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''Sargassum'' is a genus of brown (class
Phaeophyceae Brown algae (singular: alga), comprising the class Phaeophyceae, are a large group of multicellular algae, including many seaweeds located in colder waters within the Northern Hemisphere. Brown algae are the major seaweeds of the temperate and po ...
) macroalgae (
seaweed Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of '' Rhodophyta'' (red), ''Phaeophyta'' (brown) and ''Chlorophyta'' (green) macroalgae. Seaweed species such as ...
) in the order
Fucales The Fucales (fucoids) are an order in the brown algae (class Phaeophyceae). The list of families in the Fucales, as well as additional taxonomic information on algae, is publicly accessible at Algaebaseref name="Guiry and Guiry">Guiry, M.D. and ...
. Numerous species are distributed throughout the temperate and tropical
ocean The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...
s of the world, where they generally inhabit shallow water and coral reefs, and the genus is widely known for its planktonic (free-floating) species. Most species within the class Phaeophyceae are predominantly cold-water organisms that benefit from nutrients upwelling, but the genus ''Sargassum'' appears to be an exception. Any number of the normally
benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...
species may take on a
planktonic Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...
, often
pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...
existence after being removed from reefs during rough weather; however, two species (''S. natans'' and ''S. fluitans'') have become holopelagic—reproducing vegetatively and never attaching to the seafloor during their lifecycles. The
Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...
's
Sargasso Sea The Sargasso Sea () is a region of the Atlantic Ocean bounded by four currents forming an ocean gyre. Unlike all other regions called seas, it has no land boundaries. It is distinguished from other parts of the Atlantic Ocean by its charac ...
was named after the algae, as it hosts a large amount of ''Sargassum''.


History

''Sargassum'' was named by the Portuguese sailors who found it in the
Sargasso Sea The Sargasso Sea () is a region of the Atlantic Ocean bounded by four currents forming an ocean gyre. Unlike all other regions called seas, it has no land boundaries. It is distinguished from other parts of the Atlantic Ocean by its charac ...
. They called it after the wooly rock rose (''
Halimium lasianthum ''Halimium lasianthum'', the Lisbon false sun-rose or woolly rock rose, is a species of flowering plant in the family Cistaceae, native to the Iberian Peninsula (Portugal, western Spain and southwestern France) and Northwest Africa (Morocco). It ...
'') that grew in their water wells at home, and that was called ''sargaço'' in Portuguese ()Gómez de Silva, Guido 1988. ''Breve diccionario etimológico de la lengua española.'' Fondo de Cultura Económica, Mexico City, , p. 627. - from the Latin ''salicastrum''. The
Florida Keys The Florida Keys are a coral cay archipelago located off the southern coast of Florida, forming the southernmost part of the continental United States. They begin at the southeastern coast of the Florida peninsula, about south of Miami, and e ...
and mainland South Florida are well known for the high levels of ''Sargassum'' covering their shores. Sargassum or gulfweed was observed by Columbus. Although the seaweed acquired a legendary reputation for covering the entirety of the Sargasso Sea, making navigation impossible, it has since been found to occur only in drifts. ''Sargassum'' species are cultivated and cleaned for use as an herbal remedy. Many Chinese herbalists prescribe powdered ''Sargassum''—either the species ''S. pallidum'', or more rarely,
hijiki (''Sargassum fusiforme'', syn. ''Hizikia fusiformis''), sometimes called hiziki, is a brown sea vegetable growing wild on rocky coastlines of East Asia. Hijiki has been a part of the Japanese culinary sphere and diet for centuries. It is ric ...
, ''S. fusiforme''—in doses of 0.5 gram dissolved in warm water and drunk as a tea. It is called zh, c=海藻, p=hǎizǎo, labels=no in
traditional Chinese medicine Traditional Chinese medicine (TCM) is an alternative medical practice drawn from traditional medicine in China. It has been described as "fraught with pseudoscience", with the majority of its treatments having no logical mechanism of action ...
, where it is used to resolve "heat phlegm".


