After sunset, the Andaman Sea between Thailand and Myanmar transforms into a mysterious, living galaxy. Beneath the surface, beyond coral reefs and moonlit shallows, unfolds the planet’s largest nightly migration — as billions of deep-sea creatures rise from the abyss in search of food.
Blackwater diving offers a front-row seat to this breathtaking phenomenon. Suspended in the inky darkness by a tether line and surrounded by carefully placed lights, divers float above hundreds of meters of open ocean — face-to-face with glowing jellyfish, larval fish, paper-thin cephalopods, and other strange, rarely seen life forms.
Blackwater diving offers a front-row seat to this breathtaking phenomenon. Suspended in the inky darkness by a tether line and surrounded by carefully placed lights, divers float above hundreds of meters of open ocean — face-to-face with glowing jellyfish, larval fish, paper-thin cephalopods, and other strange, rarely seen life forms.
What makes Blackwater Diving So Special?
Because it is offshore, Blackwater diving isn’t your regular night dive. It’s a window into the mesopelagic zone — the twilight zone of the ocean where light barely penetrates, and bioluminescence reigns supreme. Every night, marine larvae and deep-sea organisms make brief appearances near the water surface. Each dive is unpredictable, filled with fleeting encounters that might never happen again.
Whether you're in the Andaman Sea or Blackwater diving elsewhere, these are the 10 of the most extraordinary pelagic creatures divers may only encounter on blackwater dives.
Whether you're in the Andaman Sea or Blackwater diving elsewhere, these are the 10 of the most extraordinary pelagic creatures divers may only encounter on blackwater dives.
1. Blanket Octopus (Tremoctopus spp.)
 |  The Blanket Octopus (Tremoctopus spp.) is a striking deep-sea cephalopod known for the large, web-like membranes that trail from the arms of females, resembling a flowing blanket. This structure is used for defense, making the octopus appear larger to predators. Females can grow over 2 meters long, while males are tiny, rarely exceeding a few centimeters—one of the most extreme examples of sexual size dimorphism in the animal kingdom. Found in warm open oceans worldwide, Blanket Octopuses are solitary and rarely seen. They are capable swimmers and can detach parts of their web to distract threats. Remarkably, some use the stinging tentacles of Portuguese man o’ war as tools for defense and hunting. |
2. Ctenophores (Comb Jellies)
 |  Comb jellies are among the longest-roaming invertebrate marine creatures on planet Earth. These carnivorous and voracious predators are delicate and gelatinous in structure. They possess eight rows of cilia-bearing plates used for “combing” and propelling themselves through the water. These plates can also produce and refract low levels of light. Their bodies are composed of more than 95% water and lack respiratory, circulatory, excretory, and skeletal systems. Some species, such as Beroe forskalii, have a mouth used for biting prey — often other ctenophores — and anal pores for excretion. Other species feature two tentacles covered with sticky cells called colloblasts, which are used to snare prey and draw it toward their mouths. Digestion occurs when enzymes liquefy the captured prey, with the remains expelled either through the mouth or the anal pores. |
3. Eel Larvea
 |  Eel larvae, known as leptocephali, are the transparent, ribbon-like early life stage of many marine eel species. Unlike typical fish larvae, leptocephali are laterally compressed, leaf-shaped, and nearly invisible in the water, offering excellent camouflage in the open ocean. They drift with currents for extended periods—sometimes months or years—feeding on dissolved organic matter and marine snow. During this pelagic phase, they grow before undergoing metamorphosis into the more cylindrical "glass eel" stage. From there, they begin their migration toward coastal habitats. The leptocephalus stage reflects the eel’s complex life cycle and plays a key role in marine ecosystems as both predator and prey. |
4. Paper Nautilus (Argonauta argo)
 |  The Paper Nautilus (Argonauta argo) is a rare pelagic octopus known for the delicate, paper-thin shell produced by females. Unlike true nautiluses, this shell is not for protection but serves as an egg case and buoyancy aid. Females can grow up to 30 cm and are significantly larger than the tiny, shell-less males. A. argo lives near the ocean surface and is found in warm and temperate seas worldwide. It preys on small crustaceans and jellyfish, using its webbed arms to capture food. The species is known for its graceful movement and is often seen floating or drifting with ocean currents. Despite its fragile appearance, the Paper Nautilus is a highly adapted and mysterious cephalopod, captivating scientists and divers alike with its unique reproductive behavior and ephemeral beauty. |
5. Tripod Fish Larvae
 |  Tripod fish larvae are the juvenile form of deep-sea tripod fish, typically belonging to the genus Bathypterois. Unlike their adult counterparts, which rest on the seafloor using elongated fin rays like stilts, the larvae are pelagic and drift in the open ocean. They are nearly transparent, with soft, delicate bodies adapted for life in the water column. As they develop, the characteristic elongated pelvic and caudal fin rays begin to form, eventually enabling the unique tripod stance seen in adults. These larvae feed on plankton and rely on ocean currents for transport. Their transition from free-floating juveniles to benthic ambush predators is one of the many fascinating adaptations of deep-sea life, reflecting the complexity of marine developmental stages in extreme environments. |
6. Snake Blenny Larvae
 |  Snake blenny larvae are the early life stage of elongated, eel-like fish in the family Stichaeidae, found in cold and temperate marine waters. Unlike the benthic adults that dwell near rocky or sandy substrates, the larvae are pelagic, drifting in the upper ocean layers. They are nearly transparent, with slender, ribbon-like bodies that offer camouflage from predators. Their large eyes and minimal pigmentation help them navigate and feed on microscopic plankton. As they grow, they begin to develop the characteristic elongated dorsal and anal fins of adult snake blennies. This transformation from a drifting larva to a bottom-dwelling fish illustrates the complex life cycle of many marine species, adapted for survival in both pelagic and benthic zones. |
7. Amphipods
Amphipods are small, shrimp-like crustaceans found in marine, freshwater, and even terrestrial environments. With laterally compressed bodies and no carapace, they range in size from a few millimeters to several centimeters. Amphipods are incredibly diverse, with over 10,000 known species, including pelagic, benthic, and parasitic forms. They play vital ecological roles as scavengers, herbivores, and prey for larger animals. Many species live among algae, sediment, or detritus, while others, like deep-sea amphipods, inhabit extreme environments. Their bodies are segmented, with distinct head, thorax, and abdomen regions, and equipped with specialized limbs for swimming, burrowing, or clinging. Amphipods are key contributors to nutrient cycling and food webs across ecosystems.
