The Coral Triangle

Green colonial tunicates photographed in Raja Ampat

Alyui Bay, Raja Ampat

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Nembrotha kubaryana photographed in Raja Ampat

Kubaryana’s nudibranch

The February/March 2017 Coral Triangle Adventures trip to Raja Ampat brought the group of intrepid snorkelers up close and personal to a stunning array of coral reef habitats, and to the myriad marine creatures that can be found in each. While these distinctive reefscapes – from clear water mangroves skirted by lush hard and soft corals to walls steeply plunging from just a few feet below the surface – each possessed its own appeal, the reef encounters in Alyui Bay, in western Waigeo, seemed to generate the most discussion. So what makes Alyui Bay so special? I could, of course, mention unforgettable encounters with tassled wobbegongs, Raja epaulette sharks, Pewter’s angelfish, seahorses, and spiny devilfish, but more than the sum of its parts, Alyui Bay allows snorkelers to experience unique assemblages of marine life in a mosaic of reef environments like no other. Beyond the allure of its more charismatic fauna, snorkelers are also awed by the kaleidoscope of colors, shapes, and patterns painted on the steep slopes they drift along. The visually rich seascape is a patchwork of hard and soft corals, sponges, and sea squirts, with colorful anthias and damselfishes hovering above the seafloor and sweetlips, butterflyfishes, and angelfishes moving among the corals below. When peering more intently into the reef, snorkelers are treated with macro life encounters typically experienced only by divers, such as brilliant yellow wentletrap snails feeding on the sun-burst orange polyps of cup corals, the glowing green fluorescence of moon corals, or the elegant hues of a splendid dottyback. But not all of the bay’s inhabitants are so flamboyant, instead living a stealthier existence – a scorpionfish donning the palette of its surroundings or a stonefish buried eyes-deep in the sand. Also notable are the large black corals that in most reef environments occur much deeper than even divers typically venture, but in Alyui Bay snorkelers have to carefully maneuver around large colonies that nearly reach the surface. These special corals, their name owing to the dark coloration of their flexible and spiny skeleton, often have lightly-colored polyps, with some especially beautiful white colonies resembling wispy, snow-dusted saplings. Snorkelers are also likely to see an abundance of my personal favorite type of marine creature…nudibranchs! These garish sea slugs are commonly found in the shallow waters of Alyui Bay, with the some of the more colorful (and relatively easy to see) sponge- and sea squirt-eating varieties frequently spotted along steep, current-swept walls.

Orange-banded butterflyfish (Cordon chrysozonus) photographed in Raja Ampat

Orange-banded butterflyfish

While I can’t claim to be an expert on the area, I suspect the rewarding snorkeling experiences of Alyui Bay ultimately result from the bay’s geology, biogeography, nutrient-rich waters, and tidal currents. The sites in Alyui Bay visited by CTA are set far enough away from the bay’s headwaters to avoid excessive sedimentation but close enough to benefit from the organic matter and nutrients that make their way into the bay through rivers that drain the vast watershed. The tidal currents gain speed as they move through narrow passes, bringing this abundance of food to the millions of tiny mouths that populate these well-fed reef communities. The steep terrain above and below the water line creates a partially shaded environment, with even less light making it into the narrower passes between the tall, steep-sided islands. Enough light is still present

Corkscrew wire coral (Cirripathes spiralis) photographed in Raja Ampat

Corkscrew wire coral

to allow a diverse community of hard corals to occur at many sites, but the usually prolific growth of branching and plating corals that dominate the more light-drenched reefs is tempered by the shade, making way for a menagerie of sponges, sea squirts and other types of shade-tolerant benthic organisms.

But all of this is really just a taste of what Alyui Bay has to offer. There is much more to discover in Alyui Bay, and with each visit snorkelers are rewarded with new, memorable experiences.

Join us for more adventures in Raja Ampat on our 2018 departures! Click here for more information.