Description

Species of this genus of
algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...
may grow to a length of several metres. They are generally brown or dark green in color and consist of a holdfast, a stipe, and a
frond A frond is a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group. Other botanists allow the term frond to also apply to the lar ...
.
Oogonia An oogonium (plural oogonia) is a small diploid cell which, upon maturation, forms a primordial follicle in a female fetus or the female (haploid or diploid) gametangium of certain thallophytes. In the mammalian fetus Oogonia are formed in larg ...
and
antheridia An antheridium is a haploid structure or organ producing and containing male gametes (called ''antherozoids'' or sperm). The plural form is antheridia, and a structure containing one or more antheridia is called an androecium. Androecium is also ...
occur in
conceptacles Conceptacles are specialized cavities of marine and freshwater algae that contain the reproductive organs. They are situated in the Receptacle (botany), receptacle and open by a small ostiole.Boney, A.D. (1969). ''A Biology of Marine Algae''. Hutch ...
embedded in receptacles on special branches. Some species have berrylike gas-filled bladders that help the fronds float to promote
photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
. Many have a rough, sticky texture that, along with a robust but flexible body, help them withstand strong water currents.


Ecology

Large, pelagic mats of ''Sargassum'' in the Sargasso Sea act as one of the only habitats available for ecosystem development; this is because the Sargasso Sea lacks any land boundaries. The Sargassum patches act as a refuge for many species in different parts of their development, but also as a permanent residence for endemic species that can only be found living on and within the ''Sargassum''.Laffoley, D.d’A., Roe, H.S.J., Angel, M.V., Ardron, J., Bates, N.R., Boyd, I.L., Brooke, S., Buck, K.N., Carlson, C.A., Causey, B., Conte, M.H., Christiansen, S., Cleary, J., Donnelly, J., Earle, S.A., Edwards, R., Gjerde, K.M., Giovannoni, S.J., Gulick, S., Gollock, M., Hallett, J., Halpin, P., Hanel, R., Hemphill, A., Johnson, R.J., Knap, A.H., Lomas, M.W., McKenna, S.A., Miller, M.J., Miller, P.I., Ming, F.W., Moffitt, R., Nelson, N.B., Parson, L., Peters, A.J., Pitt, J., Rouja, P., Roberts, J., Roberts, J., Seigel, D.A., Siuda, A.N.S., Steinberg, D.K., Stevenson, A., Sumaila, V.R., Swartz, W., Thorrold, S., Trott, T.M., and V. Vats. (2011). The protection and management of the Sargasso Sea: The golden floating rainforest of the Atlantic Ocean. Summary Science and Supporting Evidence Case. Sargasso Sea Alliance, 44 pp. These endemic organisms have specialized patterns and colorations that mimic the ''Sargassum'' and allow them to be impressively camouflaged in their environment. In total, these ''Sargassum'' mats are home to more than 11 phyla and over 100 different species. There is also a total of 81 fish species (36 families represented) that reside in the ''Sargassum'' or utilize it for parts of their life cycles. Other marine organisms, such as young sea turtles, will use the ''Sargassum'' as shelter and a resource for food until they reach a size at which they can survive elsewhere. This community is being affected by humans due to overfishing, trash and other types of pollution, and boat traffic, which could eventually lead to the demise of this diverse and unique habitat. Below is a list of organisms that are associated with the Sargassum in the Sargasso Sea. The Sargasso Sea plays a major role in the
migration Migration, migratory, or migrate may refer to: Human migration * Human migration, physical movement by humans from one region to another ** International migration, when peoples cross state boundaries and stay in the host state for some minimum le ...
of catadromous eel species such as the
European eel The European eel (''Anguilla anguilla'') is a species of eel, a snake-like, catadromous fish. They are normally around and rarely reach more than , but can reach a length of up to in exceptional cases. Eels have been important sources of fo ...
, the American eel, and the American conger eel. The
larvae A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...
of these species hatch within the sea and as they grow they travel to Europe or the East Coast of North America. Later in life, the matured eel migrates back to the Sargasso Sea to spawn and lay
eggs Humans and human ancestors have scavenged and eaten animal eggs for millions of years. Humans in Southeast Asia had domesticated chickens and harvested their eggs for food by 1,500 BCE. The most widely consumed eggs are those of fowl, especial ...
. It is also believed that after hatching, young
loggerhead sea turtle The loggerhead sea turtle (''Caretta caretta'') is a species of oceanic turtle distributed throughout the world. It is a marine reptile, belonging to the family Cheloniidae. The average loggerhead measures around in carapace length when fully ...
s use currents, such as the