8. Pelagic Seahorses (Hippocampus spp.)
 |  Pelagic seahorses (Hippocampus spp.) are a rare group of seahorses that live in the open ocean, drifting with currents rather than anchoring to reefs or vegetation like most of their relatives. These seahorses are often found clinging to floating debris, seaweed, or Sargassum, using their prehensile tails for stability. Their bodies are upright, armored with bony plates, and capable of subtle color changes for camouflage. Pelagic seahorses feed on tiny planktonic crustaceans, sucking them in through their tubular snouts. Males carry fertilized eggs in a specialized brood pouch until giving birth to fully formed young. Their life in the open sea makes them difficult to study, but they are a vital part of surface marine ecosystems. |
9. Larval Flounder
 |  The larval stage of flounders marks a dramatic transformation in these flatfish. After hatching, flounder larvae are symmetrical and free-swimming, resembling typical fish with an eye on each side of the head. As they develop, a unique metamorphosis occurs: one eye migrates to the opposite side, and the body flattens to adapt to a benthic lifestyle. During this stage, larvae drift in the plankton-rich upper ocean, feeding on microscopic organisms. Their bodies are mostly transparent, aiding in camouflage from predators. Once metamorphosis is complete, the juvenile flounder settles on the seafloor, lying on its blind side. This complex development allows flounders to exploit both pelagic and benthic environments during their life cycle. |
10. Squid Larvea
 |  Squid larvae, also known as paralarvae, are the early life stage of squids, emerging from eggs as miniature, free-swimming versions of adults. They are planktonic, drifting in the upper layers of the ocean where they feed on microscopic organisms. These larvae are transparent or semi-transparent, aiding in camouflage, and possess large eyes and developing tentacles. Unlike true larvae, squid paralarvae do not undergo a complete metamorphosis but gradually grow into their adult form. As they mature, they develop the muscular mantle, chromatophores, and jet propulsion used in adult locomotion. Squid larvae play a vital role in marine food webs, serving as prey for fish and other predators while beginning their own journey as agile hunters. |
Blackwater Dive Briefing – Safety, Awareness & Expectations
 | Blackwater diving is a thrilling and unique experience, but it requires preparation, awareness, and respect for others in the water to ensure a smooth and enjoyable dive for everyone. What to Expect: You’ll be tethered to a central downline, suspended in open water hundreds of meters deep, surrounded by darkness and illuminated only by strobes or torches. The environment can be disorienting at first, but it’s also incredibly exhilarating—offering glimpses of rare pelagic life. Safety & Prerequisites: ● This dive is not for beginners—advanced certification and solid buoyancy control are essential. ● Prior night diving experience is strongly recommended. ● Always stay aware of your depth and proximity to the downline. For underwater photography, use a red focus light to avoid scaring away the animals. Diver Etiquette & Spatial Awareness: ● Be mindful of your light control—waving your torch around can disturb marine life and irritate other divers. Avoid shining it in other people's eyes, especially when pupils are fully dilated in the dark. ● Always be conscious of your 3D space: move slowly, maintain vertical awareness, and never swim directly under another diver—your bubbles can scare off the subjects they’re observing. ● It's helpful to coordinate depth zones among divers during the briefing, allowing everyone enough room and reducing overlap. Agreeing on a depth rotation plan can also enhance everyone’s experience. |
Personal Tip:
 | There’s no perfect depth—what works for one diver may not work for another. I find it useful to explore away from the group and return regularly to the main line. This gives space for quiet observation while maintaining a safe reference point. Stay calm, be respectful, and enjoy the mysterious magic of the blackwater world. |
When and Where to Dive
 | In the Andaman Sea, between Thailand and Myanmar, we’ve been spotting more critters during the full moon — when tidal movement is at its peak. While blackwater diving is technically possible year-round, we only offer it during the national park season, which runs from October to May. All our cruises include one FREE blackwater dive when conditions are safe and suitable! |
Book Your Blackwater Adventure!
Ready to go beyond the reef and into the unknown? Blackwater diving is an unforgettable highlight of any dive trip — a surreal mix of science, mystery, and raw ocean wonder. Witness alien-like creatures rise from the depths in an experience like no other.
Check our cruise schedule and find the perfect departure to experience this one-of-a-kind dive...
Check our cruise schedule and find the perfect departure to experience this one-of-a-kind dive...
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