Sea bunnies, scientifically known as Jorunna parva, are a type of sea slug, or nudibranch, that are known for their distinctive, rabbit-like appearance. These small marine mollusks typically measure less than an inch (2.54 cm) in length. While often depicted in popular culture as white with black spots, they can also be yellow, orange, or brown. They primarily inhabit coastal waters throughout the Indo-Pacific Ocean, including off the coast of Japan.
Their Built-In Protection
Sea bunnies, like many nudibranchs, possess defense mechanisms that deter most predators. Their primary defense involves acquiring toxins from their diet through a process called sequestration. They primarily feed on specific species of toxic sponges, particularly those from the family Chalinidae. Rather than breaking down these harmful compounds, the sea bunny absorbs and stores the chemical defenses within its own tissues, making them unpalatable or poisonous to predators.
These sequestered toxins are stored in specialized glands or cells, often located within their skin or other body parts. When threatened, the sea bunny can release these stored chemicals, effectively deterring attackers. Their often vibrant coloration, known as aposematism, serves as a visual warning signal to predators, indicating their toxicity. The pigments that give them their color can even be derived directly from the sponges they consume.
Who Dares to Eat Them
Due to their acquired toxicity, sea bunnies face very few natural predators in their marine environment. Most marine animals avoid them because of their unpalatable or poisonous nature. However, a small number of specialized predators have evolved to consume nudibranchs. These can include certain cone snails and other nudibranch species that are either immune to the toxins or have developed strategies to bypass the toxic defenses.
Some carnivorous sea creatures, such as specific fish and crabs, might occasionally prey on them. Even with these limited predators, the risk of predation remains low for sea bunnies compared to other, non-toxic marine invertebrates.
Their Place in the Ocean’s Food Web
Sea bunnies contribute to the marine ecosystem primarily as consumers. They use a specialized feeding organ called a radula, which is a ribbon-like structure equipped with tiny teeth, to scrape off and consume particles from sponges. This specialized diet means they play a role in controlling the populations of specific sponge species within their microhabitats.
As primary or secondary consumers, sea bunnies participate in nutrient cycling. Their consumption of sponges and other small invertebrates links them to the broader marine food web. Their presence helps maintain the ecological balance where they reside.