Weedlines: A Sargassum Research Blog

Microplastics and Sargassum


Much of the debris we find are in the form of single use items like this floss pick.

Marine debris is defined as any persistent solid object that is manufactured and disposed of into the marine environment (intentionally or unintentionally). The most dominate form of marine debris is plastic (60- 80%). Plastics are easily moldable, inexpensive to produce, and durable. Their production has continually increased since the 1950s because of their popularity in the consumer world. They have a long life because of their resistance to degradation and much of it ends up in landfills, and in many cases, the ocean. As plastics float in the ocean, they gradually break down because of solar radiation, physical processes, and biodegradation. From this, smaller pieces of plastic form known as microplastics, which are pieces smaller than 5-mm in size. Microplastics can be classified as primary plastics, which are raw and manufactured at a small size (for example, microbeads), or secondary plastics, which are small pieces broken off larger pieces of plastic (for example, small chunks of plastic broken off a discarded bucket). Because many plastics are positively buoyant, they accumulate at the ocean’s surface.


Plastics associated with floating Sargassum habitat in the Gulf of Mexico.

“The only explanation which can be given, he says, seems to me to result from the experience known to all the world. Place in a vase some fragments of cork or other floating body, and give to the water in the vase a circular movement, the scattered fragments will unite in a group in the center of the liquid surface. that is to say, in the part least agitated.”

–Excerpt from Jules Verne’s book Twenty Thousand Leagues Under the Sea, 1873.

As Jules Verne describes so eloquently, any floating bodies in the ocean tend to group together in areas where water masses meet or physical ocean processes occur because of circular current movements. This means that both natural biological floating organisms or communities and man-made debris interact in the marine environment. One natural floating substrate that interacts with marine debris and floating trash is Sargassum, or Gulf weed.


“While sampling the pelagic Sargassum community in the western Sargasso Sea, we encountered plastic particles in our neuston (surface) nets.”

–Excerpt from an article, Plastics on the Sargasso Sea Surface, by E. J. Carpenter and K. L. Smith from the journal of Science, March 17, 1972.


Plastics found within the guts of fishes associated with Sargassum. Top: microplastic fibers. Bottom: blue chunk of microplastic.

Plastics have been evidenced in this floating algal community since the 1970s, but little is known about how plastics affect this community. Because this community is so diverse and supports a large number of fishes at varying life stages (larvae, juveniles and adults), there is potential for microplastics to have some kind of interaction with these associated fishes. These small pieces could be mistaken for food and be eaten which could potentially cause internal damage or possibly transmit anything attached to them such as toxins, bacteria, and maybe even viruses. Understanding interactions between microplastics, Sargassum habitats, and associated fishes can help us recognize what types of impacts microplastics could have on this diverse community.

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