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Atlantic Ocean - The Sargassum Phenomenon is a Serious Issue for Atlantic sailors

By Sue Richards last modified Aug 08, 2018 06:22 AM
Contributors: Joan Conover, Jim Franks, Donna Lange, Andrew Bishop
Single-hander Donna Lange who started a non-stop sail around the world in July from Bristol, RI, USA, kicked off a serendipitous scientific event by showing how scientists can benefit from the support of a group of people with a keen interest in the oceans - world-cruising sailors.

Published: 2015-09-20 23:00:00
Topics: Atlantic Crossing , Environment
Countries: Sierra Leone , Cape Verdes

Atlantic Ocean - The Sargassum Phenomenon is a Serious Issue for Atlantic sailors

Taken by Donna Lange

Currently in the South Atlantic, Donna is actively assisting researchers with her reports on Sargassum weed mats encountered.

Donna became caught in a huge Sargassum mat off Sierra Leone, Africa, recently and sought help from the Seven Seas Cruising Association. Whilst assisting Donna, Joan Conover of the SSCA was struck by the seriousness of this issue for cruisers. “From Donna’s reports, this problem seems to be pretty widespread, yet no one is talking about it outside of the Caribbean. It surprised me that there is currently NO way for satellites to ID weed in the oceans and there is a need to determine the extents of the weeds, or the scope of the problem which will eventually end up in the Caribbean we all love. If Atlantic cruisers can assist with Sargasso weed locations, then with enough information the extent of the issue can be mapped out.”

During 2011, massive quantities of Pelagic Sargassum occurred throughout the Caribbean, impacting aquatic resources, fisheries, shorelines, waterways, and tourism. A similar event is occurring in 2014 and continues in 2015.

However, as indicated by research and by Donna’s reports, the phenomena is not only isolated to Caribbean waters.

The Sargasso Sea, a 1.5-million-square-mile circle of ocean filled with vast rafts of free-floating algae, occupies the North Atlantic Subtropical Gyre, a large system of rotating currents within the Atlantic. The Sargasso Sea is bounded by the Gulf Stream, the North Atlantic current, the Canary Current and the North Atlantic Equatorial Current.

Jim Franks, a senior research scientist at the University of Southern Mississippi’s Gulf Coast Research Laboratory, and his colleagues, have reason to believe - based on their preliminary research - that the event most likely has no direct connection to the Sargasso Sea. See the website for information about Sargassum (

Why so much Sargassum?

Franks says, "We believe this is an on-going equatorial regional event and our research has yet to find a direct connection with the Sargasso Sea. We believe that there is a massive Sargassum bloom occurring all along the equatorial Atlantic impacting Sierra Leone and perhaps reaching to the Bay of Guinea. The Sargassum growth and mass accumulations are being 'fuelled' by very warm sea temperatures and nutrient input from a variety of sources”.

This phenomenon is a serious issue for West African and Caribbean coastal communities. In large doses, the algae harms coastal environments, even causing the deaths of endangered sea turtle hatchlings after they wriggle out of the sand where their eggs were buried. Clean-up efforts by work crews may also worsen beach erosion.

Location of Sargassum

Jim Franks, recently created a website to collect eyewitness reports of large quantities of Sargassum. Those reports confirm the seaweed is showing up in areas where before it had been seen only rarely or not all. Circulation patterns in the equatorial Atlantic have reportedly carried mats to Africa for the first time and most likely elsewhere.

Donna Lange photographed large mats of Sargassum on the 13th September in the East Atlantic off the coast of Africa at approximately 10N. It is quite possible these mats are spread all the way across the ITCZ region.

Donna reports NO weed at 5S 17W, however north of that position the situation she says, is very bad. It is hoped she will continue South and West of that position, to hopefully give an idea of where a boat could go if the weed is that much of a problem.

Is it a danger to yachts?

The mats of weed are rarely thick enough to impede a boat, however Donna Lange did get stuck in a dense mat off Sierra Leone in dead calm conditions that she reported to be at least a foot thick (see Donna has no engine, so came to a complete standstill and it is likely catamarans would be severely slowed by larger weed areas such as Donna encountered.

Depending on how large the mats are, it’s probably advisable to skirt around them if possible to avoid weed getting caught in the rudders/keel and prop keg (although this is unavoidable in the dark).  Occasional bursts of reverse when using the engine will help clear any weed from the prop and if motoring through be sure to check the raw water engine cooling pump strainer for blockages to avoid any major problems.

How can the cruising community help?

In an effort to better understand critical aspects of this phenomenon, the USM research team is accepting reports from cruisers in the Atlantic who come across large quantities of Pelagic Sargassum. Data received will help researchers identify the source and examine the movements and causes of this extraordinary event.

Data can be submitted via the web or by e-mail.

Web: USM Website -  use this form to report your sightings:

Email: For yachts at sea who only have e-mail capability, Joan Conover of the SCCA has volunteered to receive feedback and post it to the Research website. E-mail with the following findings:

  • Lat/Long from GPS
  • Date & Time
  • Description (to include direction of surface currents, approximate size, number of mats, observations of marine life)
  • Photo if possible

  • The Sargasso Sea Commission are also interested in photographs of Sargasso weed as well as feedback from cruisers in the Sargasso Sea area with large mat sightings. Sightings from this area should be posted directly to the USM Website (as above).

    Yachting Rallies helping with Research

    Participants in all Caribbean-bound rallies this Fall will also be helping collect information.

    Andrew Bishop, Managing Director of World Cruising Club, organisers of ARC Caribbean 1500, ARC+ and ARC, comments; “In last year’s ARC cruisers reported seeing large clumps of Sargasso weed on approach to the Cape Verdes. Following Donna Lange’s sightings, it appears the weed is much more widespread this year, and we are hoping that many of our rally participants will be able to report their sightings as they head to the Caribbean and assist with the research.”

    Useful Links

    Donna Lange:

    Pelagic Sargasssum Fact Sheet

    Find out more about Sargassum in the Caribbean from this noonsite article.

    Nasty Seaweed Creates Entrepreneurs in Caribbean - November 2015

    Caribbean Seaweed Invasion Story – August 2015

    The Mysterious Life of the Sargasso Sea – SAIL Magazine

    Massive Sargasso Seaweed Bloom is Choking the Caribbean

    Virgin Gorda: Fish kill, water woes blamed on Sargassum

    About the SSCA

    Seven Seas Cruising Association ( is one of cruising's oldest sailing organizations. Home based in Florida, USA, SSCA has members cruising worldwide and offers programs in support of the active and the want-to-be cruisers.

    The Cruising  Host (CS) program provides the local point of contact that cruisers know they can depend on for current information such as Customs/Import requirements, where to provision, find dockage, to find a friendly face and a helping hand in a new port. In the event of issues for a vessel, we help as best we can, many times forwarding vessel needs and contact information to hosts further along the boat route. Sometimes we locate special items and offer assistance. Its a case by case basis, but we have made many new friends over a quick potluck, or during cocktails looking out over the harbor.  With over 150 active hosts world wide, SSCA helps their members and the cruising public.

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