The Hawaiian Dascyllus

by B. N. Sullivan

A few days ago I spent over an hour sifting through my photos, looking for images to use to illustrate a post about Cerianthid tube anemones. In addition to the ones I used for that article, I came across two photos that show a solitary, very tiny juvenile fish sheltering among the tentacles of a pretty Cerianthid tube anemone.

Here are the photos of the Cerianthid with the tiny fish. I made the images small so that both of them would fit into this post, but you can click on them to see a larger view. The little fish is a juvenile Hawaiian Dascyllus (Dascyllus albisella), a member of the Damselfish family (Pomacentridae). From its size -- not even a half-inch (15 mm) long -- we reckon the tiny fish was barely past its larval stage.

Hanging out with the Cerianthid is a good survival strategy for this little fish. Not only will it be somewhat protected, it also happens to eat the same kinds of things that are part of the Cerianthid's diet, like zooplankton. I've always wondered, though, how these tiny juveniles manage to locate such a host.

This particular Cerianthid was located at a depth of about 36 meters, way out on a sandy plain with not much else of note in the immediate vicinity. There was no nearby reef -- not even a pile of rocks -- just a flat expanse of packed sand. Surely the little fishy didn't "see" the anemone out there on the sand in the middle of nowhere and decide to move in! I suppose there's some biochemical sensing at work.

The third photo on this page shows an adult Hawaiian Dascyllus, for comparison. As these fish mature, they lose those bright bluish-white spots on their foreheads completely, the white spots on their sides become very faint, and the jet black color in their scales becomes gray. The adults live in coral reef areas of coastal Hawaii where they are a common sight.

The Hawaiian Dascyllus is a local endemic: it only occurs naturally in Hawaiian waters. If you think you've seen it elsewhere, you may have seen one of its 'cousins' of the same genus that look very similar. D. trimaculatus, in particular, looks very much like the Hawaiian Dascyllus, and the juveniles of the two species are virtually identical in appearance. That species is widely distributed around the Indo-Pacific region. We've seen it in the Red Sea, and also in the waters around Indonesia and Malaysia.

I took the photos of the Cerianthid and the juvenile Hawaiian Dascyllus off the coast of Puako, Hawaii. I photographed the adult in Honaunau Bay, on the South Kona coast of Hawaii's Big Island.

Cerianthid Tube Anemones - Flowers of the Deep

by B. N. Sullivan

When most people think of scuba diving in tropical waters, they think of coral reefs. Granted, coral reefs are lush, often colorful habitats. They're a feast for the eyes, and home to a huge diversity of creatures. We love our coral reef dives, but we like to point out to people that coral reefs are not the whole show.

Awhile back I wrote a few posts about muck diving, i.e., the practice of rummaging around in the sand and rubble in places that may look less than pretty to the casual observer, but which turn out to be home to an incredible assortment of tiny creatures that can't be found elsewhere. Most avid macro photographers engage in muck diving regularly.

Most muck diving is done in locations where the water is relatively shallow, but we also do a deep water variant of muck diving. The ideal locations, we have found, are sandy areas or mud flats located near the base of reefs at depths between 100 and 150 feet (30 to 45 meters). Whole communities of creatures live in these areas -- creatures never seen around the reefs themselves.

One creature we look for when muck diving in deep water is the Cerianthid tube anemone. These creatures are related to corals and 'regular' anemones, but they usually are much smaller -- only a few inches in diameter at most. They look like beautiful flowers, and their delicate beauty is all the more striking because they are found in environments that are rather stark.

Cerianthid tube anemones differ from 'regular' anemones in a number of ways. For one thing, they live inside tubes (hence the name 'tube anemone'). Cerianthids build the rubbery tubes they live in with their own mucus secretions. Most of the tube is buried, and most of the animal stays inside that tube all the time.

