SARGASSO SEA :- THE SEA WITH NO COASTS

The Sargasso Sea is a distinctive area of open ocean situated within the North Atlantic Subtropical Gyre, bounded on all sides by the clockwise flow of major ocean currents. 

The Gulf Stream and North Atlantic Drift form the western & northern boundaries, while the Canary Current forms the eastern boundary and the North Equatorial Current and Antilles Current form the southern boundary. 

As these currents vary, the precise location of the Sargasso Sea is also variable, but it is most commonly situated in the area between latitude 25° and 32° north and longitude 35° and 70° west (Ryther 1956, Coston-Clements et al. 1991).

The Sargasso Sea, located entirely within the Atlantic Ocean, is the only sea without a land boundary. Since this area is defined by boundary currents, its borders are dynamic, correlating roughly with the Azores High Pressure Center for any particular season.

The Sargasso Sea is a vast patch of ocean named for a genus of free-floating seaweed called Sargassum. Sargasso Sea is unique in that it harbours species of sargassum that are 'holopelagic' — means the algae not only freely floats around the ocean, but it reproduces vegetatively on the high seas.

The Sargasso has long attracted the attention of conservationists and scientists because it hosts a rich diversity of wildlife, including leatherback sea turtles, humpback whales, and bluefin tuna. 

The animals eat and take shelter in a seaweed called sargassum, which floats in massive quantities in the area—some say it looks like a golden, floating rain forest—and gives the sea its name. It is a spawning site for threatened and endangered eels, as well as white marlin, porbeagle shark, and dolphinfish. 

Historically, sargassum has been a natural part of the ocean ecosystem, but in the past decade that oasis has blossomed into a nuisance capable of causing serious damage. Sargassum is a golden-hued seaweed, a large macroalgae, that’s continuously whisked atop the ocean’s currents.

Unlike other types of seaweed, such as the kelp that’s anchored to the shallow ocean floor, sargassum is adapted to life on the open sea and lives solely in floating patches. 

Much of it can be found in the western Atlantic’s Sargasso Sea, which is such an important ocean habitat to so many marine creatures it’s been called the “golden floating rainforest.” 

The sea reaches depths of 5,000–23,000 feet (1,500–7,000 m) and is characterized by weak currents, low precipitation, high evaporation, light winds, and warm, saline waters, all combining with the lack of thermal mixing to create a biological desert largely devoid of plankton, a basic food supply for fish.

The Sargasso Sea, which encompasses the Bermuda islands, was first mentioned by Christopher Columbus, who crossed it on his initial voyage in 1492. The presence of the seaweed suggested the proximity of land and encouraged Columbus to continue. 

Although other drift algal habitats do exist, diversity in the Sargasso Sea is greater for two reasons. First, research has shown that both density and diversity of associated organisms is linked to the greater area and thickness achieved by the Sargassum mats (Moser et al. 1998, Casazza and Ross 2008). 

Secondly, diversity is enhanced because some of the Sargassum originates in the Gulf of Mexico, working its way up to the Sargasso Sea via the Gulf Stream (Gower and King 2008) and collecting additional organisms along the way (Stoner and Greening 1984). 

There is a rich community of small invertebrates at home amongst the Sargassum mats, with more than 145 invertebrate species having been recorded in association with Sargassum (Morris & Mogelberg 1973). 

Many of these species are highly adapted, having evolved coloration and appendages that resemble the Sargassum and give them the additional advantage of camouflage among the floating seaweed (Sterrer 1992). 
Sargassum also provides habitat for over 100 species of finfish, including the endemic Sargassum angler fish and Sargassum pipefish, Syngnathus pelagicus (SAFMC 2002, Casazza and Ross 2008).

In addition, 23 species of seabirds have been observed foraging in association with Sargassum, with bird density being much greater in areas with Sargassum than in areas without (Haney 1986). Sargassum, once it sinks, also provides a food source for deep water and benthic communities below (Schoener and Rowe, 1970, Butler et al. 1983). 

An exception to this is the area known as the Corner Rise Seamount Complex (Vinni Chenko 1997). Explorations of these seamounts during 2005 found areas of rich deep water coral habitat, as well as areas exhibiting extensive damage caused by bottom trawling that occurred between 1976 and 1996 and showing little evidence of recovery (Waller et al. 2007).

The annual migration of humpback whales past Bermuda and through the Sargasso Sea provides opportunities for local whale watching eco-tours (Stone et al. 1987). There are also various indirect threats associated with ship traffic and exogenous contaminants. The Sargasso Sea has a high volume of maritime traffic and there is a risk that harmful substances may be discharged in the area by transiting ships (SAFMC 2002). 

The encircling currents that concentrate the Sargassum within the Sargasso Sea also serve to concentrate pollutants and floating debris. Bermuda’s marine environment has strong linkages with the Sargasso Sea and the pelagic fisheries depend on it. 

Given the migratory nature of many of the animals that depend on the Sargasso Sea, the coastal marine environments and fisheries of many jurisdictions around the wider Atlantic basin are likely to have stronger linkages to this area, sometimes called “the cradle of life in the Atlantic”.

Most of the Sargasso Sea is in the high seas, and only a small portion is under national jurisdiction, within the Exclusive Economic Zone of Bermuda. Although the high seas encompass 64% of the world's oceans, at present there is no international legal mechanism for designating marine protected areas outside of national jurisdictions.

 SARGASSUM BLOOM 

In June 2018, scientists recorded 20 million metric tons of seaweed, a 1,000% increase compared with the 2011 bloom for that month. A recent study examining the chemistry of seaweed from the 1980s up to 2019 offers the strongest evidence that, water coming from city and farm runoff has been a major contributor to expansion of the so-called Great Atlantic Sargassum Belt, which now stretches for nearly 9,000 kilometers. 

Sargassum has existed for about 30 million years, but blooms of this massive size are a rising concern. Dangerous algal blooms like red tides are often fueled by pollution, and sargassum is no different.  

When farmers spray fertilizers on land, they release chemicals laden with nutrients to help crops grow. When those fertilizers leak into rivers and make their way out to sea, they release the same plant-growing nutrients onto sea plants, unintentionally giving them a boost. 

As it decomposes it releases a gas called hydrogen sulfide that smells like rotten eggs. That gas can irritate the eyes, nose, and throat, according to the Florida Department of Health.

The seaweed, in excess, can also harm the ecosystem. The thick, tangled mass can smother coral reefs and mangroves, and tiny creatures living in the land like crabs and clams. 

The high seas account for approximately half of the world’s ocean. These waters, beyond the national jurisdiction of any country, are some of least protected and most important in the world. The Sargasso Sea Commission is committed to fulfilling a stewardship role for this distinctive area of the ocean. 

As global temperatures rise, scientists believe that rainstorms are intensifying in certain areas of the globe, including over the Amazon. Those storms are increasing the frequency of extreme flooding, which likely is pushing more nitrogen-rich runoff out to sea. Experts note that peak Amazon River flooding pushes a plume of nutrients hundreds of kilometers out to sea in March and April, coinciding with major sargassum blooms.

Scientists have also theorised that dust from the Sahara Desert, along with smoke and ash, could be contributing to the seaweed boom. As the particles are blown westward over the Atlantic Ocean, they run into clouds and get rained down as fertilising iron and phosphorus deposits in the water. Treating sewage and stopping deforestation, that’s the only way to control it.