Sargassum on our beaches

By Dr.Winston Mitchell

Sargassum is a species of brown algae. It is seen predominantly in the Sargasso Sea located in the open North Atlantic Ocean surrounding Bermuda. Sargassum is present in the Northern Gulf of Mexico and South America.

The increased amount of Sargassum noticed since 2011 is thought to be due to the damaging effects of the oil spill in the Gulf of Mexico along with warming of nutrient-rich waters and rising ocean levels.

Movement of Sargassum depends solely on ocean currents. Strong currents transport Sargassum into the open Atlantic Ocean from where it is dispersed and has become a severe threat to the Eastern Caribbean since 2011.

Is the origin of the Eastern Caribbean Sargassum from the Sargasso Sea or South America? From South America, it travels north with the North Brazil current.

In Grenada, 2015 witnessed the most substantial influx of Sargassum spread over many months in the latter half of the year. In 2018 a heavy band passed in April/May with significant accumulation on beaches along the East coast. Fewer amounts are noted weekly.

The Sargassum is observed to move from North to South on the East coast with the most extensive accumulation on the North East beaches.

In the ocean dolphin and tuna feed on Sargassum and it provides spawning ground for flying fish.

Small amounts ashore are of little concern. Small amounts help stabilise the sand and build up the beaches. The waves also remove small amounts. Moderate and large accumulations need attention.

Clean Sargassum provides useful nutrient to soil and promotes healthy soil. Uses include fertiliser, compost and in some countries, cuisine.

Onshore, moderate and large accumulations result in fouling of beaches with reduced attractiveness. Decaying Sargassum and small decomposing organisms produce an unpleasant gas, hydrogen sulfide.

There is entrapment of human litter such as plastic.

Removal of accumulated Sargassum from beaches presents a formidable challenge. Once deposited on beaches, there is a rapid accumulation of sand mixed with the Sargassum.

Sargassum should be removed as soon as possible after deposition on the beaches. Removal should not include sand. Beach erosion and beach destruction results with sand removal.

Ideally, it is best to remove Sargassum from the water along the shoreline. The seaweed will be free of sand but is not very practical.

Manual removal is the most sustainable practical method. It is labour intensive and provides employment. Hand raking is less intrusive to the beach than mechanical removal.

Mechanical methods remove large quantities of sand and sand dwellers including possible recently hatched sea turtles. Machines with claw and rake are less destructive than devices with bucket and scoop.

Bucket and scoop gouge the beach and remove large quantities of sand.

In 2015, a group of volunteers and me kept LaSagesse beach relatively clean. The beach was cleaned five to seven days per week for several months. On our first day, the seaweed was raked and dumped. The following day we noted that the deposited material was mainly sand.

This observation leads to rake, crate, wash and discard technique.

The seaweed was manually gathered, placed into agriculture crates and taken to the sea and cleaned. The sand fell through the spaces in the container and remained in the sea. After washing, the seaweed was transported to dry land on shore.

On occasions, Sargassum was transferred directly from the water when significant accumulation occurred along the shoreline.

Many farmers removed the dry Sargassum for use on their property.

I make an appeal – do not destroy our beaches with the use of Backhoe in cleaning Sargassum.

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