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 metagenome studies.

The Sargasso Sea is a portion of the North Atlantic Ocean that lies within the northern part of the Bermuda Triangle. The name comes 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 remaining Atlantic Ocean by several surrounding strong currents: the Gulf Stream, North Atlantic, Canary, and North Atlantic Equatorial. Found here is a large expanse covered with yellow Sargassum, plastic waste, 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 2 million square miles (5.18 million square kilometers) of water.

The water in the Sargasso Sea is warm, maintaining a high salinity concentration of about 36 parts per thousand (ppt); the temperature in the euphotic (sunlight-penetrated) zone averages up to 72 degrees F (22 degrees C). Hence, although many plankton species and extensive amounts of seaweed float on the surface of the water, the Sargasso Sea still lacks enough nutrients to attract large fish communities. 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 sea turtle species, such as the green turtle (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 minutus). 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 an important research location for marine biogeochemistry. In the early 2000s, the first major metagenomic research was carried out in the Sargasso Sea by J. Craig Venter and his colleagues. They have found many new lineages within the SAR11 clade, 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, Burkholderia, 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. Burkholderia was originally thought to be only a terrestrial bacterium. When this new, similar species was first discovered in the ocean, it was found to contain similar DNA and genes, suggesting genomic transfer. Terrestrial Burkholderia 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 1954, the time-series biogeochemical sampling between November 1957 and 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. In the twenty-first century, 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 microorganisms. 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 been identified as a global hotspot of microbial diversity. Research has reported a decline in floating Sargassum mats in parts of the northern Sargasso Sea since around 2015, while oceanographic studies have also documented the emergence of the Great Atlantic Sargassum Belt, a trans-Atlantic aggregation of floating Sargassum extending from the west coast of Africa to the Caribbean and Gulf of Mexico, suggesting a large-scale redistribution of Atlantic Sargassum populations. Global warming has negatively impacted the Sargasso Sea. According to a 2023 article in Frontiers in Marine Science, forty years of data collected from 1983 to 2023 at the Bermuda Atlantic Time-series Study (BATS) near Bermuda in the North Atlantic Ocean have shown that the Sargasso Sea has become 30 percent more acidic and is 1.8 degrees Fahrenheit warmer than it was forty years ago. The temperature of the sea is higher than it was several decades ago and continues to increase. Oxygen does not dissolve well in warmer waters, which has led to a nearly 7 percent decrease in oxygen in the Sargasso Sea. The burning of fossil fuels has led to carbon dioxide dissolving into the ocean, which can increase acidity. Researchers believed these changes may adversely affect marine life as well as Bermuda’s coral reefs.

Bibliography

Bates, Nicholas R. “The Sargasso Sea Has Become Warmer and Saltier, and the Loss of Oxygen and Ocean Acidification Is Accelerating.” Springer Nature Sustainability Community, 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 6 Mar. 2026.

Bates, Nicholas R., and Rodney J. Johnson. “Forty Years of Ocean Acidification Observations (1983–2023) in the Sargasso Sea at the Bermuda Atlantic Time-Series Study Site.” Frontiers in Marine Science, vol. 10, 7 Dec. 2023, doi:10.3389/fmars.2023.1289931. Accessed 24 Mar. 2025.

Gayle, Damien. “Scientists Warn of ‘Regime Shift’ as Seaweed Blooms Expand Worldwide.” The Guardian, 19 Jan. 2026, www.theguardian.com/environment/2026/jan/19/scientists-seaweed-blooms-expand-worldwide-ocean-pollution. Accessed 6 Mar. 2026.

Giovannoni, Stephen J., et al. “Proteorhodopsin in the Ubiquitous Marine Bacterium SAR11.” Nature, vol. 438, 2005.

Lipschultz, Fredric, et al. “New Production in the Sargasso Sea: History and Current Status.” Global Biogeochemical Cycles, vol. 16, 2002, article 1001.

McKenna, Sheila and Arlo Hemphil. “The Sargasso Sea.” Global Ocean Biodiversity Initiative, www.gobi.org/Our%20Work/rare-2.

Morris, Robert M., et al. “SAR11 Clade Dominates Ocean Surface Bacterioplankton Communities.” Nature, vol. 420, Dec. 2002.

“USF-Led Study Reveals Dramatic Decline in Some Historic Sargassum Populations.” EurekAlert!, American Association for the Advancement of Science, 4 Dec. 2025, www.eurekalert.org/news-releases/1108242. Accessed 6 Mar. 2026.

Venter, J. Craig, et al. “Environmental Genome Shotgun Sequencing of the Sargasso Sea.” Science, vol. 304, 2004.