MarLIN

information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Gut weed (Ulva intestinalis)

Distribution data supplied by the Ocean Biogeographic Information System (OBIS). To interrogate UK data visit the NBN Atlas.

Summary

Description

Ulva intestinalis is a conspicuous bright grass-green seaweed, consisting of inflated irregularly constricted, tubular fronds that grow from a small discoid base. Fronds are typically unbranched. Fronds may be 10-30 cm or more in length and 6-18 mm in diameter, the tips of which are usually rounded. Like other members of the genus, Ulva intestinalis is a summer annual, decaying and forming masses of bleached white fronds towards the end of the season.

Recorded distribution in Britain and Ireland

Common all round the coasts of Britain and Ireland.

Global distribution

More or less world-wide in its distribution.

Habitat

Occurs in a wide range of habitats on all levels of the shore. Where suitable support is available, it will grow on rocks, mud, sand and in rock pools. It is abundant in brackish water areas, where there is appreciable fresh water run off and in wet areas of the splash zone. It is also a common epiphyte on other algae and shells. The seaweed may become detached from the substratum, and buoyed up by gas, rises to the surface, where it continues to grow in floating masses.

Depth range

Into the sublittoral

Identifying features

Separation of species within the genus is difficult and reliant on cellular features, but

  • Simple thalli (fronds) arise from a small discoid base.
  • Thalli light to dark grass-green in colour.
  • Thallus completely tubular and elongate, increasing in width from base to mid thallus.
  • Mature specimens, are 'crisped' and irregularly inflated
  • Thalli typically unbranched (see additional information).

Additional information

Origin of species name
Adjective (Latin), relating to or found in the intestines (Guiry & Nic Dhonncha, 2002).

Identification
A recent molecular study suggested that the genus Enteromorpha is synonymous with the genus Ulva (Hayden et al., 2003). Species within the genus Ulva are difficult to identify. Identification is heavily reliant on cell detail and cell arrangement, in addition to gross morphology, but complicated by the fact that the morphology of a single species can vary in response to environmental conditions. For instance, Ulva intestinalis and Ulva compressa (as Enteromorpha) are two distinct, genetically divergent and reproductively isolated species (Blomster et al., 1998). They are, however, difficult to distinguish. The presence or absence of branching fronds was the most useful gross morphological characteristic distinguishing these two species (Ulva intestinalis being unbranched). But ambiguity exists because low salinity or salinity shock can induce branching in Ulva intestinalis. However, if environmental factors, such as salinity are taken into account, branching can be used to identify the great majority of thalli correctly (Blomster et al., 1998).

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Biology review

Taxonomy

PhylumChlorophyta
ClassUlvophyceae
OrderUlvales
FamilyUlvaceae
GenusUlva
AuthorityLinnaeus, 1753
Recent SynonymsEnteromorpha intestinalis Linnaeus, 1753

Biology

Typical abundanceHigh density
Male size range
Male size at maturity
Female size rangeLarge(>50cm)
Female size at maturity
Growth formStraplike / Ribbonlike
Growth rate0.15-0.25cm/day
Body flexibilityHigh (greater than 45 degrees)
Mobility
Characteristic feeding methodAutotroph
Diet/food source
Typically feeds onSpecies is a photoautotroph.
Sociability
Environmental positionEpifloral
DependencyIndependent.
SupportsNone
Is the species harmful?No

Biology information

Growth rate
Parchevskij & Rabinovich (1991) cultivated Ulva intestinalis (as Enteromorpha intestinalis) on horizontally and vertically suspended ropes in coastal Black Sea areas polluted with sewage and waste water effluents. Specific growth rate of the seaweed during the spring-summer period was found to be 0.15-0.25 cm/day. A harvest weight of 2600-3000 g/m2 and 3400-4700 g/m2 was obtained within two weeks on horizontal and vertical ropes respectively.

