Here’s a former article of mine, about Sargassum weed. I wrote it for Florida Wildlife Magazine.
Sargassum is common in Florida, and is often washed up on the beach, anglers look for it offshore because big game fish often hide underneath it. You’re going to be hearing a lot about Sargassum in the near future; warming ocean water and nutrients washed off the land will be soon making it a problem on Southern and Caribbean seashores. It is already appearing in quantities where it is becoming a nuisance, and in some cases a health hazard. And when it dies and rots on the beaches, the biomass decomposing becomes a major problem. The sad thing is its not just the weed that dies, but the rich biological community that has adapted to living in it, How sad. How very very sad.
Read about the bloom here:
When I was in high school I had the good fortune to be awarded a National Science Foundation grant to spend a summer as an intern at the Cape Haze Marine Laboratory, then located in Sarasota, Florida. The laboratory’s director, Dr Eugenie Clark, specialized in shark biology and most of the lab’s activities centered about these fascinating creatures. The other interns and I often went along on the collecting boat’s trips to visit the big trot lines set well offshore to catch the occasional bull, lemon or tiger shark. The trots were long lines anchored to the sea bottom at one end and with a float at the other so they could be recovered, the fish harvested and the hooks rebaited. It was an exciting job and every effort was made to bring them back alive to the lab for behavioral studies. Those that didn’t survive a night on the lines were recovered and later dissected to support a variety of ongoing research programs.
It was a long ride to where the skipper had set the trots and to pass the time on the way out and to add to the educational experience Dr Clark suggested we collect some sargassum, or gulfweed, and inventory the small creatures that made it their home. Although most common in the Sargasso Sea, that part of the Atlantic roughly coinciding with the infamous Bermuda Triangle, the gulfweed is often found floating in Caribbean and Gulf waters, as well as far north as New England. We had no trouble locating some, and the captain slowed down alongside a floating mat of it and we brought it aboard and threw it into a big collecting pan half full of fresh sea water. The interns and graduate students clustered about it and and gradually began removing the weed, shaking it out carefully so that all the tiny critters that made their home in it fell away and stood out in contrast against the white porcelain.
It was a revelation to me. The weed was the home of a thriving community of tiny animals, crustaceans and molluscs and other little beasties, all camouflaged to perfectly match the mottled yellow-brown of the weed and textured and shaped to blend in perfectly. The floating mats were a little world populated by bizarre and grotesque inhabitants perfectly adapted to living on it and in it as the plants drifted on the lifeless desert of the deep blue sea. I had never imagined this was all around me. I was a Florida boy and was very familiar with sargassum; it was a normal part of going offshore fishing or a day at the beach. The weed tickled and itched if you brushed against it in the water and collected in piles along the beach to dry out in the sun. It fouled fishing tackle and got tangled in outboard motors; at worst, a minor nuisance, at best, part of growing up on the water on the Gulf coast. I knew that game fish like dolphin (Coryphaena hippurus) patrolled the weed in search of bait fish that huddled in the shadow of the plant as it floated in the hot sun. Fishermen knew this too, and liked to troll by the mats in the hope one of these monsters would dart out and take their lure. But in spite of my long familiarity with the plant, I had never guessed that it was more than just a nondescript piece of vegetation. I had never imagined it as an entire community–sargassum was a planet all its own and it was inhabited by a multitude.
Along with tiny fish, crabs and shrimp and other assorted creepy-crawlies, the weed also has its resident monster: perfectly exposed and naked in the white collecting pan was the alpha predator that dominated this tiny world. The sargassum fish, Histrio histrio, is small, at most eight inches, and perfectly harmless to us, but it is as fierce as it is ugly. One of the tribe of anglers, it is a squat little creature that prowls around the weed devouring everything it can find smaller than itself, including its own young. Fantastically colored and shaped to match the weed, it is a clumsy swimmer that prefers to crawl about the stems on stubby fins, attracting its prey with a fleshy lure on top of its head. It’s skin is not only mottled and spotted to look like gulfweed, its body is also adorned with lobes and flaps and warts that simulate the shapes of the plant and the multicolored colonies of algae and corals and other encrusting organisms that have evolved to flourish on it. Like a chamaeleon, the little fish can also change the color of its skin to help it blend in. I know now the sargassum fish is quite common (it is prized by aquarium hobbyists) but I had never heard of it before in spite of my long familiarity with its home environment.
