Ulva lactuca 

Description  

The wafting fronds of U. lactuca  when water borne resembles lettuce leaves, hence the name 'sea-lettuce'. It is generally pale green when young, bright green when mature, and dark green when old.

 Ulva lactuca reaches lengths up to 45 cm long annually with a perennial holdfast. The fronds are often as broad as they are long, are of irregular shape, very thin, membranous, grow in bunches, and look-alike lettuce. Ulva is easily torn loose from substrate accumulating in large drifting masses or cast up on the beach.

Ulva growing on clumps of oysters in San Quitin Bay, Mexico

Distribution

Ulva lactuca in its natural state underwater 

Ulva lactuca is found worldwide in sheltered to moderately exposed situations on rocks, submerged structures, in pools and shallow waters near the low tide mark. It thrives in brackish water with organic enrichment. It is found commonly along the extent of the Irish coast more so in sheltered or moderately exposed shores, than in very exposed areas.

Ulva is a small genus of marine and brackish water green algae. It is edible and is often called 'Sea Lettuce'.

Ulva can be quite a nuisance in areas that are nutrient enriched from sewage outfalls e.g. Cork Harbour and Belfast Lough, where populations of Ulva may grow rapidly and cover large areas of bays and  mudflats in the summer. These so-called green tides are especially troublesome when they start to decompose producing a strong unpleasant odeur.

Ulva lactuca grown in tanks at the Marine Research Station in Carna, Connamara, Ireland

Nutritional analysis