Chromodoris magnifier photo taken in the Philippines

Sea Slugs of the Philippines

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Poster of sea slugs in the Philippines

Sea Slugs of the Philippines

The Philippines is one of the few places in the world where snorkelers can see a huge diversity of sea slugs in very shallow water. On all of our trips to the Philippines we focus on this amazing opportunity. On our recent snorkeling trip to the Philippines, I focused our attention on these amazing little critters and our group was immediately enamored by the color and variety that can be found on the reef. We decided to put together a poster highlighting many of the species that we encountered and look forward to spending more time looking for these fantastic marine creatures!

s pink and white bonnet anemone fish in the Solomon Islands

Anemonefish hybrids in the Solomon Islands

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White bonnet anemone fish in the Solomon Islands often share anemones with other species such as orange and pink anemone fishes

A white bonnet anemonefish…

It’s not often that we come across a naturally occurring and rather obvious hybrid animal while snorkeling. That said, there is one relatively common hybrid that exists in the Solomon Islands and the species is easily observed. It is the beautiful White bonnet anemonefish (Amphiprion leucokranos), which can show variable color patterns and lives with a number of symbiotic anemones. This unusual anemonefish is commonly found with other species of anemonefish in their host anemones and there has been a long-standing theory that A. leucokranos was a cross between Orangefin anemonefish (A. chrysopterus) and Orange anemonefish (A. sandaracinos). Using genetic evidence and field observations this theory has recently been proven correct.

white bonnet anemone fish in the Solomon Islands - coral triangle adventures

White bonnet anemonefish…

Interestingly, due to a strict size-based dominance hierarchy and protandrous hermaphrodite life history, the larger Orangefin anemonefish always act as females while the smaller Orange anemonefish serve as mating males. While snorkeling on our recent Solomon Islands adventure we were able to observe several examples of White bonnet anemonefish living with Orange anemonefish that had spawned and were protecting a healthy patch of eggs. This observation points to there being hybrid backcrosses and genetics being mixed freely within this population of White bonnet anemonefish. It also brings up the question of what a “species” really is. How we define “species” or “subspecies” does not always explain what actually exists in Nature. Whatever the case, it is absolutely fascinating that we can detect natural selection and the processes of evolution while snorkeling.

Fluorescence in Acropora millepora

Underwater fluorescence, part 1

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A lizardfish fluorescing in Komodo National Park - Coral Triangle Adventures

Fluorescence: Lizardfish

Simply put, fluorescence is the ability to absorb light of shortwave lengths and emit it at longer ones. In nature there are many animals and minerals that show this property, though we rarely see the outcome given the longer wavelengths are usually outside of the visible spectrum.But though our eyes cannot detect it, cameras can capture fluorescence with special filters that are attached to both the strobe light and the camera lens. The filter on the strobe, called the excitation filter, flashes a wavelength of light that forces the electrons in the color pigment cells to jump up several levels The filter on the lens, called the barrier filter, blocks out most incoming light except for the fluorescent light emitted from the subject.

The color most often emitted during my night sessions with the filter was green. And to some degree this makes sense. At least for corals, it has been suggested that since plankton, their primary food item, are attracted to green wavelengths, the green light would act as an attractant, drawing plankton close to their polyps where they can capture and consume them.

Fluorescence in Entacmea quadriclor taken in Komodo national park - coral triangle adventures

Fluorescence: Entacmea quadricolor

Mushroom coral fluorescing in Komodo National Park - Coral Triangle Adventures

Fluorescence: Fungid coral

Galaxea fluorescing in Komodo National Park - coral triangle adventures

Fluorescence: Galaxea

Xenia soft coral fluorescing red in Komodo National Park - coral triangle adventures

Fluorescence: Xenia

A hard coral fluorescing reds and greens in Komodo National Park - Coral triangle Adventures

Fluorescence: Hard coral

Lobophyllia brain coral fluorescing in Komodo National Park - Coral Triangle Adventures

Fluorescence: Lobophyillia

Tubastraea cup coral fluorescing - Coral triangle Adventures

Fluorescence: Tubastraea

Sinularia soft coral fluorescing in Komodo National Park - Coral Triangle Adventures

Fluorescence: Sinularia

Acropora humulis fluorescing in Komodo National Park - Coral Triangle Adventures

Fluorescence: Acropora humulis

What a treat it was to capture this amazing phenomenon. We cannot wait to bring our filters to Palau!

