Distribution
The scientific name for giant squid is Architeuthis. These animals have a worldwide distribution, but specimens that man has come into contact with are most commonly stranded in the North Atlantic (Norway and Newfoundland), or caught in the South Atlantic (South Africa), Southwest Pacific (New Zealand, Southern Australia) and the Northwest Pacific (Japan). No man has ever seen a giant squid alive in its natural habitat.

Vertical Distribution
Giant squids are vertical wanderers, which means they travel throughout the different depth zones. Adults (mantle length up to 12 feet) are believed to spend most time between 200 and 1000 meters deep. Juveniles probably stay between 100 and 300 meters deep, and young giant squids are usually caught near the surface. One tiny specimen (10.3 mm) was caught at a depth of only 20 meters!

Habitat
Not every beach is lucky enough to have giant squids wash up on it--they just cannot live there. The distribution of the giant squids is limited by its habitat needs. Just like on land, most animals in the sea live in a specific habitat. A giant squid suffocates when it finds its way into water that is too warm (near the surface), because, some scientists believe, its blood can no longer hold all the oxygen it needs to live. Just as a cold glass of carbonated soda goes flat when it gets warm, giant squid blood loses its oxygen as it warms. Warm liquids cannot hold as much gas as cold liquids.

Luckily for the giant squid, temperatures in the deep ocean are fairly constant in any given area. The seasons cause the surface waters to vary from warm to cool. Unless you are in the tropics or near the poles, swimming at the ocean beach in January is not like swimming at the same ocean beach in July! Every summer, the wind mixes and warms the surface water but cannot mix the water all the way to the bottom. The thermocline is a certain ocean depth, typically at around 300 meters, at which point a sudden change in temperature occurs. It separates the warmer surface waters from the cooler deep waters. A giant squid that accidentally swims into the thermocline would not survive the temperature change for long.

Plentiful phytoplankton (tiny one-celled marine plants) at the surface use the sun’s energy to make food and release oxygen. Phytoplankton cannot live to make more oxygen at the thermocline because it is too dark. Instead, bacteria eat the dead, sinking phytoplankton and many of animals eat each other. So much eating takes place at the ocean depths that most of the oxygen gets used up for respiration (using oxygen to break down food, as humans do). This creates an oxygen-minimum zone in the region of the thermocline, making this depth even more dangerous for the giant squid. Not only is the giant squid's warmer blood less capable of holding enough oxygen, less of the precious dissolved gas is available in the water.

Deep water temperatures in a given geographic region stay the same because the flow of water masses (like huge underwater rivers) through such areas rarely changes. But each water mass might have a temperature and salinity (saltiness) very different from those next to it. Many giant squids wash up in areas where warm and cold water masses meet.

How does a giant squid know it is getting too close to a mass of water that might be too warm? Scientists do not know for sure, but the giant squids might use their extraocular receptors. These receptors, which detect the wavelength and intensity of light, are not in the eye (that is what "extraocular" means) but somewhere else on the head instead. For example, receptors are used by many squids to help their photophores make light to match the light coming down from the sruface to erase their own silhouette! (For more information on this subject, see the lesson on Marine Bioluminescence.) During daytime or at night when the moon is out, some squids, possibly even the giant squid, might use their extraocular receptors to tell how close they are to the surface. Imagine the dangers of a new moon or an oil spill to a giant squid that wants to feed in shallower waters all night!

Depth/Pressure
Giant squids do not have any gas spaces in their bodies, which means they do not have soft bladders filled with gas to keep them from sinking as fish have. In fact, no squids do, and neither do really deep sea fishes. Air is so compressible in high pressure habitats that the bladder would be squeezed until it imploded and would be useless. How then is the giant squid able to survive in very deep waters without sinking or being crushed? The answer is ammonium ions. (Ammonia in water splits into ammonium (NH₄±) and hydroxyl (OH^-) ions.) Unlike air, liquids cannot be crushed or compacted or compacted. Ammonium also solves the sinking problem, since, like oil, it is lighter than seawater. A giant squid concentrates ammonium in its body and is either slightly buoyant (floats) or neutrally buoyant (does not float but does not sink). Ammonia is a natural waste product, like urine. Instead of eliminating or urinating waste out as humans do, giant squids store some of the waste in their bodies. This is why so many giant squids float to the surface and wash ashore when they die. That is also why giant squids are not very tasty to eat!

