Sargassum Secrets

Sargassum is the reddish brown grass that floats in the ocean and washes up on the beach, but new research shows it is also a complex island community at sea that is essential to ocean habitats.

WANCHESE — At first glance, the splotches of orange and yellow on the ocean surface are a curiosity. It could be light reflecting off the water or even a piece of floating trash.

But as you draw closer, and individual branches become visible, it becomes clear that the unusual orange and yellow “thing” bobbing on the surface is actually a floating plant.

But it’s not until you jump in the ocean and get close up and under water that you realize the drifting plant forms a unique habitat. It’s a kind of mobile transport habitat for a wide array of marine life. There are countless varieties of large and small fish seeking shelter around this floating island.

Such is the mystery of sargassum.

“Sargassum is important because it supports a lot of different organisms that are trying to survive in the open ocean,” explains Lindsay Dubbs, Research Assistant Professor at the University of North Carolina Coastal Studies Institute. “There are a lot of species that are only found in sargassum, so it adds a lot of diversity to the open ocean. In addition, the sargassum provides a lot of habitat for fish and many of those fish are commercially important species.”

Sargassum, a brown algae found in every ocean except the Antarctic, gets its name from sargazo, a Portuguese word for a type of grape. The men sailing with Christopher Columbus thought the air bladder that keeps sargassum afloat looked like a grape.

Sargassum and the habitat it creates is so important to the pelagic, or open ocean, that it is a protected fish habitat. However, not much is known about it, which is why Dubbs is studying this unique ocean drifter. Her first discovery is that satellite tracking reveals sargassum drifts a long way.

The giant algae originates in the Gulf of Mexico. Ocean currents then transport it to the Gulf Stream, which then carries it up the east coast. Because it is on the surface, sargassum is at the mercy of the wind and waves, which align it in different ways, however its ultimate voyage is controlled by the Gulf Stream.

Along the journey, some of the sargassum simply breaks off and remains floating offshore. It is usually found off the coast of North Carolina from late spring through late fall, or roughly June through November.

Some sargassum gets caught in ocean waves and washes ashore. But the majority of sargassum continues its journey, drifting up the eastern seaboard and then out to the open ocean to what is known as the Sargasso Sea. It is the only sea not bordered by land. It is a giant eddy that has trapped a huge collection of sargassum that stretches for hundreds of miles in the North Atlantic. The sargassum is trapped there because the sea is bounded on all sides by a mix of ocean currents.

While sargassum has been talked about for centuries, it is the push for renewable ocean energy that has scientists taking a closer look at this unique travelling ocean habitat.

Scientists want to know whether the installation of Gulf Stream energy turbines would affect sargassum communities. There would not be a direct interaction; turbines are anchored to the sea floor while sargassum floats on the surface. But the wake generated by the turbines would reach the surface. 

“Turbines wouldn’t be chewing up sargassum, but the wake could affect the nutrient cycling as well as nitrogen fixation,” says Dubbs. “That wake would cause more turbidity and mixing, meaning it might be difficult for the sargassum to get the nutrients it needs in cloudy, swirling water.”

To find out, researchers carefully studied the ocean environment, recording every condition that affects sargassum in the open ocean. Researchers then created mini-ocean environments in the lab. Some sargassum was subjected to a constant wake effect.

So far it appears this unique plant—which floats at the intersection of energy, ecology and the protection of fisheries habitat and endangered species—is more resilient than expected. It doesn’t appear the ocean currents affected the sargassum.

“This amazing complex of bacteria, algae, and larger organisms that you can see with your eye is completely fascinating,” gushes Dubbs. “It is very sensitive overall and extremely sensitive to sources of light, but it is an interesting, intriguing system that hasn’t been studied enough in my opinion.”

Related Resources: