Sexy Stuff on the Reef - Ruby Brittle Stars Spawning

by B. N. Sullivan

Our favorite Caribbean dive destination is the Cayman Islands. In particular, we like to stay on Cayman Brac. From there we can make day trips by boat to dive at Little Cayman, in addition to diving the many excellent sites around Cayman Brac itself.

In fact, one of our favorite night dives anywhere is a site on the north coast of Cayman Brac known as Radar Reef, which reportedly got its name from a landmark visible to boats offshore -- the antennas at a nearby telecommunications facility.

You don't need to hire a boat to dive Radar Reef at night, since it is easily accessible from shore. There is a boat ramp at the shoreline end of Kirkconnell Street at Stake Bay. Some concrete steps alongside the boat ramp lead right into the water, making it incredibly easy to enter and exit the water.

Some undersea communications cables come ashore nearby, and the trick is to locate the cables where they lie on the sandy bottom near the boat ramp, and then follow them offshore to the reef. (They're actually quite easy to spot.) At the end of the dive, you simply follow the cables back to shore again. It's next to impossible to get lost there, as long as you keep the cables in sight.

We've been to Cayman Brac a number of times, and while there, we always do a few night dives at Radar Reef. The area is well populated with small creatures, so it is a macro photographer's paradise. Particularly plentiful are critters that only come out at night. One of those is the Ruby Brittle Star (Ophioderma rubicundum), which forages only at night and hides in crevices in the reef during daylight.

Just before 7 PM one dark August evening, we waded into the water next to the boat ramp, located the cables, and swam out to Radar Reef. Fortunately I had set up my camera for macro photography in anticipation of the small critters we expected to see. Still, we had no idea what an amazing sight we were about to chance upon.

Once we arrived at the reef, in about 45 feet (14 m) of water, we shined our lights around on the coral heads to look for photo subjects. I spotted a Ruby Brittle Star almost instantly. I photographed it, and then noticed there was another of the same species very close by. As I was preparing to photograph the second one, I noticed a third, and then another and another.

Jerry was right beside me, but shining his light on a different coral head. I finished taking a photo, and he nudged me to look where he was shining his light.

There we saw more Ruby Brittle Stars -- lots more. Dozens and dozens of these critters seemed to be appearing out of nowhere, converging on the reef. They were literally draping themselves all over the coral, the sea fans, and the sponges growing on the reef. We had never seen so many Ruby Brittle Stars in one place at one time. We both had the feeling that something was going on, but we didn't know what.

I took a few more photos, and then we began to notice that some of the brittle stars appeared to be standing up. We had never seen this behavior before, but here they all were, standing up on their tippy-toes, raising their disc-shaped bodies off the corals or sponges where they had been resting flat a few moments earlier. They were beginning to look like so many miniature footstools.

Now completely fascinated, I shot frame after frame of what to us was a novel behavior. Then all of a sudden, the critters -- still balancing on the tips of their rays -- began to eject clouds of tiny red beads into the water. It took just a few seconds for the realization to hit us: these brittle stars were spawning!




As soon as they finished expelling spawn, the brittle stars ceased their peculiar uplifted posture and dropped back down into their more usual flat position, rays extended around them. Some individuals were entwined with others, but now they all just lay there. With their spawning orgy over, the brittle stars became immobile. They seemed totally spent -- in more ways than one!

We noticed little else on that dive, and I never did photograph anything but the Ruby Brittle Stars that night. I was shooting film, and I very quickly shot the entire roll of 36 frames, all the while thinking what incredible luck it was that brought us there to just the right place, at just the right time, to witness this amazing mass spawning event.

The photos on this page all were taken during that one night dive at Radar Reef. These photos are 1:2 macros. To give you an idea of the actual size of these creatures, the body disc of the Ruby Brittle Star is about a half inch (1.3 cm) across.

I have reduced the size of some of the photos on this page so that they all would fit into the text. You can click on any of them to see a larger view. In particular, you may want to look at the enlarged view of the 4th and 5th photos, so that you can see the red spawn more clearly.

Caption: "Was it good for you??"

Swing yer partner, do-si-do...

What: Caribbean Spiny Lobsters (Panulirus argus)

Where: I took this photo of the 'dancing' lobsters during a night dive
off West Caicos, in the Turks & Caicos Islands.

[Click photo for larger view.]

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About the Photos on The Right Blue

We've been getting a lot of questions recently about the photos on The Right Blue, so we thought it might be good to answer those questions in one post.

First, unless otherwise plainly noted, ALL of the underwater photos on The Right Blue were taken by Bobbie. As of this writing, there are about six underwater photos on the entire blog that are not Bobbie's original work. All are identified clearly.

