The Marine Life Information Network

Temperature increase (local)

Benchmark. A 5°C increase in temperature for one month, or 2°C for one year. Further detail

Evidence

Beggiatoa spp. mats have been reported from sulphur springs, deep water at ca 600 m, fjords, coastal marine sediments, salt marshes, organic-rich freshwater sediments, natural oil seeps and deep-sea hydrothermal vents (e.g. Spies & Davis, 1979; Hagen & Nelson, 1997; Björk et al., 2017; Salvo et al., 2017; Ramírez et al., 2021). Exton et al. (2024) reported that in rivers, Beggiatoa is known to grow from 0 to40°C, while in the Gulf of California, mats have been found in ambient background sediments at 3.8°C, temperate sediments (25 to 30°C), hot hydrothermal sediments (75 to100°C), and hot sediments (>115°C) (Ramírez et al., 2021), although the temperature requirements of individual strains of the bacterium are likely to vary. Given its occurrence in the vicinity of hydrothermal vents, it is unlikely to be affected by increases in temperature at the benchmark level. In addition, Hiscock et al. (2001) suggested that increases in temperature because of global warming may result in more thermal stratification events in enclosed areas. Increased stratification will isolate deeper waters of sheltered sites and Beggiatoa spp. biotopes may occur where they did not previously exist. Therefore, resistance and resilience are probably High, and the biotope is assessed as Not sensitive.

Temperature decrease (local)

Benchmark. A 5°C decrease in temperature for one month, or 2°C for one year. Further detail

Evidence

Beggiatoa spp. mats have been reported from sulphur springs, deep water at ca 600 m, fjords, coastal marine sediments, salt marshes, organic-rich freshwater sediments, natural oil seeps and deep-sea hydrothermal vents (e.g. Spies & Davis, 1979; Hagen & Nelson, 1997; Björk et al., 2017; Salvo et al., 2017; Ramírez et al., 2021). Exton et al. (2024) reported that in rivers, Beggiatoa is known to grow from 0 to40°C, and can tolerate extremely low temperatures when ice fails to form due to de-icer runoff from airports, although the temperature requirements of individual strains of the bacterium are likely to vary.  However, its occurrence within the East Siberian Sea (OBIS, 2016) and the deep sea suggest it is unlikely to be affected by decreases in temperature at the benchmark level. Therefore, resistance and resilience are probably High, and the biotope is assessed as Not sensitive.

Salinity increase (local)

Benchmark. A increase in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

Beggiatoa is found in hypersaline lakes, such as Lake Chiprana in Spain, which has an average salinity of ~80 ppt (Hinck et al., 2007), though tolerances of individual strains of the bacterium are likely to vary. Freshwater strains and marine strains are different so an increase in salinity in brackish water sites may remove the freshwater strains of the bacterium, e.g. freshwater strains are unable to grow in salty conditions (Williams & Unz, 1989). However, if conditions of high nutrient and low oxygen concentration remain, mats may then be formed by marine strains. Therefore, a resistance of High is   suggested but with Low confidence. Hence, resilience is High and the biotope is assessed as Not sensitive.

Salinity decrease (local)

Benchmark. A decrease in one MNCR salinity category above the usual range of the biotope or habitat. Further detail

Evidence

Beggiatoa mats form in sewage wastewater and in marine conditions. However, freshwater strains and marine strains are different so a decrease in salinity may remove the marine strains. For example, freshwater strains were unable to grow in salty conditions (Williams & Unz, 1989). Salcedo et al. (2024) assessed the impact of salinity on microbial communities in Spanish wastewater treatment plants, and reported that Beggiatoa spp. were found exclusively at sites with salinity above ~4.675 ppt (value extrapolated from figures contained in Salcedo et al., 2024). However, if conditions of high nutrient and low oxygen concentration remain, mats may then be formed by freshwater strains. Therefore, a resistance of High is suggested but with low confidence. Hence, resilience is High and the biotope is assessed as Not sensitive.