Gulf Stream The Gulf Stream, together with its northern extension the North Atlantic Current, North Atlantic Drift, is a warm and swift Atlantic Ocean, Atlantic ocean current that originates in the Gulf of Mexico and flows through the Straits of Florida a ...
, to travel to the Sargasso Sea, where they use the sargassum as cover from predators until they are mature. Organisms found in the pelagic ''Sargassum'' patches, * Arthropods **
Amphipods Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descri ...
**
Skeleton shrimp Caprellidae is a family of amphipods commonly known as skeleton shrimps. Their common name denotes the threadlike slender body which allows them to virtually disappear among the fine filaments of seaweed, hydroids and bryozoans. They are sometim ...
**
Crabs Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...
** Copepods **
Shrimp Shrimp are crustaceans (a form of shellfish) with elongated bodies and a primarily swimming mode of locomotion – most commonly Caridea and Dendrobranchiata of the decapod order, although some crustaceans outside of this order are refer ...
**
Sea Spider Sea spiders are marine arthropods of the order Pantopoda ( ‘all feet’), belonging to the class Pycnogonida, hence they are also called pycnogonids (; named after ''Pycnogonum'', the type genus; with the suffix '). They are cosmopolitan, fou ...
s * Worms **
Annelid worms The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant taxon, extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to v ...
**
Flatworms The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, ''platy'', meaning "flat" and ἕλμινς (root: ἑλμινθ-), ''helminth-'', meaning "worm") are a phylum of relatively simple bilaterian, unsegment ...
* Mollusks **
Nudibranchs Nudibranchs () are a group of soft-bodied marine gastropod molluscs which shed their shells after their larval stage. They are noted for their often extraordinary colours and striking forms, and they have been given colourful nicknames to match, ...
**
Snails A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gastro ...
**
Squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...
* Fish **
Sargassum fish The sargassum fish, anglerfish, or frog fish (''Histrio histrio'') is a frogfish of the family (biology), family Antennariidae, Monotypic taxon, the only species in its genus. It lives among ''Sargassum'' seaweed which floats in subtropical ocea ...
**
Porcupinefish Porcupinefish are fish belonging to the family Diodontidae (order Tetraodontiformes), also commonly called blowfish and, sometimes, balloonfish and globefish. They are sometimes collectively called pufferfish, not to be confused with the morpholo ...
**
Triplefin Threefin or triplefin blennies are blenniiforms, small percomorph marine fish of the family Tripterygiidae. Found in tropical and temperate waters of the Atlantic, Pacific and Indian Oceans, the family contains about 150 species in 30 genera. Th ...
**
Planehead filefish ''Stephanolepis hispidus'', the planehead filefish, is a species of bony fish, a ray-finned fish in the family Monacanthidae. Description The planehead filefish grows to a maximum length of but is more typically about long. The colour is c ...
**
European eel The European eel (''Anguilla anguilla'') is a species of eel, a snake-like, catadromous fish. They are normally around and rarely reach more than , but can reach a length of up to in exceptional cases. Eels have been important sources of fo ...
** American eel ** American conger eel * Others **
Sea turtles Sea turtles (superfamily Chelonioidea), sometimes called marine turtles, are reptiles of the order Testudines and of the suborder Cryptodira. The seven existing species of sea turtles are the flatback, green, hawksbill, leatherback, loggerhead, ...
''Sargassum'' is commonly found in the beach drift near ''Sargassum'' beds, where they are also known as gulfweed, a term that also can mean all seaweed species washed up on shore. ''Sargassum'' species are found throughout tropical areas of the world and are often the most obvious macrophyte in near-shore areas where ''Sargassum'' beds often occur near
coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. Co ...
s. The plants grow
subtidal The neritic zone (or sublittoral zone) is the relatively shallow part of the ocean above the drop-off of the continental shelf, approximately in depth. From the point of view of marine biology it forms a relatively stable and well-illuminated ...
ly and attach to coral, rocks, or shells in moderately exposed or sheltered rocky or pebble areas. These tropical populations often undergo seasonal cycles of growth and decay in concert with seasonal changes in sea temperature. In tropical ''Sargassum'' species that are often preferentially consumed by
herbivorous A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpart ...
fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
es and
echinoid Sea urchins () are spine (zoology), spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard s ...
s, a relatively low level of
phenolic Phenolic is an adjective and a substantive (noun) that may apply to : * Phenol (or carbolic acid), a colorless crystalline solid and aromatic compound * Phenols, a class of chemical compounds that include phenol * Phenolic content in wine * Phenol ...
s and tannins occurs.


