“The first time I saw Shaun the Sheep in Romblon [in the Philippines]I was surprised at how small he was, “said Ara Juan, an avid diver and ocean advocate.” The second time in Dauin, [in the province of] Negros Oriental, was more exciting – I saw five perched on a leaf, so it looked like they were grazing on a field of seaweed. “
People are captivated by the leaf sheep
“Shaun the Sheep” is what many divers in the Philippines affectionately refer to as a curious sea creature known as the leaf sheep (Costasiella kuroshimae) because of its similarity to the lively lamb. Contrary to what the name suggests, the leaf sheep is neither a leaf nor a sheep – it is a sea slug.
“They are delicate creatures and their bodies are like snails without a shell,” said Geneviève Reyes, diver and photographer. “Bighorn sheep don’t hide or retract when they sense your presence. They have a routine life, circling the leaf of an algae and grazing in their own little world.”
This marine invertebrate has pearly black eyes close to each other, rhinophores with black tips resembling sheep’s ears or insect antennae protruding from its white head, and dotted green cerata protruding from the upper surface of its body. Sea slug cerata are leaf appendages similar to an aloe vera plant or succulent zebra but usually with pink, purple, or white tips, and they contain digestive gland branches. During this time, the rhinophores pick up chemical signals in the water, giving the sea slug its sense of smell and allowing it to find food sources.
“People are captivated by the leaf sheep because it has a cute face and an interesting shape,” said Terrence Gosliner, senior curator of invertebrate zoology and geology at the California Academy of Sciences and expert in sea slugs which has focused most of its research on the myriad of species found in the Philippines. “They’re just great little slugs.”
And they’re small, reaching a maximum length of seven or eight millimeters as adults and living between six months and a year. According to Gosliner, leafy sheep are hermaphrodites (having both male and female reproductive organs) and must mate with another individual to produce an egg mass. “The eggs hatch into shelled larvae that spend a week or two in the plankton. Then they shed their shells and start life like a little slug,” he said.
Leafy sheep live on Avrainvillea, a type of fuzzy, felted algae that grows in areas with soft substrates, such as silt or fine sand. “They are not found in coral reefs but in areas close to coral reefs,” Gosliner said. “The leaf sheep spends its entire life on this species of algae, and you can often see an entire colony there – I’ve seen as many as 15 or 20 on a blade of seaweed. Sometimes you can. see the slug’s egg mass, which are tiny spiral coils. ”
Avrainvillea is not only the home of the sea slug, but also its food source. As a species of Sacoglossa, or “sap-sucking” sea slug, the leafy sheep grazes (much like its herbivorous namesake) on algae, sucks its chloroplasts (structures in algae cells that contain chlorophyll, a photosynthetic green pigment) and keeps them in the tissues of its cerata for up to 10 days, a process called kleptoplasty. This allows the leaf sheep to supplement their diet through photosynthesis, which is generally known to be done only by plants. This photosynthetic ability has earned the leaf sheep the title of “solar-powered sea slug”.
“It is one of the few multicellular organisms that can do this,” said Miguel Azcuna, assistant professor at Batangas State University in the Philippines and director of the Verde Island Passage Center for Oceanographic Research and Aquatic Sciences (VIP CORALS). “Imagine eating a salad and keeping the chloroplast in your digestive system, then all you need to do is get in the sun to make food. It is convenient to survive.
Additionally, algae chloroplasts protect leafy sheep, giving them a green color for camouflage and chemical defenses to deter predators.
Bighorn sheep are not critically endangered, but they are still threatened for their survival, including habitat loss. Practices such as illegal fishing and destructive fishing (using dynamite or cyanide, for example) destroy marine habitats and kill the animals that live there. Although these practices have been banned in the Philippines, illegal fishing and destructive fishing still persist in the country.
Climate change is also impacting the habitat of the sea slug. More intense storms and typhoons – the Philippines receives an average of 20 each year – caused by global warming could damage marine areas, with strong waves and currents creating whirlpools of sand that could break up the leaves of the sheep and uproot the algae in which they live. and more acidic oceans could also alter the animal’s behavior, as shown in a study of its cousin, the sea hare, which was less successful in foraging and made poorer decisions when he was exposed to a simulated ocean acidification and warming.
Plastic pollution poses another risk to the species. “Sometimes as part of my dive I end up picking up trash underwater,” Juan said.
More than a third of the Philippines’ 1.9 million metric tonnes of mismanaged plastic waste ends up in the ocean, making the country the third largest contributor to marine plastic debris in the world. Ingesting microplastics could clog a leaf sheep’s mouth or collect in its digestive tract, and the leached chemicals could be harmful to its health.
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To combat the growing threats to their marine environments, the Philippines has designated some habitats as Marine Protected Areas (MPAs). The island of Maricaban in Batangas, for example, was declared an MPA in 2019, limiting fishing activities and involving the community in monitoring the health of the reefs and keeping the shoreline free of litter.
Community fishing and environmental law enforcement initiatives are also in place. This includes “Bantay Dagat”, in which volunteers across the country serve as guardians of the sea, patrolling it for illegal fishing activities.
Non-governmental organizations across the Philippines are also helping. The VIP CORALS Azcuna team has partnered with the SEA Institute (where Gosliner is director) to organize eco-camps by the sea, raising awareness among students living in the coastal communities around Batangas about the importance marine ecosystems. Many dive resorts and operators also carry out regular cleanings of beaches and dive sites to collect garbage and other plastic waste from the shore and underwater.
Dive to see sheep in leaves
The leaf sheep was first discovered in 1993 on the Japanese island of Kuroshima, but it is also widely distributed across Asia, with sightings in Singapore, Thailand and the Coral Triangle, an area considered as the global epicenter of marine biodiversity encompassing the waters of Indonesia, Malaysia, Philippines, Papua New Guinea, Solomon Islands and Timor-Leste.
In Philippine waters, leafy sheep have been found in the northern, central and southern parts of the country – from coral-covered crevasses of Anilao in Batangas province of Luzon region to mud-filled bottoms of Dauin in the province of Negros Oriental of the Visayas region and the slopes and volcanic reefs of the island province of Camiguin in the region of Mindanao. The best time to visit is during the months of December to May when the waters are calm and the typhoon season is over. You can reach most of the dive sites by driving an outrigger boat called Bangka, but some dive stations have a “house reef” in front of them.
You are only a visitor to their home, so respect the marine environment
Because leafy sheep undergo photosynthesis, they can be found 9-18m below the ocean where sunlight can still penetrate. Still, sea slugs might be difficult to find due to their small size. “It would help if you had an observer with you – a local dive guide who knows where to find them at a specific dive site,” Juan said.
To ensure responsible diving, Juan’s advice is to practice proper buoyancy to avoid hitting corals or creatures and disturbing the habitat, as you will need to get up close to the leafy sheep to see them. You might also come across litter while diving, so pick up what you can and make sure you dispose of it properly after your dive. Not touching or removing plants and animals is also crucial.
“Leave it as you saw it,” Juan said. “You are just a visitor to their home, so respect the marine environment.”
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