Methods of growing and harvesting multiple species of phytoplankton are disclosed herein. The method generally includes four steps, namely: (1) collecting phytoplankton seawater containing multiple species of naturally-occurring phytoplankton directly from a source of seawater; (2) adding nutrients to the phytoplankton seawater to proliferate the multiple species of naturally-occurring phytoplankton to a predetermined density; (3) separating the multiple species of naturally-occurring phytoplankton from the phytoplankton seawater to form a phytoplankton concentrate; and (4) collecting the phytoplankton concentrate such that the collected phytoplankton of the phytoplankton concentrate remain in a substantially intact cellular state.