There are not too many terrestrial photos on The Right Blue, but those taken by anyone other than Bobbie or Jerry also are identified.

All of the underwater photos originally were shot on film, with a Nikonos V dedicated underwater camera, using an assortment of U/W Nikkor submersible lenses, with Ikelite SubStrobe and Nikonos underwater strobes for lighting. The transparencies were digitized by Jerry, using a Nikon Super COOLSCAN 5000 ED scanner.

In regard to photo editing and post-processing, we don't do a whole lot. We don't use PhotoShop at all, but we do use Picasa 2 and/or the Microsoft Digital Image Standard 2006 Editor to crop, straighten, and resize. Since the images were scanned from (old) transparencies, some had scratches which were digitally removed. We don't add effects or tinker with colors, other than to brighten some of the images, e.g., those shot inside wrecks. What you see is what was on the transparency.

The underwater photos on The Right Blue were taken over a period of many years. A few date back to the 1980s, although most are considerably more recent than that. We have an archive of over 6,000 underwater images. We know when and where each image was taken, and other details, because Bobbie is a compulsive record keeper: each image in the archive has a unique ID number that corresponds to a carefully maintained database that tells date, place, exact location, camera/lens/film information, species identification, and so on. This information was recorded as we went along.

Each underwater image ID also corresponds to a specific dive log entry. (Bobbie's dive logs are as meticulously kept as the photo logs!) So, when we want to tell about something that happened on a particular occasion at a particular dive site, we can readily find the image(s) to go with the story, and vice versa.

Some readers seem to have been confused or bewildered by the fact that we may tell a story set in Hawaii one day, in the Red Sea the next, and two days later post a photo from, say, Indonesia. How can we be in all those places in such a short space of time? Clearly they have not read our About page, or our page that tells how the Right Blue project came to be, where we explain that our stories and photos recount decades of diving experiences. These are reminiscences, not 'real-time' adventures.

But yes, we really did spend time in all those places. We really did see all those underwater sights, and we really did take all of the photos -- but it took us a lifetime!

WW #47 - Masked Butterflyfish (Chaetodon semilarvatus) - Red Sea

[Click photo for larger view.]

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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.]

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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

Tiger Sharks Don't Floss

by B. N. Sullivan

One day we were diving at Puako, Hawaii in the general vicinity of the area we call the Petting Zoo (described in a previous post). We were swimming close to the bottom edge of the rubble slope, where the sandy plain begins, looking for little creatures and seashells.

I spotted what I though might be the edge of a shell sticking out of the sand. When I picked it up, I realized that it was not a shell at all. It was a shark's tooth -- the first I had ever found in the water. I put it into the small mesh drawstring bag I always carried with me, and we continued our dive.

When we got home that day, I took the shark tooth out of my little mesh bag, washed it, and set it aside to dry out. That's it in the photos on this page. We didn't know what species of shark the tooth had belonged to, but we joked that whatever kind it was, he obviously didn't floss!

A few weeks later, an old friend of mine from Honolulu came to visit, along with her young son. To entertain the little boy while his mother and I chatted, I got out a few books that had a lot of pictures and gave them to him to look at. One of those books was about sharks. After awhile, the boy interrupted our conversation, telling us he needed to show us something right away. It was a picture of a Tiger Shark tooth, and it looked exactly like the one I had found. This was an unexpected piece of information.

Don't get me wrong -- we always knew that there were Tiger Sharks (Galeocerdo cuvier) in our waters. We knew that fishermen in the area caught one occasionally, and local surfers reported seeing them from time to time, yet in all our years of diving we had never seen one. In a way, this was surprising. Since we dived so frequently in the same area, we reckoned there was a high likelihood that sooner or later we would cross paths with at least one of everything that was out there. We had seen plenty of sharks, but no Tiger Sharks.

Much as birdwatchers do on land, we always have kept a record of every marine species we've encountered. We call it our Critter Log. Most of the sharks we had seen were reef sharks: Whitetips, Blacktips, and Grays. From time to time we would see a pelagic shark, like a Hammerhead, or a Whale Shark. We also had come face to face with one Galapagos Shark and one Thresher at Puako, but never a Tiger Shark. Still, the tooth I had found was proof that the Tiger Sharks definitely were there in what we thought of as our territory.

Surfers we knew who claimed to have seen Tiger Sharks in the water said they only appeared during dawn patrol, or just as the sun was setting. We began a lot of our dives very early in the morning, and when we did night dives at Puako, we usually entered the water at dusk. Thus, we surmised that if we ever saw a Tiger Shark at Puako, it probably would be either very early in the morning, or at the outset of a night dive. This thought was reinforced by the fact that our sighting of the Galapagos Shark was very early in the morning, and it was as we were descending for a twilight dive that we had our single encounter with a large Thresher Shark.

