Sea Lettuce – Ulva lactuca


Sea Lettuce

Ulva lactuca

I’ve seen sea lettuce washed up on the beach and growing on boulders and floating docks that are just below the surface of the water.  Its common name is fitting due to its bright green leafy appearance.  Its edges are somewhat frilled and the blades are semitransparent.  Sea lettuce adds color and interest to native salt water tanks, but I’ve been unsuccessful at keeping it from decaying, so it needs to be removed when decay is noticed to prevent it from fouling the water.

I’ve read that Sea lettuce is edible2, and is commonly used in soups and salads for international cuisine1, but I haven’t tried eating it myself.  It is a food source for many herbivores, which often leave their mark with small holes in the blade1.  The holdfast of sea lettuce is usually not present on specimens that wash up on the beach.

Size: 50 cm (20-24”) in length1,3

The two sources that described the range seemed to conflict with one describing the range from the Arctic to Long Island4 and another describing the range extending from the subarctic to the tropics2.  If you find sea lettuce south of New York, or high in the Arctic, please describe your find in our comment section.

found up to 10 m (33 ft deep)OLYMPUS DIGITAL CAMERA

Substrate: If I need sea lettuce for a salt water tank, I grab it from a floating dock in a Massachusetts Harbor.  Sea Lettuce can be found on rocks, floating docks, and pilings3.

Similar Species: Monostroma sp look similar but the texture is thinner and much more transparent so that you can distinguish your own fingerprints through the blade.  Sea lettuce has a thicker texture, and although you may be able to see your fingers, you may not be able to clearly see your fingerprints (2).


1. Watling, L., Fegley, J., Moring, J., White, S., Sulzer, A. (2003) Life Between the Tides. Tilbury House Pub

2. Gosner, Keneth L. (1978), Peterson Field Guides: Atlantic Seashore – A field guide to sponges, jellyfish, sea urchins, and more

3. Alden, P., Cassie, B. (1998). National Audubon Society Field Guide to New England. New York: Alfred A. Knopf, inc..

4. Martinez, A.J. (2011) Marine Life of the North Atlantic: Canada to Cape May. Aqua Quest Publications


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