Creature Feature: Cuttlefish



Ngerchong Inside dive site (Palau)
Photo courtesy of Liz Tuttle



Often called the "chameleon of the sea" because of its ability to change the color of its skin at will, the cuttlefish is actually not a fish at all, but really a mollusk. Belonging to the class Cephalopoda (which means head-footed), they are the cousin of the squid, octopus, and nautilus.

The cuttlefish can range in size from 1 inch to 3 feet (and even bigger in the case of the giant Australian cuttlefish which may grow to the size of a small man). It possesses eight sucker-lined arms and two prehensile tentacles (which can be withdrawn into pouches under the eyes) and a sharp, beak-like mouth which allows it to cut open flesh like a pair of scissors, so it can use its tentacles to tear out meat. It hunts during daylight, feeding primarily on small fish, crustaceans and other mollusks.

It moves about in the water by way of a complex propulsion and bouyancy system (much like a submarine). "The cuttlefish propels itself using a series of spurts, drawing water into a compression chamber which it squeezes to jet the water out a funnel under the head. Direction changes can be made by swivelling the nozzle of this funnel, and narrowing the funnel controls speed. Like a submarine, the cuttlefish fills tiny compartments in its cuttlebone with gas to help maintain neutral buoyancy. This helps the cephalopod hover above the ocean floor, because although it has a sophisticated propulsion system its large cuttlebone does not allow it to be overly active, or quick in the water. " [1]

Staying Neutral

Redrawn after Clarkson, E.,
Invertebrate Palaeontology and Evolution,
George Allen and Unwin, London,
1979 (Seventh impression 1984), p.167.

The cuttlefish is a bottom-dweller which often lies in ambush for smaller animals. For this way of life, it needs to keep itself at neutral buoyancy, so that it neither sinks nor rises...in order to be able to operate at varying depths and water densities, cuttlefish need to be able to adjust their overall density so as to always remain ‘neutral’ in the water. The cuttlefish does this by an ingenious mechanism. The bony shell actually has many narrow chambers. If these were all filled with gas, they would give a lift of up to 4% of the animal’s weight. However, they are only part-filled with gas—the darker areas shown are where it is part-filled with liquid. The cuttlefish is able to pump liquid in and out of that section as needed to keep the buoyancy ‘just right’. [1]  

The cuttlefish actually has 3 hearts - one for each set of gills and one for the remaining body. Unlike our own blood which gets its red color from the pigment hemoglobin, the cuttlefish's heart pumps blue-green blood which uses hemocyanin pigment to carry oxygen. Its skin is comprised of 3 layers of color pigment cells called chromatophores. These cells are controlled by the nervous system which signals them to expand or contract at a remarkable speed allowing for the hypnotic transformation of the cuttlefish's coloration and pattern.

"A strange fact about the cuttlefish is that it can adopt the female coloration along one side of the body as well as retain the male coloration on the other side. Male cuttlefish are extremely alert when it comes to the females, especially if she is laying the eggs. The male will guard aggressively over the female and this is when another approaching male will use his ability to have a dual look to access the female and trick the male." [2]



Close-up of a cuttlefish eye
Photo courtesy of Wikipedia



Oddly enough, even though it can put on a spectacular color display, the cuttlefish does not see color. Its w-shaped pupil only perceives polarized light which enhances its perception of contrast. Their retina has two areas of concentrated sensor cells called foveae, one to look forward and one to look more backward. There is no blind spot like we have because the optic nerve is positioned behind the retina. The eye changes focus by reshaping the entire eye, instead of reshaping the lens as in mammals.

Cuttlefish are considered to be highly intelligent, like their cousin the octopus. In fact, they have one of the largest brain-to-body size ratios of all invertebrates. Cuttlefish have ink, like squid and octopuses, which they use as a last resort to help evade predators when their camoflague fails. Their predators include dolphins, sharks, fish, seals, seabirds and other cuttlefish. Their life expectancy is about one to two years.

They are mostly shallow-water animals which inhabit tropical to temperate waters, although they have been know to descend to depths of 2,000 feet. Cuttlefish are generally found along the coasts of east and south Asia, western Europe, the Mediterranean, as well as all coasts of Africa and Australia.

[1] Weston, Paula, ‘Fascinating Cuttlefish', answersingenesis.org, March 1, 1997.

[2] Lad, Kashmira, ‘Cuttlefish Facts', buzzle.com. 

