Out of the Blue - One Big Fish!

What: Napoleon Wrasse (Cheilinus undulatus), an endangered species.
Adults are very large - about 45 inches (115 cm) long.

Where: I took this photo in the Red Sea, near Sharm el-Sheikh, Egypt.

[Click photo to enlarge.]

My previous Wordless Wednesday posts.

Hawaii's Gold Lace Nudibranch

by B. N. Sullivan

Continuing our series on nudibranchs (see previous post on Exotic Underwater Nudies...), today we present the Gold Lace nudibranch (Halgerda terramtuentis). This pretty mollusc is endemic to Hawaii -- that is, it is only found in the waters around the Hawaiian Islands.

It has a pale yellow translucent body overlaid with a lacy network of irregular yellow-orange lines, and a solid yellow-orange line bordering the entire edge of its mantle. It also has little bumps, called tubercles, all over its body, which are a lighter color -- almost white on some individuals.

As if its body were not pretty enough, take a look at those accessories: Its tree-like gills and its rhinophores -- those sensory organs protruding from its head -- are white with black speckles.

While these little critters are found only in Hawaii, they are fairly common here. Both of the individuals pictured on this page were photographed at Puako, Hawaii, where the species is plentiful along the area known as the first dropoff, where they live in small cavelets and in rocky areas. We see them most often at relatively shallow depths -- less than 10 meters/30 ft.

I took both of the photos on this page inside a small cavelet. The individual in the photo above was crawling along the ceiling of the cave, and got dislodged by our exhaled bubbles. On impulse, I snapped a shot of it as it floated downward through the water, and amazingly, it turned out to be a pretty good 'species ID' shot! The second photo is more naturalistic. Because the nudie is crawling across a red encrusting sponge, you can get an idea of its 'see-through' translucence.

Gold Lace nudies are small -- usually between one and two inches (up to 5 cm) in length. They are carnivorous, but they don't "bite." They feed on sponges and other soft organisms.

This nudibranch was officially identified relatively recently - in 1982 - by Hans Bertsch and Scott Johnson of the University of Hawaii. (Many nudibranch species have been officially recorded in the scientific literature since the 1800s.)

By tradition, the scientists who officially discover a species get to name it. This creature's species name has an interesting story. Terramtuentis means "looking at the earth with care." The name was given in honor of a group of Earthwatch volunteers who assisted Bertsch and Johnson with their research.

Ocean Abstract: Sea Fan Macro

What: Detail of a Gorgonian sea fan (Acabaria erythrea), with polyps open

Where: I took this macro photo in the Red Sea
near Sharm el-Sheikh, Egypt

[Click photo to enlarge.]

My previous Wordless Wednesday posts.

What is the difference between 'endemic' and 'indigenous' species?

by B. N. Sullivan

When I write about the creatures we have come to know, I nearly always identify both their common name, and their scientific name, and of course I tell our readers where the creatures live. In some instances, I may also mention that a creature is 'endemic' to a certain place.

A reader recently asked, "Does endemic mean the same thing as indigenous?"

The answer is, "Not exactly." Let me explain.

When we say that a species is indigenous to a place, we mean simply that it occurs there naturally. It is a native. But a species can be indigenous to a number of places at once.

In contrast, if we say a species is endemic to a place, we mean that it occurs naturally only in that place. It is a native to an exclusive or limited area. It is not widely distributed, and won't be found naturally anywhere else.

Most species inhabit specific areas of the world, but not the whole world. When people think about animals on land, they intuitively know this. They know, for instance, that giraffes exist naturally only in Africa, and that the polar bears live naturally only in the Arctic. They would not expect to see a giraffe wandering around wild near Hudson Bay, nor would they expect to see a polar bear in Kenya. Yet there are many animals that are much more widely distributed than giraffes or polar bears. Think of squirrels -- or rats!

In the sea, it is the same. Some marine animals (and plants) occur naturally only in the Caribbean, or the Mediterranean, or Hawaii, for example. Other species are found in a wider range of places.

