Macroecological patterns of phytoplankton in the northwestern North Atlantic Ocean

Many issues in biological oceanography are regional or global in scope1; however, there are not many data sets of extensive areal coverage for marine plankton. In microbial ecology, a fruitful approach to large-scale questions is comparative analysis2,3 wherein statistical data patterns are sought from different ecosystems, frequently assembled from unrelated studies4. A more recent approach termed macroecology characterizes phenomena emerging from large numbers of biological units by emphasizing the shapes and boundaries of statistical distributions, because these reflect the constraints on variation5. Here, I use a set of flow cytometric measurements to provide macroecological perspectives on North Atlantic phytoplankton communities. Distinct trends of abundance in picophytoplankton and both small and large nanophytoplankton underlaid two patterns. First, total abundance of the three groups was related to assemblage mean-cell size according to the 3/4 power law of allometric scaling in biology6,7. Second, cytometric diversity8 (an ataxonomic measure of assemblage entropy) was maximal at intermediate levels of water column stratification9. Here, intermediate disturbance shapes diversity through an equitable distribution of cells in size classes, from which arises a high overall biomass. By subsuming local fluctuations, macroecology reveals meaningful patterns of phytoplankton at large scales.