The great Atlantic Sargassum belt
July 5, 2019 4:20 PM   Subscribe

Sargassum is a rust-colored seaweed that floats. In the Atlantic Ocean, the two dominant species have now expanded so much, likely due to agricultural runoff from the Amazon or Mississippi, that blooms practically stretch from the Gulf of Mexico to West Africa. The seaweed provides a habitat for hundreds of species of fish and hatchling sea turtles, seahorses, crabs, shrimps, snails, and nudibranchs. But excessive amounts of it are washing ashore and blanketing beaches, with significant environmental and economic consequences.

According to a July Science article (, it is "the world's largest macroalgal bloom". A video overview of the Sargasso Sea, the normal habitat of these sargassum species. The Satellite-based Sargassum Watch System has monthly updates.
posted by sylvanshine (10 comments total) 21 users marked this as a favorite
A portion of the Sargassum passing through the Gulf passes through the ongoing Taylor oil leak, which has been placing roughly 1000 to 10000 gallons per day onto the surface currents, and often into Ocean fronts that collected Gulf Sargassum.

Read more here, or in recent washpost articles.
posted by eustatic at 4:46 PM on July 5, 2019 [3 favorites]

Has the Sargasso Ogre started commandeering ships? Do we need to call the mysteriously bronze skinned golden eyed hero genius Doc Savage?
posted by srboisvert at 5:40 PM on July 5, 2019 [6 favorites]

[The Sargasso Ogre is funny but a wee bit off topic, so let's call it complete on that riff and return to the main point of the post!]
posted by Eyebrows McGee (staff) at 7:05 PM on July 5, 2019 [3 favorites]

I've noticed the seaweed pile-ups getting progressively worse on the east coast of Florida over the last several years. It is stinky, and often Man O' War wash up at the same time. Fun when their tentacles get hidden in the mats.

Once I was wading in a shallow area, and noticed the seaweed was twitching. I realized it was a sargassum fish camoflauged in the seaweed. Even when it's swimming away, it's hard to tell it apart from the vegetative matter. Good job, nature!
posted by RobotVoodooPower at 7:42 PM on July 5, 2019 [8 favorites]

In the last link, they briefly mention the algae itself as an invasive species, but Sargassum also acts as habitat and as a dispersal vector for juvenile fish that wouldn't otherwise survive a trans-oceanic crossing. Much of the (tropical) fish fauna on either side of the Atlantic is similar, but there are differences, and this could serve to allow species to jump across. The article briefly mentions lionfish, but does not directly discuss the fact that they could potentially end up in the east Atlantic because of the Sargassum. (Lionfish have already made it to the Mediterranean via the Suez Canal, so we could soon see them establish an almost circumglobal distribution).
posted by deadbilly at 8:12 PM on July 5, 2019 [5 favorites]

In Hawai‘i we've seen non-native fishes introduced from the West Pacific (most likely) via floating marine debris, c.f. the Indo-Pacific sergeant. So this sort of thing is not just speculation.
posted by deadbilly at 8:16 PM on July 5, 2019 [1 favorite]

Yeah, it rots on the beach and is often mixed with fragmented Man O’war tentacles when there have been SE winds for a couple of days. But, the weed lines offshore are where you find the tasty ‘schoolie’ dolphins. Yum!
posted by sudogeek at 8:25 PM on July 5, 2019


Sashay, sashay through the sargassum...
posted by The Underpants Monster at 11:09 PM on July 5, 2019

My immediate thought was compost, and whaddaya know!

(Yes, I get it, too much of a good thing. Still, there are people working on it.)
posted by BWA at 6:02 AM on July 6, 2019

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