Diver sea fan_Frank Owens

Night Moves

Published June 1, 2014 in Diving, Habitat, Invertebrates, MARINE LIFE, Underwater Photography

Seeing Wakatobi’s reefs under the cover of night can be a magical and inspiring experience.
When the sun sets and the stars appear, the reef transforms into an even more magical place. Under the cover of darkness, divers encounter creatures that appear quite different from their daytime counterparts. Many marine animals are nocturnal, with appearance and behaviors that are adapted to live in the dark. Those who dive only during the day will miss out on seeing them, as many of these interesting and unique creatures are either hiding or sleeping through the sunlit hours. Here’s a little tour of night diving at Wakatobi and a few of the interesting finds you’ll encounter.

The stage is set

As the sun sinks into a tranquil sea, and vivid oranges and reds of the sunset turn to purple, it’s time, and the stage is set for a night dive at Wakatobi. Divers can join a scheduled boat dive, or simply gear up, turn on a light, and wade in on the House Reef. The nightlife of the reef awaits, ready to be discovered and enjoyed.

Night Diving off the Beach_Shawn Levin
At Wakatobi, divers can join a scheduled boat night dive, or simply gear up, turn on a light, and wade in on the House Reef.  Photo by Shawn Levin

Fading dayllight on the reef_Karin van de Wouw
During the transition period from the illuminated colors lit by the sun to the cover of darkness, many residents of the reef emerge.  Photo by Karin van de Wouw

The late show

As twilight deepens on the reef and the world fades to gray then black, once-vivid colors become muted, and shadows lengthen. Perceptions of distance can likewise diminish. This is a time when some residents of the reef become more vulnerable, while others turn twilight to their advantage, and emerge to begin the hunt. Take the flamboyant cuttlefish, for example: by day they stay hidden, usually buried in soft sand. When they emerge at dusk to hunt, they will light up in a wild series of pink, purple, red and yellow hues. These unique color and pattern-changing abilities can be used for camouflage, communication, or even to hypnotize potential prey. The effect can be equally hypnotic for divers fortunate enough to witness this light show, and it’s a sight not soon forgotten.

“The diverse life on the reefs at Wakatobi make for some cool night dives. We were  amazed by all the unusual, and more discoverable, critters our guide led us to. At night, there were also many nudibranchs that we do not see during the day. At Zoo, one of our favorite night dives, we encountered octopus, squid, several types of cuttlefish, mantis shrimp, a reptilian snake eel and biggest barracuda ever … to name just a few!”  Ledean Paden, May 2014

The unique color and pattern-changing abilities of many creatures such as the flamboyant cuttlefish shown in the feature image above  are used for camouflage, communication or in the case of the cuttlefish to hypnotize potential prey.  

Decorator Crab-Cor Bosman
At first glance, this small decorator crab looks like a sprig of brownish-purple weed growing on the reef. But when it moved, it gave away its true identity and the opportunity to capture this image. The only thing missing on this little guy is the banana and grapes like those found on a Brazilian dancer’s headdress. Photo by Cor Bosman

At night, Decorator crabs are also found using their creative camouflage techniques. These tiny crustaceans get their name from the habit of adding small bits of sponge, algae or other materials from the reef to cover their body, creating an effective camouflage that allows them to blend into their surroundings.

Squid with Shrimp_Allan Saben
The transformation to night is the time many of the reef’s smaller predators can more freely move about in their hunt for food, with less chance of becoming prey themselves. Here, a juvenile reef squid has emerged and successfully captured a small night shrimp in its arms. Dancing in the dark on the edge of your dive light’s illumination, the squid flashes iridescent hues looking as if an electrical current is running through its body.  Photo by Allan Saben

Reptilian Snake eel_David Gray
Reptilian snake eels resemble snakes or worms because they have virtually no fins.  Photo by David Gray

Night provides the perfect opportunity for stealthy eels like the reptilian snake eel to leave their burrow in the sand or rubble to slither about the crevices of the reef. These eels resemble snakes or worms because they have virtually no fins. They are typically found with just their head showing above the sand waiting for prey, and then prowl around at night. Some snake eels mimic banded sea kraits and can be seen out in the open during the day. They feed primarily on crustaceans and mollusks, but can also be found ambushing small fish sleeping among the rocks.

At dusk, the spotted moray eel will also emerge from its daytime shelter on coral reefs and begin actively hunting for prey. As a nocturnal prowler, he may look vicious but he’s simply on a mission to find a meal. Spotted morays are solitary animals, and as an adult will typically reach an average length of around 60 centimeters.

Spotted Moray_Steve Miller
The spotted moray eel can be found during the day peeking out from a crevice in the coral. However, he prowls at night searching for food and sporting a look that’s more bark than bite.  Photo by Steve Miller

Your torch may just catch a flatworm during a night dive, and it is easy to see how this ribbon-like animal got its name. Flatworms are really as “flat as a leaf,” and they seem to glide with a rippling motion over the rocks and sand. These willowy, undulating creatures also come in a variety of colors and patterns – from a simple, but elegant black-and-white to bright oranges, reds, yellows and purples. Did you know that flatworms have only the most rudimentary of eyes, which allow them to detect the presence of light, but little else? Look close and you’ll see the flatworm has no mouth, no obvious eyes and no gills! These primitive animals absorb oxygen and nutrients directly through the skin by a process known as diffusion.