Water flow (tidal current) changes (local)

Benchmark. A change in peak mean spring bed flow velocity of between 0.1 m/s to 0.2 m/s for more than one year. Further detail

Evidence

The biotope normally develops in areas of weak or negligible water flow rate, such as sea lochs and fjords, where hypoxic or anoxic conditions are able to develop, though some flow is required to replenish nutrients (Exton et al., 2024). Any further decrease in water flow is unlikely. . An increase in water flow is likely to result in increased mixing of the water column, and dispersal of any thermocline or halocline in the area, an increase in oxygenation of the water column and loss of the conditions required for growth of Beggiatoa spp. In a review of literature on river strains, Exton et al. (2024) noted that too fast a flow is likely to result in Beggiatoa mats being scoured away and proposed an upper limit of 0,6 m/s, though this could vary. In addition, in areas where anoxic or hypoxic conditions are caused by organic enrichment, increased water flow is likely to mitigate and reduce the level of hypoxia. However, an increase of 0.1-0.2 m/s (the benchmark) may reduce the level of hypoxia in naturally hypoxic areas.  Therefore, a resistance of Low is suggested but with Low confidence. Resilience is likely to be High so that sensitivity is assessed as Low.

Emergence regime changes

Benchmark.  1) A change in the time covered or not covered by the sea for a period of ≥1 year or 2) an increase in relative sea level or decrease in high water level for ≥1 year. Further detail

Evidence

The pressure benchmark is relevant only to littoral and shallow sublittoral fringe biotopes.

Wave exposure changes (local)

Benchmark. A change in near shore significant wave height of >3% but <5% for more than one year. Further detail

Evidence

The biotope develops in areas of very little water movement (wave sheltered to extremely wave sheltered conditions). Therefore, a further decrease in wave action is unlikely.  An increase in wave action would probably wash the mats away and increase mixing of the water column and, hence, oxygenation. However, a 3-5% change in significant wave height is unlikely to have a significant effect, .  Therefore, resistance and resilience are probably High, and the biotope is assessed as Not sensitive.

Transition elements & organo-metal contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed but evidence is presented where available.

Drewniak et al. (2016) reported that in Poland, microbial mats including Beggiatoa spp. occurred inside old gold and uranium mines and appeared to form a natural barrier, trapping heavy metals, Physiological and metagenomic analyses indicated that the bacteria are able to immobilize heavy metals and use them in respiratory processes, suggesting that they are unlikely to be negatively impacted.

Hydrocarbon & PAH contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

In many areas around the world (e.g. see Spies & Davis, 1979) mats of Beggiatoa are associated with localized intense oil seepage and so the biotope is likely to be relatively resistant to hydrocarbons. Following the Deepwater Horizon oil spill of 2010, Beggiatoa mats were reported at 58.9% of stations within 2 km of the wellhead one year later (Guarinello et al., 2022). Nevertheless, this pressure is Not assessed.

Synthetic compound contamination

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed but evidence is presented where available.

Radionuclide contamination

Benchmark. An increase in 10µGy/h above background levels. Further detail

Evidence

No evidence was found.

Introduction of other substances

Benchmark. Exposure of marine species or habitat to one or more relevant contaminants via uncontrolled releases or incidental spills. Further detail

Evidence

This pressure is Not assessed.

De-oxygenation

Benchmark. Exposure to dissolved oxygen concentration of less than or equal to 2 mg/l for one week (a change from WFD poor status to bad status). Further detail