Associated fauna
Ulva intestinalis provides shelter for the orange harpacticoid copepod, Tigriopus brevicornis, and the chironomid larva, Halocladius fucicola (McAllen, 1999). Ulva intestinalis is often the only seaweed found in supralittoral rockpools, and the copepod and chironomid species utilize the hollow thallus of Ulva intestinalis as a moist refuge from desiccation when the rockpools completely dry out. Several hundred individuals of Tigriopus brevicornis have been observed in a single thallus of Ulva intestinalis (McAllen, 1999). Many other intertidal species are often found amongst dense growths of Ulva in deep splash zone pools.

Floating masses
Ulva intestinalis may become detached from the substratum, and buoyed up by gas, float to the surface where they continue to grow. Such mats of unattached Ulva intestinalis are most frequent in summer. For instance, the occurrence of a summer mass of unattached Ulva intestinalis (as Enteromorpha intestinalis) was studied by Baeck et al. (2000) on the Finnish Baltic Sea west coast. The thalli of the seaweed lost their tubular shape, spread, and formed unattached monostromatic sheets. Mats were between 5-15 cm thick, with a biomass of 97 tonnes in an area of 3.7 km2 in 1993.

Habitat preferences

Physiographic preferencesOpen coast, Strait / sound, Ria / Voe, Enclosed coast / Embayment
Biological zone preferencesLower littoral fringe, Mid eulittoral, Supralittoral, Upper eulittoral, Upper littoral fringe
Substratum / habitat preferencesBedrock, Cobbles, Large to very large boulders, Muddy sand, Small boulders
Tidal strength preferencesNo information
Wave exposure preferencesExtremely sheltered, Moderately exposed, Sheltered, Ultra sheltered, Very sheltered
Salinity preferencesFull (30-40 psu), Low (<18 psu), Reduced (18-30 psu), See additional Information, Variable (18-40 psu)
Depth rangeInto the sublittoral
Other preferencesNo text entered
Migration PatternNot relevant

Habitat Information

Ulva intestinalis is remarkably euryhaline, in that it can grow in freshwater. However, there is evidence for the existence of genetic strains adapted to high and low salinities (Reed & Russell, 1979).

Life history

Adult characteristics

Reproductive typeAlternation of generations
Reproductive frequency Annual protracted
Fecundity (number of eggs)>1,000,000
Generation time<1 year
Age at maturitySee additional information
SeasonSee additional information
Life span<1 year

Larval characteristics

Larval/propagule type-
Larval/juvenile development Spores (sexual / asexual)
Duration of larval stageSee additional information
Larval dispersal potential Greater than 10 km
Larval settlement periodNot relevant

Life history information

Species of the genus Ulva are rapidly growing opportunists, favoured by the frequency and speed of their reproduction. The short lived plants reach maturity at a certain stage of development rather than relying on an environmental trigger. Ulva intestinalis can be found in reproductive condition at all times of the year, but maximum development and reproduction occur during the summer months especially towards the northern end of the distribution of the species (Burrows, 1991). The life history consists of an isomorphic (indistinguishable except for the type of reproductive bodies produced) alternation between haploid gametophytic and diploid sporophytic generations, but can be modified by environmental conditions (Burrows, 1959; Moss & Marsland, 1976; Reed & Russell, 1978). McArthur & Moss (1979) examined the process of gametogenesis and gamete structure using scanning and transmission electron microscopy.
The haploid gametophytes of Ulva produce enormous numbers of biflagellate motile gametes which cluster and fuse to produce a sporophyte (diploid zygote). The sporophyte matures and produces by meiosis large numbers of quadriflagellate zoospores that mature as gametophytes, and the cycle is repeated. Both gametes and spores may be released in such quantities into rock pools or slack water that the water mass is coloured green (Little & Kitching, 1996). Together spores and gametes are termed 'swarmers'. Swarmers are often released in relation to tidal cycles, with the release being triggered by the incoming tide as it wets the thallus. However, the degree of release is usually related to the stage of the spring/neap tidal cycle, so allowing regular periodicity and synchronization of reproduction (Little & Kitching, 1996). Christie & Evans (1962) found that swarmer release of Ulva intestinalis (as Enteromorpha intestinalis) from the Menai Straits, Wales, peaked just before the highest tides of each neap-spring cycle.
Mobility of swarmers belonging to Ulva intestinalis (as Enteromorpha intestinalis) can be maintained for as long as 8 days (Jones & Babb, 1968). Algae such as Ulva intestinalis tend to have large dispersal shadows, with propagules being found far from the nearest adult plants, e.g. 35 km (Amsler & Searles, 1980).