Flatworm_1_Walt Stearns
Flatworms (Platyhelminthes) are bilaterally symmetrical animals: their left and right sides are mirror images of each other. This also implies that they have distinct top and bottom surfaces and distinct head and tail ends. Photo by Walt Stearns

Like turtles, many fish that stay busy throughout the day will slow down at dusk and take refuge in the shelter of undercuts in the reef to sleep. Observant divers can often find them hiding in the tighter recesses and crevices,and nestle deep among the branches of coral. This, however, raises a question: since fish don’t have eyelids are they really sleeping? Well, in a way, they are, but it’s more like resting, and not the same deep sleep we humans enjoy. Marine biologists often refer to the sleep behaviors of fish as an “energy-saving state.”

Sleeping surgeonfish_Wayne MacWilliams
This surgeonfish appears to be wide awake nestled among the green and yellow branches of coral. Because fish do not have eyelids you can’t tell if he is actually sleeping. Biologists refer to the sleep behaviors of fish as an energy-saving state that equates to resting. Photo by Wayne MacWilliams

Some fish do more than just bed down – or rest, for the night. For example, the spot-tail butterflyfish will actually change their coloration when making the transition from day to night. During the day it’s prominent stripes and bright yellow fringe is dominant. At night, however, it’s like someone who has changed into their pajamas and is ready to turn in; the fish will feature a large black spot on the side with a couple of small, pronounced white spots. To create the dark spot, the fish relocates tiny cellular granules known as melanosomes, which can be bunched or dispersed to lighten or darken an area of skin. Why this fish changes it color pattern at night is still a mystery, but the change does confuse observers who mistake it for a similar, but different species of butterflyfish.

Spot-tail butterfly fish_01_Richard Smith
This is what the spot-tail butterflyfish will look like during daylight hours, when it can be found moving about the reef, feeding on soft corals. Photo by Richard Smith

Spot-tail butterfly fish_02_Richard Smith
Here’s the same species of spot-tail butterfly fish at night, now sporting a large black spot on the side with a couple of small but pronounced white spots. He’s changed into pajamas and is ready to turn in. Photo by Richard Smith

Parrotfish in cocoon_Walt Stearns
Parrotfish secrete a clear jelly mucous cocoon around its body at night which acts as a first line of defense, or alarm, again potential predators. Photo by Walt Stearns 

Speaking of turning in for the night, another fish you are likely to find bedded down on the reef is the parrotfish. When parrotfish get ready to retire for the night, they secrete a type of mucous that envelops their entire body like a cocoon made of clear jelly. This mucous covering serves as the first line of defense by hiding the parrotfish’s scent from potential predators. It also acts as an early warning system, like a home alarm, should something come in contact with the cocoon’s outer layer.

Nocturnal reef fish have also developed some unique adaptations that help them find their prey with little or no available light. The large eyes of the crescent-tail bigeye are highly sensitive, and not particularly tolerant of harsh sunlight. This is why, during daylight hours, you will often find them in the shadow a wall or seeking refuge under a ledge or the mouth of a cave. After dark, the pupils of the crescent-tail bigeye’s large eyes will dilate to allow even the smallest traces of light to enter and register on the retinal fronting of the optic nerve. This allows the fish to see in almost complete darkness, and though it’s view of the world is more black and white than color, this ability proves ideal for detecting the indistinct outlines of prey that only come out at night.

Crescent-tail bigeye_020_Doug Richardson
The crescent-tail bigeye’s large eyes will dilate to allow even the smallest traces of light to enter and register on the retinal fronting of the optic nerve, enabling the fish to see in almost complete darkness.  Photo by Doug Richardson

Seeing the world in a different light

When you think you’ve seen it all, then perhaps you need to “see it again” under a different light—a Fluo light. Short for fluorescence, Fluo involves illuminating an object or animal under a near-UV light source, causing it to absorb that energy wavelength and re-emit it in a totally different color spectrum. Not all forms of marine life fluoresce, but those that do can put on quite a show.

“I experienced my first Fluo night diving at Wakatobi and it blew me away! Corals come to life in a way that has to be seen to be believed. I have become a fluoro diving addict since and each time I feel like I have transported to another planet.”  Kevin Deacon, May 2014

The phenomenon of “Fluo-diving” was pioneered at Wakatobi Dive Resort. Here, divers are provided with special blue fluo lights, along with yellow colored filters that fit over the dive mask. When the lights are swept along a reef, certain corals and animals, such as the  goby below and the coral it is resting on, light up as if a switch were flipped on displaying an iridescent red and brilliant green. Under normal light, invertebrates like mantis shrimp would appear a bland brown and beige. Under Fluo lighting, it glows an eerie shade of green, as if it were radioactive.

Goby and coral flourescing_Kevin Deacon
By day this goby would likely have been transparent with a light pink or yellow coloration. Under the fluo light it takes on a vibrant, iridescent red, adding quite a contrast to the coral, which has also fluoresced to a brilliant green. Photo by Kevin Deacon

If you’ve never been on a night dive in the Indo-Pacific, you really don’t know what you are missing. At Wakatobi it’s a whole new world.

To learn about a visit to Wakatobi contact our office at office@wakatobi.com or complete a quick trip inquiry at wakatobi.com.  A guest experience representative will be in touch with you to answer any questions and provide information about your next dream dive vacation.

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