Inter-specific scaling of phytoplankton production and cell size in the field

This study tests the hypothesis that the interspecific scaling of phytoplankton production and cell size in the field follows the 3/4-power scaling law. Published data of cell size and in situ, cell-specific carbon production rates by single phytoplankton species, collected in surface waters of lakes, rivers, estuaries and oceans, are reviewed. Across more than nine orders of magnitude in cell volume, 98% of the variability in carbon production rates was explained by cell size. The slope (b) in the log-log relationship between carbon production rate and cell volume did not differ significantly from 1, either for diatoms (b = 1.01) or for dinoflagellates (b = 0.89). For all phytoplankton species considered together, which included also cyanobacteria and haptophytes, b took a value of 0.91, which is significantly higher than 3/4. The observed nearly isometric scaling relationships between production rate and cell volume suggest that there is no relationship between phytoplankton growth rate and cell size. The present analysis confirms recent evidence showing that phytoplankton metabolism in natural conditions does not follow the 3/4-power scaling rule. It is argued that allometric models of plankton growth and metabolism should incorporate scaling parameters measured in situ on natural phytoplankton assemblages, rather than those obtained in the laboratory with monospecific cultures.