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Eli’s Fish Facts – Emerald Sea Slug

Elysia chlorotica

On July 31st this year, staffers found a rare surprise in the seine net. Amidst the typical fish and invertebrates, our Outreach Coordinator saw something a little different: at first appearing like a small clump of seaweed, once it was in water it fanned out and revealed itself to be an eastern emerald elysia. Elysia chlorotica are often mistaken for nudibranchs, a type of sea slug common to brackish and environments, but they are in fact sap sucking sea slugs, a mysterious, fascinating, and increasingly rare species.

The sap sucking sea slugs are named as such because their main source of food is the sap from a type of algae – likely Vaucheria littorea in this case – which they sequester. Feeding on this algae jumpstarts them into their adult life phase, supplies them with their signature green hue, and also gives them photosynthetic abilities! These gastropods acquire chloroplasts from the algae they feed on which actually helps them act like plants, or convert sunlight into glucose. Because of this specialized ability, eastern emerald elysia are often seen floating at the top of the water, absorbing as much sunlight as they can into their cells, and can survive the rest of their adult lives without feeding on another piece of algae. Even though Elysia chlorotica tend to live in salt marshes, which is the environment on CURB’s shores, this was the first we’ve ever caught and identified in our net, which was a real treat for our staff.

Check out the swimming eastern emerald elysia here: