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Previously surveyed only by manned submersibles, the “twilight zone” depths of the Southeast Asia’s Sulu-Sulawesi Seas finally were explored earlier this year by a team of technical divers, including Aquanauts Dive Centre’s Bruce Konefe.
The expedition, lead by Bart De Gols, director of American Nitrox Divers International (Benelux), ANDI International President Ed Betts and other pioneers of technical diving, undertook 14 dives to depths of 100-150m using closed-circuit rebreather systems and housed underwater video cameras.
The dives took place on the fringing walls on the south side of Manado Tua Island, believed to be a habitat for coelacanth fish (latimeria menadoensis). The team explored a larger range of sites within the Bunaken Marine National Park, recorded extensive video footage of the most interesting and unusual fish and invertebrates encountered, and mapped areas of the twilight zone most interesting and amenable to further development as deep technical dive sites.
With some of the richest variety of coral reef plant and animal life in the world, the Sulu-Sulawesi Ecoregion covers 950,000 square kilometers bounded by Indonesia, Malaysia and the Philippines.
It is known as the global centre of marine biodiversity, and is surrounded largely by Indonesia, Malaysia and the Philippines. Covering an area of around 950,000km2, the ecoregion is physically subdivided into the Sulu Sea, the Sulawesi Sea and the inland seas of the Philippines. It is home to important ecosystems such as coral reefs, seagrass beds and mangrove forests. Its marine biodiversity includes more than 400 species of corals, 650 species of reef fishes, unusual fishes such as the coelacanth, six of the world’s eight species of marine turtles, endangered marine mammals such as the dugong, whales and many dolphins, and more than 400 species of algae and 16 species of seagrass.
Mark Erdmann, a marine biologist who has worked in BMNP for the past seven years and played the central role in establishing the existence of the 
coelacanth in the area, earlier surveyed the site from a manned submersible. The May 2004 dives where the first open-water dives to explore the twilight region below 75m in Bunaken Marine National Park.
Until recently, the twilight zone has only been accessible to submersibles and commercial technical divers. Even then, submersibles have generally concentrated on the deep oceans, while commercial technical divers have rarely, if ever, found themselves diving in the vicinity of rich tropical coral reefs.
There has thus been very little exploration and documentation of this unique habitat to date. In recent years, advances in scuba diving equipment, knowledge and techniques have greatly reduced the cost and risk of mixed-gas technical diving in the twilight zone and this trend is certain to continue into the future.
Until now, however, it seems that most technical diving at depths greater than 50m has been on deep wrecks, in cave systems or simply aimed at exploring the limits of what can be done. There was little technical diving whose primary aim was to explore and document the marine environment in the twilight zone, especially in the golden triangle of marine biodiversity centered on the Sulu-Sulawesi Seas.
The ANDI Benelux “twilight zone” expedition is the first deep technical diving expedition in the world to explore and document this marine environment. Many interesting creatures were found, including thresher sharks and other unidentified bottom sharks, nautilus, a range of cuttlefish and octopus species, red-lipped frogfish, prehistoric stalked crinoids (1.5m height) with huge commensal galatheid crabs, glass sponges, giant single-polyp soft corals on 2m stalks, and a host of fascinating benthic invertebrates that were not easily identifiable, including carnivorous tunicates.
