Biofouling

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Current measurement instrument encrusted with zebra mussels Zebra mussel GLERL 4.jpg
Current measurement instrument encrusted with zebra mussels
Plant organisms, bacteria and animals (freshwater sponges) have covered (fouled) the sheath of an electric cable in a canal (Mid-Deule in Lille, north of France). Gaine cable electrique Moyenne-Deule a Lille 03.jpg
Plant organisms, bacteria and animals (freshwater sponges) have covered (fouled) the sheath of an electric cable in a canal (Mid-Deûle in Lille, north of France).

Biofouling or biological fouling is the accumulation of microorganisms, plants, algae, or small animals where it is not wanted on surfaces such as ship and submarine hulls, devices such as water inlets, pipework, grates, ponds, and rivers that cause degradation to the primary purpose of that item. Such accumulation is referred to as epibiosis when the host surface is another organism and the relationship is not parasitic. Since biofouling can occur almost anywhere water is present, biofouling poses risks to a wide variety of objects such as boat hulls and equipment, medical devices and membranes, as well as to entire industries, such as paper manufacturing, food processing, underwater construction, and desalination plants.

Contents

Anti-fouling is the ability of specifically designed materials (such as toxic biocide paints, or non-toxic paints) [1] to remove or prevent biofouling. [2]

The buildup of biofouling on marine vessels poses a significant problem. In some instances, the hull structure and propulsion systems can be damaged. [3] The accumulation of biofoulers on hulls can increase both the hydrodynamic volume of a vessel and the hydrodynamic friction, leading to increased drag of up to 60%. [4] The drag increase has been seen to decrease speeds by up to 10%, which can require up to a 40% increase in fuel to compensate. [5] With fuel typically comprising up to half of marine transport costs, antifouling methods save the shipping industry a considerable amount of money. Further, increased fuel use due to biofouling contributes to adverse environmental effects and is predicted to increase emissions of carbon dioxide and sulfur dioxide between 38% and 72% by 2020, respectively. [6]

Biology

Biofouling organisms are highly diverse, and extend far beyond the attachment of barnacles and seaweeds. According to some estimates, over 1,700 species comprising over 4,000 organisms are responsible for biofouling. [7] Biofouling is divided into microfoulingbiofilm formation and bacterial adhesion—and macrofouling—attachment of larger organisms. Due to the distinct chemistry and biology that determine what prevents them from settling, organisms are also classified as hard- or soft-fouling types. Calcareous (hard) fouling organisms include barnacles, encrusting bryozoans, mollusks such as zebra mussels, and polychaete and other tube worms. Examples of non-calcareous (soft) fouling organisms are seaweed, hydroids, algae, and biofilm "slime". [8] Together, these organisms form a fouling community.

Ecosystem formation

Biofouling initial process: (left) Coating of submerged "substratum" with polymers. (moving right) Bacterial attachment and extracellular polymeric substance (EPS) matrix formation. Biofilm Formation.jpg
Biofouling initial process: (left) Coating of submerged "substratum" with polymers. (moving right) Bacterial attachment and extracellular polymeric substance (EPS) matrix formation.

Marine fouling is typically described as following four stages of ecosystem development. Within the first minute the van der Waals interaction causes the submerged surface to be covered with a conditioning film of organic polymers. In the next 24 hours, this layer allows the process of bacterial adhesion to occur, with both diatoms and bacteria (e.g. Vibrio alginolyticus , Pseudomonas putrefaciens ) attaching, initiating the formation of a biofilm. By the end of the first week, the rich nutrients and ease of attachment into the biofilm allow secondary colonizers of spores of macroalgae (e.g. Enteromorpha intestinalis , Ulothrix ) and protozoans (e.g. Vorticella , Zoothamnium sp.) to attach themselves. Within two to three weeks, the tertiary colonizers—the macrofoulers—have attached. These include tunicates, mollusks, and sessile cnidarians. [1]

Impact

Dead biofouling, under a wood boat (detail) Antifouling 8212.jpg
Dead biofouling, under a wood boat (detail)

Governments and industry spend more than US$5.7 billion annually to prevent and control marine biofouling. [9] Biofouling occurs everywhere but is most significant economically to the shipping industries, since fouling on a ship's hull significantly increases drag, reducing the overall hydrodynamic performance of the vessel, and increases the fuel consumption. [10]

