The Celebes Sea, or Sulawesi Sea, is a 472,000 km² (182,000 sq mi) arm of the western Pacific lying between Mindanao and the Sulu Archipelago of the Philippines to the north, the Sangihe Islands to the east, the Minahasa Peninsula of Sulawesi to the south, and Borneo (Indonesian Kalimantan and Malaysian Sabah) to the west. It measures about 605 km from north to south and 780 km from east to west, and reaches a maximum depth of 6,220 m (20,406 ft). It lies inside the Coral Triangle and holds about 580 of the world's 793 species of reef-building coral. Its best-known wildlife sites are the turtle and barracuda reefs of Sipadan in Malaysia, the stingless jellyfish of Kakaban and the coral walls of Bunaken National Park in Indonesia, and the waters off Manado Tua, where the Indonesian coelacanth was discovered in 1997.
Sipadan Island: Turtles and Barracuda on a 600-Metre Volcanic Pinnacle
Sipadan, off the east coast of Sabah, is the only oceanic island in Malaysia. It is a cap of living coral on top of an extinct volcanic cone that rises 600 m (2,000 ft) from the seabed. More than 400 species of fish and hundreds of coral species have been classified around it.
Turtles are the island's signature animals. Green and hawksbill turtles mate and nest on Sipadan. Beneath the island lies a limestone cave system known as the turtle tomb, whose tunnels hold the skeletons of turtles that lost their way and drowned before reaching the surface. Out in the blue, schools of barracuda swirl in tornado-like columns, alongside large schools of bigeye trevally and bumphead parrotfish. Manta rays, eagle rays, scalloped hammerhead sharks and whale sharks pass through, and killer whales have been seen off the island.
Protection came in stages. The colonial government of North Borneo declared Sipadan a bird sanctuary in 1933, and Malaysia re-gazetted it in 1963. Diving took off in the 1980s, and the first resort opened in 1984. In his 1989 film Borneo: The Ghost of the Sea Turtle, Jacques Cousteau called the island an untouched piece of art. In 2004 Sabah Parks made it a marine park and closed six hotel and resort facilities on the island because of their impact on the reef. The park was enlarged by 6,846 ha in 2015 to 16,860 ha. Since 2019 only 176 diving permits have been issued per day, and in November 2023 the island was closed for a month to let the ecosystem recover.
Sovereignty over Sipadan and nearby Ligitan was contested between Malaysia and Indonesia until 2002, when the International Court of Justice awarded both islands to Malaysia. Mabul Island, about 15 km to the north, is a 0.2 km² fishing village that became a base for Sipadan divers after the 1990s. Off the nearby town of Semporna, Tun Sakaran Marine Park became Sabah Parks' seventh protected area in 2004. It covers 350 km² of islands, sand cays and patch reefs, and about 2,000 people live inside it, most of them Bajau Laut who live in stilt houses and houseboats.
Kakaban and the Derawan Islands: Stingless Jellyfish and Green Turtle Beaches
On the Indonesian side of the sea, the Derawan Islands lie on the coastal shelf of East Kalimantan in Berau Regency. The group has 31 named islands, the best known being Derawan, Kakaban, Maratua and Sangalaki, plus many submerged reefs. Surveys there have counted 872 species of reef fish and 507 species of coral. The protected species include five giant clam species, two sea turtles and the coconut crab. The islands hold the largest green turtle nesting site in Indonesia, although turtle eggs there have been heavily harvested.
Kakaban is an uplifted coral atoll of 774.2 ha, raised in the Late Pleistocene or Holocene, with limestone cliffs covered in jungle to the waterline. The uplift trapped seawater in the middle of the island, forming a brackish lake up to 17 m deep that connects to the sea only through porous, cracked rock. Its name means "hug" in the local dialect, because the island wraps around the lake.
The lake is carpeted with Halimeda algae and holds thousands of jellyfish of four species: a transparent Aurelia, the fingertip-sized box jellyfish Tripedalia cystophora, Mastigias cf. papua (similar to the golden jellyfish of Palau), and the upside-down jellyfish Cassiopea ornata. None can harm a swimmer, though they still use their stinging cells on prey. The lake also has endemic sea cucumbers, including Synaptula spinifera. Indonesia has at least seven such lakes; another is Haji Buang Pond on neighbouring Maratua.
Outside the lake, Kakaban's outer wall drops to 180 m. At Barracuda Point, strong currents bring whitetip and leopard sharks, jacks, tuna, snapper and barracuda along the drop-off.
