It was while plunging down following swells through the waters of Southern New England that I had my first encounter with open-ocean sargassum in its natural habitat. I was working on a Sea Education Association ship bound for the continental shelf break to sample a warm-core eddy that had spun off of the gulf stream days earlier. This would have been a fascinating mission in and of itself. Still, I was fixated on a seaweed I knew I might see, somehow unique the world’s oceans over despite millions of years of evolution that could have produced countless other candidates to fill the same niche.
It is hard to overstate the excitement I felt seeing that first golden mat tumbling in the waves. Just to be in the presence of one of the world’s great seaweeds! Sargassum—storied to have mired ships in its dancing windrows and known to support distinctive ecosystems and pelagic nurseries.
Much has been written in recent years about the sargassum that washes ashore to considerable hand-wringing. Blooms of S. natans have been particularly prodigious and left beachgoers, fishers, and sea turtles alike pining for the early-aughts when the rafts of seaweed flooding ashore were predictable and manageable by comparison.
While an imbalance is cause for alarm, it is important to remember not only the rotting and festering piles on beaches but also the plant alive in the ocean. At sea, sargassum floats resolutely on Atlantic currents, weathers storms, and provides shelter to countless fish and crustaceans.
Not only is the balanced ecosystem beautiful, the system out of balance is beautiful in its own way. It is a reminder that sometimes, in spite of us, life finds a way.
Sargassum grows when we pollute the ocean. It is easy, then, to construe it in our heads as monstrous and foul. Living on toxic waste, this weed oozes from the deep to snarl boats and encumber wildlife. Vile sargassum, scourge of the seas, seeks out our sandy places of respite and escape to send up its gossamer tentacles of stench to strangle our olfactory receptors.
While such imaginings are easy, they are wildly afield. They are attractive because they obscure our own accountability and muddle our agency. If a villain must be cast in this story, it is us. The seaweed removes from the water the toxic waste that we live on. The waste is created in service of our own lifestyles and choices (at least in much of the developed world): we use it to grow our economies and houses and egos.
Sargassum, meanwhile, is a dogged member of the global clean-up crew. It is underappreciated, as cleaners often are, but determined. To an extent, the more nitrogen we pump into the ocean, the more seaweed will grow to soak it up. The sargassum heaps on beaches are the ocean’s small way of taking the excess nutrients we have injected and throwing them back in our faces.
When we cannot effectively manage our global soils, they start to leak some of the nutrients that are most critical to terrestrial ecosystems. Some of the nutrients are carried off by rain when concentrations are too high or plants are cleared and unable to stabilize the soil. Some of them escape through our food: we harvest crops, consume the nutrients, and then deposit those nutrients elsewhere when we are done using them, to put it politely. Often, we deposit them into the ocean.
In the ocean, these same important nutrients, in excess, become pollutants. They (indirectly) feed microbes that also consume the oxygen that fish and other animals rely on. Scientists did not beat around the bush in labeling these areas “dead zones.”
Although sargassum only returns a small fraction of the industrial fertilizers and carbon dioxide we dump in the oceans, it feels fitting. The ocean rejects these chemicals and sends them back to us as if to say, “You created these compounds. You want them, don’t you?” Waves pound thousands of tons of nitrogen, phosphorus, and carbon ashore. “Whoops, I think you might have misplaced these.”
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