Evidence

Jørgensen (1977) noted that Beggiatoa spp. was present in the upper few centimetres of oxic sediment in Limfjorden, Denmark, but mats of Beggiatoa are usually associated with hypoxic or anoxic conditions (Diaz & Rosenberg, 1995; Connor et al., 1997a, 2004). For example, during the autumn of 1993 and 1994 when the oxygen content of the bottom water in the Koljoford on the west coast of Sweden dropped, Beggiatoa mats covered the seafloor (Gustafsson & Nordberg, 1999). In Maine coastal waters in the U.S.A, the formation of Beggiatoa mats was linked to lack of oxygen when current speed was reduced for 2 hours or longer during a tidal cycle. At a chemocline formed by the meeting of oxygen- and sulphide-rich waters in the Red Sea, Beggiatoa mats covered 25-55% of the seafloor, with hypoxic waters being the main driver of their distribution (Jessen et al., 2016). In Sannäsfjord, Sweden, Beggiatoa mats formed after oxygen-depleted water entered the fjord in the summer of 2008 and were maintained by organic particles sinking to the bottom, resulting in anoxia (Björk et al., 2017). The formation of Beggiatoa mats only occurs when oxygen supply is reduced below the threshold level required to oxidize sedimented organic matter (Findlay, 2002). In Caol Scotnish, Loch Sween, bacterial mats of Beggiatoa were reported in the immediate vicinity of salmon cages in 1987. By 1988, the bacterial mats covered most of the seabed in the basin and the sediment was close to anoxic (Atkinson, 1989; Hughes, 1998a). Similarly, Beggiatoa mats have been reported immediately beneath mussel farms in Sweden (Bergström et al., 2024) and have been strongly associated with flocculent matter around salmon farms in Newfoundland, Canada (Salvo et al., 2017).

Therefore, the development of the biotope is dependent on hypoxic and anoxic conditions in the sediment.  The biotope is assessed as Not sensitive (resistance and resilience are High) to deoxygenation. However, the biotope would be destroyed and lost by increased oxygen levels.

Nutrient enrichment

Benchmark. Compliance with WFD criteria for good status. Further detail

Evidence

Mats of Beggiatoa are usually associated with and develop in the presence of high organic loadings such as those found under salmon farm cages (Lumb, 1989; Davies et al., 1996, Atkinson, 1989; Salvo et al., 2017), mussel farms (Bergström et al., 2024), and coastal areas of eutrophication (Graco et al., 2001). In Sannäsfjord, Sweden, Beggiatoa mats formed after oxygen-depleted water entered the fjord in the summer of 2008 and were maintained by organic particles sinking to the bottom, resulting in anoxia, after the levels of nitrogen carried by the nearby river increased from 21 tons/year between 1988 and1992 to 35 tons/year between 2004 and2008 (Björk et al., 2017). In a systematic literature review, Exton et al. 2024) confirmed that Beggiatoa spp. is a key component of “sewage fungus”, a buildup of bacterial mats triggered by organic pollution. In laboratory culture, Beggiatoa spp. starved of phosphorus for five generations exhibited extremely rapid (within 10 minutes) uptake when phosphorus was reintroduced, suggesting a highly variable uptake capacity of 0.6 to 6 mmol/m²/day in coastal sediments (Iakovchuk et al., 2025). Therefore, an increase in nutrients will encourage the development of the bacterial mats.  The biotope is probably Not sensitive (resistance and resilience are High) to nutrient enrichment.

Organic enrichment

Benchmark. A deposit of 100 gC/m²/yr. Further detail

Evidence

Mats of Beggiatoa are usually associated with and develop in the presence of high organic loadings such as those found under salmon farm cages (Lumb, 1989; Davies et al., 1996, Atkinson, 1989; Salvo et al., 2017), mussel farms (Bergström et al., 2024), and coastal areas of eutrophication (Graco et al., 2001). In Sannäsfjord, Sweden, Beggiatoa mats formed after oxygen-depleted water entered the fjord in the summer of 2008 and were maintained by organic particles sinking to the bottom, resulting in anoxia, after the levels of nitrogen carried by the nearby river increased from 21 tons/year between 1988 and1992 to 35 tons/year between 2004 and2008 (Björk et al., 2017). In a systematic literature review, Exton et al. 2024) confirmed that Beggiatoa spp. is a key component of “sewage fungus”, a buildup of bacterial mats triggered by organic pollution. In laboratory culture, Beggiatoa spp. starved of phosphorus for five generations exhibited extremely rapid (within 10 minutes) uptake when phosphorus was reintroduced, suggesting a highly variable uptake capacity of 0.6 to 6 mmol/m²/day in coastal sediments (Iakovchuk et al., 2025). Therefore, an increase in organic enrichment will encourage the development of the bacterial mats.  The biotope is assessed as Not sensitive (resistance and resilience are High) to organic enrichment.

