In general, algae adapted to coastal environments by anchoring are called seaweeds. Here's an exception, a seaweed that re-adapted to the open ocean by becoming free-floating again, Sargassum. The Phactor doesn't know his seaweeds well enough to know for certain, but clonal clumps of this algae get picked up by the Gulf Stream and then transported north from the Sargasso Sea to the coast of North America where it washes up on the beach. You can see the flotation devices, pnematocysts. For some reason most "young" people don't know the term pneumatic although it used to refer to your car or bicycle tires meaning they were inflated with air. Even less well-known among today's college students is that pneumato- starts with a p. Cyst is the cell or structure that is inflated. It's no wonder such terms are just a puzzlement. This little clump looks really fresh because it it was just after high tide and very early in the morning, early enough that the beach was still nice (vacant).