Bunaken National Park: 390 Coral Species on the Manado Walls
At the opposite, south-eastern corner of the sea, Bunaken National Park lies off the city of Manado at the tip of North Sulawesi. Established in 1991, it was among the first of Indonesia's marine parks and covers 890.65 km², 97% of it sea. The other 3% is land on five islands, Bunaken, Manado Tua, Mantehage, Nain and Siladen, and the park's southern section takes in part of the mainland coast at Tanjung Kelapa. There is almost no continental shelf, so the reefs fall straight down the slope, and the water between the islands is 200 to 1,840 m deep.
About 390 species of coral have been recorded in the park. Its best-known feature is a vertical coral wall 25 to 50 m high, home to 13 coral genera. Around 2,000 species of fish live in the park, including emperor angelfish, spotted seahorses and bluestripe snappers. Its molluscs include giant clams, horned helmet shells and chambered nautilus.
The shallows matter as much as the walls. Around Mantehage and Nain, seagrass meadows of Thalassia hemprichii, Enhalus acoroides and Thalassodendron ciliatum cover the flats. Mantehage, a flat island that seems to be slowly sinking, has extensive mangrove flats partly separated by saltwater channels, and the park's mangrove forest of Rhizophora and Sonneratia shelters crabs, lobsters and molluscs. On land, the Celebes crested macaque, Timor deer and Sulawesi bear cuscus live on the park's islands.
Manado Tua and the Indonesian Coelacanth, Found in 1997
Manado Tua, the volcanic cone inside Bunaken National Park that rises more than 600 m above the sea, is where a second living species of coelacanth came to light. On 18 September 1997, Mark and Arnaz Erdmann, on their honeymoon, saw a strange brown fish in a market on the island. Mark Erdmann thought it looked like the coelacanth of the Comoros, which is blue. He photographed it before it was sold, then came back in November 1997 to interview fishermen.
On 30 July 1998 a fisherman, Om Lameh Sonatham, caught a second specimen, 1.2 m long and weighing 29 kg. It lived for six hours, long enough for Erdmann to record its colour and fin movements, and the specimen went to the Bogor Zoological Museum. The discovery was announced in Nature in September 1998, and in 1999 the species was described as Latimeria menadoensis, named after Manado. Locally it is called raja laut, "king of the sea".
The fish was given protected status under Indonesian regulation No. 7/1999 soon after its discovery, and the IUCN lists it as Vulnerable. Most sightings come from North Sulawesi, around Manado Bay and the islands of Talise and Gangga, and it was first filmed alive in its habitat off Manado Tua in 2009. It is one of only two living coelacanth species; the other lives in the western Indian Ocean.
Sarangani Bay and General Santos: The Sea's Tuna Grounds
The open sea supports pelagic fish such as yellowfin and other tuna and marlin, along with whales and dolphins. The Philippine shore shows how much those fish matter. Sarangani Bay, at the southern tip of Mindanao, opens onto the Celebes Sea, and at its head stands General Santos, a city of 722,059 people at the 2024 census. It has been nicknamed the "Tuna Capital of the Philippines" since at least 1970 and is the country's largest producer of sashimi-grade tuna.
The city lands the second-largest daily fish catch in the Philippines after Navotas in Metro Manila. Its fishing industry can handle 750 tonnes of fish a day and employs about 7,800 workers. General Santos has seven tuna processing plants. The fish port complex at Barangay Tambler has a 750 m quay and a 300 m wharf for refrigerated carriers of 2,000 gross tonnage.
The bay itself was declared a protected area under the Expanded National Integrated Protected Areas System Act, Republic Act No. 11038, signed in July 2018. In August 2024 the Philippine News Agency reported the first recorded dugong sighting in Sarangani.
A 42-Million-Year-Old Ocean Basin 6,220 Metres Deep
The wildlife sits on unusual geology. The Celebes Sea is a fragment of an ancient ocean basin that formed about 42 million years ago, far from any landmass. By 20 million years ago, plate movement had carried it close enough to the Indonesian and Philippine volcanoes to receive their ash. By 10 million years ago it was filling with debris, including coal, shed from young mountains on Borneo, and had docked against Eurasia. Its oceanic plate is now being subducted along both its northern and southern edges. Strong currents, deep trenches, seamounts and active volcanic islands give the sea its complex oceanography.
The sea is closed to the north by the Sibutu–Basilan Ridge, which divides it from the Sulu Sea. To the south-west it opens through the Makassar Strait into the Java Sea. On 23 May 2013 the Philippines and Indonesia signed an agreement fixing the boundary of their overlapping exclusive economic zones across it. Deep basin and fringing reefs together place the sea inside the Coral Triangle, which covers six countries and 5.7 million km² of tropical ocean.