Inundations

In limited amounts, washed-ashore ''Sargassum'' plays an important role in maintaining Atlantic and Caribbean coastal ecosystems. Once ashore, sargassum provides vital nutrients such as carbon, nitrogen, and phosphorus to coastal ecosystems which border the nutrient-poor waters of the western North Atlantic tropics and subtropics. Additionally, it decreases
coastal erosion Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. The landward ...
. However, beginning in 2011, unprecedented quantities of ''Sargassum'' began inundating coastal areas in record amounts. Coastlines in Brazil, the Caribbean, Gulf of Mexico, and the east coast of Florida saw quantities of sargassum wash ashore up to three feet deep. The first major ''Sargassum'' inundation event occurred in 2011 and had a biomass increase of 200 fold compared to the previous eight years average bloom size. Since 2011 increasingly stronger inundation events have occurred every 2–3 years. During a ''Sargassum'' inundation event in 2018, one ''Sargassum'' bloom measured over 1600 square kilometers, more than three times the average size. Recent inundation events have caused millions of dollars of lost revenue in the tourism industry, especially hurting small Caribbean countries whose economies are highly dependent on seasonal tourism. While the Sargasso Sea is a known source of sargassum blooms, variations in the sargassum types composing these inundation events have led researchers to believe that the Sargasso Sea is not the point of origin of inundating ''Sargassum''. ''Sargassum natans I'' and ''Sargassum fluitans III'' are the dominant sargassum species found in the Sargasso Sea. Recent net sampling studies have found ''Sargassum natans VIII'', a previously rare type, is constituting a dominating percentage of ''Sargassum'' biodiversity in the Western Atlantic and Sargasso Sea.


Biological impacts

Unprecedented ''Sargassum'' inundation events cause a range of biological and ecological impacts in affected regions. The decomposition of large quantities of ''Sargassum'' along coastlines consumes oxygen, creating large oxygen-depleted zones resulting in fish kills. Decomposing sargassum additionally creates hydrogen sulfide gas, which causes a range of health impacts in humans. During the sargassum inundation event in 2018, 11,000 Acute Sargassum Toxicity cases were reported in an 8-month span on just the Caribbean islands of Guadalupe and Martinique. Massive amounts of floating ''sargassum'' present a physical barrier preventing corals and seagrasses from receiving sufficient light, fouling boat propellers, and entangling marine turtles and mammals. With every ''Sargassum'' inundation event, large amounts of nutrients are transported from the open ocean to coastal environments. This greatly increases nutrient transport, and its effect on marine and coastal ecosystems are still unknown. Understanding the causes and drivers of ''Sargassum'' inundations is critical as they become more commonplace.


