How old is the sargasso sea

While there are many different types of algae found floating in the ocean all around world, the Sargasso Sea is unique in that it harbors species of sargassum that are 'holopelagic' — this means that the algae not only freely floats around the ocean, but it reproduces vegetatively on the high seas.

Other seaweeds reproduce and begin life on the floor of the ocean. Sargassum provides a home to an amazing variety of marine species.

Turtles use sargassum mats as nurseries where hatchlings have food and shelter. The boundaries of this sea are vague, defined not by landmasses but by five major currents that swirl in a clockwise embrace around Bermuda. Far from any mainland, its waters are nutrient poor and therefore exceptionally clear and stunningly blue. The seaweed may seem unremarkable at first glance—just bunches of drifting plant matter—but as Lapointe has helped illuminate through his work, sargassum is the basis of a complex ecosystem that nurtures a stunning array of marine life.

It serves as a mobile shelter and a movable feast. He wanted to figure out where the weed comes from, how it moves, what it sustains, and what sustains it—and to unravel the complex relationship sargassum has with other forms of marine life, from seahorses to great white sharks. Only by learning about this vital resource, he says, can we protect it from potential threats, such as ocean acidification and pollution. During the past few years, sargassum has been making the news not as life-giving manna but as a scourge, mounds of it fouling beaches in the Caribbean and Mexico.

Early explorers noted that the air bladders keeping the seaweed afloat reminded them of a grape they called sargazo. Sargassum originates in nutrient-rich zones close to the coast of the Americas, particularly in the Gulf of Mexico. Oceanographer Sylvia Earle, who helped initiate an effort to make the Sargasso Sea the first high seas marine protected area, likens sargassum to a golden rainforest.

Sargassum brings to my mind a floating reef or even a marine grassland—a Serengeti of the sea. Its tangled tresses support an astonishing diversity of organisms that hide in and feed off the weed—the larvae and juveniles, according to one study, of different species of fish, as well as hatchling sea turtles, nudibranchs, seahorses, crabs, shrimps, and snails. The seaweed in turn is nourished by the excrement of these organisms.

Larger creatures such as fish and turtles find plenty to eat amid the sargassum, and they attract bigger predators—triggerfish, tripletails, filefish, mahi-mahis, and jacks, on up the chain of life to sharks, tuna, wahoos, and billfish. Tropic birds, shearwaters, petrels, terns, boobies, and other birds of the open ocean roost and forage on sargassum mats.

As a consequence of this life unmoored, the translucent gold- to amber-colored mats exist at the whim of the winds and currents, pulled apart in storms and reassembling in calmer seas, their edges locking together like Velcro. The weed masses vary in size from several miles long to pieces no bigger than your hand. The teeming life associated with sargassum must constantly adjust to the coming together and breaking apart of the nurturing islands.

The Sargasso Sea has long been associated with mystery. Eighteenth-century sailors referred to this part of the Atlantic as the horse latitudes because, the story goes, ships would get becalmed there and have to dump their horses overboard as freshwater supplies dwindled.

A recent paper by MBARI researcher Crissy Huffard and others shows that in and this animal community was much less diverse than it was in the early s, when the last detailed studies were completed in this region. During three cruises in and , Smith's team steamed across the Sargasso Sea and used dip nets to collect samples of Sargassum seaweed and its associated animals at six different locations.

They then classified and counted all the animals at each site. The researchers chose their sampling and counting methods carefully so that they could compare their results with previous surveys that had been conducted in and in the same general part of the Sargasso Sea.

Amazingly, the researchers could find no other studies between and during which scientists had systematically counted the Sargassum animal communities in this area. When the team analyzed the data from the recent cruises, they were surprised to find that animal communities in the Sargassum rafts were significantly less diverse than those observed in the s.

For example, 13 species of animals in several different groups worms, nudibranchs, crustaceans, and sea spiders were observed in the historical samples but were missing from the recent samples. Unfortunately, the researchers did not have enough data to determine whether the differences they observed were the result of long-term shifts in ocean conditions in the Sargasso Sea or natural variations from place-to-place, month-to-month, or year-to-year.

The authors note that ocean conditions were much cooler than normal during February and that there were large differences in animal communities observed just six months apart, in August and February So it is possible that this area routinely sees large natural variations in the types of animals present. As Huffard put it, "If this is a long-term decline [in biodiversity], then it is a very significant one.

But we don't know if this is part of the natural variability in this community. Previous studies indicate that much of the seaweed that ends up in the Sargasso Sea originates in the Gulf of Mexico and is carried into the central Atlantic by the Gulf Stream and other currents.

This suggests that, in addition to local ocean conditions , large-scale variations in ocean currents and conditions in the Gulf of Mexico could affect the animals in Sargassum communities. To tease out these confounding variables, Smith and Huffard are hoping to conduct a series of follow-up expeditions to the Sargasso Sea.

They plan to focus on the northern part of the Sargasso Sea, near Bermuda, where more detailed historical data are available. They are presently working on a proposal for a grant that would allow them to analyze satellite imagery and collect field samples twice a year for three years. The proposed study would show how much year-to-year variability is normal for this region. At first glance, the animals that live in Sargassum rafts seem isolated from the rest of the world.

But, like the seaweed they live in, these animal communities have many links to larger ocean food webs. For example, Sargassum animals provide essential food for sea birds, sea turtles, and bluefin tuna—all long-distance migrators. In fact, Sargassum rafts have been designated as "essential fish habitat" by the South Atlantic Fishery Management Council.

The world's oceans are changing, with water temperatures and ocean acidity on the rise and oxygen concentrations on the decline. At first glance, the animals that live in Sargassum rafts seem isolated from the rest of the world.

But, like the seaweed they live in, these animal communities have many links to larger ocean food webs.

For example, Sargassum animals provide essential food for sea birds, sea turtles, and bluefin tuna -- all long-distance migrators. In fact, Sargassum rafts have been designated as "essential fish habitat" by the South Atlantic Fishery Management Council.

The world's oceans are changing, with water temperatures and ocean acidity on the rise and oxygen concentrations on the decline. In the Sargasso Sea, as in many other locations, detecting the biological effects of these long-term trends is a formidable challenge because animal communities can vary dramatically over short time periods.

This study shows that animal communities in the Sargasso Sea are definitely changing. The next step is to find out why. Note: Content may be edited for style and length. Science News. Journal Reference : C. Huffard, S.