Throughout the ecozone, freshwater discharges from the Fraser, Skeena, Nass, and other rivers carry vast amounts of nutrients to the ocean, stimulating the growth of phytoplankton, algae, and other marine plant life. Near the southern end of Vancouver Island, deep water upwelling encourages a prolific ocean ecosystem. Unlike its Atlantic counterpart, the Pacific Marine Ecozone has little physical connection with the Arctic, so it has different populations and distributions of species such as plankton. In the intertidal zones (between high and low tide and always underwater) lie vast forests of Macrocystis, or Giant Kelp, along with several varieties of seaweed and coral reefs.

Soon after records of Captain Cook's voyages were published in 1784, British and American fur traders sailed to the Pacific waters in search of sea otters. By the early 1930s, the Pacific population of sea otters had been extirpated. Sea urchin populations, once controlled by the otters, subsequently exploded, decimating many of the kelp forests and their associated algae communities. Today, re-introduced otter populations are rising and the kelp habitat may also recover. Along the water's edge, coastal salt marshes and mudflats contain large beds of eelgrass, important spawning sites for Pacific Herring schools.