The Right Blue: June 2009

You can't always identify a fish by its color

by B. N. Sullivan

You know that old cliché: You can't judge a book by its cover. In a sense, the same can be said for many fish species. Countless species exhibit different colors and patterns as they develop. In fact, sometimes juveniles and sub-adults look markedly different from the adults of their kind.

This is confusing to divers trying to learn the names of the fishies they see underwater, and in some cases it even has tricked scientists. Taxonomic records of fish species have many, many examples of fishes that were thought at first to be two distinct species, but later turned out to be different color phases of the same species.

The two individuals in the photo at right are an example of this phenomenon. They are both Whitespotted Filefish (Cantherhines macroceros), a Caribbean species common on reefs around Belize and the Cayman Islands. They appear in two distinct color phases: one with spots, and one without.

Of course, this happens on land, too. Just think of Bambi, for instance. As a fawn, Bambi had spots on his back -- spots he outgrew as he matured into an adult deer.

The fishes in the photo at least resemble one another, but some fish species undergo really radical color changes as they mature. Not only that, many reef fishes even change sex! Some species begin life as females, and later turn into males, a condition called protogyny. Then there are the protandrous species, which begin life as males and ultimately become females. There are even a few species that can change sex in both directions. Talk about gender-bending!

Like a lot of land animals, many fish species are sexually dimorphic, that is, the two sexes differ in appearance. The males are usually (but not always) the ones that are larger and more brightly colored. I've always thought that sexual dimorphism made obvious sense; if the two sexes look different, than each should be more readily able to spot a potential mate.

It turns out, though, that mate attraction is a much more complex process, probably less dependent on visual cues like color and size, than on subtle biochemical sensing (i.e., scent, or the fishy equivalent thereof). In any case, when critters -- including fishes -- need to find a mate, they know what to look for.

And that reminds me of a conversation we had one time with ichthyologist Jack Randall of the Bishop Museum in Honolulu. We described to him a peculiar individual fish we saw regularly at a certain patch of the reef at Puako. The fish was a Yellow Tang (Zebrasoma flavescens) with an odd color pattern. Usually that species is solid yellow, but this individual had irregular white blotches on it, such that it looked like it had been splashed with bleach! Dr. Randall told us that similarly patterned Yellow Tangs had been noted occasionally, and that it was presumed to occur because of some mutation to the genes that control pigmentation.

Another diver who was present said he had seen a Yellow Tang with similar white blotches several miles south of where we regularly saw 'our' little mutant. We mused aloud about what might result if we could get those two fishies with the aberrant color patterns to mate. Maybe we could capture one and release it near the other in the hope that they would produce some interesting offspring.

But then Jerry asked, "What if both are males or both are females?" Both sexes of Yellow Tangs look exactly alike. There's no way to tell them apart visually.

Jack Randall just grinned and winked. "Don't worry," he said. "They know."

Nassau Grouper: Overfished and Now Endangered

What: Nassau Grouper (Epinephelus striatus). Valued as a food fish,
but over-harvested -- now classified as Endangered by the World Conservation Union (IUCN).

Where: I took this photo during a night dive off the coast of West Caicos, Turks & Caicos Islands.
Nassau Groupers are found throughout the tropical West Atlantic and Caribbean.

Click here to learn more about the Nassau Grouper.

Click in the photo to enlarge.

Another Dimension of The Right Blue

Visitors to The Right Blue may have noticed that we added a Twitter button to our sidebar awhile back. On the other hand, those who read The Right Blue via the RSS feed would not have known about that Twitter button. So, we decided it might be a good idea to post a quick announcement about our Twitter feed: @therightblue

Jerry is the primary Twitterer for The Right Blue. He tweets the title and link to each new post on the blog, of course, but that is just a small fraction of what we view as a new dimension for The Right Blue.

As @therightblue, Jerry tweets news and other information about all things ocean: scuba diving, underwater photography, maritime archaeology, ocean conservation and ecology, developments in oceanography and marine biology -- and whatever else strikes his fancy on a given day! He also passes along information about upcoming events related to all those topics via re-tweets.

