question: How does sargassum harm marine life?
comment: I can only tell you that turtles can suffocate under it. Someone else will have to jump in with the effects on other species.
passages: Section::::"Sargassum" crisis in the Caribbean Sea.
  
  In summer 2015, large quantities of different species of "Sargassum" accumulated along the shores of many of the countries on the Caribbean Sea. Some of the affected islands and regions include the Caribbean coast of Mexico, the Dominican Republic, Barbados, and Trinidad and Tobago. Another large outbreak occurred in 2018.
   Section::::Repartion areas, invasiveness, impacts.:Invasiveness and impacts.
  
  Its proliferation is important especially during the summer, which causes economical and ecological problems.
  
  Ecological: Because of its large size and dense ramifications, "S.muticum" forms a screen within the water column preventing the penetration of light. It also captures the nutrients in disfavor of other species such as phytoplankton. However, "S.muticum" also serves as shelter and protection for fish larva or crustaceans as well as laying support for cuttlefish.
   Biological—there are few natural predators, one example is a little copepod that will eat only the unhealthy and damaged parts of "S. muticum."
  
  Currently the distribution is stabilized, and only mechanical removal is performed.
  
  Section::::Uses.
  
  There are some potential uses for "Sargassum muticum."
  
  In agriculture, algae are used as sources of nitrate and potash for fertilization.
   The algae wash ashore, pile up on beaches, and decay, often causing a foul odor, releasing fumes of sulphur compounds that rust metals, can turn taps black in shore houses, damage modern conveniences, and cause respiratory problems, particularly for asthmatics. A doctor in Guadeloupe recorded 52 patients as having "Sargassum"-related symptoms. Insurance problems arise for tourist operators and homeowners, where the household and business losses do not fall into previous insurance categories. Wildlife also suffer; for example, sea turtle hatchlings die on their way to open water. The affected countries and territories are discussing causes of the outbreak, potential solutions, and the negative effects on tourism.
   Researchers say that the "Sargassum" outbreak started in 2011, but it has become worse over the years. As it is cleaned up on the shorelines, in a matter of a week, the shorelines are once again filled in masses. It is still a recurring problem, in June 2019 the Mexican government said they would spend $2.7m (£2.1m) to build four boats designed to remove seaweed as well as new barriers to retain it.
   Section::::Effects on Marine Life.
  
  Marine mammals and seabirds have displayed adverse effects when in contact with Domoic acid including neurological effects and mortality. However, organisms such as shellfish and fish can ingest and accumulate domoic acid without ill effects. Despite these organisms not being effected, they can contribute to toxicity accumulating in the organisms that eat them. Domoic acid can accumulate up the food chain and cause adverse effects in marine organisms that are in higher trophic levels. It can cause neurological syndromes, gastrointestinal syndromes, acute retina issues, motor sensory abnormalities, heart defects, and morphological brain changes.
   Section::::History.
  
  "Sargassum" was named by the Portuguese sailors who found it in the Sargasso Sea after the wooly rock rose ("Halimium lasianthum") that grew in their water wells at home, and that was called "sargaço" in Portuguese ().
  
  The Florida Keys and mainland South Florida are well known for their high levels of "Sargassum" covering their shores. Gulfweed was observed by Columbus. Although it was formerly thought to cover the entirety of the Sargasso Sea, making navigation impossible, it has since been found to occur only in drifts.
   Section::::Effects.
   Monterey Bay, located in central California, experienced a toxic "P. australis" algal bloom in the spring of 2015 leading to detrimental ecological issues such as marine organism illness and mortality. This bloom was caused by an unusual prolonged period of oceanic warming and upwelling which created conditions that allowed for an explosion of the "P. australis" species. The increase of available nitrogen from upwelling allowed for an increase in domoic acid synthesis. This bloom event lead to the temporary closure of fisheries such as razor clam and crab fisheries up the west coast from California to Washington due to the harmful impacts of domoic acid on human health. The closure of fisheries led to a request from the governor of California for a federal disaster declaration Effects of this harmful algal bloom on wildlife included mortality and seizures of a wide variety of marine species off of the coast. Domoic acid was detected in marine mammals such as whales, dolphins, sea lions, seals, and porpoises. 
   Water treatment: the cell walls of "S. muticum" contains alginates and fucoidans. The association of both molecules forms a bigger molecule and this one can be a flocculant. This process can be a method to catch organic matter present in sewage. This flocculant, rich in proteins and oligoelements, is easily biodegradable and could be used for fertilizer.
  
  Previous studies have shown that "Sargassum muticum" is able to carry out the biosorption of heavy metals like cadmium, chlorophenolic compounds, and nickel.
   Section::::Distribution and habitat.
  
  The sargassum fish has a cosmopolitan distribution in tropical and subtropical seas down to a depth around . It is found in parts of the Atlantic Ocean and the Indo-Pacific Ocean, where drifting seaweed accumulates. In the western Atlantic, it ranges from the Gulf of Maine south to Uruguay. It has been reported from northern Norway, but that sighting is likely to be as a result of its having been carried along by the North Atlantic Current.
  
