Abundance of Sargassum Seaweed Washing Ashore Across St. John

A rare juvenile grey triggerfish, above, was recently spotted enjoying a snack on sargassum off Hawksnest Bay.

Don’t worry about those large clumps of brown seaweed washing ashore across St. John.

Residents across the island have reported seeing a lot of sargassum floating around and accumulating at east- and south-facing shorelines.

Far from being harmful, those bunches of seaweed are actually home to a thriving community of marine life, explained U.S. Geological Survey marine biologist Caroline Rogers.

“Sargassum has been reported lately coming up on a lot of different islands,” said Rogers. “These floating mats are naturally detached like this in the open ocean and they break up and float ashore. It’s unusual that there is so much of it, but it’s not harmful.”

After hearing a report of a small triggerfish among the sargassum on the North Shore, Rogers went snorkeling at Hawksnest and was delighted to spot a rare juvenile grey triggerfish, she explained.

“And that is only one of several fish which are found with sargassum,” said Rogers. “There is an amazing variety of really cool animals associated with this stuff. Sargassum support a thriving little eco-system of its own.”

Sargussum has also been spotted across the British Virgin Islands and scientists’ best guess is that different ocean currents are bringing a high concentration of the seaweed into local waters, according to Rogers.