Of course it's not all titles and links. Jerry adds his own brief comments, and the Twitter feed is liberally sprinkled with Jerry-style one-liners and dialog with fellow Tweeps.

If you're on Twitter, and you want to stay current with all things ocean, we invite you to follow @therightblue. Click on the button near the top of the side bar on the blog, or on the big fat Twitter button on this post.

One more thing: If you're not on Twitter, Jerry says he's got some eight-track tapes he'd like to sell you. ;-)

Playing with Critters: Cleaner Shrimp

by B. N. Sullivan

As a rule we don't handle the creatures we encounter in the ocean. Some bite or sting, of course, but even when they don't, it's not a good idea to handle them. In fact, most creatures will try to escape if you pick them up (wouldn't you??).

Many critters are quite fragile, and they can get injured if you handle them. Crustaceans, for example, can lose a limb or break their antennae while trying to get away.

Many kinds of sea creatures -- including fish -- are covered with a thin layer of protective mucus. If you handle them, that protective layer gets disturbed and that can subject them to infection.

Another problem with handling critters is that people forget to put them back exactly where they found them. If you pick up a creature and then put it down somewhere else, it's the critter equivalent to alien abduction!

Most reef creatures have quite a small range. They eat, rest, feed and mate in some little patch and rarely venture far. In most instances, the smaller the creature, the smaller the range. Put some little creatures down just a meter from where you picked them up and they become completely disoriented. Displaced, they don't know where to find food, or where to hide from predators.

Some reef creatures mate for life. You wouldn't want to tear some little guy away from its permanent mate just so you can pet it, would you?

For all these reasons, we usually advise against petting or playing with creatures you find in the ocean. But there is an exception: some creatures seem to like to interact with divers. Well, maybe 'like to' is not precisely correct, but in any case, there are some animals that will approach us.

One such critter is the cleaner shrimp.

Now, these little guys have an important job in nature: they clean other animals. Cleaner shrimp usually occupy a patch of coral or a rocky spot at the edge of a reef. Animals -- mostly fish -- stop by when they need to be cleaned. The shrimp remove parasites, dead scales and skin, and bits of debris from their fish clients. They also serve as the dental hygienists of the reef. It's not at all unusual to see a moray eel, mouth agape, with one or two cleaner shrimps poking around inside, picking out bits from between the eel's teeth.

If you happen to discover a cleaning station inhabited by these shrimp, you may be able to engage their services. Get close, and then be very still. Chances are, the shrimp will come out and give you a once-over.

In the first two photos on this page, a cleaner shrimp is working diligently on Jerry's glove. If you offer a bare hand, you can expect to have your nails cleaned and your cuticles nipped. It doesn't hurt, though. In fact, it tickles like crazy -- partly from the cleaning action per se, and partly because those long white antennae constantly sweep over the surface of your skin. They are the shrimp's crud detectors!

A number of reef-dwelling shrimp species serve as cleaners at least part-time. The species in the photos on this page, Lysmata amboinensis, are full-time cleaners.

This species is common, and is widely distributed throughout the Indo-Pacific region. We have seen them everywhere from the Red Sea in the west, all the way east to Hawaii. We also have seen a nearly identical species, Lysmata grabhami, in the Caribbean and along the coasts of south Florida.

All of the images on this page are of the same individual cleaner shrimp. I took the photos at a spot known as 'the 110-foot rock' off the coast of Puako, Hawaii. [Click on any of the photos for a larger view.]

Lunar Fusiliers on a shallow Malaysian reef

What: Pretty blue fishies called Lunar Fusiliers (Caesio lunaris)

Where: I took this photo while diving at Pulau Sipadan, Malaysia.

Click in the photo to enlarge.

How do critters get their scientific names, and what do they mean?

by B. N. Sullivan

In most cases, the scientists who first identify a species, i.e., discover it and/or describe it in the scientific literature, get to choose a name for the species. Stories about why creatures were given a certain name always are interesting. Some names are obvious choices, others not so obvious -- at least to the casual observer.

In the obvious category are names that refer to a creature's geographic origin. It should not be difficult to guess the provenance of a creature with a name like Conus mediterraneus -- the Mediterranean cone shell. Ditto for Cyrpaea arabica -- the Arabian cowrie.