I had found the Tiger Shark tooth well offshore, and at a depth of more than 100 ft. Thus, in addition to believing there was a good probability that one day we would cross paths with a Tiger Shark at Puako, we imagined there also was a strong likelihood that we would see it well away from shore, in deep water. After all, these are large, pelagic animals -- and anyway, that was where I had found the tooth!

From time to time we discussed all this, usually in conjunction with showing what we now knew was a Tiger Shark tooth to another diver. As it turned out, our first and only encounter with a Tiger Shark was nothing like we had anticipated. It happened in the early afternoon, inshore, in relatively shallow water. So much for probabilities and likelihoods!

In the next post we'll tell you all the details of that first encounter with a Tiger Shark.

WW #45 - Emperor Angelfish (Pomacanthus imperator) - Red Sea

[Click photo for larger view.]

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Another Side of The Right Blue

This will be quick: I just have to share something.

As I do most days, this morning I opened my Google Reader and began to browse the feeds of some blogs I follow. When the feed for Go Visit Hawaii loaded, I was taken aback by what I saw. It was a photo of the view from my window!

Sheila has been running an interesting series on Go Visit Hawaii called "The Colors of Hawaii." She asked readers to submit photos of Hawaii that highlight a particular color. Unbeknownst to me, Jerry submitted one in the blue category (of course!), and Sheila published it today.

Click on over and have a look at Colors of Hawaii: Big Island Blues on the Go Visit Hawaii blog. And while you're there, you might enjoy looking at some of the other Colors of Hawaii, too.

P.S. I hear that Sheila is still accepting photos for The Colors of Hawaii, so if you have one you'd like to share, send it to her. The details are here.

UPDATE Aug. 6, 2008: Sheila has put a new post on her Go Visit Hawaii blog that lists all the Colors of Hawaii posts so far. She's still accepting more photos.

Meet the Mantis Shrimp

by B. N. Sullivan

Let me introduce you to one of our favorite marine creatures: the mantis shrimp. Why are they a favorite? They're cute (sort of), they're very smart (for a crustacean), and they're fun to watch. Unfortunately, they're also difficult to photograph -- more on this a little later!

The individual in the photos on this page is a Shortnose Mantis Shrimp (Odontodactylus brevirostris), from Hawaii. I know that the critter looks pretty big in these photos, but it's not. These are macro images. The mantis shrimp in these pictures was only about two inches (5 cm) long. You can click on any of the photos to see a larger view.

Despite the name, mantis shrimps are not true shrimps. I guess I don't need to explain that they are not mantises, either -- although they apparently acquired their name because they resemble praying mantises somewhat. Like crabs and lobsters and true shrimps, mantis shrimps are Crustaceans.

All mantis shrimps belong to the order Stomatopoda. Stomatopods have a number of features that set them apart from other crustaceans. Among the most notable -- and noticeable -- are their raptorial arms, and eyes that are highly evolved.

Mantis Shrimp Eyes

I've always wondered what the undersea world looks like through the mantis shrimp's eyes, because their eyes are like no other eyes. Take a look at the photos, and notice that the eyes are set at the end of stalks. Each eye is independently movable -- and they seem to move constantly, giving the critters a hyper-alert look. Each eye is trinocular, that is, each has three separate perceptual regions. This would be sort of like having built-in trifocal lenses, except that instead perceiving things at three different levels of magnification, each eye region is specialized to perceive a different kind of visual information -- but all at once.

Mantis shrimp eyes are capable of hyperspectral vision. In other words, not only can they see the visible light spectrum, like we can, but they also can see spectra of light that we cannot, including infrared and ultraviolet. Very recently it was discovered that mantis shrimps have the ability to perceive circular polarized light, too.

Raptorial Appendages

The mantis shrimp's raptorial appendages actually are legs that have evolved into claw-like arms, specialized for killing prey. There are two types: some species have thin, barbed raptorial arms that can spear prey; others have club-like raptorial appendages that smash their prey. (The mantis shrimp species in the photos is a 'smasher'.) When mantis shrimps are at rest or walking about, they keep those killer appendages folded up like closed jack-knives against their bodies, just as the creature in these photos is doing. When they go after prey, those appendages unfold at an incredible speed and they spear or whack the prey.

The spearers tend to choose soft-bodied prey like worms and little fish. The spearers are ambush predators. That is, they sit quietly and concealed until prey comes along and then they attack. In contrast, the smashers usually pursue their prey -- and that is one of the mantis shrimp behaviors we love to watch, when we get the chance.

