Thesea lettuces comprise thegenusUlva, a group of ediblegreen algae that is widely distributed along the coasts of the world'soceans. The type species within the genusUlva isUlva lactuca,lactuca beingLatin for "lettuce". The genus also includes the species previously classified under the genusEnteromorpha,[1] the former members of which are known under the common namegreen nori.[2]
Individual blades ofUlva 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. Their structure is a leaflike flattenedthallus.[3][4]
Sea lettuce is eaten by a number of different sea animals, includingmanatees and the sea slugs known assea hares. Many species of sea lettuce are a food source for humans inScandinavia,Great Britain,Ireland,China, andJapan (where this food is known asaosa). Sea lettuce as a food for humans is eaten raw insalads and cooked insoups. It is high inprotein, solubledietary fiber, and a variety ofvitamins andminerals, especiallyiron.[5] However, contamination withtoxic heavy metals at certain sites where it can be collected makes it dangerous for human consumption.[5]
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 inrefugia 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.
In August 2009, unprecedented amounts of these algae washed up on the beaches ofBrittany,France, causing a major public health scare as it decomposed. The rotting leaves produced large quantities ofhydrogen sulfide, a toxic gas. In one incident nearSaint-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.[6] Environmentalists blamed the phenomenon on excessive nitrogenous compounds washed out to sea from improper disposal of pig and poultry animal waste from industrial farms.
A newly discovered Indian endemic species ofUlva with tubular thallus indistinguishable fromUlva intestinalis has been formally established in 2014 asUlva paschima Bast.[8]Ten new species have been discovered in New Caledonia:Ulva arbuscula,Ulva planiramosa,Ulva batuffolosa,Ulva tentaculosa,Ulva finissima,Ulva pluriramosa,Ulva scolopendra andUlva spumosa.[9]
^BAST, F., JOHN, A.A. AND BHUSHAN, S. 2014. Strong endemism of bloom-forming tubularUlva in Indian west coast, with description ofUlva paschima Sp. Nov. (Ulvales, Chlorophyta.PLoS ONE 9(10): e109295. doi:10.1371/journal.pone.0109295
^Lagourgue, Let al 2022 The new species ofUlva (Ulvophyceae, Chlorophyta) discovered in New Caledonia genetic and morphological and diversity, and bloom potential.British Phycological Society57;458 - 478.
