BIOTIC Species Information for Ulva intestinalis
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Researched byGeorgina Budd & Paolo Pizzola Data supplied byMarLIN
Refereed byThis information is not refereed.
Scientific nameUlva intestinalis Common nameGut weed
MCS CodeZS156 Recent SynonymsEnteromorpha intestinalis (Linnaeus) Link 1820

PhylumChlorophycota Subphylum
Superclass ClassUlvophyceae
Subclass OrderUlvales
Suborder FamilyUlvaceae
GenusUlva Speciesintestinalis

Additional Information

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

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).
Taxonomy References Dickinson, 1963, Hayward et al., 1996, Fish & Fish, 1996, Howson & Picton, 1997, Blomster et al., 1998, Burrows, 1991, Clay, 1960b, Guiry & Nic Dhonncha, 2002, Hayden et al., 2003,
General Biology
Growth formStraplike / Ribbonlike
Feeding methodPhotoautotroph
Mobility/MovementSee additional information
Permanent attachment
Environmental positionEpifloral
Typical food typesPhotoautotroph HabitAttached
BioturbatorNot relevant FlexibilityHigh (>45 degrees)
FragilityFragile SizeLarge(>50cm)
Height10 -30 cm. Growth Rate0.15-0.25 cm/day
Adult dispersal potentialNot relevant DependencyIndependent
General Biology Additional InformationGrowth 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.
Biology References McAllen, 1999, Baeck et al., 2000, Parchevskij & Rabinovich, 1991, Clay, 1960b,
Distribution and Habitat
Distribution in Britain & IrelandCommon all round the coasts of Britain and Ireland.
Global distributionMore or less world-wide in its distribution.
Biogeographic rangeNot researched Depth rangeIntertidal to a few metres sublittorally
MigratoryNon-migratory / Resident   
Distribution Additional InformationNone entered

Substratum preferencesSmall boulders
Large to very large boulders
Muddy sand
Physiographic preferencesStrait / sound
Ria / Voe
Open coast
Enclosed coast / Embayment
Biological zoneSupralittoral
Upper Littoral Fringe
Lower Littoral Fringe
Upper Eulittoral
Mid Eulittoral
Wave exposureModerately Exposed
Very Sheltered
Extremely Sheltered
Ultra Sheltered
Tidal stream strength/Water flowInsufficient information
SalinityFull (30-40 psu)
Variable (18-40 psu)
Low (<18 psu)
Reduced (18-30 psu)
Habitat Preferences Additional InformationUlva 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).
Distribution References Dickinson, 1963, Hayward et al., 1996, Fish & Fish, 1996, Amsler & Searles, 1980, Reed & Russel, 1979, JNCC, 1999, Guiry & Nic Dhonncha, 2002,
Reproduction/Life History
Reproductive typeVegetative
Alternation of generations
Developmental mechanismSpores (sexual / asexual)
Reproductive SeasonAll year with summer maximum Reproductive LocationWater column
Reproductive frequencyAnnual protracted Regeneration potential No
Life span<1 year Age at reproductive maturitySee additional information
Generation time<1 year FecundityNot relevant
Egg/propagule sizeNot relevant Fertilization typeExternal
Larval/Juvenile dispersal potential>10km Larval settlement periodNot relevant
Duration of larval stageSee additional information   
Reproduction Preferences Additional InformationSpecies 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).
Reproduction References Amsler & Searles, 1980, Knight & Parke, 1931, Little & Kitching, 1996, Burrows, 1959, Jones & Babb, 1968, Moss & Marsland, 1976, Reed & Russel, 1978, McArthur & Moss, 1979,
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