Sensitivity reviewHow is sensitivity assessed?

Physical pressures

 IntoleranceRecoverabilitySensitivityEvidence/Confidence
High Very high Low Moderate
Ulva intestinalis, forms a permanent attachment to a solid substratum (although the species may continue to grow in mats if displaced from the substratum, it requires a substratum for development), so would be intolerant of substratum loss. Intolerance has been assessed to be high and recoverability very high (see additional information below).
High Very high Low Moderate
Ulva intestinalis is a filamentous seaweed without structural support for its thalli, therefore it is likely that entire plants would be smothered by an additional covering of 5 cm of sediment. Smothering would interfere with photosynthesis and over the period of one month the seaweed may begin to rot. Intolerance to smothering has been assessed to be high. However, on return to prior conditions the species is likely to rapidly recolonize the available substratum (see additional information below) and recoverability has been assessed to be very high.
Intermediate Very high Low Low
The effects of increased suspended sediment on adults is likely to be indirect but include smothering (above) as a result of siltation, and increased turbidity and therefore light attenuation (see below). In areas where Ulva intestinalis occurs on the shore, current flows are reduced and siltation is likely to be increased. Spores, germlings and juveniles are likely to be highly intolerant of sediment scour and smothering (Vadas et al. 1992). However, Ulva intestinalis also occurs in estuarine environments where elevated levels of suspended sediment are likely to be experienced, so the species may demonstrate some tolerance. Intolerance has been assessed to be intermediate, as a proportion of the population , especially germlings may be adversely affected by increased suspended sediment. Recoverability has been assessed to be very high (see additional information below).
Tolerant Not relevant Not sensitive Not relevant
Ulva intestinalis is unlikely to be affected by a decrease in suspended sediment concentrations, and an assessment of tolerant has been made.
Low Very high Very Low Moderate
Ulva intestinalis is often very abundant on the high shore where desiccation stress is the primary factor controlling seaweed distribution, and may even be found above the tidal limits of the shore. Ulva intestinalis (studied as Enteromorpha intestinalis) can survive several weeks of living in completely dried out rock pools, while becoming completely bleached on the uppermost layers, but remaining moist underneath the bleached fronds. Its ability to survive out of water for so long makes it an ideal refuge for copepods in supralittoral rockpools (McAllen, 1999). Several studies have indicated that stress from aerial exposure can cause high mortality to algal propagules. Baker (1910) found a positive correlation between the vertical distribution of a species and the ability of zygotes to develop in desiccated environments. Hruby & Norton (1979) found that 7-14 day old germlings of Ulva (studied as Enteromorpha) were more tolerant of desiccation than earlier stages, so an increase in desiccation stress may impact more adversely on newly settled germlings than more mature plants. An intolerance assessment of low has been made to the benchmark change in desiccation and recoverability recorded to be very high (see additional information below).
Tolerant* Not relevant Not sensitive* Low
Ulva intestinalis is often very abundant on the high shore where desiccation stress is the primary factor controlling seaweed distribution, and may even be found above the tidal limits of the shore, so is tolerant of emergence to some extent. Furthermore, above Mean High Water Springs (MHWS) level, Ulva intestinalis tends to preferentially inhabit rock pools or is associated with trickles of freshwater that cross the shore, and in such positions the risk of desiccation is reduced. Owing to increased emergence, the species that graze on Ulva intestinalis are likely to be less active, owing to risk of desiccation, and the seaweed may benefit from reduced grazing pressure. An assessment of tolerant* has been made.
Low Very high Very Low Low
Ulva intestinalis is unlikely to be directly affected by a decrease in the emergence regime, as occurs into the subtidal zone. However, it is the preferred food resource of the snail Littorina littorea (Lubchenco, 1978) and is grazed by other prosobranchs, all of which will probably be more active grazing during periods of immersion, so that the additional grazing pressure is likely to affect the population. An intolerance assessment of low has been made. A recoverability of very high has been recorded (see additional information, below).
Intermediate Very high Low Very low