The smashers use their raptorial arms not just to kill prey, but also to break it apart to eat. The species in the photo eats things like small crabs, and gastropod snails that live in shells. When the mantis shrimp sees one of those and goes after it, first he punches it silly, then he uses his raptorial arms to crack open the shell so that he can pick out the meat with his little forward legs, which are also specialized for that purpose.

The Star of the Puako 'Petting Zoo'

The mantis shrimp in the photos on this page lives off the coast of Puako, Hawaii in an area where we have made countless dives. When you dive in the same area again and again and again over a period of years, you become aware of things that a visiting diver probably never would notice in the course of just a few dives. One thing you learn is where all the different types of creatures live. Except for pelagics that roam the open sea, most marine creatures have a relatively small range. Once you spot where they live, you can usually count on seeing them in the same general area any time you go there. Once you know where to look, there they will be.

Puako has a wonderful fringing reef that parallels the shoreline for a couple of miles. The coral reef area is beautiful, and very accessible, but there are areas beyond the reef that are just as fascinating, if not quite so pretty. Where the seaward edge of the reef ends there is a steep slope. The top of the slope has many rocks and is still covered with quite a lot of coral, but deeper on the slope where less sunlight penetrates there is little live coral. There are more rocks, plus lots and lots of coral rubble -- lumps of dead coral washed down the slope from the reef over time. At the base of the rubble slope the terrain levels out into a sandy plain.

There is an area near the base of the rubble slope, at a depth of about 100 ft (30 meters), that we named the Petting Zoo. We called it that because it teems with small creatures. Sometimes we would go directly to the Petting Zoo, plop ourselves down in one spot, and spend the entire dive watching all the little creatures go about their business. You can learn a lot about marine creatures' behavior that way.

On one of our visits to the Petting Zoo, we noticed this particular mantis shrimp. Some mantis shrimp species are nocturnal, i.e. they only come out at night. This species works the day shift. We first saw him when he emerged from his burrow and began scurrying about. Mantis shrimps can swim a bit. If you look at the second photo above, you'll notice that this creature has a tail not unlike that of a lobster. They can use their tails to propel themselves through the water for short distances, but their more usual method of locomotion is to run about. Notice I said run. They move quickly -- usually too quickly to get a good macro shot.

Mantis shrimps live in burrows. This one had excavated a double-ended tunnel under the sand. I have no idea what it's like inside the burrow -- we used to joke that he probably had an overstuffed chair and a TV in there for all we knew. We did notice that outside the entrance to the burrow we would sometimes see pieces of broken shell in little piles. A few times we saw the critter in the process of housecleaning -- literally throwing bits of shell out the door.

On successive visits we saw this mantis shrimp stalk and kill prey -- usually a small crab. One time we saw him smack a crab that was bigger than he was, dismember it, and drag the body to the opening of his burrow. The mantis shrimp disappeared inside the burrow for a few minutes, then re-emerged and whacked the shell of the now legless crab a couple of times to crack it open and began to dig out the 'meat' for his feast. We watched him until it was time for us to begin our ascent. He was still working on the crab when we left. When we came back a day or two later we looked for the remains. Sure enough, there was a recognizable piece of the crab's empty shell not too far away from the entrance to the mantis shrimp's burrow.

I mentioned in the first paragraph of this article that mantis shrimps can be difficult to photograph. That's because they seem to be in motion constantly when they are outside their burrows. It's not too difficult to get a shot of one peeking out of its burrow, but capturing an image of the whole animal had eluded me for years.

Then one day at the Puako Petting Zoo, this little mantis shrimp came out of its burrow and just stood there looking at us. And -- Hallelujah! -- not only did I have my camera, it was set up for macro photography. Moving as slowly as I could, not to startle the critter, I lay down on my belly on the sand at the edge of the rubble slope, and sort of inched toward the mantis shrimp. He didn't run away.

I focused carefully on his wonderful eyes and pressed the shutter release, figuring this would probably be my one and only shot. So often in underwater nature photography, the flash of the strobe startles a photo subject and it quickly leaves, so one shot is all you get. But no, not this mantis shrimp. I expected him to high-tail it to his burrow, but instead he actually came toward me a bit, stopped and turned sideways, almost posing. Now practically touching him with the end of the lens port, I took another shot, and a third.

Then he turned the other way and positioned himself as if to say, "How's this? Can you see my tail a little better now?" I shot once more, and then he finally scampered over to his burrow and disappeared inside. I did press the shutter one more time while he was in retreat, but his movements had stirred up the sand by then.

I've often wondered what it was that made that mantis shrimp decide to be such a cooperative photo model that day. I've never again had an opportunity like that.