The Sargasso Sea has large pelagic mats of
Sargassum and this is one of the few areas that can develop an ecosystem in the open-ocean region that has no land boundaries. Drifting
Sargassum patches acts 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. These endemic organisms have specialized patterns and colorations that mimic the
Sargassum and allow them to be camouflaged in their environment. In total,
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. Below is a list of organisms that are associated with the
Sargassum. The Sargasso Sea plays a major role in the
migration of
catadromous eel species such as the
European eel, the
American eel, and the
American conger eel. The
larvae 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. It is also believed that after hatching, young
loggerhead sea turtles use currents, such as the
Gulf Stream, to travel to the Sargasso Sea, where they use the
Sargassum as cover from
predators until they are mature.
Sargassum also serve as a trophic link between the ocean surface and the seabed. Isopods of the species
Bathyopsurus nybelini at depths of 5002–6288 m in the
Puerto Rico Trench and
Mid-Cayman spreading center have been observed consuming
Sargassum. They even exhibit several adaptations for it, such as microbiomes capable of breaking down the seaweed and fixing nitrogen, specialized swimming strokes, and serrated, grinding mouthparts. Organisms found in the pelagic
Sargassum patches, In tropical
Sargassum species that are often preferentially consumed by
herbivorous fishes and
echinoids, a relatively low level of
phenolics and
tannins occurs.
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
Guadeloupe 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.
Sargassum influx imposes major problems of organic matter and nutrients in the offshore and inshore waters, changing the nutrient balance and possibly influencing the quality of oceanic waters. As much as these transfers might have short time positive effects on productivity, long term ecological impacts of these transfers are not well understood. Further investigations into the environmental causes, nutrient, and biogeochemical feed-backs of the
Sargassum blooms are also necessary, since the occurrence has become more common and intense over the tropical Atlantic and Caribbean.
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. 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. 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.
"Coastal inundations" by washed-ashore Sargassum 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. 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. Since 2011, increasingly stronger inundation events have occurred every 2–3 years. During a
Sargassum inundation event in 2018, one
Sargassum bloom measured over 1,600 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.
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. == Resource management ==