Ulva intestinalis is not of a growth form that offers resistance to tidal flow. The fronds would conform to the direction of the flow until drag effects caused tearing of the fronds or dislodgement of the holdfast. Increased scour from sand mobilized by increased tidal streams may cause more damage to the seaweed than increased water flow itself. However, recovery of the species is unlikely to be inhibited by increases water flow. For instance, Houghton et al. (1973) observed that swarmers of Ulva were able to settle onto surfaces subjected to water speeds of up to 10.7 knots. Intolerance has been assessed to be intermediate, as a proportion of the population may be damaged by increased water flow. Recruitment is not likely to be adversely affected and has been assessed to be very high (see additional information, below).
Tolerant Not relevant Not sensitive Not relevant
Ulva intestinalis is unlikely to be adversely affected by a decrease in water flow rate, as it occurs in locations, e.g. rockpools, where water flow is negligible. An assessment of tolerant has been made.
Tolerant* Not relevant Not sensitive* High
Ulva intestinalis occurs to the south of the British Isles, so is likely to be tolerant of a chronic increase in temperature of 2°C. Also, it is characteristic of upper shore rock pools, where water and air temperatures are greatly elevated on hot days. Clarke (1992) reviewed the influence of cooling water effluent on shore communities. Effects are usually restricted to the immediate vicinity of the outfall, but brown seaweeds of the genus, e.g. Ascophyllum and Fucus were eliminated from a rocky shore heated to 27-30 °C by a power station in Maine, whilst Ulva intestinalis (as Enteromorpha intestinalis) increased significantly near the outfall (Vadas et al., 1976). The evidence suggests that Ulva intestinalis would probably tolerate the benchmark increase in temperature and may benefit indirectly (through loss of competitors) and an assessment of tolerant* has been made.
Tolerant Not relevant Not sensitive High
Ulva intestinalis occurs to the north of the British Isles, so is likely to be tolerant of a chronic decrease in temperature of 2°C, and one of the factors contributing to its success as a fouling organism, is its ability to withstand a wide range and variation of temperature Ulva sp. (as Enteromorpha) were reported to be tolerant of a temperature of -20°C (Kylin, 1917). The evidence suggests that Ulva intestinalis would tolerate the benchmark decrease in temperature.
Low Very high Very Low Low
The light attenuating effects of increased turbidity are likely to impact on the photosynthetic efficiency of Ulva intestinalis, with consequential effects on growth. An intolerance assessment of low has been made to reflect the effect of increased turbidity on the viability of the species. On return to prior conditions recovery is likely to be rapid and growth resume, a recoverability of very high has been recorded.
Tolerant* Not relevant Not sensitive* Low
As a photoautotroph, Ulva intestinalis, is likely to benefit from reduced turbidity, as the light attenuating effects of turbid water reduce photosynthesis. An assessment of tolerant* has been made.
Low Very high Very Low Moderate
Wave induced scouring and burial of habitats by sand tends to prevent seaweed growth, except for those that are stress tolerant, robust perennials, or opportunistic ephemeral species such as Ulva intestinalis. This species settles when disturbance is at a minimum and rocks are bare, reproduces and disappears when physical disturbance begins again. In wave exposed locations, it is likely that an increase in wave exposure would inhibit settlement of propagules belonging to Ulva intestinalis so that a population would become impoverished. An intolerance assessment of low has been made to reflect the probable impact on the species recruitment. On return to prior conditions, recovery is likely to occur within a matter of weeks, and recoverability has been assessed to be very high (see additional information, below).
Tolerant Not relevant Not sensitive Low
Ulva intestinalis occurs in locations with a variety of wave exposures. It is unlikely that the species would be directly adversely affected by decreased wave exposure. An assessment of tolerant has been made.
Not relevant Not relevant Not relevant Not relevant
Seaweeds have no known mechanism for noise perception.
Not relevant Not relevant Not relevant Not relevant
Seaweeds have no known mechanism for visual perception.
High Very high Low Moderate
Ulva intestinalis is likely to be susceptible to abrasion as it is not of a resilient growth form and would easily be scraped from the substratum by dragging objects. Therefore, intolerance has been assessed as high. However, Ulva intestinalis reproduces rapidly to colonize available substrata, and recoverability has been assessed to be very high (see additional information below).
Tolerant Not relevant Not sensitive Moderate
Ulva intestinalis typically forms a permanent attachment to suitable substrata, suggesting that it would be intolerant of displacement. However, in some circumstances, the algae may becomes detached from the substratum, and buoyed-up by gas, it floats up to the surface and continues to grow in mats (e.g. Baeck et al., 2000). The thalli of the seaweed tend to loose their tubular shape, spread, and formed unattached monostromatic sheets. On account of the ability of the algae to continue growing as an unattached mat, following displacement, an assessment of not sensitive has been made.

