Kelp forest in the Channel Islands National Marine Sanctuary and National Park.

Some seaweeds are microscopic, such as the phytoplankton that live suspended in the water column and provide the base for most marine food chains. Some are enormous, like the giant kelp that grow in abundant “forests” and tower like underwater redwoods from their roots at the bottom of the sea. Most are medium-sized, come in colors of red, green, brown, and black, and randomly wash up on beaches and shorelines just about everywhere.

The vernacular “seaweed” is a bona-fide misnomer, because a weed is a plant that spreads so profusely it can harm the habitat where it takes hold. (Consider kudzu, the infamous “mile-a-minute vine” that chokes waterways throughout the U.S. Southeast). Not only are the fixed and free-floating “weeds” of the sea utterly essential to innumerable marine creatures, both as food and as habitat, they also provide many benefits to land-dwellers, notably those of the human variety.