  Section::::Biology.
   Organisms found in the pelagic "Sargassum" patches,
  
  BULLET::::- Arthropods
  
  BULLET::::- Amphipods
  
  BULLET::::- Skeleton shrimp
  
  BULLET::::- Crabs
  
  BULLET::::- Copepods
  
  BULLET::::- Shrimp
  
  BULLET::::- Sea Spiders
  
  BULLET::::- Worms
  
  BULLET::::- Annelid worms
  
  BULLET::::- Flatworms
  
  BULLET::::- Mollusks
  
  BULLET::::- Nudibranchs
  
  BULLET::::- Snails
  
  BULLET::::- Squid
  
  BULLET::::- Fish
  
  BULLET::::- Sargassum fish
  
  BULLET::::- Porcupinefish
  
  BULLET::::- Triplefin
  
  BULLET::::- Planehead filefish
  
  BULLET::::- European eel
  
  BULLET::::- American eel
  
  BULLET::::- American conger eel
  
  BULLET::::- Others
  
  BULLET::::- Sea turtles
  
  "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.
   Oil pollution toxicity to marine fish
  
  Oil pollution toxicity to marine fish has been observed from oil spills such as the "Exxon Valdez" disaster, and from nonpoint sources, such as surface runoff, which is the largest source of oil pollution in marine waters.
   However, bacterial-phytoplankton interactions in the phycosphere could be parasitic. In the same low nutrient oligotrophic regions of the ocean, phytoplankton that are nutrient stressed may not be able to produce this protective mucus layer or its associated antibiotics. The bacteria, who are also food stressed, could kill the phytoplankton and use it as a food substrate.
   Section::::History.
   TFM toxicity has not been thoroughly investigated for humans, but is considered an irritant, respiratory irritant, and toxic by the manufacturer. Toxicity studies of other mammals have generally found it to be non-toxic at concentrations expected to be found in treated areas . Impact on other fish species may be controlled by selective application during the larvae season for lampreys and other management of its concentration. TFM does not accumulate, since it breaks down within several days. 
   Section::::Habitat.
  
  "Sargassum muticum" grows from half-tide to infralittoral areas (to a depth of 10 m.). It is fixed on solid substrates like rocks, stones, shells. It is highly tolerant towards temperature and salinity variations. The optimal temperature is between 17 and 20 °C but it tolerates -9 and 30 °C.
  
  Section::::Repartion areas, invasiveness, impacts.
  
  Section::::Repartion areas, invasiveness, impacts.:Repartition areas.
   Section::::Effects.:Proposed mechanism of toxic action.
  
  While it has been proven that different classes of PAHs act through distinct toxic mechanisms due to the variations in their molecular weight, ring arrangements, and water solubility properties, the specific mechanisms of PAH toxicity to fish and fish development are still unknown. Toxicity depends on the extent to which chemical in the oil will mix with water: this is referred to as the water associated fraction of the oil. The proposed mechanisms of toxicity of PAHs are toxicity through narcosis, interaction with the AhR pathway, alkyl phenanthrene toxicity, and additive toxicity by multiple mechanisms.
   "Sargassum" species are also cultivated and cleaned for use as an herbal remedy. Many Chinese herbalists prescribe powdered "Sargassum"—either the species "S. pallidum", or more rarely, hijiki, "S. fusiforme"—in doses of 0.5 gram dissolved in warm water and drunk as a tea. It is called in traditional Chinese medicine, where it is used to resolve "heat phlegm".
  
  Section::::Description.
   In 2000, Shaw Institute began long-term research focused on marine sentinel species to characterize the extent of contamination of the northwest Atlantic marine ecosystem from Maine to New York, funded by the National Oceanic and Atmospheric Administration (NOAA). This work has shown that levels of toxic chemicals, such as polychlorinated biphenyls (PCBs), in northwest Atlantic harbor seals are among the highest in the world.
   Section::::Environmental considerations.
  
  Generally, the environmental impacts of SIs are complicated further by combination of other chemicals applied through exploratory, drilling, well-completion and start-up operations. Produced fluids, and other wastes from oil and gas operations with high content of different toxic compounds are hazardous and harmful to human health, water supplies, marine and freshwater organisms. For instance trails of increased turbidity resulting from oil and gas exploratory activities on the eastern shelf of Sakhalin in Russia have been reported with consequential adverse effects on salmon, cod and littoral amphipods.
   Other mechanisms impacted by biofouling include microelectrochemical drug delivery devices, papermaking and pulp industry machines, underwater instruments, fire protection system piping, and sprinkler system nozzles. In groundwater wells, biofouling buildup can limit recovery flow rates, as is the case in the exterior and interior of ocean-laying pipes where fouling is often removed with a tube cleaning process. Besides interfering with mechanisms, biofouling also occurs on the surfaces of living marine organisms, when it is known as epibiosis.
   Section::::History.:"Deepwater Horizon" oil spill.
   Section::::Effects on Humans.:Economics.
  
  "P. australius algal" blooms can have a negative effect on fisheries and local economies. Due to amnesic shellfish poisoning (ASP) and its major threat to human health, fisheries are required to close when domoic acid levels reach an unsafe level in order to protect human safety. In New Zealand, one fishery had to shut down for four years while the domoic acid levels were considered too high to be safe.
  
  Section::::Notable "P. australis" Blooms.
  
  Section::::Notable "P. australis" Blooms.:Monterey Bay.
   One method of cleaning is by spade and barrow onshore, and it can be collected by raking boats offshore. Barrages of shallow nets floated by long buoys can be used to ward off algae drifts, depending on wave height and current. On the Caribbean island of Saint Martin, backhoes are also used in the process of clean up once the "Sargassum" weed reaches the shorelines.
  