Eelgrass Communities

By Taeven Lopatecki and Quynn Stafford

Peer below the shallow water in one of the protected bays of the Pacific Northwest coast, and chances are you will discover an enchanting underwater meadow of emerald stalks waving back. Seagrass meadows lie at the wide mouths of estuaries and in the grey silts and sands of the intertidal and foreshore. This beautiful and biodiverse ecosystem hosts a great diversity of life. From the sub-tropics in Baja California, Mexico, to the Arctic in Alaska, Canada, and Greenland, the most common species of seagrass in North America is the eelgrass Zostera marina. Along the west coast of North America, this native species is also found alongside the introduced dwarf eelgrass, Z. japonica, which originated from Northeast Asia (1).

Wading deeper into these seagrass meadows, the richness of life here slowly reveals itself. Seagrass is a foundation species that creates a complex habitat, thereby providing shelter for a diverse number of species. Eelgrass meadows form critical nurseries for many species’ young, including juvenile salmon and flatfish, and serve as a spawning ground for herring (2,3). They also provide rich foraging habitat for numerous invertebrates and many larger creatures, including heron and geese (4,5).

Other functions of seagrass meadows include filtering excess nutrients from the nearshore environment, preventing shoreline erosion, and storing carbon (3). Carbon stored in seagrass meadows, along with salt marshes and mangroves, is referred to as “blue carbon” (6). These coastal habitats play a major role in carbon sequestration, storing about twice the average amount of organic carbon per hectare as terrestrial soils (7). Protection and conservation of these areas is thus important not only for biodiversity and marine species health, but also for worldwide climate change mitigation. Indeed, seagrass meadows comprise 10–18% of all carbon buried in the ocean (8).

Seagrass ecosystems are easily damaged by a range of factors. Coastal development is a top concern, caused primarily by underwater building, dredging, and intertidal hardening which lead to habitat loss (3,9). Hardening is the increasing use of stone and cement walls to prevent property damage and erosion, without considering the buffer against erosion that is naturally provided by seagrass and healthy nearshore ecosystems. Decreasing water quality caused by pollution and other runoff leads to an excess of nutrients and lack of oxygen, diminishing the health of seagrass meadow inhabitants (3,9). These stressors, combined with warming ocean temperatures, and the monospecific nature of seagrass meadows, have led to another challenge: the spread of seagrass wasting disease across the Pacific Northwest (10). This disease is caused by the protist Labyrinthula zosterae, which destroys seagrass tissue leading to a decrease in habitat (11). Like coral reefs, mangroves, and tropical rainforests, seagrass meadows are among the most threatened ecosystems on the planet (9). Ten of 72 seagrass species worldwide are at risk of extinction, while three others are considered endangered (12). 

Beyond their visual ties to terrestrial meadows, seagrass ecosystems provide a solid link between the ocean and the land. These tidal meadows are nourishing places where sunlight, freshwater, saltwater, and sediments combine, giving rise to food webs that allow life of all kinds to flourish, from microscopic bacteria and algae to larger animals like crabs, fishes, birds, and bears (13). Indeed, the interconnectivity emergent in these places extends well beyond the ocean’s physical borders, making seagrass meadows vital to the health of our coastal ecosystems