The sea slug is definitely not the most charismatic sea creature, but it may be one of the most innovative. Scientists at Rutgers University recently discovered that a certain species of sea slug can steal photosynthetic cells from algae and use those cells to survive off only the sun.
This particular species of sea slug is called Elysia chlorotica.
Wikimedia/Karen N. Pelletreau et al.
It lives in intertidal zones between Nova Scotia and Massachusetts, as well as in Florida. It's only about 2 inches long and eats a type of algae called Vaucheria litorea, but it does not completely digest all of the algae.
Algae have organelles called plastids, which can convert sunlight into sugar via the process of photosynthesis. When Elysia chlorotica consumes algae, it extracts the plastids and stores them in the lining of its gut. Once the slug has accumulated enough plastids, it can survive just on photosynthesis for six to eight months.
Scientists still don't know exactly how the slug keeps the plastids working once they are inside the gut lining — this is an area for further study.
There are a number of aquatic species that rely on photosynthesis for food, but the process is a little different than Elysia chlorotica.
For example, many species of giant clams have a symbiotic relationship with algae. The algae live in the part of the clam that is exposed to sunlight. In exchange for a place to live, the algae produce glycerol and feed some to the clam.
In an even more bizarre relationship, many spotted salamander embryos actually have algae living inside their cells. The embryos produce nitrogen-rich waste, which helps the algae with photosynthesis. The algae increases the oxygen content of the water, which helps the embryos develop.
The difference between Elysia chlorotica and other animals that have photosynthesis happening in their bodies is that all the other animals actually have complete algae organisms living inside them.
The sea slug is the only animal that actually takes the plastids out of the algae and then keeps the plastids functioning inside its own body, without the rest of the algae.
This ability has truly never been seen before in the animal kingdom. If researchers can figure out the slug's secret, we may be able to harness the power of plastids for our own green energy.