Biofouling is also found in almost all circumstances where water-based liquids are in contact with other materials. Industrially important impacts are on the maintenance of mariculture, membrane systems (e.g., membrane bioreactors and reverse osmosis spiral wound membranes) and cooling water cycles of large industrial equipment and power stations. Biofouling can occur in oil pipelines carrying oils with entrained water, especially those carrying used oils, cutting oils, oils rendered water-soluble through emulsification, and hydraulic oils.[ citation needed ] [11]

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. [2] [8] 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. [11] [ citation needed ]

Medical devices often include fan-cooled heat sinks, to cool their electronic components. While these systems sometimes include HEPA filters to collect microbes, some pathogens do pass through these filters, collect inside the device and are eventually blown out and infect other patients. [12] Devices used in operating rooms rarely include fans, so as to minimize the chance of transmission. Also, medical equipment, HVAC units, high-end computers, swimming pools, drinking-water systems and other products that utilize liquid lines run the risk of biofouling as biological growth occurs inside them. [13]

Historically, the focus of attention has been the severe impact due to biofouling on the speed of marine vessels. In some instances the hull structure and propulsion systems can become damaged. [3] Over time, the accumulation of biofoulers on hulls increases both the hydrodynamic volume of a vessel and the frictional effects leading to increased drag of up to 60% [5] The additional drag can decrease speeds up to 10%, which can require up to a 40% increase in fuel to compensate. [5] With fuel typically comprising up to half of marine transport costs, biofouling is estimated to cost the US Navy alone around $1 billion per year in increased fuel usage, maintenance and biofouling control measures. [5] Increased fuel use due to biofouling contributes to adverse environmental effects and is predicted to increase emissions of carbon dioxide and sulfur dioxide between 38 and 72 percent by 2020. [6]

Biofouling also impacts aquaculture, increasing production and management costs, while decreasing product value. [14] Fouling communities may compete with shellfish directly for food resources, [15] impede the procurement of food and oxygen by reducing water flow around shellfish, or interfere with the operational opening of their valves. [16] Consequently, stock affected by biofouling can experience reduced growth, condition and survival, with subsequent negative impacts on farm productivity. [17] Although many methods of removal exist, they often impact the cultured species, sometimes more so than the fouling organisms themselves. [18]

Detection

Shipping companies have historically relied on scheduled biofouler removal to keep such accretions to a manageable level. However, the rate of accretion can vary widely between vessels and operating conditions, so predicting acceptable intervals between cleanings is difficult.

LED manufacturers have developed a range of UVC (250–280 nm) equipment that can detect biofouling buildup, and can even prevent it.

Fouling detection relies on the biomass' property of fluorescence. All microorganisms contain natural intracellular fluorophores, which radiate in the UV range when excited. At UV-range wavelengths, such fluorescence arises from three aromatic amino acids—tyrosine, phenylalanine, and tryptophan. The easiest to detect is tryptophan, which radiates at 350 nm when irradiated at 280 nm. [19]

Methods

Antifouling

Antifouling is the process of preventing accumulations from forming. In industrial processes, biodispersants can be used to control biofouling. In less controlled environments, organisms are killed or repelled with coatings using biocides, thermal treatments, or pulses of energy. Nontoxic mechanical strategies that prevent organisms from attaching include choosing a material or coating with a slippery surface, creating an ultra-low fouling surface with the use of zwitterions, or creating nanoscale surface topologies similar to the skin of sharks and dolphins, which only offer poor anchor points. [1]

Coatings

Non-toxic coatings
A general idea of non-toxic coatings. (Coating represented here as light pea green layer.) They prevent proteins and microorganisms from attaching, which prevents large organisms such as barnacles from attaching. Larger organisms require a biofilm to attach, which is composed of proteins, polysaccharides, and microorganisms. ProteinAdsorptionPrevention.png
A general idea of non-toxic coatings. (Coating represented here as light pea green layer.) They prevent proteins and microorganisms from attaching, which prevents large organisms such as barnacles from attaching. Larger organisms require a biofilm to attach, which is composed of proteins, polysaccharides, and microorganisms.

