Wireweed (Sargassum muticum)
The common names of many animals and plants can vary among regions and even experts. For example, this brown seaweed is called Wireweed in one seaweed-identification book, Japanese weed in another and Sargassum in a third. It always is good to know the scientific name; it will not change based on where you are or who you talk to.
Many of you might have heard the scientific name before because another related species occurs in the middle of the Atlantic Ocean in what is called the Sargasso Sea. The name was given by Christopher Columbus’ crew apparently based on the presence of vast amounts of floating seaweed. By the way, the Sargasso Sea is not a sea but an area where large-scale Atlantic currents bring in drifting material and keep it there forming a unique ecosystem.
This species today can be found in Japan and from Alaska to Southern California. It was introduced to the Northwest in the early 1900s, when the first oysters were imported from Japan to expand the local oyster-culture program. It occurs in the lower intertidal and upper subtidal zones, including tide pools. While normally occurring in sheltered waters, it also can be found in wave-affected areas within Puget Sound.
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Sargassum is characterized by long, thin stems with multiple side branches supported by small, round bladders or floats. Like other introduced species, it can outcompete local species and form an extensive floating canopy.
David W. Jamison is a Boston Harbor resident and marine biologist.