Corals are holobionts (host-symbiont partners) – the coral host living in symbiosis with algae (and an array of other micro-organisms, including bacteria, fungi, and other algae). The symbiosis from these algae provide the coral with nutrients, explaining why coral reefs thrive in nutrient poor waters. Problems then arise when temperatures get warm – the algae and coral become stressed, and the coral host kicks out the algae. If the temperatures are prolonged or severe enough, the coral host will inevitably die due to starvation and disease.

Enter the green sea slug. Instead of relying on a constant supply of intracellular algae within the host tissues, this slug can actually produce the photosynthetic pigment chlorophyll a, essentially allowing the creature to become self sufficient and solar-powered. Through horizontal gene transfer, the slug actually acquired algal ‘photosynthetic genes necessary to produce proteins, making the slug truly part animal, part plant. More below from Wired magazine:

Shaped like a leaf itself, the slug Elysia chlorotica already has a reputation for kidnapping the photosynthesizing organelles and some genes from algae. Now it turns out that the slug has acquired enough stolen goods to make an entire plant chemical-making pathway work inside an animal body, says Sidney K. Pierce of the University of South Florida in Tampa.

The slugs can manufacture the most common form of chlorophyll, the green pigment in plants that captures energy from sunlight, Pierce reported January 7 at the annual meeting of the Society for Integrative and Comparative Biology. Pierce used a radioactive tracer to show that the slugs were making the pigment, called chlorophyll a, themselves and not simply relying on chlorophyll reserves stolen from the algae the slugs dine on.

“This could be a fusion of a plant and an animal — that’s just cool,” said invertebrate zoologist John Zardus of The Citadel in Charleston, S.C.