Some obvious names refer to a visible characteristic. For example, the scientific name of the Blue Dragon nudibranch, Pteraeolidia ianthina, refers to the critter's color. 'Ianthinus' means violet-blue in Latin.

Coloration is not the only feature a name can describe. Recently we posted a photo of the Lined Butterflyfish (Chaetodon lineolatus). As you can probably guess, lineolatus means 'lined' and refers to the pattern on the fish's flanks.

You also may recall our story about the mantis shrimp. The species featured in that tale was Odontodactylus brevirostris. The species name, brevirostris, means 'short-nosed'.

Less obvious than coloration or size are behaviors, at least to the casual observer. Yet it is not uncommon for a species name to reflect a behavioral characteristic of an animal. The scientific name of the nudibranch in the picture on this page is Chromodoris vibrata. If you guessed that the meaning of the species name vibrata has something to do with vibration, you would be absolutely correct. Like a lot of Chromodorids, this species of nudibranch has a habit of vibrating its little gills (that clump of feathery-looking structures near its tail end). The rapid wiggling of the gills presumably helps to increase oxygenation, by the way.

Sometimes creatures are named to honor an individual or group. For example, Commerson's Frogfish (Antennarius commerson) was named for Dr. Philibert Commerçon, an 18th century French naturalist.

One of our favorite naming stories is that of the Gold Lace nudibranch (Halgerda terramtuentis). The species name, terramtuentis, means 'looking at the earth with care'. The scientists who first described the species gave it that name to honor a group of Earthwatch volunteers who had helped them with their research.

That's not a plastic bag, it's a Comb Jelly!

What: Comb Jelly - unidentified species,
but our best guess is that it belongs to the genus Beroe

Where: I took this photo of Jerry and the Comb Jelly
while diving off the coast of Puako, Hawaii.

Can you think of a good caption for this photo? Tell us in the Comments.

Click in the photo to enlarge.

World Oceans Day: Our Oceans, Our Responsibility

Today, June 8, is World Oceans Day. The theme of this year's World Oceans Day is "Our Oceans, Our Responsibility." Please take some time today to learn something about the ocean, and to reflect on how essential it is that we all do what we can to preserve and protect ocean environments -- for the health and well being of the entire planet.

We have the good fortune to live near the ocean, and we have spent countless hours in, under, and near the sea. Our perspective as divers has prompted a special interest in certain issues related to ocean health and conservation.

We decided that today, World Oceans Day, would be a good day to reprise some of what we have written in the past two years about ocean conservation issues. Here are some examples of our concerns:

We hope you are wearing something blue today to commemorate World Oceans Day. (Make sure it's The Right Blue!)

Here is a lovely video with images of the ocean and some of its inhabitants. We hope you enjoy it.

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

Diving with a Partner: Pre-dive checks are essential for dive safety

by B. N. Sullivan

I don't think there is a diver training program anywhere in the world that does not teach -- and emphasize -- the importance of the 'buddy system' for sport divers. The idea is to dive with a partner so that you can watch out for each other, and help each other if a problem arises.

In order for the buddy system to work optimally, dive partners need to know some things about each other's abilities, skill level, and equipment prior to entering the water. This is easier to do if you have one or more partners with whom you dive regularly, but it should be kept in mind regardless of whom you are paired with for a dive.

Let's take the case of diving with someone you don't know well or have just met. Don't be shy about asking the diver about the extent of his or her dive experience: what kind of training they have had, how often they dive, and how recently they have been in the water.

Certifications alone do not tell the whole story. A diver with a basic certification who does 50 dives a year may be a much more capable diver than, say, a certified rescue diver who only gets into the water a few times a year. Skills get rusty, and both competence and confidence erode with lack of practice.

The point of asking your prospective dive partner about experience and skills is not just a case of idle curiosity. You need to know the amount of monitoring your partner may need, and conversely, to what extent you can rely on that person to help you if you have a problem. If it sounds like there is a significant disparity between you and the other diver, it is wise to begin with very easy 'G-rated' dives with the person in order to minimize the risks while you get a fix on their skill level and comfort in the water.

