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Ocean pollution is boosting Sargassum seaweed in the Atlantic

Regions in the Caribbean have seen tons of orange-brown algae called Sargassum washing up on coastlines over spring and summer, in an ‘invasion’ that is getting more severe each year. Is that a bad thing?

At face value, the great span of Atlantic Ocean between Florida and West Africa looks as if it would be completely empty.

Perhaps it would be, if not for the presence of a specific type of algae: Sargassum seaweed. This spiky, orange-brown coloured seaweed is native to the area named after it, the Sargasso Sea, and can be expected to bloom around spring and summertime.

Floating on the ocean surface and pushed along by ocean currents, the seaweed’s unique shape allows it to tangle up into a mat-like structure.

At this point, the Sargassum becomes a sort of floating island, teeming with life in an area sparsely dotted with actual landmasses. Scientists often compare these large seaweed swathes to rainforests, where a myriad of different organisms and tiny animals thrive.

In recent years, scientists – and those living on coastlines – have noticed that the amount of smelly seaweed eventually washing up on their beaches has grown astronomically.

Largest ever mass of Sargassum seaweed drifts toward North America

A possible culprit

It’s no secret that various kinds of ocean pollution have spiralled out of control, significantly changing the landscape of the marine world from top to bottom. As a consequence, the creatures beneath the water are changing too.

Though Sargassum has been around since, well, probably forever, the size of its algal blooms has noticeably skyrocketed since 2011. Now, the largest groupings of Sargassum seaweed floating on the ocean surface can be pictured from space.

With its numbers still rising, researchers at the University of Southern Florida have pointed to various human behaviours as the most likely causes.

Booming agricultural industries on either side of the ocean have allowed water polluted by fertiliser and other man-made chemicals to empty into the Atlantic, fuelling the amount of seaweed that is able to bloom.

Pair that with deforestation activity, which causes higher quantities of nutrient-rich sediment to empty into the ocean, and you have a perfect food system for all kinds of algae to thrive – including Sargassum.

They also suggest that changes in weather patterns, ocean currents, and water temperatures are also contributing to creating the perfect cocktail for more of this seaweed to end up on the coastlines of Florida and neighbouring Caribbean islands.

Until we enforce stricter policies on polluted runoff water globally, it’s likely we’ll see algal blooms continue to grow in size.

Is too much Sargassum a bad thing?

Frankly, the answer to that question depends on who you ask.

Once the Sargassum washes up on the shorelines of popular beaches and swimming spots, it dries out in the sun in huge piles. In the process, it releases hydrogen sulphide.

For the non-chemistry buffs out there, that’s a gas that smells of rotten eggs. As you can imagine, this doesn’t provide an ideal ambience for a relaxing day by the seaside.

While it’s still in the ocean though, an increased abundance of Sargassum seaweed does create a pretty nice situation for marine animals that depend on it.

Those thick, mat-like Sargassum patches are home to a diversity of life while floating along the ocean’s surface. Their dense leaves create a nursery for young animals, including fish, crabs, turtles, and seabirds – many of which can only be found in this area.

The species found here include fish that humans love to eat, including jacks, mackerel and tuna. Also sheltering amongst the leaves are Sargassum shrimp and Sargassum frogfish which are native to this habitat. More species are likely still to be discovered.

And while the seaweed is annoying to the noses of humans dwelling on the coastline, it appears to only harm the surrounding natural ecosystem when it blocks coral reefs from getting enough sunlight.

Otherwise, Sargassum has proven to provide a protective oasis for tiny and rare marine animals, a source of food for seabirds, and can even prevent the severity of coastal erosion.

So while it may not smell or look great once it washes ashore, humans will again have to deal with the consequences of their actions by getting bigger shovels and trucks to clean up the mess.