The genus Sargassum is a widespread and common set of related brown algae, found in all the world’s oceans. Many species live rooted to the ocean floor, a few float freely on the open sea. As a young sailor crossing the the wide Pacific on a destroyer I remember seeing the great mats scattered across the endless blue, but I never got a very close look at it. The Atlantic cousins include two closely related and similar species, S. natans and S. fluitans, and their habitat is the center of the great clockwise gyre of ocean currents that dominate the Atlantic between Africa and North America. At the center of this planetary whirlpool floating objects tend to collect and this creates the ideal conditions to maintain a stable environment for these remarkable algae. The organism is perfectly adapted to this desolate sea and it forms, as we have seen, a place where others have joined with it to exploit this harsh place. Both floating forms lack roots or holdfasts but have developed tiny floats, little gas-filled bladders, to keep it at the surface near the life-giving sun. Their name originates from these floats, which resemble a common form of Portuguese grape of that name, and it was so named by the early mariners of that seafaring nation. Supposedly, early sailors were terrified of the weed, afraid that their ships would become entangled and helpless. This is not very likely, the mats are usually small, under a few yards across, and generally several hundred feet apart; sometimes, under the influence of the wind, they arrange themselves in long strings miles long, but certainly not dense enough to trap a small yacht, much less a ship. A small sailing vessel might occasionally get some sargassum entangled in her rudder, but it would have been infrequent, and easily remedied. Still, one can’t blame the first sailors penetrating these seas, seeing mile after mile of floating weed for weeks, even months at a time, it must have given them just one more thing to worry about.
Vagaries and eddies in the current help disperse the gulf weed into Florida waters and it can be found on both coasts of the state. Rafts of it get caught in the Gulf Stream and move north along the North American coast until the water cools and kills it and its cargo of hitchhikers. The mid-ocean gyre that is the heart of the Sargasso Sea is one of the largest environments on the planet, several million square miles of very deep ocean, but it is not a hospitable place. Very little lives there and there is not much to support life or even give it a place to make a stand. Any floating object quickly becomes an oasis in this desert, from driftwood to styrofoam cups, and once things get swept into the whirlpool they tend to stay. The gulfweed is nature’s exception, and over immense time life has evolved to seek it out and its shelter. Many organisms have become associated with it, such as the sargassum crab (Portunus Sayi), the sargassum sea spider (Endeis espinosa), and the tiny sargassum snail (Litiopa melanostoma), just to mention a few. All have evolved habits and appearance to help them live there. Many of these creatures don’t even look like animals, such as the bryozoans, corals, and colonial ascidians that encrust the weed and feed off the thin plankton soup the raft rides in. There are visitors here too, the algae mat provides shade and cover from aereal attack for small fish that rest under it. It is said that the weed also provides sanctuary for young sea turtles until they become large and mobile enough to survive in the open and it is known that the plant plays a role in the development of eel larvae. Traveling through the Sargasso Sea on a small boat is a particularly moving experience: the floating island universes of sargassum are spaced about as far apart, relative to their size, as are the galaxies of deep space. It’s a sobering thought, and a reminder that the patterns of nature tend to repeat, but always with exquisite variations.
Many years after my first encounter with the sargassum fish, I found myself once again sailing the waters of my home state. I was on my honeymoon and my new bride had accompanied me on a fishing trip to the Florida Keys. She was a Pittsburgh girl and this was all new and wonderful to her. I pointed out the clumps of weed floating about the boat, and asked the skipper to come alongside one so I could bring it aboard. Scooping it up along with some water, I dumped it all into a large plastic bait bucket where I proceeded to separate and shake out the weed, leaving it on the deck but allowing its living cargo to remain in the bucket. It was a roundup of the usual suspects, tiny crabs, shrimp, fish, and shells, and eventually, when I least expected it, a full grown sargassum fish! With its splendid camouflage it had almost gone unnoticed. I was totally surprised, I had not expected to get lucky like this twice in my life–you don’t often get to catch fish with your bare hands! After admiring the befuddled passengers in the bucket, we carefully placed the weed back in the sea and poured the contents of the bucket on top of it, so they too could resume their journey.