Elysia crispata (Lettuce Sea Slug) It will do well in an aquarium, if provided with ample room to forage. It prefers an aquarium with live rock so that it can graze on algae. The Lettuce Sea Slug incorporates the chloroplasts (the portions of the cell responsible for photosynthesis) from the algae into its tissues, and thus relies on photosynthesis for part of its energy. It can be harmed by pump intakes and drains, so care should be taken to screen these off. It is sensitive to high levels of nitrate and will not tolerate copper-based medications.