Located in the Coral Triangle, South Halmahera offers divers some of the most biodiverse reefs on the planet. Here, Pierre Constant visits Sali Kecil to explore this underwater paradise.
Sleeping bicolour parrotfish, House Reef, Sali Bay
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Having visited Southeast Sulawesi in the first half of my trip to Indonesia, my goal now was a small island to the west of the big island of Halmahera in North Maluku: Sali Kecil. A Garuda Indonesia flight took me from Jakarta to Ternate in the middle of the night. Early in the morning, a Wings Air flight linked Ternate to Bacan Island, further south. An overland transfer followed, taking me through the forested, mountainous interior to the east coast. Finally, a 50-minute speedboat crossing brought me to Sali Kecil, where Sali Bay Resort was cradled in a natural bay, surrounded by tropical jungle.
Halmahera is an archipelago of 17,780km2, located at 0°65’ N and 127°90’ E in the northern part of the Maluku Islands. This is the far east of Indonesia, close to New Guinea Island. The highest elevation is found at Mount Gamkonora, at 1,560m.
The population of 667,161 people (in 2024) is composed of various ethnic groups, including Galela, Ternate, Makian, Tobelo, Bugis and Togutil. Native languages in the north are West Papuan languages, while in the island’s southern part, languages belong to the Austronesian (Malayo-Polynesian) family. Half of the inhabitants are Muslim, the other half Christian. In Halmahera’s interior, people subsist by hunting, fishing and collecting sago starch. Coastal people cultivate rice and grow coconuts, cocoa, cloves, nutmeg and coffee as cash crops.
Complex geology
Halmahera’s geology is highly complex due to its position at the junction of three main tectonic plates—the Eurasian, Indo-Australian and Philippine Sea Plates—resulting in a K-shaped island. Just like Sulawesi, to the west, the eastern wing of Halmahera is a piece of the Australian mainland that broke off in the late Cretaceous. Composed of uplifted ophiolitic rocks, it drifted to the northwest and entered a collision with the West Halmahera Volcanic Arc.
The north-south aligned western region has numerous active volcanoes due to the subduction of the Molucca Sea Plate beneath Halmahera. The island is subject to regional fault systems. South of Halmahera, the Sorong Fault extends east to west from the Bird’s Head Peninsula on the New Guinea mainland. Just like in New Caledonia, the obducted part of Central and North Halmahera means that nickel and cobalt mining are actively underway, one of the world’s largest nickel mining operations.
Prehistory
The latest scientific research (Science Advances, 2025), based on archaeological data and genetic analysis, proves that the first migration of Homo sapiens from Sundaland to New Guinea and Australia, also known as the supercontinent of Sahul, dates back approximately 60,000 to 65,000 years. Two migration routes were used: a northern one and a southern one. The northern one went through Sulawesi and the Moluccas (Halmahera, Ambon, Ceram) to reach the Doberai Peninsula, the western extremity of New Guinea. The second route went through the Sunda Islands, via Flores and Timor, to reach the sites of Nauwalabila 1 and Madjedbebe in the Northern Territory of Australia.
Historical notes
The largest of the Spice Islands, Halmahera, was formerly known as Jailolo. Long before Europeans had even heard of the “Spice Islands”, cloves and nutmeg from the Moluccas had been traded in Asia.
When the Portuguese established themselves on the islands in 1512, they came into conflict with the Sultans of Tidore and Ternate. It lasted for decades, causing a great loss of life. Later on, the Spanish, English and Dutch disputed the riches. Eventually, the Dutch expelled the Portuguese in 1609, taking over the spice trade. During a revolt of Prince Nuku, Sultan of Tidore, against the Dutch, the islands were occupied by the British in the late 1790s, before they fell back to the Dutch in 1816.
Indonesia declared independence in 1945, but the Dutch officially granted it in 1949, including the Moluccas. Christian Ambonese of southern Maluku led a revolt against the young republic in 1950, forming the short-lived Republic of South Moluccas, which was suppressed by the Indonesian army. Ambon saw horrific fighting between Muslims and Christians from 1999 to 2005, and many Christians fled. Since then, calm has returned, and Christians and Muslims are on equal footing in all island groups.
Flora and fauna
In the 19th century, British naturalist Alfred Russel Wallace, in his book The Malay Archipelago, was the first to demonstrate a difference of flora and fauna between the Asian region (Sunda) and the Australian region (Sahul). Considering the extent of land at the time of the Last Glacial Maximum—when sea level was 110m below present—the deep water of the Lombok Strait (between Bali and Lombok) and the deep Makassar Strait (between Borneo and Sulawesi) provided a natural barrier, which prevented fauna from crossing from Asia further east and vice versa.
