Lettuce Nudibranch

Unlike most other sea slug species, Sea Lettuce Nudibranchs (Elysia sp.) are among the best suited for reef aquariums. As opposed to many other sea slug species who often select for very specific types of prey, Sea Lettuce Nudibranchs have adapted to thrive on consuming a variety of soft green algae species. This trait has made them a popular choice in the home aquarium for their ability to tackle some of the most annoying filamentous green algae species, including bryopsis and hair algae. In addition to consuming a number of these nuisance algae, Sea Lettuce Nudibranchs are also capable of integrating the chloroplasts of the algae they consume into their own tissues (kleptoplasty), allowing them to photosynthesize by proxy and survive for moderate periods in the absence of algae. Sea Lettuce Nudibranchs perform best in reef aquariums with an abundance of green algae and in the absence of predators such as wrasses and butterflyfish.

Quick Care Guide

Care Level: Moderate
Minimum Tank Size: 20 gallons with established algae growth
Temperament: Peaceful
Diet: Herbivore (green algae)
Reef Safe: Yes
Adult Size: About 2 inches
Region: Caribbean and Western Atlantic
Scientific Name: Elysia crispata

Lettuce Sea Slug or Nudibranch?

Although it is sold as the Lettuce Nudibranch, Elysia crispata is technically a sap-sucking sea slug (a sacoglossan) rather than a true nudibranch. The frilly, lettuce-like folds along its back give it its common name and house the chloroplasts it collects from the algae it eats.

Tank Requirements

Choose a mature reef aquarium with a steady supply of green algae. A newly set-up tank or one that is already spotless rarely has enough food to support this slug for long.

Cover pump intakes, overflow openings, and powerhead guards with foam or mesh. Sea slugs roam freely and can be pulled into equipment. Moderate lighting and gentle to moderate flow are ideal.

Diet and Feeding

The Lettuce Sea Slug feeds by piercing algae cells and drawing out their contents. It prefers green filamentous and bubbly algae, and many aquarists use it to help manage bryopsis and hair algae. Results vary between individuals and algae types, so it works best alongside nutrient control rather than as a sole cure.

Few prepared foods are accepted. If algae begins to run out, move the slug to a system that still has growth or be prepared to rehome it before it loses condition.

Temperament and Tankmates

This slug is peaceful toward fish, corals, and other invertebrates, and several can share a large tank with plenty of algae. Avoid wrasses, butterflyfish, puffers, and other fish known to pick at slugs and soft-bodied invertebrates.

Reef Compatibility

The Lettuce Nudibranch is reef safe. It grazes only algae and does not harm corals, clams, or crustaceans.

Water Parameters

Temperature: 75–80°F
Specific Gravity: 1.024–1.026
pH: 8.1–8.4
Alkalinity: 8–12 dKH

Drip acclimate slowly and keep salinity steady. Invertebrates are highly sensitive to copper, and copper-treated water or medications should never be added to an aquarium that houses them.

Common Considerations

• Needs algae to survive: Only add this slug to a tank with visible green algae it can graze.

• Guard your pumps: Intake covers prevent slugs from being injured by pumps and overflows.

• Not a guaranteed bryopsis cure: Treat it as one tool alongside nutrient control and manual removal.

• Watch its body shape: A thin, shrunken appearance usually means it is running out of food.