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Biology

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Species of Enteromorpha are summer annuals; they decay at the end of the season, producing masses of decaying bleached fronds (3). These seaweeds are fast-growing species that are able to reproduce quickly (3). The life cycle passes through a number of stages. The 'gametophyte' stage produces massive amounts of mobile sex cells or gametes that fuse together to form the 'sporophyte' stage. This stage then produces mobile spores, which develop into the gametophyte stage, and the cycle begins once more (3). The gametes and spores are produced in such massive quantities that the water becomes green. Their release is synchronised with the tidal cycles (3). In some parts of the world gut weed (E. intestinalis) is sold as a foodstuff (4).
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Conservation

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Conservation action is not required for these species.
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Description

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Species within the genus Enteromorpha are very difficult to identify as differences between species are small and hard to spot (3). They are green seaweeds, with tubular and elongate fronds that may be branched, flattened or inflated (2). They are bright green in colour and may occasionally be bleached white, particularly around rock pools (4). They attach to the substrate by means of a minute disc-like holdfast (4). The fronds of a species may vary in appearance due to changes in environmental conditions, which further confuses identification, and microscopic examination of cell details is often necessary to identify a species with certainty (3).
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Habitat

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These green seaweeds are found at all levels of the shore, and seem to particularly thrive in areas where freshwater run-offs occur (2). They are also found in estuaries and saltmarshes, and is able to withstand low salinities (2). Where conditions are calm the seaweed may detach and survive as free-floating clumps (2).
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Range

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This genus is widespread in north-west Europe and has a wide global distribution with gutweed (E. intestinalis) having a global distribution (3). Enteromorpha compressa, E. intestinalis (gut weed) and E. linza are all common and widespread around the British coast (3).
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Status

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Not threatened (2).
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Threats

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These species are not threatened.
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Brief Summary

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During a walk on the mudflats, you are bound to find ulva growing in certain areas. The fishermen call it 'flap'. In Brittany, this green seaweed forms a plague. It is still a common species in the tidal regions around the North Sea however it has been declining in the past decennia in the Wadden Sea. This is because there are fewer nutrients in the water. Ulva readily tears off from its root, but continues to grow further just the same. Sometimes you see what looks like toilet paper on the flats or in the flood mark on the beach. In most cases, it is dried up ulva that has been bleached by the sun.
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Brief Summary

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Ulva is a genus of green algae known commonly as sea lettuce or green laver. Ulva seaweeds are found worldwide in nitrogen-rich marine habitats attached to rocks in the mid to low intertidal zone (Lee 2008; Kirby 2001). The fronds of Ulva usually grow as sheets, but some species exist in a hollow cylindrical form. These cylindrical species were previously classified as a distinct genus, Enteromorpha, but are now included in Ulva. (Lee 2008; Hayden et al 2003). The blades can grow up to 40 cm long, but are very thin—only 2 cells thick (Lee 2008).

Ulva is eaten by humans in soups, salads, and sushi (Lee 2008 and references within; Kirby 2001).

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Distribution

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Ulva is found worldwide.

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Habitat

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Lives in marine environments, and sometimes found in brackish waters in estuaries, however, Ulva needs nitrogen-rich waters. Ulva attaches to rocks in the mid to low intertidal zone (Lee 2008; Kirby 2001).

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Life Cycle

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Ulva goes through an isomorphic alternation of generations. Adult gametophytes produce only female or male gamets, which are positively phototactic, and move with flagella. They are released in swarms coordinated by lunar cycles and tides. When the zygote is formed it becomes negatively phototactic and swims to the bottom to settle, and germinates within a few days. The haploid phase of the life cycle (the sporophyte), produces sporophytes which, like the gametes, are also motile using a set of four flagella to swim (Lee 2008; Guiry and Guiry 2011).

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Morphology

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The fronds of Ulva usually grow as sheets, but some species exist in a hollow cylindrical form. These cylindrical species were previously classified as a distinct genus, Enteromorpha, but have been synonymized with Ulva. The blade morphology of Ulva is dependent on bacterial composition in the environment (Lee 2008; Hayden et al 2003).

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Risk Statement

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Ulva is considered the main component of "green tide" events in bays especially near large cities in Japan and elsewhere. Its prolific growth becomes a nuisance, especially in run-off waters containing high nutrient levels. In these environments it can outcompete other organisms and reduce diversity in benthic communities. It also creates a nuisance on beaches when it is washed up and decomposes in large amounts as the rotting algae produces hydrogen sulfide gas (Lee 2008; Yabe 2009).

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Size

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The blades can grow up to 40 cm long, but are very thin - only 2 cells thick (Lee 2008).

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Uses

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Ulva is eaten by humans, although the literature has some disagreement about how tasty and digestible it is. It is eaten in soups, salads and sushi (Lee 2008 and references within; Kirby 2001).