Question to consider:

How can giant squids survive so much poisonous ammonia in their bodies? Answer

Locomotion

The more the squid jets away, the more it breathes! Squids expand their muscular mantle (as you expand your chest to breathe) to bring water in through the open end, around the neck. The blood is oxygenated as this water passes over the gills. When the mantle squeezes and closes tightly around the head, the only way the water can jet out is to jet through the funnel. This muscular tube can bend and rotate, giving the squid control of its direction when it jets backward or forward. Waste comes out of the funnel with the water being expelled, as does ink when the animal is startled or threatened.

Can a giant squid out-swim a hungry sperm whale chasing after it at ten knots (11.2 mph)? Scientists do not know, and until they see the pair in action, they can only guess. The funnel retractor muscles that help pull the head into the mantle to force water out of the funnel, and the funnel valve that prevents the backwash of water into the funnel, are well developed in giant squids. Certain arms on giant squids have keels, just as in squids known to be strong swimmers. These characteristics give smaller squids the speed to out-jet a predator, but they may be necessary to the giant squid simply to get such a great mass into motion. On the other hand, certain parts of the giant squid's body are like those of other types of squids known to swim sluggishly. Many fast squids are able to retract and move so quickly because they have giant axons (nerve fibers) that signal the mantle muscles to contract. The speed of a nerve impulse is directly proportional to the nerve diameter, and squids have the thickest axons in the world 1.5 mm (1500 micrometers) in diameter! That is 50 times as thick as in most other animals, including humans. Giant squid axons are not nearly as thick (137-210 micrometers in diameter), making them more like slow-swimming squids. The fins are relatively small. The funnel-locking apparatus, which keeps the mantle closed tightly around the body when a squid ejects water from the funnel, is weak in giant squids and the mantle is not extremely muscular. Using all these anatomical clues, scientists can deduce that giant squids are not very fast jetters.

Question to consider:

If squids have the biggest nerve fibers, do they also have the fastest reaction times of any animal in the world? Answer

Breathing

Most squids have no specific mechanism for ventilating the gills without moving. They are pelagic in the water column, which means they never stop swimming. As the animal jets or hovers, there is a constant supply of oxygen-rich water flowing over the gills (see Locomotion). Oxygen passes through membranes in the gills and chemically binds with a pigment (hemocyanin) in the blood pumped through the gills. Other chemical reactants then free hemocyanin of its oxygen as the blood flows past muscles and organs where it is used for respiration.

Circulatory System

Cephalopods, the scientific class to which giant squids belong, have a well-developed circulatory system. It is considered closed because blood is confined in vessels and hearts, so it does not flow freely around the bodily tissues. The blood is blue when oxygenated because the respiratory pigment (hemocyanin) contains copper. (Human blood is red because our respiratory pigment, hemoglobin, contains iron that becomes red when oxygenated.) Cephalopod blood is colorless when deoxygenated, after delivering oxygen to muscles or when the animal is dead, making the vessels and hearts sometimes hard to find during a dissection.

Two branchial hearts (one per gill) pump blood into the gills where water restores it with oxygen. The blood then goes to the systemic heart (between the gills) which pumps it throughout the rest of the body. Squids need this third heart to work against the hydrostatic skeleton. Muscles squeeze other bodily liquids and provide strength and shape to the body. [Hydrostatic skeleton note: hydro (water) static (movement) skeleton (support). Remember, if you squeeze water into a tube, it gives support and shape to that tube.]

Each blood vessel has its own nerves and can contract independently, making some injuries less dangerous. If an arm is bitten off by predator, the blood supply to that arm is shut off quickly and the squid or octopus does not bleed to death. Imagine the effects on humans with such an ability!