Tailspot blenny in Raja Ampat, Indonesia

Tailspot blennies in Raja Ampat

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“Dave, did you see a tailspot blenny on that snorkel?”, Lee said, chuckling, as we climbed aboard the Sea Safari after exploring yet another stunning coral reef in Raja Ampat. I deserved it, I really did. What prompted this running joke was my exuberant glee after having seen my first tailspot blenny early in the trip, and Lee’s amusement at the juxtaposition between that reaction and the sheer abundance of this species. The tailspot blenny, Ecsenius stigmatura, is commonly observed in Raja Ampat, and, indeed, I saw several at just about every site we visited during our ten-day snorkeling adventure to this center of marine biodiversity. While abundant in Raja Ampat, the tailspot blenny has a relatively restricted range, only found in eastern Indonesia and the southern Philippines. Perhaps I should have known better – I’m a coral reef ecologist and have been working in the tropical Pacific for many years. But, then again, I had never been to Raja Ampat before, and as much as I’ve learned about Indo-Pacific marine life over the years, the jaw-dropping diversity of life in Raja Ampat meant that there were likely to be reef inhabitants I had yet to encounter in my travels. In defense of my excitement at that first encounter, the tailspot blenny truly is a beautiful fish; the blue head grading into a mandarin orange, the bright orange and yellow rings around the eyes, the sharp lines on the head, and, of course, the black spot at the base of its tail, set this species apart from many other reef-dwelling blennies. But its diminutive size (2-3 cm) make spotting even such a strikingly colored fish somewhat difficult, especially for the uninitiated. So, if you’re lucky enough to find yourself snorkeling on the reefs of Raja Ampat, I encourage you to turn your attention away, if only briefly, from the dazzling reefscapes and dizzying schools of fish and peer intently at a group of corals at arm’s length, and you, too, will be awed by the commonly seen, but uncommonly beautiful, tailspot blend.


sunbeams behind a school of barracuda in Raja Ampat

Going to School in Raja Ampat

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There’s no single way to accurately describe the experience of being in Raja Ampat’s waters. One could use every adjective known in the attempt to generate a picture of what it’s like. One of the many common themes found on just about any Raja Ampat snorkeling site are massive schools of fish, which begs the question: why do fish school?

A rather obvious purpose for schooling behavior is to reduce the chances of being preyed upon. Predators may have a more difficult time focusing on a single prey when there are hundreds of other fish within close proximity. Increasing the efficiency of feeding is another purpose for some schooling fish. Mob feeding is an example. When a school of surgeonfish and/or parrotfish swarm over a reef feeding on algae they overwhelm species, such as farmerfish, that may be trying to protect their algal food sources. Often associated with lunar periodicity, many species of fish school together to spawn. It’s a lot easier to find a mate within a large school than it would be to find a single fish of the opposite sex just meandering along any reef. And, another purpose for fish schooling, especially in areas with strong currents, would be for the increased hydrodynamic efficiency. In other words, fish within a school can draft off one another and save energy better put to use in other ways.

Silversides hover above a reef in Raja Ampat, Indonesia


Scad school around man-made docks and jetties in Raja Ampat, Indonesia

School of scad

Golden sweepers hover near a sponge in Raja Ampat

Golden sweepers

There may be other purposes that fish school depending on the species and the environmental context in which they live so it is an interesting question to ponder while out observing the incredible reefs of Raja Ampat!

For more stories about Raja Ampat and to read the latest trip report from our recent time there, please go to our Trip Reports/Blog page.

