LAUSR

The response of phytoplankton to different temperatures has been studied for decades, and although the general relationship of growth to temperature is known to be exponential, the responses at very low temperatures (from −2 to +2°C) are poorly constrained. To address this uncertainty, we conducted a series of growth experiments with eight species of polar phytoplankton; each was grown in batch culture at temperatures ranging from −1.5 to 4°C, and growth rates determined from changes in cell abundance and chlorophyll. We found that different species responded differently to temperature, although the general response was an increase in growth rate at higher temperatures. The mean response from all taxa was less (ca. 35% less) than predicted from the classic [Eppley, R. W. (1972) Temperature and phytoplankton growth in the sea. Fish. Bull., 7, 1063–1085.] formulation. Maximum growth rates also were most reliable when determined from changes in cell abundance. If the variability in maximum growth rates among taxa is reflective of in situ responses to polar temperature increases, it will be challenging to predict the assemblage response to elevated in situ temperatures in future years.