The seas of Asia

To the south of the Philippines, separated from the Sulu Sea by an ocean ridge, is the Celebes Sea.

Part of the Coral Triangle, the Celebes Sea reaches the coast of northern Sulawesi in Indonesia, an incredibly rich & diverse part of Asia that is home to Bunaken National Park and the legendary Lembeh Strait- considered by many to be the earth’s engine room of marine evolution. The Celebes Sea is part of an ancient ocean basin and plummets to depths of over 6 kilometers.

To the east, the Celebes Sea opens out in the the Pacific Ocean, while to the south, it meets the Makassar Strait.

This region sprung to prominence among scientists in the 19th century, when the Wallacea Line theory was proposed. This line passes from the Celebes Sea, through the straits of Makassar & Lomok then out into the Indian Ocean. It marks the boundary between two distinct groups of wildlife. To the south & east, animals are of Australian origin, while to the west, wildlife is distinctly Asian. In days of lower sea levels, many of south east Asia’s islands were linked by land, but this deep stretch of water that marks the line of Wallacea prevented further expansion, explaining the distinct wildlife groups on adjacent islands.

Crossing to the southern hemisphere and heading east to Papua New Guinea, we find the Bismark & Soloman Seas. The marine life here bears greater similarities to that of the Great Barrier Reef and Coral Sea off Australia’s north-eastern coast. The area marks the south-eastern tip of the Coral Triangle and, until fairly recently, was thought to possess the greatest diversity of coral & fish species on earth.

That accolade is currently held by the tiny Halmahera Sea off the north eastern tip of Western Papua. Sitting almost exactly on the equator, this sea is home to 600 different species of coral and around 1300 fish species. It is possible to dive at Raja Ampat & Fak-Fak, in the Halmahera Sea, by Liveaboard from slightly less remote parts of Indonesia.

To the south of here, the shallow Arafura Sea stretches across to the northern coast of Australia and, in the west, meets the Timor Sea. The Timor Sea, like the Arafura, is primarily a shallow sea, with the exception of a deep trough to the north. It empties out into the southern Indian Ocean to the west. 

To the north of this area, we re-enter the Coral Triangle through the strait of Alor and find the Banda Sea - home to the Moluccas, a group of islands famed in days gone by as the Spice Islands. The Banda Islands and Ambon are two of the excellent dive spots in the area, along with Alor to the south.

Wakatobi, off the south-eastern arm of Sulawesi, lies between the Banda Sea the Flores Sea. Wakatobi is one of the few areas that has all 3 types of reef system - fringing reef, barrier reef and atolls. The Flores Sea is another incredibly productive sea, with spectacular marine life off the southern arms of Sulwesi and all around Flores, Komodo & Sumbawa to the south.

The straits between the Nusa Tengarra island chain of Indonesia, including Flores, Sumbawa & Lombok, have some of the strongest currents on earth due to the Indonesia throughflow. The Indonesian throughflow is a massive transference of water from the Pacific to the Indian Oceans, which has to squeeze through the small channels between the islands. These ripping currents make for tricky diving conditions, but incredibly healthy marine eco-systems as they flood the area with the nutrients required to support a huge array of life.

Bali, to the west, is where the Flores Sea meets the Java Sea and marks the south-western tip of the Coral Triangle. The relatively shallow Java Sea separates Java, Indonesia’s most populous island from Borneo, the world’s largest island to the north. To the west, it meets Sumatra, separating it from the Andaman Sea and the Indian Ocean, where our journey began.