Chemical pressures

 IntoleranceRecoverabilitySensitivityEvidence/Confidence
Intermediate High Low High
Ulva intestinalis has been assessed to have an intermediate intolerance to synthetic chemical pollution as available evidence highlights adverse effects upon the species viability and damage leading to death.
For instance, although herbicides tend not to be used directly in the marine environment, they can enter estuarine areas via river discharge and runoff. Paraquat and 3AT were tested for their effects on the settlement, germination and growth of Ulva (as Enteromorpha) (Moss & Woodhead, 1975). They found that zygotes were able to develop into filaments in the presence of Paraquat at 7 mg/L, but that germination was deferred at higher concentrations. Zygotes demonstrated increased resistance when they settled in clumps on the substratum, and green thalli of Ulva were more susceptible than ungerminated zygotes. Ulva was more intolerant of 3AT than to Paraquat.
However, synthetic chemicals used as antifouling agents may be directly introduced into the marine environment. Scarlett et al. (1997) analyzed water samples taken from the Plymouth Sound locality for the presence of the s-triazine herbicide, Irgarol 1051, which is an ingredient of antifouling paints used on pleasure boats and ships. Irgarol 1051 was detected at all sampling sites within the Sound; the highest levels were found in close proximity to areas of high boat density, especially where water flow was restricted within marinas, although concentrations within the semi-enclosed Sutton Harbour were less than values predicted from leach rate data. The highest detected concentration of over 120 ng/L significantly inhibited the growth of Ulva intestinalis (as Enteromorpha intestinalis) spores under laboratory conditions; the no effect concentration was 22 ng/L. Photosynthetic efficiency in the adult frond of Ulva intestinalis from Sutton Harbour marina was inhibited by Irgarol 1051 in the laboratory with an EC 50 (72 h) of 2.5 µg/L. A small adverse impact on Ulva intestinalis reproduction within harbours is therefore likely.
Following the Torrey Canyon tanker oil spill, copious amounts of solvent based detergents were sprayed directly on to the shore. Algae on the higher shore was especially affected, and included Ulva intestinalis (as Enteromorpha intestinalis in high level rock pools where it was killed (Smith, 1968).
Assuming deterioration of contaminants, recoverability has been assessed to be high (see additional information below).
Heavy metal contamination
Low Very high Very Low Moderate
The order of metal toxicity to algae varies, with the algal species and experimental conditions, but generally the order is Hg>Cu>Cd>Ag>Pb>Zn (Rice et al., 1973; Rai et al., 1981). The effects of copper on macrophytes have been more extensively studied than the effects of any other metal owing to its use in antifouling paints. Lewis et al. (1998) investigated the influence of copper exposure and heatshock on the physiology and cellular stress response of Ulva intestinalis (as Enteromorpha intestinalis). Heat shock proteins (HSPs) are known to be expressed in response to a variety of stress conditions, including heavy metals (Lewis et al., 1999). Ulva intestinalis was exposed to a range of copper concentrations (0-500 µg -1 for 5 days, to assess the effect of copper exposure on stress proteins (Stress-70 levels) and physiology of the seaweed. Stress-70 was induced by copper exposure, but was found to be no better an indicator of copper exposure than measurement of growth, which is inhibited by copper.
Species of the genus Ulva seem to be especially suitable for monitoring heavy metals in coastal areas and estuaries as it is ubiquitous in both and laboratory experiments have shown that accumulation of Cu, Zn, Cd and Pb by four different species of Ulva (as Enteromorpha) was sufficiently similar to justify pooling samples of the genus for field monitoring (Say et al., 1990). The interactions of salinity and temperature with toxicity are not always clear. For instance, Munda (1984) found that the Zn, Mn and Co accumulations in Ulva intestinalis (as Enteromorpha intestinalis) could be enhanced by decreasing the salinity.