A crown of tentacles protrudes from the tube to feed. The tentacles, which are armed with stinging nematocysts, are arranged in two sets. The outer set of tentacles are longer. The inner set of tentacles are much shorter, and often are a different color or shade. I think it's this arrangement that makes the Cerianthids look like flowers. The outer tentacles are like flower petals, while the short inner tentacles resemble the center of a flower.

The outer tentacles are the food grabbers. Tidbits of food -- plankton, for example -- are snagged by the longer, outer tentacles, and then transferred to the shorter, inner tentacles, which then move the food along to the mouth in the center of the array. One thing we find fascinating about Cerianthids is that they can (and do) move each long tentacle independently and purposefully. We have watched them snag a tidbit on one outer tentacle, then bend that tentacle in toward the center and deposit the catch onto the shorter tentacles. We've never seen a regular reef anemone that is able to do this.

Cerianthids come in assorted, mostly pale, colors, but one variety that we have here in Hawaii is a dark maroon color. In fact, because it lives in deep water where most of the color spectrum of natural light is filtered out, when we first came upon this variety, it looked black. You can't tell what its true color is until you illuminate it with artificial light from a flashlight or camera strobe.

Cerianthids can be difficult to photograph for several reasons. First of all, since they live in deeper water, well offshore, it's almost impossible to get to the area where they live, find them (they're small!), set up the shot and photograph them adequately within the time limits for a 'no decompression' dive. Thus, in order to have enough time to do all that needs to be done to photograph Cerianthids, a planned decompression dive usually is necessary, with all of the advance preparations that requires.

Another reason Cerianthids are difficult to photograph is that the creatures are, well, touchy! They do not like to be disturbed. If you happen to touch their tentacles -- zip! -- they retract into their tubes. In fact you don't even have to actually touch them to elicit that response. A bit of turbulence in their immediate area will do the trick, so you have to be sneaky in your approach. Many Cerianthids react to light, as well -- especially the big blast of light emitted by a camera strobe. So, often you get only one or two shots of a Cerianthid before it retracts, pulling its pretty flower-like crown inside the tube. Once that happens, you might as well leave. It won't re-emerge very quickly.

Of course, you can always take a photo of the tube!

WW #46 - In case of shark attack...

DIVER TIP: Never enter the water without one of these Hawaiian Shark Sticks!

"If attacked by shark or moray eel, hold stick vertically and insert into animal's mouth to prevent closing of jaw... If the animal should bite you, insert stick in animal's eye and push. DO NOT BLEED! This will only excite the shark or eel..."

[Click on the image to read the rest of the easy instructions.]

My previous Wordless Wednesday posts.

Wordless Wednesday home page.

The Day We Met the Landlord

by B. N. Sullivan

If you ask someone to name a large, predatory shark a likely response is the Great White Shark (Carcharodon carcharias). That was the species featured in the film Jaws as the villain -- albeit in greatly exaggerated form. Thanks in large part to that film, sharks in general, and Great Whites in particular, tend to evoke fear in the minds of many people.

There are occasional sightings of Great White Sharks in Hawaiian waters, but the Tiger Shark (Galeocerdo cuvier) is generally acknowledged to be the top predator shark in tropical seas around the world, including Hawaii. There have been very few documented cases of attacks on humans by Great White Sharks in Hawaii, but about once a year, on average, someone is bitten by a Tiger Shark in the our waters. I should add that most of these 'attacks' are not fatal. Far more people drown than are killed by sharks: there are about 50 drownings per year in Hawaii, according to the Hawaii State Department of Health.

That said, the Tiger Shark still commands considerable respect. In fact, some surfers we know refer to the Tiger Shark as "The Landlord." That Landlord is imposing in size -- up to about 18 feet (550 cm) in length -- and is known to have an equally big appetite. It eats various kinds of fish, including other sharks. It also eats octopuses, crabs, lobsters, and sea turtles (which it can swallow whole).