Non-toxic anti-sticking coatings prevent attachment of microorganisms thus negating the use of biocides. These coatings are usually based on organic polymers. [20]

There are two classes of non-toxic anti-fouling coatings. The most common class relies on low friction and low surface energies. Low surface energies result in hydrophobic surfaces. These coatings create a smooth surface, which can prevent attachment of larger microorganisms. For example, fluoropolymers and silicone coatings are commonly used. [21] These coatings are ecologically inert but have problems with mechanical strength and long-term stability. Specifically, after days biofilms (slime) can coat the surfaces, which buries the chemical activity and allows microorganisms to attach. [1] The current standard for these coatings is polydimethylsiloxane, or PDMS, which consists of a non-polar backbone made of repeating units of silicon and oxygen atoms. [22] The non-polarity of PDMS allows for biomolecules to readily adsorb to its surface in order to lower interfacial energy. However, PDMS also has a low modulus of elasticity that allows for the release of fouling organisms at speeds of greater than 20 knots. The dependence of effectiveness on vessel speed prevents use of PDMS on slow-moving ships or those that spend significant amounts of time in port. [2]

The second class of non-toxic antifouling coatings are hydrophilic coatings. They rely on high amounts of hydration in order to increase the energetic penalty of removing water for proteins and microorganisms to attach. The most common examples of these coatings are based on highly hydrated zwitterions, such as glycine betaine and sulfobetaine. These coatings are also low-friction, but are considered by some to be superior to hydrophobic surfaces because they prevent bacteria attachment, preventing biofilm formation. [23] These coatings are not yet commercially available and are being designed as part of a larger effort by the Office of Naval Research to develop environmentally safe biomimetic ship coatings. [4]

Biocides

Biocides are chemical substances that kill or deter microorganisms responsible for biofouling. The biocide is typically applied as a paint, i.e. through physical adsorption. The biocides prevent the formation of biofilms. [1] Other biocides are toxic to larger organisms in biofouling, such as algae. Formerly, the so-called tributyltin (TBT) compounds were used as biocides (and thus anti-fouling agents). TBTs are toxic to both microorganisms and larger aquatic organisms. [24] The international maritime community has phased out the use of organotin-based coatings. [25] Replacing organotin compounds is dichlorooctylisothiazolinone. This compound, however, also suffers from broad toxicity to marine organisms.

Ultrasonic antifouling

Ultrasonic transducers may be mounted in or around the hull of small to medium-sized boats. Research has shown these systems can help reduce fouling, by initiating bursts of ultrasonic waves through the hull medium to the surrounding water, killing or denaturing the algae and other microorganisms that form the beginning of the fouling sequence. The systems cannot work on wooden-hulled boats, or boats with a soft-cored composite material, such as wood or foam. The systems have been loosely based on technology proven to control algae blooms. [26]

Energy methods

Pulsed laser irradiation is commonly used against diatoms. Plasma pulse technology is effective against zebra mussels and works by stunning or killing the organisms with microsecond-duration energizing of the water with high-voltage electricity. [8]

Similarly, another method shown to be effective against algae buildups bounces brief high-energy acoustic pulses down pipes. [27]

Other methods

Regimens to periodically use heat to treat exchanger equipment and pipes have been successfully used to remove mussels from power plant cooling systems using water at 105 °F (40 °C) for 30 minutes. [28]

The medical industry utilizes a variety of energy methods to address bioburden issues associated with biofouling. Autoclaving typically involves heating a medical device to 121 °C (249 °F) for 15–20 minutes. Ultrasonic cleaning, UV light, and chemical wipe-down or immersion can also be used for different types of devices.

Medical devices used in operating rooms, ICUs, isolation rooms, biological analysis labs, and other high-contamination-risk areas have negative pressure (constant exhaust) in the rooms, maintain strict cleaning protocols, require equipment with no fans, and often drape equipment in protective plastic. [29]

UVC irradiation is a noncontact, nonchemical solution that can be used across a range of instruments. Radiation in the UVC range prevents biofilm formation by deactivating the DNA in bacteria, viruses, and other microbes. Preventing biofilm formation prevents larger organisms from attaching themselves to the instrument and eventually rendering it inoperable. [30]

History

Biofouling, especially of ships, has been a problem for as long as humans have been sailing the oceans. [31]

The earliest attestations of attempts to counter fouling, and thus also the earliest attestation of knowledge if it, is the use of pitch and copper plating as anti-fouling solutions that were attributed to ancient seafaring nations, such as the Phoenicians and Carthaginians (1500–300 BC). Wax, tar and asphaltum have been used since early times. [31] An Aramaic record dating from 412 BC tells of a ship's bottom being coated with a mixture of arsenic, oil and sulphur. [32] In Deipnosophistae , Athenaeus described the anti-fouling efforts taken in the construction of the great ship of Hieron of Syracuse (died 467 BC). [33]

A recorded explanation by Plutarch of the impact fouling had on ship speed goes as follows: "when weeds, ooze, and filth stick upon its sides, the stroke of the ship is more obtuse and weak; and the water, coming upon this clammy matter, doth not so easily part from it; and this is the reason why they usually calk their ships." [34]

Before the 18th century, various anti-fouling techniques were used, with three main substances employed: "White stuff", a mixture of train oil (whale oil), rosin and sulfur; "Black stuff", a mixture of tar and pitch; and "Brown stuff", which was simply sulfur added to Black stuff. [35] In many of these cases, the purpose of these treatments is ambiguous. There is dispute whether many of these treatments were actual anti-fouling techniques, or whether, when they were used in conjunction with lead and wood sheathing, they were simply intended to combat wood-boring shipworms.