Pontoh's seahorse found at Wakatobi Resort

A rare find in Wakatobi

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Pontoh's seahorse (Hippocampus pontohi) is a rare treat for underwater naturalists

Pontoh’s seahorse

Finding seahorses anywhere is not the easiest of things to do but occasionally we come across one on our snorkeling adventures, giving us a sense of accomplishment and reaffirming that our eyesight is still somewhat adequate. All seahorse species, of which there are over 45, can accurately call themselves masters of camouflage since they cannot rely on speed to avoid predation unlike their terrestrial namesake. These diminutive carnivores that feed primarily on planktonic organisms have adapted their shape and color patterns to effectively blend into shallow marine environments around the world. As one might expect, the greatest diversity of seahorses occurs in the Coral Triangle and every few Coral Triangle Adventures trips we are able to spot one. But, on our most recent trip to the reefs of Wakatobi, off the southeastern coast of Sulawesi, we were granted a super-rare treat – Pontoh’s pygmy seahorse (Hippocampus pontohi), found in just 15 feet of water. This tiny animal, just over 1 cm in length and looking more like a human embryo than a fish, has thus far only been recorded within the Coral Triangle and is not often seen. It goes to show that snorkeling slowly, paying attention to the environment, and learning to free dive, even to shallow depths, can pay off and can provide us once-in-a-lifetime views of creatures that appear as if they were dreamed up by a Hollywood FX artist.

Commensal crustaceans of Kimbe Bay

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Secretive commensal crustaceans are the norm in Kimbe Bay, Papua New Guinea

crinoid squat lobsters live exclusively on crinoid feather stars

Crinoid squat lobsters…

One of the most impressive things about snorkeling in Kimbe Bay was the relatively easy access to some of the smaller commensal critters that often elude even the sharpest eyes. While nudibranchs, sea horses, and juvenile fishes are hard to spot, they are nothing compared to the masters of camouflage like crinoid (feather star) shrimp, soft coral crabs, squat lobsters, and gorgonian spider crabs. The common theme among these critters is that their chosen habitats revolve completely around the host organism and, as such, they have evolved a physical appearance that mimics the host’s appearance. It is the evolution towards a perfect form of camouflage. The obvious advantage is that they remain well hidden, and thus protected from potential predators.

feather star shrimp in Kimbe Bay, Papua New Guinea

Feather star shrimps…

Crinoid shrimp and squat lobsters live exclusively on crinoid feather stars, gorgonian spider crabs prefer to dwell on gorgonian sea fans, and soft coral crabs are found only on the colorful dendronephthya soft corals. Sea fans, crinoid feather stars and dendronphthya soft corals are all filter feeders, settling in areas where water movement brings them their preferred food item, plankton. The tiny commensals that live upon them scavenge food from debris that collects on the host or may even feed on the host itself, but do not appear to impact their host by doing so. It is thought that even though, for example, squat lobsters may feed upon their host, they also protect their host from potential predators by discouraging a predator by pinching at them with their claws.

The attention to detail among these commensal crustaceans is remarkable. Soft coral crabs that live on dendronphtheya soft corals not only take the physical appearance by appearing white with small reddish bumps on their carapace that resemble the red polyps of the soft coral, they even have whitish streaks on their shell that mimic the white spicules embedded in the tissue of their host soft coral.

soft coral crabs live on dendronphthya soft corals

Soft coral crabs…

soft coral crabs are masters of camouflage, even mimicking the spicules of the soft coral host

The attention…

While these critters are worth the time invested in looking for them, it is hard to realize the payout when 30 minutes into the endeavor, peering into yet another nest of feathery arms of a crinoid comes up empty once again. As we found out, it seems that gorgonian sea fans, crinoid feather stars and soft corals in Kimbe Bay, Papua New Guinea, have an over abundance of these amazing crustaceans. At times, finding one was just a matter of deciding to look for one. See a soft coral, there was probably a soft coral crab living upon it. There’s a gorgonian sea fan, and a gorgonian spider crab was sure to be hiding out on it. Few, if any, other places in the Coral Triangle can boast such a claim!