In the absence of evidence to the contrary, an intolerance assessment of low has been made, as available evidence suggests that Ulva is relatively tolerant of heavy metal exposure at environmentally realistic concentrations, but experiences reduced growth. On return to prior conditions, and assuming deterioration of the contaminants recovery would probably be rapid.
Hydrocarbon contamination
High Very high Low High
Ulva intestinalis is likely to demonstrate intolerance to hydrocarbon contamination. Likely effects include smothering, inhibition of respiration and photosynthesis, bleaching and interference with reproduction, so that affected populations may be destroyed. Intolerance has been assessed to be high. However, the species tends to recover very rapidly from oil pollution incidents. For instance, after the Torrey Canyon tanker oil in 1967, grazing species were killed, and a dense flush of ephemeral green algae (Ulva, Blidingia) appeared on the rocky shore within a few weeks and persisted for up to one year (Smith, 1968). Recoverability has been assessed to be very high (see additional information, below).
Radionuclide contamination
No information Not relevant No information Not relevant
Ulva sp. are known to be able to acquire large concentrations of substances from surrounding water. In the vicinity of the Sellafield nuclear plant, England, Ulva (as Enteromorpha) sp. accumulated zirconium, niobium, cerium and plutonium-239, however the species appeared to be unaffected by the radionuclides (Clark, 1997).
Changes in nutrient levels
Tolerant* Not relevant Not sensitive* Moderate
Nitrogen enrichment enhances growth of Ulva intestinalis (as Enteromorpha intestinalis) (Kamer & Fong, 2001), making the species a useful indicator of nutrient enrichment, although it also thrives in 'un-enriched' water. High levels of nutrient enrichment were found to mitigate the negative effects that reduced salinity can have on the growth of the species (Kamer & Fong, 2001). An assessment of tolerant* has been made as Ulva intestinalis is likely to increase in abundance as a consequence of nutrient enrichment.
However, excessive growth of green seaweeds in response to nutrients derived from sewage effluent is becoming an increasingly common phenomena in sheltered marine bays (e.g. Soulsby et al., 1985). An overabundance of Ulva (as Enteromorpha) on the tidal flats of the Wadden Zee during summer was attributed to eutrophication by adjacent sewage effluents (Reise, 1983). Mats were initially composed of Ulva, but later joined by Cladophora, Chaetomorpha and Porphyra. The mats became anchored to the feeding tunnels of the abundant Arenicola marina, and so avoided displacement by tidal currents. Although the mats lasted little longer than a month, the sediment beneath the algal mats became anoxic, and the species composition was affected.
Tolerant Not relevant Not sensitive Moderate
Ulva intestinalis has a cosmopolitan distribution throughout coastal areas and estuaries and is considered to be a remarkably euryhaline species, tolerant of extreme salinities ranging from 0 psu to 136 psu.
However, on the basis of evidence available, it is likely that some populations of the algae would be more intolerant of an increase in ambient salinity than others. Reed & Russell (1979) found that the response (ability to regenerate from cut thalli) of individual populations varied according to the salinity conditions of the original habitat, and that the pattern of euryhalinity in parental material and offspring was in broad agreement. This led Reed & Russell (1979) to suggest that salinity tolerances of selected populations have a genetic basis. For example;