Ships brought ashore on the Torres Strait and careened in preparation for cleaning the hull Lebreton engraving-07.jpg
Ships brought ashore on the Torres Strait and careened in preparation for cleaning the hull

In 1708, Charles Perry suggested copper sheathing explicitly as an anti-fouling device but the first experiments were not made until 1761 with the sheathing of HMS Alarm, after which the bottoms and sides of several ships' keels and false keels were sheathed with copper plates. [31]

The copper performed well in protecting the hull from invasion by worm, and in preventing the growth of weed, for when in contact with water, the copper produced a poisonous film, composed mainly of oxychloride, that deterred these marine creatures. Furthermore, as this film was slightly soluble, it gradually washed away, leaving no way for marine life to attach itself to the ship.[ citation needed ] From about 1770, the Royal Navy set about coppering the bottoms of the entire fleet and continued to the end of the use of wooden ships. The process was so successful that the term copper-bottomed came to mean something that was highly dependable or risk free.

With the rise of iron hulls in the 19th century, copper sheathing could no longer be used due to its galvanic corrosive interaction with iron. Anti-fouling paints were tried, and in 1860, the first practical paint to gain widespread use was introduced in Liverpool and was referred to as "McIness" hot plastic paint. [31] These treatments had a short service life, were expensive, and relatively ineffective by modern standards. [1]

By the mid-twentieth century, copper oxide-based paints could keep a ship out of drydock for as much as 18 months, or as little as 12 in tropical waters. [31] The shorter service life was due to rapid leaching of the toxicant, and chemical conversion into less toxic salts, which accumulated as a crust that would inhibit further leaching of active cuprous oxide from the layer under the crust. [36]

The 1960s brought a breakthrough, with self-polishing paints that slowly hydrolyze, slowly releasing toxins. These paints employed organotin chemistry ("tin-based") biotoxins such as tributyltin oxide (TBT) and were effective for up to four years. These biotoxins were subsequently banned by the International Maritime Organization when they were found to be very toxic to diverse organisms. [37] [38] TBT in particular has been described as the most toxic pollutant ever deliberately released in the ocean. [24]

As an alternative to organotin toxins, there has been renewed interest in copper as the active agent in ablative or self polishing paints, with reported service lives up to 5 years; yet also other methods that do not involve coatings. Modern adhesives permit application of copper alloys to steel hulls without creating galvanic corrosion. However, copper alone is not impervious to diatom and algae fouling. Some studies indicate that copper may also present an unacceptable environmental impact. [39]

Study of biofouling began in the early 19th century with Davy's experiments linking the effectiveness of copper to its solute rate. [31] In the 1930s microbiologist Claude ZoBell showed that the attachment of organisms is preceded by the adsorption of organic compounds now referred to as extracellular polymeric substances. [40] [41]

One trend of research is the study of the relationship between wettability and anti-fouling effectiveness. Another trend is the study of living organisms as the inspiration for new functional materials. For example, the mechanisms used by marine animals to inhibit biofouling on their skin. [42]

Materials research into superior antifouling surfaces for fluidized bed reactors suggest that low wettability plastics such as polyvinyl chloride (PVC), high-density polyethylene and polymethylmethacrylate ("plexiglas") demonstrate a high correlation between their resistance to bacterial adhesion and their hydrophobicity. [43]

A study of the biotoxins used by organisms has revealed several effective compounds, some of which are more powerful than synthetic compounds. Bufalin, a bufotoxin, was found to be over 100 times as potent as TBT, and over 6,000 times more effective in anti-settlement activity against barnacles. [44]

One approach to antifouling entails coating surfaces with polyethylene glycol (PEG). [45] Growing chains of PEG on surfaces is challenging. The resolution to this problem may come from understanding the mechanisms by which mussels adhere to solid surfaces in marine environments. Mussels utilize adhesive proteins, or MAPs. [46] The service life of PEG coatings is also doubtful.

