Life in the North Atlantic depends on this floating seaweed

Sargassum plants are a nuisance on some beaches, but they are a shelter and a feast for a complex and amazing variety of marine life.

A clump of sargassum weed the size of a soccer ball drifts near Bermuda in the slow swirl of the Sargasso Sea, part of the North Atlantic gyre. A weed mass this small may shelter thousands of organisms, from larval fish to seahorses.

‘There’s nothing like it in any other ocean,’ says marine biologist Brian Lapointe. ‘There’s nowhere else on our blue planet that supports such diversity in the middle of the ocean—and it’s because of the weed.’

Lapointe is talking about a floating seaweed known as sargassum in a region of the Atlantic called the Sargasso Sea. The boundaries of this sea are vague, defined not by landmasses but by five major currents that swirl in a clockwise embrace around Bermuda. Far from any mainland, its waters are nutrient poor and therefore exceptionally clear and stunningly blue.

The Sargasso Sea, part of the vast whirlpool known as the North Atlantic gyre, often has been described as an oceanic desert—and it would appear to be, if it weren’t for the floating mats of sargassum.

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