Here in Hawaii, we have a high percentage of endemic species, compared to other places in the world. This is true both on land and in the ocean. Because the island chain is so geographically isolated -- separated from other land masses in every direction by thousands of miles of open ocean -- there has been less opportunity for species from elsewhere to wander here spontaneously and establish themselves. Likewise, it has been difficult for many species that have evolved here in Hawaii to make their way to other areas of the world.

The photos on this page show examples of fish species that are found in Hawaiian waters. The first photo on this page shows a fish called the Saddle Wrasse (Thalassoma duperrey) being serviced by a smaller fish called the Hawaiian Cleaner Wrasse (Labroides phthirophagus). Both of these species are endemic to Hawaii. They occur naturally nowhere else in the world. Each has 'cousins' of the same genus in other regions. Some of those cousins look quite similar, but they are not anatomically identical. I took the photo at Puako, Hawaii.

The second photo shows a small squadron of Moorish Idols (Zanclus cornutus). These fish are indigenous to Hawaii -- they occur here naturally -- but they are not endemic. They also occur naturally elsewhere in what is known as the Indo-Pacific region and the tropical eastern Pacific. Indeed, we have seen them and photographed them in quite a number of places. These four were photographed at Honaunau, Hawaii.

When we speak of an animal's provenance, there is a third category that is important: the introduced species. Introduced species are those that do not occur naturally in a given place. They are brought there -- introduced -- from somewhere else. Sometimes this happens accidentally (as when a caged parakeet escapes), or when an animal hitch-hikes to a new location on a ship or plane, and manages to establish itself there. In other instances, animals are introduced deliberately, for a variety of reasons. Here in Hawaii, for example, there are a number of game birds that were intentionally introduced decades ago for the benefit of sport hunters. Other species were intentionally introduced as a food source.

In the third image on this page are some Bluestripe Snappers (Lutjanus kasmira), photographed at Puako, Hawaii. These fish were intentionally introduced from the Marquesas in the 1950s as a food fish. As so often happens, their introduction had unintended consequences. Some people in Hawaii do fish for them, and we do see them for sale in some fish markets, but they are not exactly prized. Worse, they have proliferated greatly and they compete with other, more valuable fish. It is also believed that they have contributed to the depletion of the population of a particular kind of crab upon which they prey.

So, to review: Endemics are native to, and live naturally, only in one place; indigenous species are native, but may be more widely distributed; introduced species are 'immigrants' of a sort.

Jerry Dives the Wall at Shark Reef

Where: I took this photo of Jerry swimming along the wall at Shark Reef,
Ras Mohammed, at the tip of Egypt's Sinai Peninsula

[Click photo to enlarge.]

My previous Wordless Wednesday posts.

Video: Spanish Dancer Nudibranch

Yesterday we introduced our readers to Hexabranchus sanguineus, a large red nudibranch species also known by its common name, the Spanish Dancer. Have a look at this video, and you will understand how the creature came to be called the Spanish Dancer.



If the video does not play or display properly above, click here to view it on YouTube.

Tip of the hat to YouTube user ALxFONS for posting the video.

Exotic Underwater Nudies - The Spanish Dancer

by B. N. Sullivan

Among the marine invertebrates that divers are likely to encounter in tropical and subtropical waters, some of the most colorful are the nudibranchs (pronounced NOOD-i-brank). These are marine gastropod snails without shells. These molluscs are also known as sea slugs -- a non-scientific term -- but divers and marine scientists alike often refer to nudibranchs by the short-form nickname "nudies."

Nudibranchs are wonderful subjects for underwater macro photography, because most of them are small and very colorful. We have encountered an assortment of nudies literally everywhere we ever have dived, and I have photographed many of those. We thought our readers would like to see and learn about some of the nudies we have come to know, so we decided to run a series on The Right Blue, featuring various 'exotic underwater nudies' (and you all can thank Jerry for coming up with the playful series title!).

