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Nuisance seaweed blooms: too much of a good thing

Published:Saturday | February 21, 2015 | 2:00 AM
Sargassum bloom at Discovery Bay Marine Lab.

Large mats of brown seaweed were observed blanketing marine areas around Jamaica in 2014. The phenomenon, occurring across the Caribbean and as far north as Massachusetts, is affecting fisheries, aquaculture, shorelines and tourism. The beached seaweed interferes with shore-based activities. If not removed, it rots to produce a smelly mass.

These nuisance blooms have occurred before in 2011. However, marine biologists at the University of the West Indies believe the 2014 occurrence has had a greater effect on Jamaica. Although the algae are non-toxic, they can cause problems for humans. Work on the seagrass beds of the Port Royal cays with a class of students was made almost impossible, as we were overwhelmed by a huge blanket of seaweed. The water became uncomfortably warm and darkened, so that it was difficult to see the sea bottom until the wind moved the huge blanket towards the shore. The mass of seaweed also contained stinging organisms (most likely tiny anemone, hydroids or jellyfish) that caused rashes and itching for days after.

The algal mats comprise primarily Sargassum, a genus of macroalgae that floats at the surface of the sea and reproduces there without having to be attached to the sea bottom. The plant simply breaks into fragments and each piece grows to create the huge floating mats in the open ocean.

The Sargasso Sea is where these algae can normally be found in large mats kept together by the North Atlantic gyre (near circular current). Columbus, on his first voyage in 1492, was afraid that his ships would get caught in the huge algal mats of the Sargasso Sea. The Sargasso Sea is an important feature of the marine environment, as it creates a huge (3,520,000 km2, 2 million square miles or about the size of Australia) 'coastal environment' in the middle of the ocean and has been called the 'golden floating rainforest of the Atlantic Ocean'.

The Sargassum mats provide a home for turtles, glass eels, tunas and jacks, as well as other vulnerable juvenile species that are protected from being eaten by predators by living within the floating mats of Sargassum. Here they find food and shelter until they are large enough to survive in the open.

While the exact reason for the proliferation is unknown, scientists believe the growth and spread of the algae throughout the Atlantic and Caribbean is a sign of a larger problem. The oceans are under threat and particularly sensitive areas like the Sargasso Sea act as indicators of the problem. The cause could be related to ocean warming (the Sargassum plant can now extend its range) and increased nutrients that fertilise the blooms. Scientific studies into the 'nuisance' Sargassum blooms have increased as those who know of the value of the Sargassum seek to understand, predict and control its proliferation.

Besides providing habitat and food for unique marine species, Sargassum is a valuable raw material and could become regarded as a 'potential crop rather than harmful weed'. The Sargassum plant's ability to sequester carbon is also being promoted, as it removes more than phytoplankton (five times higher carbon:nitrogen ratio) and rapidly sinks to the deep-sea floor.

So until we understand more, and can make use of the resource, the algal blooms will continue to be too much of a good thing.


Mona K. Webber (PhD)

Marine Biologist, UWI (Mona)