Nutrient factors

The Sargasso Sea, a known source area for ''Sargassum'' blooms, is classified as an oligotrophic region. With warm, oxygen-poor waters and low nutrient contents, biomass production is limited by what little nutrients are present. Historically, low nutrient levels in the Sargasso Sea have limited ''sargassum'' production; however, new influxes of nitrogen and phosphorus are driving factors in increased biomass production. Recent studies have found three likely drivers of nutrient influx linked to increasing ''Sargassum'' biomass: an increase in nutrient output from the Amazon River, increased nutrients in the Gulf of Mexico, and coastal upwelling off the West African Coast which transfers deep nutrient-rich waters to the upper water column where sargassum resides. Nutrient output from the Amazon River has been shown to have a direct, yet delayed, effect on large Sargassum inundation events, with events occurring one to two years following years of high nutrient output. Phosphates and iron transported via the trade winds from North Africa have been reported to have a fertilizing effect on sargassum growth; however, further data is required to understand its role in causing inundating ''Sargassum'' blooms. Researchers globally agree that continued research is required to quantify the effect of marine chemical changes and other environmental factors in the recent increase in Sargassum biomass and inundation events.


Currents and winds

The physical drivers behind ''Sargassum'' inundation events are prevailing winds and ocean surface currents. The Caribbean is located in a region heavily affected by trade winds. Trade winds are strong, consistent northeasterly winds which blow dust-filled dry air from the Sahara across the Atlantic. Trade winds additionally play a critical role in the annual hurricane season in the Western Atlantic. The Caribbean Current and Antilles branch of the Atlantic North Equatorial Current are the major current transporters of ''Sargassum'' in the region. Researchers have recently begun using Moderate Resolution Imaging Spectroradiometer satellite imagery and ocean current data to track and forecast inundation events with a high level of accuracy.


Human impact

The effects of deforestation, waste-water runoff, and commercial agriculture fertilizer on facilitating the excess accumulation of nutrients in aquatic and marine environments have been well studied and shown to be driving factors in eutrophication. Since detrimental ''Sargassum'' inundation events did not begin until 2011, it is likely that an unknown nutrient threshold was reached and surpassed. Given current agricultural policies and practices, it is unlikely these inundation events will disappear on their own without human intervention. Sargassum (F. Sargassaceae) is an important seaweed excessively distributed in tropical and subtropical regions. Different species of Sargassum have folk applications in human nutrition and are considered a rich source of vitamins, carotenoids, proteins, and minerals. Many bioactive compounds chemically classified as terpenoids, sterols, sulfated polysaccharides, polyphenols, sargaquinoic acids, sargachromenol, and pheophytin were isolated from different Sargassum species. These isolated compounds and/or extracts exhibit diverse biological activities, including analgesic, anti-inflammatory, antioxidant, neuroprotective, anti-microbial, anti-tumor, fibrinolytic, immune-modulatory, anticoagulant, hepatoprotective, and anti-viral activities.


Climate change

Variations in sea level, salinity, water temperature, chemical composition, rainfall patterns and water acidity all play roles in regulating algae blooms. As anthropogenic forces increase the variability of these factors, the frequency, duration, severity and geographic range of harmful algae blooms have increased, causing millions of dollars of lost revenue as well as damaging fragile coastal and coral ecosystems.


References


Further reading

* * *


External links


algaebase.orgseaweed.ieSargassum in Northern Ireland.habitas.org.ukirishseaweed.comSargassum Early Advisory System
Texas

US Department of Commerce, National Oceanic and Atmospheric Administration. (2013, June 1). {{Taxonbar, from=Q865061 Edible algae Fucales Fucales genera Marine biota of North America