Masses of seaweed invade Cayman shores

Caribbean sargassum arrivals forecast to diminish in coming months

Sargassum floats ashore at Cayman Brac. – Photo: Sister Islands News Agency

Weeks after government workers cleared 200 tons of sargassum from Grand Cayman’s coastlines, the invasive seaweed has returned to the island.

Fresh masses of the plant began accumulating this week in West Bay, with thick mats gathering around the West Bay Dock and Cemetery Beach. Lesser quantities were observed in Prospect.

The impact was also felt in Cayman Brac, where large masses began to build up around the southwest side of the island.

Back in Grand Cayman, Divetech’s Courtney Criswell said the accumulation around West Bay Dock had caused some difficulty for boats using the dock, but that overall, dive operations had not been negatively impacted.

“The thickness of it has caused a little bit of issues for some of the boat handling coming in and out, just because it’s so deep. It hasn’t prevented anybody [from diving], but it has caused people to need to be a little more careful coming in and out of there,” Criswell said.

“But once you get away from shore, the patches of it and everything haven’t been any issue for the diving. It hasn’t affected the visibility.”

She said diving under the mats can be a bit eerie, but that up close, they give a snapshot of a living ecosystem, full of juvenile fish and other marine life.

“We’ve kind of theorised that it might be one of the reasons we’ve seen an increase in the sighting of seahorses over the past months,” she said.

“At our store location at Lighthouse Point, we’ve had a couple of sightings of seahorses out in that area. They tended to be few and far between before. But we’ve seen them more, recently, than in the past.”

Workers from Vivo restaurant at North West Point said they had not yet experienced a negative impact from the sargassum.

With the seaweed only having washed ashore in recent days, most of it had not yet decomposed, so the foul smell associated with the plant had not fully set in.

Environmental concerns

The Department of Environment advised that heavy equipment for sargassum clean-up can be detrimental to turtle nesting.

“Vehicles and heavy equipment on beaches can crush turtle nests or destroy nesting habitat through sand compaction or excavation. We have not had any reports of this happening yet, but it is still just at the mid-point of the nesting season,” a DoE statement read.

A draft plan on turtle conservation, currently in the public consultation phase, would establish best practices for seaweed clean-up to minimise the environmental impact.

The plan proposes making it unlawful to operate motor vehicles and equipment on turtle nesting beaches from 1 May to 30 Nov. Exceptions would include permitted beach-cleaning vehicles, ambulances and law enforcement vehicles, and construction vehicles with planning permission.

While sargassum mats at sea provide a habitat for sea life, once they arrive on coastlines, the environmental impact can be far reaching, according to researcher Brigitta van Tussenbroek with the Caribbean Seagrass Lab of the National Autonomous University of Mexico.

Van Tussenbroek is working to advise officials in Mexico on best practices to avoid issues such as beach erosion and damage to coral reefs.

“The huge masses cause what we started to call ‘sargassum brown tide’ and they cause anoxia [lack of oxygen], lower pH and light inhibition. They kill basically all the benthos [marine organisms] which are there, and the benthos also fix the sand, so [that causes] more beach erosion,” she said.

“Also, all those nutrients, they’re being flooded into the reef system and even if you don’t see that actual brown tide … its effects are [seen] even further than the barrier reef, which for us, is about 2 kilometres from shore.”

She has observed an expansion of the ‘sargassum season’ since 2015 and said it can now be expected to impact the Caribbean from March until November.
Sargassum forecast

The overall amounts of sargassum in the Caribbean Sea diminished from July to August, according to a 31 Aug. forecast from the University of South Florida Optical Oceanography Lab.

Across the central-west Atlantic and Caribbean Sea, USF observed around 7 million metric tons of sargassum in August, down from 11 million in August 2018.

“Looking ahead, although reduction in Sargassum amount in the [Caribbean Sea] is expected to continue, the amount is projected to be relatively higher than most previous years (except 2018 and 2015),” the USF forecast read.

“This is because 1) there is still a large amount in the [Caribbean Sea], and 2) the large amount in the [central-west Atlantic] is going to be transported to the [Caribbean Sea].”

This means sargassum beach arrivals can be expected to continue across the region, but in lower quantities through the coming months.

“The exact Sargassum amount, timing, and location of the beaching events are hard to predict as they will depend on local ocean circulations and winds,” the forecast said.

The Cayman Islands Ministry of Commerce did not confirm if clean-up crews would be redeployed to tackle the latest influx. Six workers with the National Community Enhancement Project, known as NiCE, were tasked with sargassum collection in August.

At that time, the eastern reaches of Grand Cayman felt the greatest impact from sargassum. Workers cleared 200 tons of the seaweed from Frank Sound boat ramp, Coe Wood Beach in Bodden Town, Cayman Kai Public Beach in North Side and Colliers Beach in East End.

The impact was also felt in Cayman Brac, where large masses began to build up around the southwest side of the island.

Editor’s Note: This story has been amended to reflect that the Ministry of Commerce was the government entity involved in the NiCE clean-up campaign.