Sargasso Sea ecology
The Sargasso Sea is a distinctive region of the North Atlantic Ocean, notable for its lack of coastlines and significant presence of floating Sargassum seaweed. Spanning approximately 700 miles wide and 2,000 miles long, it covers over 1.35 million square miles. The sea is characterized by warm waters with high salinity and is often referred to as a "desert among oceans" due to its low nutrient levels, which limit the proliferation of larger fish populations. Despite this, the Sargassum provides an essential habitat for diverse marine life, including several endemic species of invertebrates, fish, and sea turtles, such as the threatened green sea turtle.
Research has highlighted the Sargasso Sea as a critical site for studying marine biogeochemistry, particularly through initiatives like the Bermuda Atlantic Time-series Study. This area is home to a rich microbial community, including notable species such as SAR11 bacteria and Prochlorococcus marinus, which play vital roles in the ocean's carbon cycle. However, the ecologies of the Sargasso Sea are facing potential impacts from global warming, with rising temperatures and changing chemical conditions. Understanding the unique ecology of the Sargasso Sea is crucial for appreciating its role in the broader marine ecosystem and the implications of environmental changes.
On this Page
Subject Terms
Sargasso Sea ecology
Category: Marine and Oceanic Biomes.
Geographic Location: Atlantic Ocean.
Summary: An open ocean area surrounded by strong currents, this biome is the site of important marine research including biogeochemical and prokaryotic meta-genome studies.
The Sargasso Sea is a part of North Atlantic Ocean that overlaps the northern part of the Bermuda Triangle. The name is from the abundant Sargassum seaweeds (dominated by S. natans and S. fluitans) floating on the surface water in the region. They were reported by Christopher Columbus and his crew during their expedition to the New World. The Sargasso Sea is a slow-moving gyre area separated from the rest of the Atlantic Ocean by several surrounding strong currents: the Gulf Stream, North Atlantic, Canary, and the North Atlantic Equatorial. Found here is a large expanse covered with yellow Sargassum, plastic wastes, and occasional shipwreck derelicts (the source of many legends).
The Sargasso Sea is one of the few areas of the world lacking coastlines but designated as a sea; it is approximately 700 miles (1,100 kilometers) wide and 2,000 miles (3,200 kilometers) long, covering an area of at least 1.35 million square miles (3.5 million square kilometers) of water.
The water in the Sargasso Sea is warm, maintaining a high salinity concentration of around 36 percent; the temperature in the euphotic (sunlight-penetrated) zone averages up to 72 degrees F (22 degrees C). For these reasons, even though there are several species of plankton and massive amounts of seaweed floating on the water surface, the Sargasso Sea is still not nutritious enough to attract large communities of fish. The factors of low wind, low nutrients, and high salinity are chief reasons why the Sargasso Sea is sometimes considered a “desert among oceans.”
Flora and Fauna
The Sargassum weed is known to harbor epiphytes (micro and macro), diverse fungi, over 100 invertebrate species, dozens of fish species, and about four seaturtle species—one of which is the threatened green seaturtle (Chelonia mydas). The abundant floating vegetation of Sargassum provides a habitat for several endemic (found nowhere else) species of marine animals, including Sargassum pipefish (Syngnathus pelagicus), Sargassum snail (Litiopa melanostoma), slender Sargassum shrimp (Latreutes fucorum), and the Sargassum crab (Planes minutes). In addition, the deeper reaches that feature drift algae provide critical spawning sites for major eel species including American eel (Anguilla rostrata) and European eel (A. Anguilla).
This generally nutrient-poor, or oligotrophic, sea has been one of the best-characterized oceans in its physical and biogeochemical properties, especially at the Bermuda Atlantic Time-series Study (BATS) site. Since the late 1950s, the Sargasso Sea has been important research location for marine biogeochemistry. More recently, the first major meta-genome research was carried out in the Sargasso Sea by J. Craig Venter and his colleagues. They have found many new lineages for the clade (or family) of SAR11 bacteria, which later were shown to constitute a major proportion of all marine prokaryotes (both bacteria and Archaea) from the major oceans. This bacterium can surprisingly replicate efficiently in a low-nutrient environment, and is one of the smallest self-replicating cells found.
Other microbes sustained here include cyanobacteria, luminous bacteria, Berkholderia, and Shewanella. One of the cyanobacteria, Prochlorococcus marinus, though among the smallest photosynthetic organisms known, is a major phototroph in the ocean and greatly impacts the carbon cycle. Berkholderia was originally thought to be only a terrestrial bacteria. When this new, similar species was first discovered in the ocean, it was found to contain similar DNA and genes, suggesting genomic transfer. Terrestrial Berkholderia bacteria are known to be able to biodegrade a very toxic class of industrial product, the polychlorinated biphenyls (PCBs). Because of this ability, the bacteria have an important ecological and commercial potential for bioremediation, and sequencing this genome may play a major role in environmental protection.
Human Interaction
Beginning with the establishment of Hydrostation S in 1957, the time-series biogeochemical sampling between November 1957 to April 1960 by D. M. Menzel and J. H. Ryther effectively set the foundation for the modern science of marine biogeochemistry. They defined the seasonal cycle of primary productivity, and proposed many profound topics related to global biogeochemistry and global climate change. More recently, genomics research has allowed scientists to find evidence of genes that form the basis of the key chemical processes of ocean-dwelling microbes.
This genetic research has shed light on many new, and as yet unknown, micro-organisms. The Sargasso Sea, once the source for many legends and science fiction, has been a self-supporting environment for unique marine biota including some endemic fish and shells. It has also now been identified as a global hot spot of microbial diversity.
The projected effects of global warming on the Sargasso Sea biome are difficult to predict. It is known that sea surface temperature here has been more or less constantly increasing over the last 300 years; researchers tend to see this as a return to the historic norm, however. Global sea-level rise will affect this oceanic area, but consequences to its biota are unclear. A 2020 study of more than forty years of data on the Sargasso Sea has shown the sea’s carbon dioxide levels are rising as its oxygen levels falls. The sea is also warming and becoming more acidic and salty.
Bibliography
Bates, Nicholas R. “The Sargasso Sea Has Become Warmer and Saltier, and the Loss of Oxygen and Ocean Acidification Is Accelerating.” Springer Nature, 16 Oct. 2020, sustainabilitycommunity.springernature.com/posts/the-sargasso-sea-has-become-warmer-and-saltier-and-the-loss-of-oxygen-and-ocean-acidification-is-accelerating. Accessed 2 Sept. 2022.
Giovannoni, Stephen J., et al. “Proteorhodopsin in the Ubiquitous Marine Bacterium SAR11.” Nature 438 (2005).
Lipschultz, Fredric, et al. “New Production in the Sargasso Sea: History and Current Status.” Global Biogeochemical Cycles 16, no. 1001 (2002).
McKenna, Sheila and Arlo Hemphil. “The Sargasso Sea.” Global Ocean Biodiversity Initiative. http://www.gobi.org/Our%20Work/rare-2.
Morris, Robert M., et al. “SAR11 Clade Dominates Ocean Surface Bacterioplankton Communities.” Nature 420 (December 2002).
Venter, J. Craig, et al. “Environmental Genome Shotgun Sequencing of the Sargasso Sea.” Science 304 (2004).