See also

Related Research Articles

A biocide is defined in the European legislation as a chemical substance or microorganism intended to destroy, deter, render harmless, or exert a controlling effect on any harmful organism. The US Environmental Protection Agency (EPA) uses a slightly different definition for biocides as "a diverse group of poisonous substances including preservatives, insecticides, disinfectants, and pesticides used for the control of organisms that are harmful to human or animal health or that cause damage to natural or manufactured products". When compared, the two definitions roughly imply the same, although the US EPA definition includes plant protection products and some veterinary medicines.

<span class="mw-page-title-main">Anti-fouling paint</span> Specialized paint for ship hulls

Anti-fouling paint is a specialized category of coatings applied as the outer (outboard) layer to the hull of a ship or boat, to slow the growth of and facilitate detachment of subaquatic organisms that attach to the hull and can affect a vessel's performance and durability. It falls into a category of commercially available underwater hull paints, also known as bottom paints.

<span class="mw-page-title-main">Fouling</span> Accumulation of unwanted material on solid surfaces

Fouling is the accumulation of unwanted material on solid surfaces. The fouling materials can consist of either living organisms or a non-living substance (inorganic). Fouling is usually distinguished from other surface-growth phenomena in that it occurs on a surface of a component, system, or plant performing a defined and useful function and that the fouling process impedes or interferes with this function.

<span class="mw-page-title-main">Tributyltin oxide</span> Chemical compound

Tributyltin oxide (TBTO) is an organotin compound chiefly used as a biocide (fungicide and molluscicide), especially a wood preservative. Its chemical formula is [(C4H9)3Sn]2O. It is a colorless viscous liquid. It is poorly soluble in water (20 ppm) but highly soluble in organic solvents. It is a potent skin irritant.

<span class="mw-page-title-main">Tetrabutyltin</span> Chemical compound

Tetrabutyltin is the organotin compound with the molecular formula Sn(CH2CH2CH2CH3)4 or SnBu4, where Bu is butyl −CH2CH2CH2CH3. Sometimes abbreviated TTBT, it is a colorless, lipophilic oil.

<span class="mw-page-title-main">Tributyltin</span> Group of organotin compounds

Tributyltin (TBT) is an umbrella term for a class of organotin compounds which contain the (C4H9)3Sn group, with a prominent example being tributyltin oxide. For 40 years TBT was used as a biocide in anti-fouling paint, commonly known as bottom paint, applied to the hulls of oceangoing vessels. Bottom paint improves ship performance and durability as it reduces the rate of biofouling, the growth of organisms on the ship's hull. The TBT slowly leaches out into the marine environment where it is highly toxic toward nontarget organisms. TBT toxicity can lead to biomagnification or bioaccumulation within such nontarget organisms like invertebrates, vertebrates, and a variety of mammals. TBT is also an obesogen. After it led to collapse of local populations of organisms, TBT was banned.

Imposex is a disorder in sea snails caused by the toxic effects of certain marine pollutants. These pollutants cause female sea snails to develop male sex organs such as a penis and a vas deferens.

<span class="mw-page-title-main">Fouling community</span> Community of organisms found on artificial surfaces

Fouling communities are communities of organisms found on artificial surfaces like the sides of docks, marinas, harbors, and boats. Settlement panels made from a variety of substances have been used to monitor settlement patterns and to examine several community processes. These communities are characterized by the presence of a variety of sessile organisms including ascidians, bryozoans, mussels, tube building polychaetes, sea anemones, sponges, barnacles, and more. Common predators on and around fouling communities include small crabs, starfish, fish, limpets, chitons, other gastropods, and a variety of worms.

<span class="mw-page-title-main">Copper toxicity</span> Type of metal poisoning

Copper toxicity is a type of metal poisoning caused by an excess of copper in the body. Copperiedus could occur from consuming excess copper salts, but most commonly it is the result of the genetic condition Wilson's disease and Menke's disease, which are associated with mismanaged transport and storage of copper ions. Copper is essential to human health as it is a component of many proteins. But hypercupremia can lead to copper toxicity if it persists and rises high enough.

<span class="mw-page-title-main">Environmental impact of paint</span>

The environmental impact of paint can vary depending on the type of paint used and mitigation measures. Traditional painting materials and processes can have harmful effects on the environment, including those from the use of lead and other additives. Measures can be taken to reduce its environmental effects, including accurately estimating paint quantities so waste is minimized, and use of environmentally preferred paints, coating, painting accessories, and techniques.

