Sea lettuce

Lore & Background

Individual blades of Ulva can grow to more than 400 mm in size, but only in sheltered areas. The alga is light to dark green, attached by a disc holdfast, with a leaflike flattened thallus. Sea lettuce is eaten by manatees and sea hares, and by humans in several regions, where it is consumed raw in salads or cooked in soups. It is high in protein, soluble dietary fiber, and vitamins and minerals, especially iron, and can be chopped into bread dough to enhance flavor and fortify it. However, contamination with toxic heavy metals at certain collection sites makes it dangerous for human consumption.

Reader's Guide

Sea lettuce's significance lies in its dual role as a nutritious food source and a potential public health hazard. In August 2009, unprecedented amounts washed up on beaches in Brittany, France, causing a major health scare as decomposing algae 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 fumes; in another, a lorry driver carrying decomposing sea lettuce passed out, crashed, and died, with toxic fumes claimed as the cause. Environmentalists blamed the phenomenon on excessive nitrogenous compounds from improper disposal of pig and poultry slurry and from chemical fertilizers used in arable farming. The genus includes many species, with a newly discovered Indian endemic species, Ulva paschima, established in 2014, and ten new species found in New Caledonia.

Did You Know?

• The type species Ulva lactuca has the Latin name meaning 'lettuce'.
• Sea lettuce can grow to more than 400 mm in sheltered areas.
• In August 2009, decomposing sea lettuce in Brittany, France, produced toxic hydrogen sulfide gas.
• A newly discovered Indian endemic species, Ulva paschima, was formally established in 2014.