Sea Lettuce (Ulva lactuca) – A Beginner’s Guide

Sea Lettuce

Sea Lettuce, known by its scientific name Ulva lactuca, is an edible green alga that belongs to the family Ulvaceae.

It’s the type species of the genus Ulva and is sometimes called U. fenestrata because of its ‘windowed’ or ‘holed’ appearance.

What Does Sea Lettuce Look Like?

Ulva lactuca is a thin, flat, green alga that grows from a discoid holdfast.

It has a ruffled and often torn margin and can reach up to 7.1 inches (18 centimeters) in length and 12 inches (30 centimeters) across.

The alga is two cells thick, soft, translucent, and attaches to rocks or other algae with a small disc-shaped holdfast.

What Is the Structure of Sea Lettuce Cells?

Sea Lettuce is formed of two layers of cells that are irregularly arranged. The chloroplast inside the cells can be cup-shaped or a parietal plate with one to three pyrenoids.

There are other species of Ulva that look similar and can be challenging to tell apart.

Where Is Sea Lettuce Found?

Sea Lettuce has a worldwide distribution, including Europe, North America, Central America, Caribbean Islands, South America, Africa, Indian Ocean Islands, South-west Asia, China, Pacific Islands, Australia, and New Zealand.

It’s very common on rocks and other algae along the coasts of the British Isles, France, the Low Countries, and Denmark.

What Are the Preferred Conditions for Sea Lettuce Growth?

Sea Lettuce grows well in areas with abundant nutrients.

For example, off the coast of Brittany, France, intensive farming results in high levels of nitrates washing into the sea, promoting the growth of large quantities of Ulva lactuca.

What Happens when Sea Lettuce Washes up On Beaches?

When large amounts of Sea Lettuce wash up on beaches, their decay produces gases such as methane, hydrogen sulfide, and others.

In some cases, this can lead to the algae spreading over vast areas and causing health concerns.

In August 2009, unprecedented levels of Sea Lettuce washed up on Brittany’s beaches, leading to public health warnings as the rotting algae released toxic hydrogen sulfide gas.

What Are the Dangers of Hydrogen Sulfide from Decaying Sea Lettuce?

Hydrogen sulfide is a toxic gas that can inhibit cellular respiration, resulting in critical cellular hypoxia. Exposure to this gas can be dangerous or even fatal.

In one incident in France, a horse rider lost consciousness, and his horse died after breathing in the seaweed fumes.

In another case, a truck driver died after hauling three truckloads of Sea Lettuce without protective gear. It was later determined to be cardiac arrest resulting from pulmonary edema, an indication of possible hydrogen sulfide poisoning.

Dead animals found on algae-clogged beaches have also been linked to toxic fumes.

What Is the Life Cycle of Sea Lettuce?

The life cycle of Sea Lettuce involves both sporangial and gametangial thalli, which look alike.

The diploid adult plant produces zoospores through meiosis, making them haploid.

These zoospores settle and grow into haploid male and female plants, similar in appearance to the diploid plants.

When the haploid plants release gametes, they unite to form a zygote that germinates and grows into the diploid plant.

What Are the Uses of Sea Lettuce?

Sea Lettuce has various uses as food and in traditional practices. In Scotland, it’s used in soups and salads.

In Hawai’i, it’s called Limu Palahala and can be eaten in different ways, such as mixed with other algae, salted and served with raw fish, boiled in water and served as a soup, or served with chili pepper, onions, soy sauce, and sugar.

What Are the Traditional Uses of Sea Lettuce in Hawai’i?

In Hawai’i, Sea Lettuce has traditional uses as a fertilizer and as adornment for hula dances.

When used for hula, it’s called Limu Papahapaha.

Ulva lactuca Characteristics

Care Level:Easy
Growth Rate:Fast
Nutrient Uptake:Excellent
Required Lighting:Moderate High
Required Water Flow:Moderate
Is Palatable?Yes
Maximum Size:24 in (61.0 cm)

Scientific Classification

Scientific Name:Ulva lactuca
Also Known As:Sea Lettuce
Conservation Status:Unknown

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