What's to Know About the Seaweed Epidemic

by Ron Paulick

Vast mats of seaweed on the beaches … my first real experience with this weed was in Belize in 2007. We were visiting this lovely country on vacation after many trips to Mexico ,where my wife, Kathy, and myself never saw this on the beaches and it was a new experience for us. It looked dirty and, after being cleared away in heaps, had an awful odor. As unsightly as it was, it made me wonder what other uses this weed might have and why it gathers like it does to clutter our beaches.

Most mornings in Akumal, and on every beach on the Caribbean coastline, as well as the outer islands and many other areas, the seaweed is seen on the beaches then cleaned up (sometimes). Then the whole scenario is played out the next time the waves roll in, to some degree.

The main source of the sargassum found throughout the Gulf of Mexico, Atlantic Ocean and Caribbean Sea is the Sargasso Sea. This is a region in the middle of the northern Atlantic Ocean with a mat of sargassum approximately 3 million square km in size, an area three times the size of South Africa! This expanse is called the Sargasso Sea. Originally named by Christopher Columbus as "Sargaco," he called it this due to the resemblance of the air bladders on the seaweed, that keep it afloat, to little grapes. The Sargasso Sea has the Gulf Stream to its west, the North Atlantic Current to the north, the Canary Current on the east, and the North Atlantic Equatorial Current on the south. This system of currents forms the North Atlantic Subtropical Gyre.

These prevailing currents surrounding the Sargasso Sea work to keep the sargassum centrally located. However during this time of year, strong winds, storm activity and currents that turn in a spiral tend to disperse the weed throughout the region. As currents mix with the edges of the Sargasso Sea, parts of the larger sargassum mat are broken away. The currents carry the seaweed along, eventually dispersing it westerly towards the Caribbean islands, where the local currents wash it to shore. This is a naturally occurring cyclical event. Unfortunately, once ashore sargassum is very slow to decompose, resulting in foul smells of rotting vegetation, fish and flies, which makes it aesthetically unpleasant to beach-going patrons and land owners.

Since July, Mexico alone has committed in excess of $9 million to clearing its valuable money-making vacation waterfront of the problem. To clear one popular stretch of beach, the government of Cancun offered petty criminals a way out of the drunk tank in exchange for their help with its sargassum problem. Over a small period of time, they ended up clearing over 500,000 cubic feet of seaweed—which translates to more than 1,000 truck loads. The collected floating mat of refuse can then be used to shore up sand dunes or be processed back into fertilizer.

In addition, the Navy of Mexico sent its oceanographers on a trip out to try and track the weed while it is at sea, as a first step to keeping it from reaching beaches. There are plans to use hydraulic pumps or to put up floating barriers to hold off the sargassum but, so far, they are only theoretical and time will tell if anything comes of this.

So what is this seaweed we call sargassum, how did it get that name, and what else should we know about this often annoying and unsightly problem that plagues us?

The weed is called Sargassum muticum and is only one form of this particular plant. It's a large, brown, bushy-type seaweed. In some habitats it can grow up to 36 feet high. It is held to the bottom by a base that attaches itself to a rocky bottom; from there the plant has many branches with leaves. These branches sport small leaf-like blades with toothed margins bound together with small, round, gas-filled floats on tiny branchlets, which make it float after release. The overall appearance of this seaweed is of an olive-brown, wiry, yet bushy plant.

The plant has a rather long lifespan (3 to 4 years) and high growth rate (1/2 inch per day), which makes it able to outlast many others. This seaweed has a very efficient reproduction, a quality which, along with a long life, outcompetes many native seaweed species and becomes a dominant invasive alga in much of its range. The plant can reproduce in multiple ways. The reproductive fronds are even able to continue spreading once detached, a mechanism which allows for long dispersal distances. Lost fronds can also continue to grow into new plants, forming dense floating mats on the surface of the sea, which is what we see on our shores throughout the year. It is believed that wave action, storms and global warming are contributing to the plants coming loose from their rooted bases, and this is why they come floating to our shores in vast mats of green islands.

As it turns out, there are some uses for the weeds after the cleanup, as well as harvesting them in their natural state for food, which is done in many places throughout the world. So let's take a look at that.

Sargassum mats are often harvested while floating, being used in medicine, for fertilizer, and also as food for animals and fish bait. Asian medicine makes use of various species of sargassum to treat afflictions such as fever, high cholesterol, and skin ailments, and many coastal populations use the weed as a food source. It is reported to taste very bitter but is high in minerals and nutrients. The weed can be made more edible through different preparation techniques. Kelp certainly can be used as food. Also, many seaweeds and kelps are used as thickening and stabilizing agents in the food industry.

However, it is not advisable to collect it from the beaches and use it for foods or medicine. The reasons for this are very obvious once you consider a few facts. First, the floating mats become home to some smaller species of smaller fish , shrimps , nudibranchs and turtles. It also becomes a haven for seabirds while it floats, and it picks up flies and other items on its journey. So as it hits the shoreline, some of these other elements get caught up and, upon becoming stranded, this mishmash of things begins to break down, which creates the foul smell that comes off the heap. The actual weeds don't really smell bad as they dry;, it is the other elements that cause the worst part of the smell, which is why it is best that we clean it up where we can.

See this link for more on medicinal uses: www.seaweed.ie/uses_general/medicinaluses.php

There have been other invasive species we have dealt with in the past and present such as lionfish, which we have found some use for and have tried to reduce its presence while making them useful in our daily lives. As far as I can see, this may be the best alternative for the sargassum problem.

Through food and medicine uses, as well as drying the plants to be used as fertilizer, which is happening in other areas of the Caribbean as a for-profit business, we may be able also to profit from the matter at hand. There are also fuel experiments happening to see if we can find other uses for this noxious pest and, if we continue to expand our thinking, who knows what other products may be able to be made using the seaweed that is an eyesore right now.

To summarize, the mats of sargassum weed washing up on Caribbean shores are a natural phenomenon and not a direct result of pollution. Also, the sargassum ecosystem is one of the most unique and important in the world. The weeds will eventually break down or be taken away by wave action, but in areas where it is aesthetically unpleasant, it can be trucked away to an appropriate landfill area. This problem is here for now but will not go on forever.

When life hands you lemons … make lemonade. The next time you smell sargassum, you may be inhaling the smell of money.

Editor’s Note: we’ve included this dated article to give readers an idea of what this problem was like when it first started to Mexico’s attention. For more up to date information try Sargassum Monitoring.