In the classic 1951 sci-fi novel The Day of the Triffids, made into a 1962 film, a strange meteor shower renders everyone who watches it (which of course is the vast majority of the population of planet Earth) blind, after which mobs of triffids, a genetically engineered toxic, carnivorous, and mobile (can't beat that combo!) plant resembling a sunflower on steroids, find the sightless humans easy prey. (At a scientific conference some years ago, I met a graduate student whose first name was 'Triffid;' she admitted her parents were particularly fond of that story.)
Photo: Sargassum seaweed washed up on a Cuban beach, note the spherical gas-filled bladders. "Sargassum on the beach, Cuba" by Bogdan Giușcă (Bogdan Giuşcă (talk)) - Own work. Licensed under Public Domain via Wikimedia Commons -
While not nearly as apocalyptic as the Triffid plot, an oceanic seaweed has lately been causing major problems for beach managers and tourists along the shores of the Caribbean, Gulf of Mexico, and Eastern US.
Sargassum is a golden-brown alga with gas-filled bladders that buoy up the fronds. The genus includes species that grow, as do most large sea algae, attached to hard bottoms such as Gray's Reef off the Georgia coast. The sargassum weeds causing beach problems are species that proliferate unattached in the open ocean, from South America northward. The central gyre of the North Atlantic, the Sargasso Sea, was named for this pelagic seaweed. Portuguese sailors noted rafts of the stuff as they passed through on the way to fishing grounds off the American coast. 'Sargasso' may have originated from the pea-sized floats that the sailors thought looked like 'salgazo,' little grapes, or from a freshwater aquatic plant called 'sargaco' in Portuguese.
Floating sargassum is an integral part of the open ocean ecosystem in the Caribbean and central North Atlantic. Distinctive species of fish, shrimp and swimming crabs have adapted to live in and around the alga by assuming camouflage patterns mimicking the colors of their seaweed home. Juvenile fish and baby sea turtles shelter beneath clumps of sargassum, hiding from the sharp eyes of predators swimming below or flying above.
The sargassum fish, Histrio histrio, is perfectly camouflaged with color patterns and weedy protrusions to blend into the alga as it waits among the fronds for likely prey to pass by. "Fish4283 - Flickr - NOAA Photo Library" by SEFSC Pascagoula Laboratory; Collection of Brandi Noble, NOAA/NMFS/SEFSC. - NOAA Photo Library: fish4283. Licensed under Public Domain via Wikimedia Commons.
(John and Mildred Teal, authors of 'Portrait of an Island' based on their experiences while living on Sapelo, wrote about sargassum in their 1975 book 'The Sargasso Sea.')
But, in recent years the biomass of pelagic sargassum has exploded. Some of the luxuriant growth of the seaweed is cast up onto shores. Along many coasts, from Barbados to Florida to Texas, thick brown drifts of sargassum have covered beach sands, driving tourists away. Besides the difficulty of walking through the seaweed deposits to the surf, which is often clogged with additional sargassum, the alga stinks as it decays, and swarms of flies hover over the mess.
Causes of the recent mass growth of sargassum weed are uncertain. Since it is a tropical alga, warming ocean waters may be encouraging the spread of the seaweed. Plant nutrients flowing into the Caribbean Sea, resulting from increasing pollution from agriculture, human wastes, and deforestation in the Amazon Basin, are entrained into currents carrying the fertilizers north to the Gulf of Mexico and Atlantic Ocean via the Gulf Stream. The extra nutrients could then lead to sargassum blooms.
Whatever is behind the increase of open ocean sargassum, the phenomenon is certainly causing massive headaches for seacoast tourism.
Fortunately for vacationers along the Georgia coast, the great distance of the sea islands from the Gulf Stream and Sargasso Sea insulates these beaches from a similar sargassum nightmare. The occasional strands of sargassum washed up on the Georgia shore are likely broken off from the species of this seaweed that grow on hard bottoms offshore.