Leaf Sheep: These sea slugs are a delight to observe

leaf sheep - costasiella kuroshimae

Leaf sheep sea slugs have a cartoon lamb-like appearance.

If you thought sea bunnies were cute, wait until you see what leaf sheep look like.

Here’s another underwater treasure that will make you say “aww!”.Sea slug Costasiella kuroshimae (also known as “leaf sheep” or “Shaun the sheep”) resembles an adorable cartoon sheep with its beady eyes and flat face.

The phosphorescent, leaf-like body and droopy feelers on this little darling may just make it the cutest slug in the sea!

Known to grow up to five millimetres, Costasiella kuroshimae can be found in the Philippines, Indonesia, and Japan. Their food is algae, and they use chloroplasts to manufacture their own energy in a process known as kleptoplasty. In addition to being the only non-plant organism capable of photosynthesis, leaf sheep can survive for up to a few months on the energy produced from kleptoplasty.

Sheep of the ocean? Sea slugs like this one eat so much algae that they can photosynthesize.

Performing photosynthesis

These plants live on Avrainvilleas, fuzzy, felty plant life that grows in soft sand and silt. Gosliner explained that they live near coral reefs, not on coral reefs themselves.

Leaf sheep live their whole lives on that type of algae, and you can often see a whole colony of them there – I have seen up to 20 on one blade of algae. The slug’s egg mass is sometimes visible as tiny coils of spirals.

Environmental threats – Costasiella kuroshimae

Despite not facing critical threats to survival, leaf sheep still face threats such as habitat loss. Legal, illicit, and destructive methods of fishing (such as dynamite and cyanide) destroy marine habitats and kill the animals living there. In spite of Philippine law banning destructive fishing and illegal fishing, these practices still exist.

The sea slug’s habitat is also being affected by climate change. A warming world could cause more intense storms and typhoons – the Philippines gets 20 on average each year – damaging marine environments, causing whirlwinds of sand that would uproot leaf sheep and harm the algae they live in. A study on the sea hare demonstrated that animals exposed to simulated acidification and warming were less successful in foraging and made worse decisions.

Another threat to the species is plastic pollution.

The Philippines generates more than 1.9 million metric tons of mismanaged plastic waste, which puts it as the third biggest contributor to the global problem. When leaf sheep ingest microplastics, they may obstruct their mouths or accumulate in their digestive tracts, and the chemicals leaching out could be harmful.

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

leaf sheep - costasiella kuroshimae

Diving to see leaf sheep

Leaf sheep were first discovered in 1993 on the Japanese island of Kuroshima, but have been observed throughout Asia, including in Singapore, the Philippines, Thailand and the Coral Triangle, which encompasses Indonesia, the Solomon Islands Malaysia, Papua New Guinea, and Timor-Leste.