Sea sheep? The woolly, horn-horned animals do not only exist in the prairies, but the ocean also has its sheep as well, and they’re better known as Costasiella Kuroshimae. With a body size of 4-10 mm, small black eyes, and a color ranging from yellowish brown to bright green, including other colors such as blue, yellow, green, red, purple, white, and brown on its body, the sea sheep is one of the sun-feeding animals of the sea.
Since it is one of the few non-plant organisms that can photosynthesize, as its “leaves” can survive for up to a couple of months because of the energy produced, one could say that the Costasiella kuroshimae is a “solar-powered sheep.”
Sheephead, the Unique Sea Slug
It was discovered in 1993 off the coast of the island of Kuroshima, Japan, although it has also been found in the waters of the Philippines and Indonesia. But, beyond their appearance, the most curious thing about these sea creatures is their way of making the most of the algae they feed on at the bottom of the sea, with which they maintain a very particular symbiotic relationship, which also helps to maintain the balance of algae populations in their habitats. Although this is not the only reason that makes them special.
Some of their characteristics are:
- The protuberances that these slugs have on their heads are not the horns of a sheep, but ‘rhinophores,’ a sensory organ of prosobranch mollusks that serve as chemical sensors, which function as taste receptors.
- These slugs are hermaphrodites, that is, they are both female and male, and once reproduction begins, they will lay between 2,000 and 4,000 eggs that hatch after about 4 days, giving rise to larvae that will soon acquire the characteristic sheep shape.
- The algae on their body allow them to carry out the kleptoplasty process.
- They prefer to inhabit areas with lush marine vegetation, as this provides not only camouflage but also food.
- They feed on key marine plants, such as Avrainvillea and Halimeda, which are green algae.
- The vibrant green color of leaf sheep sea slugs comes from ingested chloroplasts, which makes them resemble small underwater sheep grazing on aquatic vegetation.
Costasiella Kuroshimae Can Perform Kleptoplasty
Within the sea slug, chloroplasts produce food from organic materials in the cell and sunlight. This is a strategy, since the sea slug, instead of always having to fetch food, allows it to be stored inside itself, thus generating energy and matter when it needs it. And this theft of chloroplasts is known as a “kleptoplasty” process.
Some studies have found that chloroplasts can carry out photosynthesis inside sea sheep for up to nine to 12 months, and during that period, they continue to nourish the animal. What is not yet understood is how the slug can maintain these chloroplasts for so long inside its organism.
Their Population Is at Risk
Like all exotic animals, sea sheep face several threats, including habitat loss due to human activity and pollution. Coastal development, trawling, and climate change-induced ocean acidification are all factors that can negatively impact the delicate habitats that these sea slugs depend on for survival. In addition, over-collection for the aquarium trade may lead to further population declines.
This last point, endangers the population, as they are often hunted for a home aquarium, which is not recommended, because sea sheep require a specific environment, including clean water and a constant temperature, to thrive, mainly because their diet consists of specific algae, such as the green algae called Avrainvillea, which can be difficult to obtain and maintain in captivity.
This story was written in Spanish by Perla Vallejo in Ecoosfera