The Eye

Cephalopods do not see in color. Instead, they detect polarized light with each separate component (wavelength) making up that color and intensity. Squids rely heavily on eyesight to detect predators, locate prey, and check out their surroundings. Cephalopod eyes are large in comparison to their total body size. In fact, the eyes of some small cephalopods can weigh up to 50% of their total body weight. Giant squid eyes are the largest in the animal kingdom, 25-40 centimeters in diameter. A primary lid can cover the lens, but in general, sea water flows freely over the lens. The lens is the hard, spherical ball made of special proteins through which light passes to the retina. The large bunch of nerves that transports messages from the eyes to the brain is called the optic ganglion.

• Optic ganglion--large bundle of nerves that transports messages from the eye to the brain
• Orbit--a protective cartilaginous cup behind the eye
• Primary lid--a membrane that can cover the lens

Depth Zones

Littoral (intertidal): high tide line to low tide line

Sublittoral: benthic (on the bottom) zone from low water line to 200 meters deep.

• Inner--The photic (lighted) zone of the sublittoral zone: low tide line to the limits of photic depths, the depth to which one percent of light from the surface still penetrates. The rest of the light is either absorbed or reflected (about 50 meters) depending on water clarity.
• Outer--The aphotic (not-lighted) zone of the sublittoral zone; zone of the sublittoral zone (about 50- 200 meters) where less than one percent of the light from the surface penetrates.

bathyal: deep sea benthic zone 200- 4000 meters deep (Submarine limits 790 meters; diving limits of sperm whales and giant squids about 2000 meters)

abyssal: benthic zone 4000- 5000 meters deep

hadal: benthic zone deeper than 5000 meters to deepest depth of the oceans

oceanic: water above the Bathyal, Abyssal and Hadal zones

epipelagic: oceanic water from the surface to about 200 meters deep.

mesopelagic: oceanic water between 200 and 1000 meters

bathypelagic: oceanic water between 1000 and 4000 meters

abyssopelagic: oceanic water below 4000 meters

Luminescence in Squids

Bacteria play a role in the luminescence of squid in some species (Sepiolids and some Loliginids species, for example). The luminescent bacteria are cultured in a special chamber of the ink sac, then ejected when the squid discharges ink. The bacteria start to luminesce as soon as they hit the sea water, where the oxygen stimulates the action.

• Sources of luminescence in cephalopods (squids)
  • photophores--chemical
  • bacteria

• Photophores
  • "light organs" is another term for photophores
  • similar to cold light of fireflies (a firefly squid flashes light periodically as does the insect), glow worms, fungi
  • size range from pinpoints to AA battery
  • located on different parts of the body

• Makeup of photophores
  • range from a simple to complex
  • some contain lens, mirrors, color screens, and even "eyelids"
  • deepwater sail squid (Histioteuthis) has arms, mantle, and a head that contain light organs with diaphragms, focusing mechanism, color filters
  • colors include white, blue, yellow, pink, red (These are the actual colors of the photophores. The actual color of light they emit is in the spectral frequency of the blue-green area.)

• Functions and purposes of luminescence
  • presently do not know all purposes and functions--much is still unknown
  • identification of same species
  • attract and identify mate
  • attract food/prey
  • protection from enemies/predators by distraction and startling or by counterillumination (The underside of animal is illuminated so that its silhouette is eliminated. Remember there is more visibility as one gets closer to the surface of the ocean.)

• Other interesting information
  • Bobtailed squid use biological light produced by luminescent bacteria contained in a gland near squid's ink sac. The squid shoots glowing ink which acts as a decoy or distracter and then turns off own body lights and escapes
  • "Any purpose that is fulfilled by color or pattern in the illuminated terrestrial or coastal environment can also be achieved by luminescence in the dark of the deep sea." Peter J. Herring, 1977

Answers:

• Poisonous Ammonia--The ammonia is in ionic state; thus, it is not noxious in the way "household" ammonia is. Or, it might be in the form of ammonium chloride, as in many other deep sea species of squids. The actual form in Architeuthis has not been determined to Dr. Clyde Roper's knowledge. Back

• Nerve Fibers--Logic would suggest that was the case, since the speed of transmission of the impulse is proportional to the diameter of the axon. But remember that the impulse has to travel some distance (the very reason for the large diameter); whereas, responses much closer to the point of generation of the impuse, the brain, might be quicker. The initial response of a giant axon to a stimulus is 50 milliseconds. Back