Under the weed, life abounds

A frog fish, the size of a thumbnail and camouflaged in the streaky brown colour of sargassum, lives its entire life within the weeds.

Sargassum may be a scourge to tourist-based communities when it washes ashore, but on the open ocean it is home to a weird and wonderful community of unusual creatures.

The large floating mats of algae provide shelter for juvenile fish, eels and sea turtles. Flying fish lay their eggs amid this tangled mass. A vast cast of eclectic critters, like the thumbnail-sized sargassum frog fish, live their entire lives within the weed.

Underneath, dolphinfish school in the shadow of these floating forests.

While the proliferation of sargassum across the central Atlantic and Caribbean in recent years has undoubtedly been bad for some coastal communities, whether this upsurge is bad for the natural world is a more complex question.

It is true that clogged-up beaches and inlets have created problems for nesting sea turtles and their hatchlings.

But offshore, in the wide expanse of the Atlantic, mats of sargassum are an oasis for marine life.

“Although it is presenting humans with many problems when it washes ashore, while at sea it is one of the most dynamic and significant marine environments,” says Jim Franks, senior research scientist at the University of Southern Mississippi’s Gulf Coast Research Laboratory.

Captain Nemo and the Sargasso Sea

Sargassum is typically found in the Sargasso Sea. The body of water is unique in nature because it has no land boundaries and is bordered instead by a powerful system of circulating currents in the North Atlantic around Bermuda.

Perhaps one of the most eloquent descriptions of the area and its eponymous floating weed comes from Jules Verne in his classic 19th century novel, ‘20,000 Leagues Under the Sea’, about the voyage of the Nautilus submarine.

“Such was the region our Nautilus was visiting just then: a genuine prairie, a tightly woven carpet of algae, gulfweed, and bladder wrack so dense and compact a craft’s stempost couldn’t tear through it without difficulty. Accordingly, not wanting to entangle his propeller in this weed–choked mass, Captain Nemo stayed at a depth some meters below the surface of the waves.”

“It is more than a habitat; it is an entire ecosystem in the open ocean.”

A wide variety of animals rely on sargassum for food, shelter and habitat, says Franks, whose lab was among the first research groups to identify the massive new bloom of this macro algae that is fuelling the inundation of Caribbean beaches.

Analysis by the University of South Florida has since demonstrated that sargassum, which barely registered on satellite imagery in the central Atlantic prior to 2010, exploded to the point where an estimated 20 million tons of it, spanning 5,500 miles of ocean, were recorded in 2018.

The question that researchers are now trying to answer is if this explosion of new habitat may bring with it an accompanying explosion of marine life.

“That is something we don’t fully understand yet,” says Franks.

Marine organisms typically found in clumps of sargassum in its natural habitat, the Sargasso Sea surrounding Bermuda, are showing up in the new blooms further south.

“We don’t know what impact this is having on mahi mahi or sea turtles, for example. It is something that we really need to study,” Franks says.

While he acknowledges that much of the research around the new sargassum bloom will focus on how to stop or suppress it, Franks believes there is scope to study its impact on marine life.

“We realise the hardship that this is bringing to many people, but this is also an extremely important habitat,” he added.