To introduce the series, today's featured nudibranch is the Spanish Dancer (Hexabranchus sanguineus). This is the largest nudi we have ever encountered, and some say it is the largest nudibranch in the world, period, growing to a length of up to 40cm (about 15 in). The first three photos on this page are of the same individual Spanish Dancer, photographed during a night dive in the Red Sea. We estimate that it was roughly a foot long (30 cm). When these guys are flattened out on the reef, or crawling on the sand, they look a bit like red doormats!

We chose the Spanish Dancer to introduce our series about nudies because it is large (for a nudibranch) -- and since it is large, it's easier to see its most important external organs. The first photo on this page is a head-on shot of a Spanish Dancer. The two things sticking up are not horns, they are the critter's rhinophores.

Rhinophores are sensory organs that work much like our noses do. They sense 'smells' in the water. Nudies use their rhinophores to locate their food. (Spanish Dancers eat sponges, by the way.) They probably sniff out potential mates with their rhinophores, too.

You might notice that the critter does not seem to have any eyes. Nudies do have eyes of a sort, but no eyeballs. Instead they have little sensory specks embedded on their skin that sense light and dark, but that's all. So, you could conclude that their rhinophores actually are their most important sensory organs.

The name 'nudibranch' means "naked gills," and in the case of the Spanish Dancer, the gills are not only naked, they can't be retracted. Many species of nudies are able to retract their gills into a pouch on their back, but the Spanish Dancer's gills are always exposed. The second photo on this page is a macro image of the Spanish Dancer's six beautiful tree-like gills. The genus name of this creature, Hexabranchus, refers to the presence of six gills.

For comparison, have a look at the photo of two Risbecia pulchella nudibranchs that we posted recently. You can see their rhinophores and their gills quite clearly, but notice that the gills on this much smaller species are not nearly as elaborate as those on the Spanish Dancer.

You might be wondering how the Spanish Dancer got its common name. If you ever saw one of these creatures swimming underwater you would know the answer immediately.

While Spanish Dancers can crawl along surfaces just like any other snail, they have an alternative means of locomotion as well. They can launch themselves into the water column, and 'swim' for short distances by flexing their bodies rhythmically to achieve an undulating motion. The white ruffled margin of their mantle usually is tucked in when they are crawling or at rest, but when they swim, it is exposed. The visual effect is reminiscent of the swirl of a female flamenco dancer's skirt, thus the name Spanish Dancer.

The third photo on this page shows a Spanish Dancer nudibranch as it swam, with its lovely mantle ruffle fluttering this way and that. I have to say, though, that still photos are insufficient to illustrate this behavior. I don't shoot video underwater, but I did manage to find a brief Spanish Dancer video on YouTube, which I will post tomorrow.

Nudibranchs reproduce sexually. They line up side by side to mate, and then lay eggs in a ribbon-like mass. Some nudibranch species lay eggs as a flat ribbon. Others, the Spanish Dancer included, attach the edge their egg mass ribbons to solid surfaces in a spiral pattern. The Spanish Dancer's egg mass is easy to recognize. It is distinctive in that the ribbons are comparatively wide, and once set down in a spiral, they look like a reddish ruffled rosette.

The first photo below shows a Spanish Dancer's egg mass rosette. The second photo below is a macro image that shows the texture.

Hard Corals on a Shallow Red Sea Reef

[Click photo for larger view.]

My previous Wordless Wednesday posts.

The Yellowline Arrow Crab (Stenorhynchus seticornis)

by B. N. Sullivan

One of my favorite macro photography subjects on Caribbean reefs is the Yellowline Arrow Crab (Stenorhynchus seticornis). At first glance, these creatures resemble pointy-headed, long-legged spiders. The way they skitter around on those long legs also lends to that first impression.

Once you see a good macro photo of the Arrow Crab, however, you will notice some features that you would never see on a spider. First there is that elongated pointy head, with the goofy eyes protruding on either side. Next you will notice that their legs are jointed, and their 'knees' are a bright yellow color. At the end of each of their forelegs is a little claw. The claws are violet, making them look as if they've just come from the nail salon.