The Tiger Shark can swim long distances in the open ocean, but tracking studies carried out by the Hawaii Institute of Marine Biology Shark Research Group have shown that the species also spends time in coastal areas. Every now and then, Tiger Sharks are spotted fairly close to shore by fishermen and surfers, and they are seen occasionally by divers as well.

In an earlier post, I promised to tell about our first and only encounter with a Tiger Shark while diving at Puako, on the Big Island of Hawaii. As I mentioned previously, we reckoned we would cross paths with a Tiger Shark sooner or later, since we spent so much time in and under the water. But when it finally happened, the where and when and how were completely at odds with what we had imagined would be the case. In fact, everything about the encounter was a surprise.

Early one fine November afternoon, we entered the water from shore for our second dive of the day. Although we have been known to cram as many as five dives into each day of a dive trip, at home we seldom do more than one dive on any given day. On this particular day, though, we had been working on an offshore project during our early morning dive (more on that in a later post). Before we had finished our underwater tasks, we ran out of time and had to ascend. So, after we surfaced we decided to rest for a couple of hours, get fresh air cylinders, and make a second dive.

We had decided ahead of time that on the second dive, we would complete the tasks we had begun during the morning dive as quickly as we could, and then spend the rest of the dive in relatively shallow water. According to my dive log, both dives had been to a maximum depth of about 125 ft (38 meters), so it was prudent to spend as long a time as possible in shallow water at the end of the second dive 'off-gassing' some of the nitrogen our bodies had absorbed at depth.

This procedure is an easy and pleasant thing to do at Puako, thanks to the underwater topography. The inshore edge of the fringing reef at Puako is at the base of a cliff-like dropoff created by old lava flows. For long stretches, the depth at the base of the dropoff is between 20 and 30 ft (roughly 6 to 10 meters), ideal for decompressing after a deeper dive. The best part is that the dropoff is not straight. It meanders in and out, and there are canyons and cavelets, and arches -- all kinds of nooks and crannies to explore, and all of those full of critters. In short, you'll run low on air long before you run out of things to see there.

We spent most of our shallow time that day in a particular canyon that was less than a ten minute swim from our exit point. We looked for shells, we watched an octopus pair who were courting, we saw a lobster hiding in a cavelet, we spotted a scorpion fish perched on a rocky shelf -- all very enjoyable and entertaining. Our time was nearly up, but since we were so close to shore, we were not in a hurry to leave.

We pottered along toward the mouth of the canyon, where we would round an outcropping and then swim into the next canyon. That canyon would lead us to our exit point. This was a backyard dive. We knew the route and the terrain by heart.

Conditions that day were about as ideal as they could be. According to the notes in my logbook, both the water temperature and the air temperature were 80 F (27 C). There was virtually no wind, and the surface was calm and glassy. Horizontal visibility underwater was about 125 ft (38 meters). So, as we left the mouth of the little canyon, we could see the vast coral garden very well.

I looked out across the expanse of coral. While I hovered there, enjoying the view, I spotted something unusually large swimming along the far edge of the coral garden. There had been several sightings of a juvenile Whale Shark in the area during the past week, and I thought immediately that's what it must be. Jerry was following a short distance behind me, so I banged on my scuba tank to get his attention, and pointed toward what I thought was the junior Whale Shark. When I banged on the tank, the big fish heard it, too. It changed course immediately and began swimming straight toward us. "Oh, goody," I thought. "What a treat."

As it swam in our direction, we had a head-on view. I noticed that it had a wide blunt snout, a feature that momentarily confirmed in my mind that it was indeed a juvenile Whale Shark. Then, when it was about 20 feet (6 meters) away from us -- and just as I was about to swim toward it to meet it, and maybe even pet it -- it turned a bit, to alter its course. The instant it turned I could see the markings on its flanks. The flash of realization hit me: this was no Whale Shark, it was a great big Tiger Shark! We were meeting the Landlord.

