Seaweeds are members of a large group called algae.
Although we often encounter seaweed floating at the water's edge or thrown up on shore after a storm, these large algae are actually benthic organisms that have been dislodged from the bottom. Seaweeds have a basal organ called a holdfast that anchors the plant firmly to a solid bottom or substrate. Because seaweeds grow attached, they can be found in abundance in areas of rocky substrate. When found along beaches at the Cape Cod National Seashore, it is most likely the result of wind direction, waves, current drift, or a storm. The moon is the primary force that causes tides.