Gorgonian spider crabs mimic the color and pattern of gorgonian sea fans which allows them to remain well camouflaged

Gorgonian spider crabs…

The allure of these critters is easy to understand. And while we admire their strategy and success, it is also what makes them frustratingly hard to find…except in Kimbe Bay, Papua New Guinea.

Shallow reefs of Raja Ampat

Marine Habitats of Raja Ampat

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Wayag in Raja Ampat is an example of an archipelago of limestone islands

Azure blue…

Raja Ampat is well known among the scientific community, as well as the snorkeling and diving industry, for its spectacular marine biodiversity. Numerous factors play a role in why this region harbors such a vast array of species but one is quite obvious upon exploring the islands there. One of the most important reasons for such an incredible collection of fish and invertebrates is the diversity of marine habitats found among the islands, most, if not all, of them easily accessible as shallow snorkeling sites.

mangroves grow throughout the Bird's Head Seascape

Sunbeams through…

There are a number of different coral reef varieties that exist among the many islands of Raja Ampat, most of them fringing reefs that differ in their composition depending on how exposed they are to current and sunlight. Reefs surrounding calm bays vary in regards to both invertebrate and fish communities from the reefs exposed to swift, plankton-rich currents in narrow channels. But coral reefs are just part of the marine ecosystem here. Extensive stands of seagrass meadows and mangrove forests play vital ecological roles as nurseries, providing calm, protected habitats where scores of young organisms can grow to adulthood. There are also numerous species that utilize these calm habitats for their entire life histories, not just while they are young.

algae creates an almost surreal snorkeling experience in a marine lake of Raja Ampat

A snorkeler floats…

Perhaps the most distinctive of all the marine habitats in Raja Ampat are its marine lakes. These saltwater environments, set amid high limestone islands, are not easily accessible by either human, fish, or invertebrate. Due to their inaccessibility, each marine lake contains distinctive sets of life specifically adapted to the chemistry, depth, sunlight, and amount of food available. Each lake is like a large, unique Petri dish of life.

It’s hard to imagine any area on Earth harboring more species and habitats as Raja Ampat, which means this area is of great importance to the world’s overall marine biodiversity. Come explore the area for yourself as this region continues to offer some of the most spectacular snorkeling on the planet.

Red-spotted nembrotha (nembrotha sp.)

Nudibranchs of Raja Ampat

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Tambja morosa

Gloomy tambja

Snorkeling over a shallow reef in Raja Ampat our group was on the hunt. What started out as a few sightings of a group of attractive mollusks known as nudibranchs, became an obsession to find as many as we could. Fortunately we had two things going for us: First we were snorkeling in the coral triangle, a term that describes the region that possesses the world’s highest levels of marine biodiversity and second, we were snorkeling on one of the best reefs in all of Raja Ampat where nudibranchs are particularly plentiful.

Nudibranchs are colorful snails that lost their shell in favor of chemical defenses against potential predators. They are generally small (averaging 10cm in length) and disc shaped with external gills (nudi = naked, branch = gills) located either as a bouquet of feather-like

Nembrotha kubaryana

Green-lined Nembrotha

structures at the anterior portion of the body or as two longitudinal rows that grow from each side of the body. As part of their defense many of the over one thousand species have bright color patterns that act as warning to deter a predator from attacking the tiny snail.

It is the dazzling colors of nudibranchs that excites our group to seek them out amongst the kaleidoscope of soft corals, sponges, and tunicates. With many eyes on the search, we found no less than 20 species during our snorkeling session and were quite happy with our collection of photographs! Next time we vowed to beat that record and in a place like Raja Ampat, we have no doubt that we will.


Flabellina exoptata

Much-desired Flabellina

Pteraeolidia ianthina

Blue dragon

Roboastrea luteolineata

Yellow-lined nudibranch

Goniobranchus reticulatus

Red-netted nudibranch

Aegires gardeniri

Mating banana slugs

Chromodoris kuniei

Kuni’s chromodoris