Biodiversity & Conservation

Gut weed - Ulva intestinalis

Ulva intestinalis

Image Steve Trewhella - Ulva intestinalis. Image width ca 4 cm.
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Distribution map

Ulva intestinalis recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

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Ulva intestinalis is not listed under any importance categories.

Taxonomy icon Taxonomy Taxon English term
Phylum Chlorophyta Green seaweeds and stoneworts
Class Ulvophyceae
Authority Linnaeus, 1753
Recent synonyms Enteromorpha intestinalis (Linnaeus) Link 1820
Map icon Recorded Distribution in Britain and Ireland Common all round the coasts of Britain and Ireland.
Habitat information icon Habitat information 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.
Text page icon 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.
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 icon 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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This review can be cited as follows:

Georgina Budd & Paolo Pizzola 2008. Ulva intestinalis. Gut weed. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 03/09/2010]. Available from: <http://www.marlin.ac.uk/speciesinformation.php?speciesID=4540>