Physical loss (to land or freshwater habitat)

Benchmark. A permanent loss of existing saline habitat within the site. Further detail

Evidence

All marine habitats and benthic species are considered to have a resistance of ‘None’ to this pressure and to be unable to recover from a permanent loss of habitat (resilience is ‘Very Low’).  Sensitivity within the direct spatial footprint of this pressure is, therefore ‘High’.  Although no specific evidence is described confidence in this assessment is ‘High’, due to the incontrovertible nature of this pressure.

Physical change (to another seabed type)

Benchmark. Permanent change from sedimentary or soft rock substrata to hard rock or artificial substrata or vice-versa. Further detail

Evidence

If sedimentary substrata were replaced with rock substrata the biotope would be lost, as it would no longer be a sedimentary habitat as described under the habitat classification.  Jørgensen (1977) noted that Beggiatoa was absent from fine and medium sands in the Limfjorden, Denmark but abundant on muds. Therefore, a change to rock substratum would probably result in loss of Beggiatoa mats.

Sensitivity assessment. Resistance to the pressure is considered ’None‘, and resilience ’Very low‘ or ‘None’ (as the pressure represents a permanent change) and the sensitivity of this biotope is assessed as ’High’.

Physical change (to another sediment type)

Benchmark. Permanent change in one Folk class (based on UK SeaMap simplified classification). Further detail

Evidence

Beggiatoa spp. is recorded from muds and decaying plant matter (Jørgensen, 1977). Jørgensen (1977) noted that Beggiatoa was absent from fine and medium sands in the Limfjorden, Denmark but abundant on muds. Similarly, this biotope (IFiMu.Beg) is only recorded from muds (Connor et al., 2004). Therefore, a change in sediment type by one Folk class (see Long, 2006), e.g. from mud to sandy mud and sand would result in loss of the biotope. Therefore, a resistance of None is recorded. As the change is permanent, resilience is Very low and sensitivity is assessed as High.

Habitat structure changes - removal of substratum (extraction)

Benchmark. The extraction of substratum to 30 cm (where substratum includes sediments and soft rock but excludes hard bedrock). Further detail

Evidence

The mats of Beggiatoa spp. sit on the surface of the substratum. Extraction of sediment to 30 cm (the benchmark) could remove the bacterial mats in the affected area.  Hence, the resistance is probably None and resilience is probably High, resulting in a sensitivity of Medium.

Abrasion / disturbance of the surface of the substratum or seabed

Benchmark. Damage to surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

The bacteria produces a polysaccharide matrix that binds the bacteria together and to the substratum. But mats of Beggiatoa form on soft mud and so are likely to be broken up by abrasion or physical disturbance. Therefore, a resistance of Low is suggested with Low confidence. However, resilience is probably High so that the sensitivity is assessed as Low.

Penetration or disturbance of the substratum subsurface

Benchmark. Damage to sub-surface features (e.g. species and physical structures within the habitat). Further detail

Evidence

The bacteria produces a polysaccharide matrix that binds the bacteria together and to the substratum. But mats of Beggiatoa form on soft mud and so are likely to be broken up by abrasion or physical disturbance. Therefore, a resistance of Low is suggested with Low confidence. However, resilience is probably High so that the sensitivity is assessed as Low.

Changes in suspended solids (water clarity)

Benchmark. A change in one rank on the WFD (Water Framework Directive) scale e.g. from clear to intermediate for one year. Further detail

Evidence

Beggiatoa spp. has no dependency on light or detritus, and no feeding structures to clog with sediment. This biotope is recorded from sheltered areas, on fine sediments, subject to high suspended sediment loads. Therefore, resistance is probably High and, hence, resilience is also High, and the biotope is probably Not sensitive at the benchmark level.

