Plankton interactions and community compositions in the North Pacific Ocean

Across the North Pacific Ocean, most plankton species cope with differential resource availability via specific interactions. With organisms competing or providing complementary resources for each other, the diversity of plankton is ultimately shaped by ecological interactions like symbiosis, resource competition or predation. In a series of cruises transiting between the North Pacific Subtropical Gyre, the Transition Zone and the Subpolar Gyre, we imaged plankton species (>4 μm) present in the surface layer of the North Pacific and performed experiments to characterize phytoplankton grazing and resource competition. Imaging flow cytometry revealed strong shifts in community composition in response to ambient nutrients concentrations. Low stocks of macronutrients (N, P) favor certain classes involved in mixotrophy or symbiosis (e.g cyanobacteria, dinoflagellates or coccolithophores) whereas higher concentrations seem to mark the presence of diatoms of various sizes. Outputs of a Generalized Lotka-Volterra model show that the species-specific growth and grazing rates vary predictably across biogeochemical gradients in the North Pacific.