This led Wallace to draw a line that now bears his name (1859). It separated the biogeographic realm of Southeast Asia from “Wallacea”, a transitional zone between Asia and Australia. After Ternate, he spent a few months on Bacan Island in 1858, where he was puzzled by the occurrence of the Celebes crested macaque (Macaca nigra), which is endemic to Sulawesi. He assumed, rightfully, that it must have been introduced by man.
He also discovered an amazing bird (in fact, shot by one of his men) with emerald-green plumage and four white feathers sticking out of its shoulders: the Wallace’s standardwing, Semioptera wallacii, which is endemic to Bacan. This, he concluded, was the westernmost extension of the birds-of-paradise, originally from New Guinea’s mainland. Wallace’s research brought up the emerging theory of evolution, at the same time as Darwin published The Origin of the Species in 1859.
The resort
Established in 2015 by two Italian partners, Roberto and Roberto, Sali Bay Resort is nestled in a little bay to the southeast of Sali Kecil (the smaller of the two Sali Islands), precisely between Bacan and Halmahera, in the middle of Selat Patinti (Patinti Strait), 25km east of the Bacan coast. Twelve luxury beachfront villas and four rooms in the beachfront Divers Lodge run along the sandy shoreline, lined with coral rubble. A wide, open-air restaurant faces the bay, exposed to the southeast trade winds. A bit further is the swimming pool, with lounge chairs on a wooden deck, a camera room next to the office, and a massage parlour. Beyond the jetty, at the far end, is the dive centre, a compressor room, and dive staff quarters. The resort caters mainly for a well-to-do, elderly clientele, mostly from Germany, but also from Holland, England, Canada and the United States, as it turned out during my stay.
Diving
After breakfast at 7 a.m., two boat dive trips were planned for 8 a.m., with an afternoon dive at 3 p.m. A night dive was offered on the House Reef at 6:30 p.m. Three of the four dive guides were on duty on two dive boats, depending on the situation and the needs.
The 78 dive sites were spread out between Bacan Island’s east coast and Halmahera’s west coast. No fish schools and no big fish indicated that the area had been fished out a long time ago, judging by the number of fishing lines underwater, and old longlines already encrusted with algae or even coral. Consequently, the work of the dive guides consisted of searching for small stuff and critters, and anything of interest on the seafloor. As for me, I was fortunate enough to have the experienced Pippo as a guide, who was excellent at finding marine life and nudibranchs.
Dive sites
Robi 1 was located in a protected bay on the east side of Sali Besar Island. The gentle slope was covered in Montipora leaf coral species. I encountered a yellow and black double-banded soapfish, Diploprion bifasciatum, and an ornate ghost pipefish, Solenostomus paradoxus, hiding in a yellow feather star. There was a superb Ardeadoris cruenta (formerly Glossodoris cruenta) nudibranch, which was beige and had a white margin with red spots along it. A large, pimpled Phyllidiella pustulosa nudibranch was also spotted, as well as lots of pale blue or brown tube sponges. A green sea turtle, which appeared suddenly, was rather cautious, and a scrawled filefish (Aluterus scriptus) was unusually tame.
Nanas Reef South was located at a small island with a few houses on stilts in the water. Some barcheek jacks (Carangoides plagiotaenia) cruised by. The Navarchus angelfish (Pomacanthus navarchus) was common, as was the regal angelfish. Clusters of dark blue tunicates (Clavelina robusta), which had white girdles, were very attractive. Just like in New Guinea, the blackstriped angelfish (Genicanthus lamarck) roamed everywhere. I noticed a racing stripe flatworm (Pseudoceros bifurcus) crawling among ascidians.
House Reef. The night dive provided an encounter that was on my wish list: the endemic Halmahera epaulette shark (Hemiscyllium halmahera). Creeping in shallow water after dark, it was discovered in the North Maluku Sea (at Ternate and Bacan Islands) and described by ichthyologists Gerry Allen and Mark Erdmann and shark biologist Christine L. Dudgeon in 2013. Quickly labelled a “walking shark”, this 40 to 63cm-long, shy creature is distinguished by inconspicuous dark bands and brown spots all over a cream-coloured body.
Other sights included a small octopus, a leopard sea cucumber (Bohadschia argus), a broadclub cuttlefish (Ascarosepion latimanus, formerly Sepia latimanus) and a scrawled filefish sleeping against a vermillion-red sponge. Clusters of orange cup coral (Tubastraea coccinea) added vibrant colours to the dark environment. A few fimbriated morays (Gymnothorax fimbriatus), with a yellow head and white body with black blotches, were also roaming around inquisitively.