Smothering and siltation rate changes (light)

Benchmark. ‘Light’ deposition of up to 5 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

Beggiatoa spp. sit at the anoxia/hypoxia interface and can ‘glide’ across the surface of the substratum. It occurs in muds in sheltered areas and is probably adapted to high sediment loads and accretion rates. In Newfoundland, Canada, Salvo et al. (2017) reported that Beggiatoa mats were particularly associated with flocculent matter (accumulated faeces and fish food) in the immediate vicinity of salmon farms, with 60% of identified mats occurring on this substratum and persisting after 15 months of fallowing (the pausing of farm production to reduce impacts on the benthic environment and/or as a pest management tool). However, no information on rapid sedimentation was found. The bacterium is found within the top few centimetres of the sediment (Jørgensen, 1977) so that the bacterium itself would probably survive smothering but the mats would probably disappear temporarily.  Therefore, a resistance of Low is suggested with Low confidence, but resilience is High so that the sensitivity is assessed as Low.

Smothering and siltation rate changes (heavy)

Benchmark. ‘Heavy’ deposition of up to 30 cm of fine material added to the seabed in a single discrete event. Further detail

Evidence

Beggiatoa spp. sit at the anoxia/hypoxia interface and can ‘glide’ across the surface of the substratum. It occurs in muds in sheltered areas and is probably adapted to high sediment loads and accretion rates. In Newfoundland, Canada, Salvo et al. (2017) reported that Beggiatoa mats were particularly associated with flocculent matter (accumulated faeces and fish food) in the immediate vicinity of salmon farms, with 60% of identified mats occurring on this substrate and persisting after 15 months of fallowing (the pausing of farm production to reduce impacts on the benthic environment and/or as a pest management tool). However, no information on rapid sedimentation was found. The bacterium is found within the top few centimetres of the sediment (Jørgensen, 1977) so that the bacterium itself would probably survive smothering but the mats would probably disappear temporarily.  Therefore, a resistance of Low is suggested with Low confidence but resilience is High so that the sensitivity is assessed as Low.

Litter

Benchmark. The introduction of man-made objects able to cause physical harm (surface, water column, seafloor or strandline). Further detail

Evidence

Not assessed.

Electromagnetic changes

Benchmark. A local electric field of 1 V/m or a local magnetic field of 10 µT. Further detail

Evidence

Evidence on the effect of electromagnetic fields (EMFs) on benthic organisms is still severely lacking. Some studies have investigated the effect of anthropogenically induced EMFs on benthic invertebrates at intensities ranging between 2 nT and 40 mT, which is often much higher than in-situ measurements from subsea cables. While some report changes to behaviour, physiology, reproduction, development, immunology, cytotoxicity and orientation, others demonstrate no effect from exposure to the EMF (Albert et al., 2020; Hutchison et al., 2020), depending on the study species and duration and intensity of exposure. There have been no studies investigating the effect of EMFs at the population or community level for benthic organisms. 

Sensitivity assessment. Given the lack of data at the level of individual biotopes, resistance and resilience to EMFs cannot be robustly assessed. Sensitivity is therefore recorded as 'Insufficient evidence'.

Underwater noise changes

Benchmark. MSFD indicator levels (SEL or peak SPL) exceeded for 20% of days in a calendar year. Further detail

Evidence

Motile bacteria may respond to local vibration but the important characteristic species are unlikely to respond to noise as described under this pressure.
 

Introduction of light or shading

Benchmark. A change in incident light via anthropogenic means. Further detail

Evidence

Beggiatoa spp. utilize sulphides leaching from the sediment and oxidize them to sulphate to liberate energy for growth, but also require simple organic acids and alcohols for growth (Williams & Unz, 1989; Hagen & Nelson, 1997). The other organisms present (e.g. ciliates, nematodes, and euglenoid flagellates) are probably decomposers, feeding on organic matter. However, Bernhard et al. (2000) noted several species of protist contained symbiotic bacteria that were presumably chemoautotrophs. The sediment below the mats is populated by chemoautotrophic bacteria that remineralize organic matter, producing methane or sulphides of hydrogen (H₂S), iron or manganese and are probably very similar to microbial communities found at depth in other sediments (for a summary see Davies et al., 1996).  Grim et al. (2023) reported that freshwater Beggiatoa strains were more abundant in the North American Great Lakes in autumn due to lower light levels, which promoted more anoxygenic photosynthesis, although it is unclear whether the same is true of marine strains. In mats consisting of Beggiatoa spp. and cyanobacteria, the mat structure can change depending on ambient light conditions, with cyanobacteria migrating to the top of the mat in both low- and high-light acclimation treatments (75 and 1000 75 μmol photons /m²/s, respectively), while in dark-acclimated mats, Beggiatoa formed the top layer instead. Therefore, the biotope has no dependency on light and resistance is assessed as High. Resilience is High and the biotope is assessed as Not sensitive.