The big fish sort of glided past us, and then continued on its way -- no rush, no hurry -- heading northward along the reef. My heart was pounding then, I admit, but I felt excitement rather than panic. I even had the presence of mind to take a mental snapshot of the Tiger Shark as it passed in front of me: the nose was right above that coral head, and the base of its tail was over this one. The next day we returned with a measuring tape and, playing it out between the landmarks I had committed to memory in that instant, we determined that the shark was roughly 12 to 13 ft (about 4 meters) in length.

At the moment, though, all we knew was that it was big, and that it was a Tiger Shark, and that it was right there! The last we saw of it -- and the image sticks in my mind clearly to this day -- was the tall dorsal lobe of its tail, gently sweeping back and forth as it swam away from us, unhurried. It was elegant.

When it was completely out of sight, I turned to Jerry. He was hovering there in the water, hands calmly folded at his waist, just staring after the shark.

In a moment of Supreme Duh, I made the hand signal for 'shark.' Jerry nodded. I stretched both my arms out wide, and then signaled 'shark' again: B-i-i-i-g-g Shark! Jerry nodded again. I held my left arm horizontally across my waist, and with the index finger of my right hand, I drew imaginary hash marks along my forearm, then signaled 'shark' again: Tiger Shark. But by then Jerry was no longer watching me tell him the obvious with my hand signals. He seemed more interested in his dive computer.

Jerry turned his computer toward me so that I could see the face the instrument, and pointed at the numerals it displayed. I thought he was trying to tell me that we were out of time (which we nearly were) and that we should end the dive. No, he was showing me the depth. We were hovering at just barely 20 ft (6 meters). Jerry pointed in the direction of where we had last seen the shark, then pointed at his computer, and wound up the wordless communiqué with the hand signal for 'crazy.' He was telling me he couldn't believe we had seen that Tiger Shark at such a shallow depth.

Indeed, we always had imagined that if we saw a Tiger Shark, it would be in deep water, and well offshore. We also had been led to believe that we were more likely to see one around dawn or dusk. We never, ever imagined that we would see one just after midday, in less than 30 feet of water, right along the edge of the dropoff, so close to shore. We had just come face to face with a big Tiger Shark, but it was at a time and place we never would have predicted. It was a little hard to take in.

Then, via another flurry of hand signals, we agreed it was time to swim to our exit point, but with one of us swimming face-forward, and the other swimming backward. Just in case the Tiger Shark decided to circle around and come by for another look at us (as sharks sometimes do), we wanted to spot it as soon as possible. It didn't come back. Anyway, when we saw it, the shark did not appear to be hunting. Rather, it was in sightseeing mode -- just cruising through -- and we were merely one of the sights.

One more thing. After we waded ashore, we both turned around and looked out to sea. I think we half expected to see some evidence of the Tiger Shark -- a dorsal fin, perhaps? Of course we didn't see any sign of it, and it had been silly to think we would have. What we did see was a catamaran that serves as a snorkel charter boat, tied up at a mooring on the reef, just a stone's throw from where we had seen the Tiger Shark. There must have been a dozen or so people -- tourists from a resort down the coast -- paddling around, splashing on the surface.

We wondered aloud what they would do if the Tiger Shark suddenly appeared beneath them. A few minutes later, we saw that the catamaran crew were beginning to help the snorkelers back aboard the vessel, but without any urgency or excitement. Their time was up, their snorkel excursion was finished, and they had missed meeting the Landlord.

About the images on this page: The first image was scanned from page 76 of the book, Sharks of Hawaii, by Leighton Taylor, (Honolulu: University of Hawaii Press, 1993).

The second image, a photo of Tiger Shark just below the surface, by Bill Curtsinger, for National Geographic. Click on the photo to download it as a wallpaper from the National Geographic website.

More About Tiger Sharks:

Tiger Shark Research Program, Hawaii Institute of Marine Biology, University of Hawaii

Tiger Sharks, Florida Museum of Natural History