  • eulittoral zone material showed decreased percentage regeneration in all salinities (dilute: 0, 4.25, 8.5, 17 & 25.5 psu, and concentrated seawater: 51, 68, 95, 102 & 136 psu) except 34 psu, when compared to littoral fringe populations of Ulva intestinalis (as Enteromorpha intestinalis).
  • none of the eulittoral zone material was able to regenerate in freshwater or concentrated seawater, whilst littoral fringe and rock pool material was able to do so.
Increased salinity is most likely to occur in the region of the littoral fringe and supralittoral zone. For instance, during the summer, owing to excessive evaporation brine precipitation may occur in rockpools containing Ulva intestinalisand salinity has been reported to rise as high as 180 psu (Reed & Russell, 1979). In follow-up experiments, littoral fringe specimens showed an increased capacity to survive in media of extreme salinity, a significant decrease in regeneration only being recorded after exposure to concentrated seawater (102 psu and 136 psu) for > 7 days.
At the benchmark level an assessment of not sensitive has been made for the average population of the species.
Tolerant Not relevant Not sensitive Moderate
Ulva intestinalis has a cosmopolitan distribution throughout coastal areas and estuaries and is considered to be a remarkably euryhaline species, tolerant of extreme salinities ranging from 0 psu to 136 psu. However, on the basis of evidence available, it is likely that some populations of the algae would be more intolerant of reductions in ambient salinity than others. For instance, Reed & Russell (1979) found that the response (ability to regenerate from cut thalli) of individual populations varied according to the salinity conditions of the original habitat, and that the pattern of euryhalinity in parental material and offspring was in broad agreement. This led Reed & Russell (1979) to suggest that salinity tolerances of selected populations have a genetic basis. For example;
  • eulittoral zone material showed decreased percentage regeneration in all salinities (dilute: 0, 4.25, 8.5, 17 & 25.5 psu, full: 34 psu and concentrated seawater: 51, 68, 95, 102 & 136 psu) except 34 psu, when compared to littoral fringe populations of Ulva intestinalis (as Enteromorpha intestinalis).
  • none of the eulittoral zone material was able to regenerate in freshwater or concentrated seawater, whilst littoral fringe and rock pool material was able to do so.
Reduced salinity has also been reported to affect the growth rate of Ulva intestinalis. Martins et al. (1999) observed that in years with high precipitation and significant increase of freshwater runoff to the Mondego estuary (west Portugal), that Ulva intestinalis (as Enteromorpha intestinalis) failed to bloom. In the laboratory, the growth rate of Ulva intestinalis was measured against a range of salinities, from 0 to 32 psu. Ulva intestinalis showed the lowest growth rates at extremely low salinity values (less than or equal to 3 psu), and for salinity less than or equal to 1 psu, the algae died. Growth rates at a salinity lower than 5 psu and higher than 25 psu were also low, in comparison to growth between a salinity of 15 and 20 psu, where Ulva intestinalis showed the highest growth rates. Martin et al. (1999) concluded that episodes of reduced salinity were an important external parameter in controlling the growth of Ulva intestinalis. However, elsewhere Ulva intestinalis is known to thrive in areas of the supralittoral zone that receive freshwater runoff.
At the benchmark level an assessment of not sensitive has been made for the average population of the species. Furthermore, Kamer & Fong (2001) found that high nitrogen enrichment mitigated the negative effects that reduced salinity had on Ulva intestinalis (as Enteromorpha intestinalis) dry biomass, wet : dry biomass, tissue nutrients and ability to remove phosphorus from the water column.
No information Not relevant No information Not relevant
There is insufficient information available to make an assessment about the effects of reduced oxygen in the water column upon Ulva intestinalis.

