Marine & AlgaeBeginner🌗 Medium light

Sea lettuce

Ulva lactuca · also called Ulva, Green laver, Sea lettuce, Aosa

🐾 Pet-safe

Generally non-toxic to cats and dogs.

Ulva, or sea lettuce, is a bright-green macroalgae that grows as thin, translucent, ruffled leaf-like sheets (a thallus only two cells thick). It is a fast-growing nutrient exporter for refugiums AND an excellent live vegetable food for herbivorous fish such as tangs and angelfish. Easy and hardy, but its speed means it can sheet over a tank if nutrients run high.

Educational only. KinStation content is reviewed by licensed veterinarians but cannot replace an in-person exam. Always consult a licensed veterinarian or board-certified specialist for diagnosis, treatment, or any decision affecting your pet's health.

Quick facts

Category	Marine & Algae
Family	Ulvaceae
Native origin	Cosmopolitan — found along ocean coasts worldwide in temperate and tropical waters
Care difficulty	Beginner
Light	Medium light
Pet toxicity	Pet-safe

Light

Grows under a wide range; medium refugium or display lighting is plenty. Brighter light = faster growth and more nutrient uptake. As a thin green sheet it is not demanding on PAR and will grow on glass, rock, and equipment.

Water

Standard reef parameters: temperature 18-26 C (64-79 F) — tolerates cooler water; salinity ~1.025 SG, pH 8.1-8.4, alkalinity 8-11 dKH. A heavy feeder that strips nitrate and phosphate quickly, which is why it is used for nutrient export. Iron and trace elements support deep green color. No CO2 (marine).

Soil & potting

Attaches loosely with a small disc holdfast or is grown free / tumbled like chaeto. In a refugium it is left to drift or wedged against a baffle; in a display it clings to rock. No substrate, aquasoil, or root tabs required.

Environment — humidity, temperature, placement

Submersed only. No CO2 (marine). Moderate, turbulent flow keeps the sheets clean and rotating. Excellent as a fast refugium macro for nutrient export, or clipped into the display as fresh grazing for tangs and herbivores. Harvest regularly to actually export the nutrients it has absorbed.

Propagation

Spreads by simple vegetative growth and by releasing spores; in practice you just tear off a piece and move it to start a new culture, and harvest excess. Note that in the wild Ulva drives nuisance 'green tide' blooms in nutrient-rich coastal waters, decomposing into toxic hydrogen-sulfide masses — an indicator of how vigorously it grows given excess nutrients.

Toxicity detail

Completely safe and in fact beneficial — one of the best vegetable foods for tangs, angelfish, and other herbivores, and reef-safe with corals and shrimp. Edible to humans too (eaten in many cuisines). Not a regulated aquarium species. As with all macros, do not release into the wild — its bloom-forming tendency in eutrophic water makes responsible disposal important.

Growth stages

How this plant changes through its life — each stage often has its own care, diet and space needs.

Photo coming soon

Spore / recruit

Aquatic plants and macroalgae establish from spores, seeds, or drifting fragments that settle and attach to substrate or rock. Many freshwater aquarium plants and marine macroalgae also spread readily from a detached piece that takes root or holdfast.

Photo coming soon

Young growth

Young growth puts out its first blades, fronds, or leaves and anchors with roots or a holdfast. Submersed plants may look different from their emersed form, and growth speeds up as the plant adapts to the water's light and nutrients.

Photo coming soon

Mature

A mature aquatic plant or macroalga reaches its full size and characteristic shape, forming the dense growth, runners, or fronds typical of the species. Established plants spread to fill space and can be divided or trimmed to propagate.

Reviewed and signed off by: KinStation Editorial — pre-launch draft (pending horticulture review) on 2026-06-10

Sources

Sea lettuce (Ulva) - Wikipedia (encyclopedia)
Sea Lettuce / Ulva macroalgae - MosaicMacros (care guide)