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Sea lettuce

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The sea lettuces comprise the genus Ulva, a group of edible green algae that is widely distributed along the coasts of the world's oceans. The type species within the genus Ulva is Ulva lactuca, lactuca being Latin for "lettuce". The genus also includes the species previously classified under the genus Enteromorpha,[1] the former members of which are known under the common name green nori.[2]

Description

Individual blades of Ulva can grow to be more than 400 mm (16 in) in size, but this occurs only when the plants are growing in sheltered areas. A macroscopic alga which is light to dark green in colour, it is attached by disc holdfast.[3]

Nutrition and contamination

Sea lettuce is eaten by a number of different sea animals, including manatees and the sea slugs known as sea hares. Many species of sea lettuce are a food source for humans in Scandinavia, Great Britain, Ireland, China, and Japan (where this food is known as aosa). Sea lettuce as a food for humans is eaten raw in salads and cooked in soups. It is high in protein, soluble dietary fiber, and a variety of vitamins and minerals, especially iron.[4] However, contamination with toxic heavy metals at certain sites where it can be collected makes it dangerous for human consumption.[4]

Aquarium trade

Sea lettuce species are commonly found in the saltwater aquarium trade, where the plants are valued for their high nutrient uptake and edibility. Many reef aquarium keepers use sea lettuce species in refugia or grow it as a food source for herbivorous fish. Sea lettuce is very easy to keep, tolerating a wide range of lighting and temperature conditions. In the refugium, sea lettuce can be attached to live rock or another surface, or simply left to drift in the water.

Health concerns

In August 2009, unprecedented amounts of these algae washed up on the beaches of Brittany, France, causing a major public health scare as it decomposed. The rotting leaves produced large quantities of hydrogen sulfide, a toxic gas. In one incident near Saint-Michel-en-Grève, a horse rider lost consciousness and his horse died after breathing the seaweed fumes; in another, a lorry driver driving a load of decomposing sea lettuce passed out, crashed, and died, with toxic fumes claimed to be the cause.[5] Environmentalists blamed the phenomenon on excessive nitrogenous compounds washed out to sea from improper disposal of pig and poultry animal waste from industrial farms.

Species

Species in the genus Ulva include:[6]

Accepted species
Nomina dubia

A newly discovered Indian endemic species of Ulva with tubular thallus indistinguishable from Ulva intestinalis has been formally established in 2014 as Ulva paschima Bast.[7]

References

  1. ^ a b Hillary S. Hayden; Jaanika Blomster; Christine A. Maggs; Paul C. Silva; Michael J. Stanhope & J. Robert Waaland (2003). "Linnaeus was right all along: Ulva and Enteromorpha are not distinct genera" (PDF). European Journal of Phycology. 38 (3): 277–294. CiteSeerX 10.1.1.330.5106. doi:10.1080/1364253031000136321. ISSN 1469-4433. Archived from the original (PDF) on 2011-08-07.
  2. ^ M.D. Guiry & G.M. Guiry (2012). "Enteromorpha Link in Nees, 1820". AlgaeBase. National University of Ireland. Retrieved February 11, 2012.
  3. ^ Burrows, E.M. 1991. Seaweeds of the British Isles. Volume 2 Chlorophyta. Natural History Museum, ISBN 0-565-00981-8
  4. ^ a b Yaich, H.; Garna, H.; Besbes, S.; Paquot, M.; Blecker, C.; Attia, H. (2011), "Chemical composition and functional properties of Ulva lactuca seaweed collected in Tunisia", Food Chemistry, 128 (4): 895–901, doi:10.1016/j.foodchem.2011.03.114
  5. ^ "Seaweed suspected in French death". BBC. September 7, 2009. Retrieved September 7, 2009.
  6. ^ M.D. Guiry (2012). Guiry MD, Guiry GM (eds.). "Ulva Linnaeus, 1753". AlgaeBase. National University of Ireland, Galway. World Register of Marine Species. Retrieved February 11, 2012.
  7. ^ BAST, F., JOHN, A.A. AND BHUSHAN, S. 2014. Strong endemism of bloom-forming tubular Ulva in Indian west coast, with description of Ulva paschima Sp. Nov. (Ulvales, Chlorophyta. PLoS ONE 9(10): e109295. doi:10.1371/journal.pone.0109295

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Sea lettuce: Brief Summary

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" Ulva intestinalis

The sea lettuces comprise the genus Ulva, a group of edible green algae that is widely distributed along the coasts of the world's oceans. The type species within the genus Ulva is Ulva lactuca, lactuca being Latin for "lettuce". The genus also includes the species previously classified under the genus Enteromorpha, the former members of which are known under the common name green nori.

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Habitat

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Known from seamounts and knolls
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bibliographic citation
Silva, P.C.; Basson, P.W.; Moe, R.L. (1996). Catalogue of the Benthic Marine Algae of the Indian Ocean. <em>University of California Publications in Botany.</em> 79, xiv+1259 pp. ISBN 0–520–09810–2. Stocks, K. 2009. Seamounts Online: an online information system for seamount biology. Version 2009-1. World Wide Web electronic publication. Guiry, M.D. & Guiry, G.M. (2019). AlgaeBase. <em>World-wide electronic publication, National University of Ireland, Galway.</em>
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