/(23.91 + PFD)] best described E. huxleyi maximum growth rate as a function of PFD. In addition, an expression combining the Monod function (this study) and the power function relating growth rate to temperature (Fielding 2013; Limnol Oceanogr 58:663-666) was calculated: when both temperature (T, degrees C) and PFD are known, the resulting expression mu = (0.199 x T-0.716) x [PFD/(14.2 + PFD)] predicts maximum E. huxleyi specific growth rate. Current literature models either overestimate or underestimate maximum growth rate by up to 3-fold over a wide range of PFDs. The use of the Monod function and the combined expression presented here is therefore recommended for future models incorporating the growth rate of E. huxleyi when either light or both temperature and light are known.