Yellowline Arrow Crabs are abundant throughout the Caribbean, but they are very small, and they are sometimes hard to spot during the day. They tend to find resting spots in nooks and crannies where they stay put during daylight hours. They actively forage at night, so they are quite easy to find on night dives when they are roaming around the reef looking for a meal. By the way, they are carnivores, but you don't have to worry about getting chomped by an Arrow Crab. They eat tiny worms and other itty-bitty animals that populate coral reefs.

They don't seem to be afraid of divers -- even divers with bright lights and cameras -- so once you locate an Arrow Crab, it is fairly easy to photograph it. They don't spook when the camera strobes flash, so the photographer usually will have plenty of time to take a number of shots of a given individual.

I photographed the Yellowline Arrow Crab on this page during a night dive at Little Cayman. This is a 1:2 macro shot. The creature is only about two inches (5 cm) long.

Video: Mantis Shrimp vs. Crab

Last month we introduced readers of The Right Blue to the Mantis Shrimp. Among other features unique to this animal, we described their raptorial appendages. Some Mantis Shrimp species spear their prey, and others smash their prey with their raptorial appendages. The species in the photos that accompanied our article was a 'smasher'.

I wrote:

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.

Here is a video I came across on YouTube that shows a Mantis Shrimp in an aquarium doing exactly what I described. Although the Mantis Shrimp in the video is a different species from the one in my photos, it also is a smasher. Have a look (but don't blame me for the choice of background music):



(If the video does not play or display properly above, click here to view it on YouTube.)

Tip of the hat to YouTube user accubyrd, on whose page there are a few more Mantis Shrimp videos.

Sneaky Shark

Caption: Why underwater photographers should have rear-view mirrors!

Where: I took this photo of the sneaky shark during a dive
at Pulau Sipadan, off the coast of Borneo.

[Click photo for larger view.]

My previous Wordless Wednesday posts.

Trailing behavior in Risbecia nudibranchs

by B. N. Sullivan

You just never know what you're going to find out next about marine creatures. The photo on this page is a case in point.

We are planning to run a series soon on The Right Blue about nudibranchs. In case you are unfamiliar with the name, nudibranchs are marine gastropod snails without shells -- also known as sea slugs. In order to prepare, we have been going through our photos and notes, and looking up certain bits to make sure we have our facts straight. (After all, we don't want to misinform our readers.)

One thing I always do is double check that the species name I have recorded for a creature is correct before I publish it. In my notes, I had recorded the species of the two nudibranchs in this photo as Risbecia pulchella. I did a quick search on the name to see what would come up -- hoping to see images that looked like mine, or a detailed description. Sure enough, I found a few authoritative sources that confirmed that the nudibranchs in my photo were correctly identifed. They are indeed Risbecia pulchella nudibranchs. But I learned something else, too.

A page on the Sea Slug Forum -- a wonderful source of information about nudibranchs, run by the Australian Museum in Sydney -- detailed a behavior said to be typical of nudibranchs in the genus Risbecia. The writer called it 'trailing' behavior:

Also known as queueing or tail-gating, all species of the chromodorid genus Risbecia exhibit this behaviour where they seem to play "follow the leader". Perhaps its a behaviour which has evolved amongst relatively uncommon animals to ensure they find each other for mating. When tailing, one animal appears to follow the mucous trail of the other until they actually make contact. Then the following animal, as can be seen in thse photos, keeps contact by touching the 'tail' of the leader. Sometimes 3 or 4 animals can be seen together.

I have to tell you, my jaw dropped. That is exactly what the two nudibranchs in my photo are doing!

For the record, I photographed these two Risbecia pulchella nudibranchs engaging in 'trailing' in the Red Sea. More precisely, they were photographed at Ras Mohammed, near the remains of the wreck of the Jolanda, at a depth of about 13 meters (42 feet).

I took the photo a number of years ago, but only now did I realize the significance of the behavior that I just happened to record. As I said, you just never know what you're going to find out next about marine creatures.