Low. On the east side of Bacan Island, the rubble slope did not look very attractive, but Pippo kept a keen eye on the seafloor, spotting three specimens of brown-margined glossodoris or caramel nudibranch (Glossodoris rufomarginata), an ornate ghost pipefish and a charming orang-utan crab (Achaeus japonicus). Fungia coral and bubble coral hosted a few cleaner shrimps. Black with white bands, the saddleback anemonefish (Amphiprion polymnus) fluttered frantically above its anemone. A big-footed cerianthid anemone (Pachycerianthus nobilis) caught my attention.
Jalan Masuk 1 was located west of Kusu Island, in the channel between Bacan and Sali Kecil. A big bumphead parrotfish (Bolbometopon muricatum) showed up by surprise. A banded sea krait (Laticauda colubrina) foraged in every hole. A shy blacktip reef shark (Carcharhinus melanopterus) zoomed by like a ghost in the deep, although Indonesia is known for its lack of sharks. I spotted a Doriprismatica atromarginata(formerly Glossodoris atromarginata) nudibranch, which was white with a black margin and had black rhinophores and gills. In the shallows, a beautiful garden of Montipora leaf coral shared the space with Acropora staghorn coral.
Early morning was the right time to catch a furtive glimpse of a couple of Blyth’s or Papuan hornbills (Rhyticeros plicatus) flying with a conspicuous thrumming sound of the wings. A species originally from New Guinea, they liked to land on a tall tree behind the restaurant.
Valentine was located on the northeast side of Sali Besar Island, in a calm bay facing Halmahera Island. The dive site had a scenic ridge underwater, but the slope lacked decoration. Instead, our focus was the search for critters again.
A ribboned sweetlips (Plectorhin-chus polytaenia) gazed at me from the safety of a small cave. There were spot-tail butterflyfish (Chaetodon ocellicaudus), with yellow faces and diagonal stripes on their white bodies, and orange-fin anemonefish (Amphiprion chrysopterus), which resembled Clark’s anemonefish (A. clarkii), but with noticeable white tails. A big cuttlefish hovered at depth, and a school of bigeye snappers (Lutjanus lutjanus), with a yellow lateral line, cruised leisurely along the ridge. The vermiculated angelfish (Chaetodontoplus mesoleucus) was an unusual sight. I spotted a reticulated chromodoris nudibranch (Goniobranchus reticulatus, formerlyChromodoris reticulata), which was red with white spots and had white gills and rhinophores.
Jabu. The strong current forced us to move south, behind a small island. There, we found a mixed school of two-spot snappers (Lutjanus biguttatus) and bigeye snappers, typical of the New Guinea region. Barrel sponges (Xestospongia testudinaria) and blue tube sponges were a common occurrence. I was awestruck by a magnificent chromodoris (Chromodoris magnifica) nudibranch on an ascidian. Blackstriped angelfish were conspicuous here. Pippo pointed out a tiny, citrus-coloured Diversidoris crocea nudibranch with a white margin, a rare species that I have never seen before. Our safety stop in the shallows was done over an attractive coral garden of Pocillopora and Acropora stony corals.
That afternoon, I took a hike over a ridge in the forest to reach the fishermen’s village of Kampung Sali. People offered friendly smiles, and joyful children followed me around like a swarm of colourful butterflies.
Tanjung Bakou 1. We went back to Bacan Island, on the eastern side, for two morning dives on a rubble slope. Blue with white antennae, a juvenile painted lobster (Panulirus versicolor) crawled out of a hole, showing no fear. Some orange-rimmed juvenile pinnate batfish (Platax pinnatus) came close to check me out. A school of yellowtail fusiliers (Caesio cuning) flashed by into the blue.
During the interval, close to the rocky shore, an inquisitive Celebes crested macaque (Macaca nigra) suddenly showed up. It took advantage of a few bananas thrown by the dive crew. Its serious expression and elongated muzzle reminded me of a baboon with black fur.
Tanjung Neraka, which was nearby, was nothing special. Encounters included mimic surgeonfish (Acanthurus pyroferus) and a colourful yellowtail wrasse (Coris gaimard). Pippo spotted an exquisite Coryphellina rubrolineata (formerly Flabellina rubrolineata) nudibranch adorned with a purple line and purple and white-tipped cerata.
Kusu Selatan was on the south side of Kusu Island. There, the threespot angelfish (Apolemichthys trimaculatus), which was lemon yellow with blue lips, was a delight. A school of midnight snappers (Macolor macularis) was rather tame. A Goniobranchus coi nudibranch was another photographic must! Ascending the slope to the shallows, in less than 10m of water, the coral garden of Montipora leaf coral was absolutely impressive.