Now, about equipment -- yours and your partner's. While all training agencies teach that you should dive with a buddy, some (I'm sorry to say) do not stress what is known as the pre-dive buddy check. The purpose of the buddy check is to ensure that each dive partner has all the essential equipment, that it is in good working order, and that each diver knows how to work the other's equipment.

The buddy check, plain and simple, is, "You show me yours and I'll show you mine."

We all use the same items of equipment when we dive, but there is a lot of variation among brands and models in regard to design and placement of controls. During the buddy check each diver shows the partner the location of every piece of critical gear, and demonstrates how it operates.

The idea is that if something untoward happens underwater, neither diver has to waste precious time fumbling about, trying to figure out how a partner's gear works. If I am your dive partner, I will want to know the following things -- at minimum -- about your equipment, and then I will show you the same things about mine.

Show me that the valve on your cylinder is turned on, and show me the display on the instrument you are using to gauge the remaining gas in your cylinder. I want to know how much air you have at the outset of the dive.
Show me your primary regulator, and demonstrate how the purge valve works. Then show me your back-up second stage - where it is stowed, and how it is released from where it is stowed. Then tell me whether you plan to hand off your primary or back-up second stage to me in an emergency.
Demonstrate your buoyancy compensating device (BCD). Show me how to inflate it, and also point out all the dump valves so I will know where they are.
Are you wearing a weight belt or are your weights integrated with your BCD? Do you have any extra weights in your pocket or in any unconventional places?
Show me the location of all the releases on your gear and how to work them -- especially for your weight system and BCD. Are they snaps, buckles, Velcro, pull-cords? I need to know what I am looking for in an emergency.
Show me your computer or other instruments. I don't want to have to figure out where to look on an unfamiliar display for critical information during an emergency.

Many divers are shy about asking a new dive partner to perform a buddy check and cross-check. Don't ever be shy about this. Be the one to initiate the buddy check; your partner will then doubtless go along.

If you are fortunate enough to have one or more regular dive partners, you probably are familiar with their equipment and know how it operates. But don't be complacent! Always check each other's gear configuration before entering the water. Weights in place? Air turned on? Instruments operating and displaying what you expect them to display?

I once had an experience that taught me not to ignore these things just because I was diving with someone I knew well. A frequent dive companion and I entered the water without doing a buddy check. We had been chatting and laughing while gearing up, creating just enough distraction so that we skipped cross-checking each other's equipment.

We were nearing 40 meters (about 130 ft), the deepest point of a our planned dive route, when I heard my companion shriek, right through her regulator. When I looked her way, I could see that she was alarmed. She turned the face of her air-integrated dive computer toward me, excitedly jabbing her finger at it. The display was blank -- no lights, no numerals, no data, nada!

We had to abort the dive then, of course. We stayed very close together as we gradually ascended during the hurried five minute swim back to our exit point. We had no idea how much air she had left, for openers. In fact, while we were swimming, it occurred to me that I did not even know how much air she had at the outset of the dive, since we had not done the buddy check and cross-check.

Once back on shore, we discovered that the problem was a dead battery in her computer. She admitted that she hadn't paid much attention to her computer display before the dive, since she 'knew' she had a full tank of air. For my part, I had never checked her equipment before the dive. I was annoyed with her, but I was really angry at myself. I knew better than that.

Had we done a routine check and cross-check, one of us might have noticed the low battery indicator. In any case, I would have known how much air she had started out with and might not have been quite so anxious during the swim back to shore from the depths.

Luck had been on our side, but it could have been a disaster. I learned my lesson. That was the last time I began a dive without a buddy check and cross-check.

The British Sub-Aqua Club (BSAC) is one training agency that does a good job of teaching and emphasizing the buddy check and cross-check to divers. They teach a mnemonic device to help divers remember the essential elements of the buddy check: B-A-R.

B is for Buoyancy
A is for Air
R is for Releases

Regardless of which agency trained you, think about adopting BSAC's 'B-A-R' to help you remember the items that need to be checked and cross-checked before you enter the water.