Chris' Dive Experiences: "Blue Corner", Palau, Micronesia (Part 2)

As we approached the dive site, "Blue Corner", our divemaster, Steve, jumped into the water to check the current. I found out he did this in order to check the direction of the current so that we could start our dive along the wall at the right spot and easily drift to the corner of the reef.

After a thorough dive site briefing which included a quick lesson on how to use our reef hooks, we back-rolled off the boat and descended onto a nice wall. As we drifted along this wall, enjoying visibility that was around 100 feet, we saw lobster, turtles, large schools of fish, colorful sponges and corals.

Photo Courtesy of Rod Tuttle

As the dive time lengthened the current picked up, pushing us along. Steve signaled that "Blue Corner" was just ahead and we should prepare to use our reef hooks. As I neared the point, the current was ripping, making it easy for me to ascended to the top of the reef. There I turned to face the edge of the wall, quickly securing my hook into the reef, I then inflated my BCD. Hooked in with my BCD inflated allowed me to stay in one spot while I floated in the water above the reef. Without a reef hook, it would have been impossible to stay in one spot because the current was so strong.

Now what makes this one of the top 10 dive sites in the world is the view. Imagine you are floating above a cliff and looking out and down on hawks flying below you and other animals moving around on the ground. Now place yourself underwater. As I looked out into the water column, there were huge schools of barracuda and trevally moving with the current. The next thing I saw was my first shark - a big grey reef shark, and then another and another. The water was just teeming with life moving by us. Everywhere you looked, underwater life was passing right by us as we floated and watched.

Photo Courtesy of Liz Tuttle

Camera strobe lights were firing every few seconds, as divers filled their memory cards with wide angle shots overflowing with life. Out of the corner of my eye I saw something  coming near me. I turned and saw the friendly, HUGE, resident napoleon wrasse that Steve had mentioned in our briefing. He was very curious. He came right up to me and checked me out. I swear he was almost as big as I was.

Too soon Steve our dive master signaled to unhook. We had been at the site for 30 minutes and it was time to go. We unhooked and were pushed by the current away from the edge of the point and into shallower water for our safety stop. Even as we drifted up and away from this top dive site we saw tons and tons of life everywhere we looked.

Back on the boat, divers were hooting and hollering and giving high fives as our boat cruised to our lunch and surface interval destination. The boat neared a couple of the rock islands and turned into a little cove where we saw a picture perfect little sandy beach. As we sat eating our lunch, we talked at length about the fantastic dive we just completed, all the while being the only people enjoying this perfect little island.

This is diving in Palau!

Chris' Dive Experiences: "Blue Corner", Palau, Micronesia (Part 1)

Photo Courtesy of Lesley Alstrand

After an overnight trans-Pacific flight, our plane touched down after midnight in a torrential downpour. Even if we could have kept our eyes open during the bus transfer to the resort, we wouldn’t have been able to see anything through the rain. It was not long before we reached our destination of the beautiful Palau Pacific Resort (often referred to as PPR). After being greeted and checking into our rooms, our heads thankfully hit our plush pillows.

We awoke later that morning to the ringing of the phone. It was Rod (owner of TDS) wanting to know if Lesley and I were ready to go diving. We couldn’t wait!

This was my first time out of the states, and I will never forget my initial feeling as we went to meet up with the rest of the group for breakfast. I was so impressed by the peace and quiet, the scenery of the island, and the beach. It was everything you would imagine when you think of an exotic and tropical location! Now on to the best part - the diving! If the view from the resort was considered beautiful and exotic, the boat rides to the dive sites would be described as absolutely stunning!

Palau is made up of over 200 rock islands. For me, the closest thing that I can compare these islands to are the floating islands in the movie Avatar. Your dive boat speeds in and around these islands on the way to your dives, and if you aren’t careful, you could fill your camera's memory card just on the way to your dive site with the topside scenery. As we neared "Blue Corner", one of the world’s top dive sites, we sped through another great dive site, "German Channel".



Photo Courtesy of Liz Tuttle

"German Channel" was an access channel created by the German military for their ships during World War 2 by dynamiting through a shallow reef. As we approached this channel the first time, all you could hear were ooh’s and aah’s from all the divers on the boat. The water displayed every single hue of blue, green and turquoise you could ever imagine as you cruised along this very shallow to deep dive site. It is just impossible to fully capture the channel's beauty in pictures. This is another one of those things you just have to see for yourself at least once in your life!