Trait measurements for growth, nutrient uptake, and cell volume for nine genotypes each of the phytoplankton species Chaetoceros affinis and Emiliania huxleyi individually during 4 days of cultivation at seven nitrate levels. Nitrate levels for genotypes of C. affinis were 2.5, 5, 7.5, 12.5, 20, 30, and 45 μmol L−1 with 2 μmol L−1 phosphate and 2.5, 5, 7.5, 10, 15, 20, and 25 μmol L−1 with 1.5 μmol L−1 phosphate for genotypes of E. huxleyi.