<i>Amphibalanus improvisus</i> Species of barnacle

Amphibalanus improvisus, the bay barnacle, European acorn barnacle, is a species of acorn barnacle in the family Balanidae.

<span class="mw-page-title-main">Copper alloys in aquaculture</span>

Copper alloys are important netting materials in aquaculture. Various other materials including nylon, polyester, polypropylene, polyethylene, plastic-coated welded wire, rubber, patented twine products, and galvanized steel are also used for netting in aquaculture fish enclosures around the world. All of these materials are selected for a variety of reasons, including design feasibility, material strength, cost, and corrosion resistance.

A biomimetic antifouling coating is a treatment that prevents the accumulation of marine organisms on a surface. Typical antifouling coatings are not biomimetic but are based on synthetic chemical compounds that can have deleterious effects on the environment. Prime examples are tributyltin compounds, which are components in paints to prevent biofouling of ship hulls. Although highly effective at combatting the accumulation of barnacles and other problematic organisms, organotin-containing paints are damaging to many organisms and have been shown to interrupt marine food chains.

An antimicrobial surface is coated by an antimicrobial agent that inhibits the ability of microorganisms to grow on the surface of a material. Such surfaces are becoming more widely investigated for possible use in various settings including clinics, industry, and even the home. The most common and most important use of antimicrobial coatings has been in the healthcare setting for sterilization of medical devices to prevent hospital associated infections, which have accounted for almost 100,000 deaths in the United States. In addition to medical devices, linens and clothing can provide a suitable environment for many bacteria, fungi, and viruses to grow when in contact with the human body which allows for the transmission of infectious disease.

Pettit Marine Paint is a manufacturer of marine (boat) coatings, antifouling boat bottom paint, varnish and epoxies for consumer and commercial markets. The company was established in 1861, its headquarters are located in Rockaway, New Jersey.

Ultra-low fouling is a rating of a surface's ability to shed potential contamination. Surfaces are prone to contamination, which is a phenomenon known as fouling. Unwanted adsorbates caused by fouling change the properties of a surface, which is often counter-productive to the function of that surface. Consequently, a necessity for anti-fouling surfaces has arisen in many fields: blocked pipes inhibit factory productivity, biofouling increases fuel consumption on ships, medical devices must be kept sanitary, etc. Although chemical fouling inhibitors, metallic coatings, and cleaning processes can be used to reduce fouling, non-toxic surfaces with anti-fouling properties are ideal for fouling prevention. To be considered effective, an ultra-low fouling surface must be able to repel and withstand the accumulation of detrimental aggregates down to less than 5 ng/cm2. A recent surge of research has been conducted to create these surfaces in order to benefit the biological, nautical, mechanical, and medical fields.

Ultrasonic antifouling is a technology that uses high frequency sound (ultrasound) to prevent or reduce biofouling on underwater structures, surfaces, and medium. Ultrasound is just high frequency sound. Ultrasound has the same physical properties as human-audible sound. The method has two primary forms: sub-cavitation intensity and cavitation intensity. Sub-cavitation methods create high frequency vibrations, whilst cavitation methods cause more destructive microscopic pressure changes. Both methods inhibit or prevent biofouling by algae and other single-celled organisms.

<span class="mw-page-title-main">Ships husbandry</span> Maintenance and upkeep of ships

Ships husbandry or ship husbandry is all aspects of maintenance, cleaning, and general upkeep of the hull, rigging, and equipment of a ship. It may also be used to refer to aspects of maintenance which are not specifically covered by the technical departments. The term is used in both naval and merchant shipping, but naval vessel husbandry may also be used for specific reference to naval vessels.

In-water cleaning, also known as in-water surface cleaning, is a collection of methods for removing unwanted material in-situ from the underwater surface of a structure. This often refers to removing marine fouling growth from ship hulls, but also has applications on civil engineering structures, pipeline intakes and similar components which are impossible or inconvenient to remove from the water for maintenance. It does not generally refer to cleaning the inside of underwater or other pipelines, a process known as pigging. Many applications require the intervention of a diver, either to provide the power, or to direct a powered tool.

<i>Syringodium isoetifolium</i> Species of aquatic plant

Syringodium isoetifolium, commonly known as noodle seagrass, is a species of flowering plant in the family Cymodoceaceae, growing underwater in marine habitats. It forms seagrass meadows in shallow sandy or muddy locations in the Indian and Pacific Oceans.

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Further reading