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Thursday, February 20, 2025

Why is so much brown seaweed washing ashore?

Ex­perts ac­count for the heavy pres­ence of sar­gas­sum in the Caribbean

by

20150506

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A lot of con­cern has been raised about the­large de­posits of pelag­ic sar­gas­sum along Trinidad's shore­lines. Pelag­ic sar­gas­sum is the brown al­ga that has been show­ing up in large quan­ti­ties on some of Trinidad's coast­lines.Among the af­fect­ed are fish­er­men, who have had dif­fi­cul­ty us­ing their nets in the af­fect­ed ar­eas.A pa­per pub­lished by a pair ofre­searchers in Apri­lad­dress­es some com­mon ques­tions and con­cerns about sar­gas­sum. An edit­ed ex­tract of the pa­per is pub­lished be­low.

Sar­gas­sum is an emerg­ing is­sue on the coasts of the wider Caribbean. In 2011, large quan­ti­ties of pelag­ic sar­gas­sum were seen through­out the Caribbean, im­pact­ing aquat­ic re­sources, fish­eries, shore­lines, wa­ter­ways and tourism. Sim­i­lar events oc­curred in 2014.

What is it?

Pelag­ic sar­gas­sum is a brown al­ga, or sea­weed that floats free in the ocean and nev­er at­tach­es to the ocean floor. These free-float­ing forms are on­ly found in the At­lantic Ocean. Sar­gas­sum pro­vides refuge for mi­gra­to­ry species and es­sen­tial habi­tat for some 120 species of fish and more than 120 species of in­ver­te­brates. It's an im­por­tant nurs­ery habi­tat that pro­vides shel­ter and food for en­dan­gered species such as sea tur­tles and for com­mer­cial­ly im­por­tant species of fish.

There are two species of sar­gas­sum in­volved in the in­flux: Sar­gas­sum natans and Sar­gas­sum flui­tans.

Where does it come from?

Sar­gas­sum trav­els on ocean cur­rents. Sci­en­tists are able to de­ter­mine where the sar­gas­sum comes from by back-track­ing from its strand­ing lo­ca­tion us­ing ocean mod­els and da­ta on move­ments of satel­lite track­ers that are de­ployed at sea. It is be­lieved that the re­cent in­flux­es are re­lat­ed to mas­sive sar­gas­sum blooms oc­cur­ring in par­tic­u­lar ar­eas of the At­lantic, not di­rect­ly as­so­ci­at­ed with the Sar­gas­so Sea, where nu­tri­ents are avail­able and tem­per­a­tures are high. The sar­gas­sum con­sol­i­dates in­to large mats and is trans­port­ed by ocean cur­rents to­wards and through the Caribbean.

Will the sar­gas­sum in­flux oc­cur every year?

While it is not known whether the in­flux will hap­pen every year, signs from the East­ern Caribbean are that we'll be see­ing sar­gas­sum in the re­gion pe­ri­od­i­cal­ly through­out 2015. Some sci­en­tists as­so­ciate the cause of sar­gas­sum with high­er than nor­mal tem­per­a­tures and low winds, both of which in­flu­ence ocean cur­rents, and they draw links to glob­al cli­mate change.

The sar­gas­sum does not nec­es­sar­i­ly af­fect the same lo­ca­tion in the Caribbean all year. As it's trans­port­ed on cur­rents it pro­gres­sive­ly af­fects dif­fer­ent lo­ca­tions across the re­gion. At any one time of the year there are mul­ti­ple lo­ca­tions that can be af­fect­ed.

Is it a prob­lem to leave it to rot on the beach?

Sar­gas­sum oc­curs nat­u­ral­ly on beach­es, in small­er quan­ti­ties. It plays a role in beach nour­ish­ment and is an im­por­tant el­e­ment of shore­line sta­bil­i­ty. For ex­am­ple, sand dune plants need nu­tri­ents from the sar­gas­sum, and sea birds de­pend on the sea life car­ried in the sar­gas­sum for food. Dur­ing de­com­po­si­tion there will in­evitably be a smell and in­sects around. The ex­pe­ri­ence in lo­ca­tions that have left the sar­gas­sum on the beach is that it will even­tu­al­ly get washed away or buried in the next storm, with rain eas­ing the smell. Leav­ing sar­gas­sum on the beach has proven to be the sim­plest ap­proach, al­so avoid­ing po­ten­tial neg­a­tive im­pacts as­so­ci­at­ed with beach clean­ing.

Are there any hu­man health con­cerns as­so­ci­at­ed with sar­gas­sum?

Al­though it can smell as it de­com­pos­es, this process is not tox­ic to hu­mans. Sar­gas­sum does not sting. De­pend­ing on the type of sar­gas­sum you're see­ing, you might feel the pointy ends of the buoy­an­cy pods of Sar­gas­sum natans. When it de­com­pos­es on sand you might no­tice a black lay­er un­der­neath, but this is nor­mal and a sign of na­ture do­ing its work of in­cor­po­rat­ing the sar­gas­sum in­to the beach.

What can we do about it?

In em­brac­ing the chal­lenge of sar­gas­sum, good com­mu­ni­ca­tions be­tween agen­cies and the pri­vate sec­tor, with the press, and with lo­cals and vis­i­tors is es­sen­tial to mak­ing sure that every­one knows where clean beach­es can be found.

In many coun­tries, the law does not re­quire agen­cies to re­move sea­weed since it's not ma­rine de­bris but is a nat­ur­al part of the ecosys­tem. Where pri­vate sec­tor ca­pac­i­ty ex­ists to clean beach­es, coastal man­agers agree on bal­anc­ing the im­por­tance of sar­gas­sum for nat­ur­al process­es and as life-giv­ing nour­ish­ment for beach­es and seabirds, with pres­sure to ad­dress neg­a­tive im­pacts on com­mu­ni­ties. Es­tab­lish­ing clear poli­cies about where, when and how to clean beach­es is the next step.

Im­ages show heavy de­posits of sar­gas­sum at Ma­yaro on Mon­day. Pho­tos: Abra­ham Di­az

Source: Doyle, E. and J. Franks. 2015. Sar­gas­sum Fact Sheet. Gulf and Caribbean Fish­eries In­sti­tute.


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