# Laboratory Rearing of the Photosynthetic Sea Slug Elysia crispata (Gastropoda, Sacoglossa): Implications for the Study of Kleptoplasty and Species Conservation

## TL;DR

This paper describes a method to rear the sea slug Elysia crispata in the lab, which helps study how it keeps functional chloroplasts from algae and supports conservation efforts.

## Contribution

A standardized protocol for rearing Elysia crispata in the lab across multiple generations is presented.

## Key findings

- A detailed protocol successfully facilitated embryonic development, larval metamorphosis, and juvenile-to-adult transition.
- Two groups of Elysia crispata were characterized based on kleptoplasts acquired from different macroalgae.
- The protocol supports experimental reproducibility and reduces the impact of the marine aquarium trade.

## Abstract

The sea slug Elysia crispata is commonly used in the study of kleptoplasty, a mechanism by which host cells can capture and retain long-term functional chloroplasts—kleptoplasts—from their algal prey. This extraordinary act of thievery has intrigued scientists for over a century. Moreover, E. crispata is commonly acquired by marine aquarium hobbyists because of its ability to eat nuisance macroalgae in reef aquariums. This study presents a detailed protocol for the successful rearing of multiple generations of E. crispata and characterizes two groups retaining kleptoplasts from two different prey macroalgae. This opens new options in experimentally addressing the kleptoplasty conundrum not possible using sea slugs collected from the wild, while also potentially contributing to species conservation.

Some Sacoglossa sea slugs are capable of stealing and maintaining functional intracellular chloroplasts—kleptoplasts—from their macroalgal prey for periods of up to several months, a process known as kleptoplasty. Although the cultivation of these marine invertebrates under laboratory conditions is crucial for research in various fields (e.g., endosymbiosis, animal physiology, discovery of new marine natural products), rearing protocols are scarce. This study presents a standardized protocol for the laboratory rearing of large numbers of the sacoglossan tropical sea slug Elysia crispata. The detailed protocol successfully facilitated embryonic development, larval metamorphosis, and juvenile-to-adult transition, allowing the rearing of multiple generations. Two groups, characterized by acquiring different kleptoplasts, were obtained by feeding the sea slugs with two different prey macroalgae: Bryopsis sp. and Acetabularia acetabulum. Usually referred to as lettuce sea slug among marine aquarium hobbyists, E. crispata is a highly valued organism for its striking appearance and ability to control nuisance algal growth in reef aquariums. This protocol allows experimental reproducibility and access to specimens under different development stages, potentially boosting research on kleptoplasty while also contributing to reducing the impact of the marine aquarium trade on natural populations.