Biological pressures

 IntoleranceRecoverabilitySensitivityEvidence/Confidence
No information Not relevant No information Not relevant
No information was found concerning the effects of microbial pathogens on Ulva intestinalis.
Not relevant Not relevant Not relevant Not relevant
Ulva intestinalis is not known to be adversely affected by non-native species.
Intermediate Very high Low Moderate
The benchmark for extraction is the removal of 50% of the Ulva intestinalis population from the area under consideration. Intolerance has therefore been assessed to be intermediate and recoverability very high as a localized populations of the species will remain from which recruitment can occur (see additional information below).
Not relevant Not relevant Not relevant Not relevant
No other species are identified to be host or prey items for Ulva intestinalis.

Additional information

Recoverability
Ulva intestinalis is generally considered to be an opportunistic species, with an 'r-type' strategy for survival. The r-strategists have a high growth rate and high reproductive rate. For instance, the thalli of Ulva intestinalis, which arise from spores and zygotes, grow within a few weeks into thalli that reproduce again, and the majority of the cell contents are converted into reproductive cells. The species is also capable of dispersal over a considerable distance. For instance, Amsler & Searles (1980) showed that swarmers of a coastal population of Ulva (as Enteromorpha) reached exposed artificial substrata on a submarine plateau 35 km away.
Ulva intestinalis is amongst the first multicellular algae to appear on substrata that have been cleared following a disturbance, e.g. following the Torrey Canyon oil spill in March 1967, species of the genus Ulva rapidly recruited to areas where oil had killed the herbivores that usually grazed on them, so that a rapid greening of the rocks (owing to a thick coating of Ulva) was apparent by mid-May (Smith, 1968). The rapid recruitment of Ulva to areas cleared of herbivorous grazers was also demonstrated by Kitching & Thain (1983). Following the removal of the urchin %Paracentrotus lividus% from areas of Lough Hyne, Ireland, Ulva grew over the cleared area and reached a coverage of 100% within one year. Therefore, evidence suggests that Ulva intestinalis is likely to have a considerable ability for recovery within a year.

Importance review

Policy/legislation

- no data -

Status

Non-native

Importance information

  • Ulva intestinalis is used by the copepod Tigriopus brevicornis as a refuge from desiccation (McAllen, 1999)
  • Green algae in the form of membranes or flat tubes (e.g. Ulva and Monostroma) are eaten extensively in Asia (Guiry & Blunden, 1991)
  • The potential of Ulva intestinalis (as Enteromorpha intestinalis) for use in the treatment of secondary municipal sewage and biomass for energy conservation has been investigated (Guiry & Blunden, 1991).

Bibliography

  1. Amsler, C.D. & Searles, R.B., 1980. Vertical distribution of seaweed spores in a water column off shore of North Carolina. Journal of Phycology, 16, 617-619.

  2. Baeck, S., Lehvo, A. & Blomster, J., 2000. Mass occurrence of unattached Enteromorpha intestinalis on the Finnish Baltic Sea coast. Annales Botanici Fennici, 37, 155-161.

  3. Blomster, J., Maggs, C.A. & Stanhope, M.J., 1998. Molecular and morphological analysis of Enteromorpha intestinalis and Enteromorpha compressa (Chlorophyta) in the British Isles. Journal of Phycology, 34, 319-340.

  4. Burrows, E.M., 1959. Growth form and environment in Enteromorpha. Botanical Journal of the Linnean Society, 56, 204-206.

  5. Burrows, E.M., 1991. Seaweeds of the British Isles. Volume 2. Chlorophyta. London: British Museum (Natural History).

  6. Clark, R.B., 1997. Marine Pollution, 4th ed. Oxford: Carendon Press.

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Citation

This review can be cited as:

Budd, G.C. & Pizzola, P. 2008. Ulva intestinalis Gut weed. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. Available from: http://www.marlin.ac.uk/species/detail/1469

Last Updated: 22/05/2008