Mystery beach castaway is normally floating alga

Sea if you know this one.

This is a species of marine algae. It is commonly found washed up along our southern beaches, dying (or dead), especially after storms or rough weather.

This is, indeed, one of the many species of "seaweeds." a very non-technical term, but a term that is useful.

Botanists consider the true seaweeds to be members of a group called the "brown" algae, a group which includes the giant kelps of the northern Pacific. The brown algae are all oceanic and are most common in cold, nontropical waters. Their pigments often give them a dark, often brownish color.

Although many are fairly large plants with rubbery, tough texture, others are smaller and fairly delicate. A number of "the browns" are attached to rocks or other substrates, whereas some float.

There is considerable economic use made of the various edible species in cuisines of eastern Asia (and elsewhere), including the alga providing us with "kombu."

Other algal groups, whether oceanic or fresh-water, are also based upon their pigmentation (among other technical features); thus we have green, golden, and red algal species groups, as well as the browns.

Any alga (the singular form of the word "algae") floating in the surf, or for that matter any other plant washed up onto the sand, is likely to be referred to offhandedly as a "seaweed," but this term really only refers to brown algae.

If you are at the beach this summer, you might run into it. Washed up on the beach, it is a common component of what we call beach "wrack," or accumulated naturally occurring debris. Beach wrack is normally associated with the highest tide lines, where it provides habitat for a surprising number of animal species, and may assist with germination of some plants' seeds. As it decomposes, nutrient recycling takes place.

When amounts are sufficient, wrack is sometimes harvested as a source of compost or green manure. (Unfortunately these days, the wrack on many beaches contains more and more plastic and styrofoam - not to mention worse stuff, like oil - and becomes something of an eyesore.)

Our beach castaway is normally a floating alga, commonly found in the Sargasso Sea, off Bermuda, where vast mats float languidly in the relatively calm waters.

Tons of these plants, while floating together, form effective nurseries for many animal species, including shrimp, crabs, jellyfish and marine worms, as well as fish. Young sea turtles often spend a portion of their early life cycle within these floating mats, attaining some safety from predators.

Most people don't think about algae such as this one too much, but I hope you'll agree that this is an important species, both ecologically and economically.

John Nelson is the curator of the Herbarium at the University of South Carolina, in the Department of Biological Sciences. As a public service, the Herbarium offers free plant identifications. For more information, visit www.herbarium.org or call (803) 777-8196.

(Answer: "Sargasso weed," "Sea holly," Sargassum natans)

Photo by John Nelson