Zostera marina is commonly known as eelgrass. Eelgrass is a perennial aquatic plant that lives along the ocean shoreline in cool northern waters. Rhizomes hold branching slender stems with flat thin leaves to the ocean floor in shallow, protected areas. Flowers and seeds distinguish it as an aquatic herb rather than a seaweed.
Eegrass provides an important intertidal habitat for fish and shellfish. Beds, also called eelgrass meadows, flourish in spring and summer, then die back in fall and winter. You often find huge mats washed up on shore, or floating in masses across the ocean surface.
An eelgrass study was conducted in 2003 in Okeover and Malaspina Inlets north of Powell River. The study discovered 40% of the shore had soft sediment or protected areas suitable for eelgrass. The remainder of the area had cliffs, steep boulders, or rocky beaches. Twenty-one sites with 32 beds were identified in the inlets. Because the area is important for oyster and clam production, it's important to keep it unpolluted and health.
Here's a YouTube video by Shaw's Oceancast TV.