Barrier to species movement

Benchmark. A permanent or temporary barrier to species movement over ≥50% of water body width or a 10% change in tidal excursion. Further detail

Evidence

Not relevant - this pressure is considered applicable to mobile species, e.g. fish and marine mammals rather than seabed habitats. Physical and hydrographic barriers may limit the dispersal of seed.  But seed dispersal is not considered under the pressure definition and benchmark.

Death or injury by collision

Benchmark. Injury or mortality from collisions of biota with both static or moving structures due to 0.1% of tidal volume on an average tide, passing through an artificial structure. Further detail

Evidence

Not relevant to seabed habitats. 

Visual disturbance

Benchmark. The daily duration of transient visual cues exceeds 10% of the period of site occupancy by the feature. Further detail

Evidence

Not relevant

Genetic modification & translocation of indigenous species

Benchmark. Translocation of indigenous species or the introduction of genetically modified or genetically different populations of indigenous species that may result in changes in the genetic structure of local populations, hybridization, or change in community structure. Further detail

Evidence

No evidence of genetic modification, breeding, or translocation was found.

Introduction of microbial pathogens

Benchmark. The introduction of relevant microbial pathogens or metazoan disease vectors to an area where they are currently not present (e.g. Martelia refringens and Bonamia, Avian influenza virus, viral Haemorrhagic Septicaemia virus). Further detail

Evidence

No evidence was found.

Removal of target species

Benchmark. Removal of species targeted by fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

Beggiatoa spp. are unlikely to be targeted by commercial or recreational fisheries or other harvest. The presence of mats of Beggiatoa spp. indicate that conditions are anoxic and potentially abiotic.

Removal of non-target species

Benchmark. Removal of features or incidental non-targeted catch (by-catch) through targeted fishery, shellfishery or harvesting at a commercial or recreational scale. Further detail

Evidence

The presence of mats of Beggiatoa spp. indicate that conditions are anoxic and potentially abiotic. Affected areas are unlikely to be targeted by commercial or recreational fisheries or other harvest.

The American slipper limpet, Crepidula fornicata

Evidence

The anoxic conditions required for Beggiatoa mats to form actively exclude the majority of other benthic taxa, Furthermore, the muddy sediment that characterizes this biotope is unsuitable for Crepidula fornicata. The biotope is therefore assessed as ‘Not sensitive’.

The carpet sea squirt, Didemnum vexillum

Evidence

The anoxic conditions required for Beggiatoa mats to form actively exclude the majority of other benthic taxa, Furthermore, the muddy sediment that characterizes this biotope is unsuitable for Didemnum vexillum. The biotope is therefore assessed as ‘Not sensitive’.

The Pacific oyster, Magallana gigas

Evidence

The anoxic conditions required for Beggiatoa mats to form actively exclude the majority of other benthic taxa, Furthermore, the muddy sediment that characterizes this biotope is unsuitable for Magallana gigas. The biotope is therefore assessed as ‘Not sensitive’.

Wireweed, Sargassum muticum

Evidence

The anoxic conditions required for Beggiatoa mats to form actively exclude the majority of other benthic taxa, Furthermore, the muddy sediment that characterizes this biotope is unsuitable for Sargassum muticum. The biotope is therefore assessed as ‘Not sensitive’.

Wakame, Undaria pinnatifida

Evidence

The anoxic conditions required for Beggiatoa mats to form actively exclude the majority of other benthic taxa, Furthermore, the muddy sediment that characterizes this biotope is unsuitable for Undaria pinnatifida. The biotope is therefore assessed as ‘Not sensitive’.

Other INIS

Evidence

The anoxic conditions required for Beggiatoa mats to form actively exclude the majority of other benthic taxa, however no evidence was found on which to base an assessment.