Tanjung Lusa. At Sali Kecil, the current came into the strait from the north. The photo harvest here included a soft coral crab (Hoplophrys oatesii), a black ribbon eel (Rhinomuraena quaesita), an orange-dotted tuskfish (Choerodon anchorago) and a school of blue-and-yellow fusiliers (Caesio teres).
George Point. It took half an hour to reach this distant dive site on Halmahera’s west coast. The dark, sandy beach was fringed by coconut trees. Underwater, it was a muck dive with fine silt. “It is for macro only, not wide angle!” informed Pippo, with a smile.
Not even five minutes into the dive, we saw three mobula rays flying overhead. But the dive guide distracted my attention at once with a porcelain anemone crab (Neopetrolisthes ohshimai) at work. A thorny seahorse (Hippocampus histrix) attached to seaweed came next, then a baby cuttlefish and a superb Glossodoris hikuerensis nudibranch. There was also a wire coral crab (Xenocarcinus tuberculatus), which was a stunner. A tiny Thecacera sp. nudibranch, which was grey and black and had rabbit-like ears, blew my mind. The highlight came as we saw a blue-ringed octopus (Hapalochlaena sp.) crawling on the bottom.
Kubur. Last but not least, my stay ended with a night dive in the secluded lagoon on the eastern side of Sali Besar Island. This dive site was a slope of volcanic rubble and black sand, with lots of small, black rocks. At an average depth of 17m, we encountered a flashy, orange, slender T-bar nudibranch (Ceratosoma gracillimum), a pulsating variable sea urchin (Asthenosoma varium) in iridescent colours, and a small white-spotted puffer (Arothron hispidus). A pinkish-red spiny devilfish (Inimicus didactylus) was innocently crawling among the pebbles. A hinge-beaked shrimp (Cinetorhynchus sp.), with bulging green eyes, rested on a decaying leaf. A translucent, yellow-spotted anemone shrimp (Ancylomenes luteomaculatus), with blue and white-banded pincers, was dancing on a piece of seaweed.
Absolutely stunning (and a species I had never seen before) was a giant nudibranch, Otinodoris sp. 1 (a kind of Asteronotus nudibranch), which had a complex pattern. It was host to an imperial shrimp (Zenopontonia rex, formerly Periclimenes imperator). Definitely a new species for me!
Pippo pointed to a cute, red freckled frogfish (Antennarius coccineus), which did not show any sign of anxiety. With an extended, striated, tubular appendage in front of its shell, a bat volute (Cymbiola vespertilio) sea snail glided by with purpose, on its foot, among the small rocks. Several anemone crabs completed the scene, with the occasional cerianthid (tube-dwelling anemone) and a large, crimson purple Platydoris nudibranch. A truly enchanting and productive night dive in very calm waters.
Biodiversity hotspot
Slightly north of the equator, Halmahera is in the Coral Triangle, a global hotspot for marine biodiversity. Its prime location between the Philippine Sea and the North Banda Basin means that there is a constant flow of water between Ternate and Sorong in West Papua, in one direction or the other, which is globally part of the Indonesian Throughflow (ITF).
The Indonesian Throughflow consists of several currents, all bringing the Pacific Ocean waters into the Indian Ocean. The main input is through the Makassar Strait, Halmahera Sea and Maluku Sea.
Located in the heart of the Coral Triangle, Indonesia hosts an incredible number of fish, ranging from over 3,000 to 6,000 species. It also boasts over 570 to nearly 700 species of coral. Instead of mindless plundering of resources and shameful plastic pollution without limits, this global epicentre of marine life needs more awareness, conservation and protection initiatives. ■
For more information on Sali Bay Resort in Halmahera Selatan, Maluku Utara, visit: salibayresort.com
Sources and references:
Allen G, Erdmann MV, Dudgeon CL. Hemiscyllium halmahera. A New Species of Bamboo Shark (Hemiscyllidae) From Indonesia. Aqua. 2013;19(3):123–136.
Allen G, Steene R, Humann P, Deloach N. Reef Fish Identification: Tropical Pacific. New World Publications; 2003.
Encyclopedia Britannica
Gandini F, et al. Genomic Evidence Supports the “Long Chronology” for the Peopling of Sahul. Sci. Adv. 2025;11(48).
Gosliner T, Valdès A, Behrens DW. Nudibranch and Sea Slug Identification Indo-Pacific. 2nd Ed. New World Publications; 2018.
Humann P, Deloach N. Reef Creature Identification: Tropical Pacific. New World Publications; 2005.
Marinespecies.org
Wikipedia.org
