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Marine Life | |
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Introduction Not all animals glide or fly in the air. Many marine (water) animals are masters of "flight" and speed under the water. Ocean, or water, environments cause these animals to adapt (change to fit that environment). Underwater Dynamics (bodies in motion)
A fish will float on top of the water if it weighs less than the amount of water it displaces (pushes away). Most fish weigh more than the water they displace and would sink to the ocean floor. But, most fish do not spend their lives on the ocean floor. They can do this because of an organ called a swim-bladder ( a built-in gas filled chamber) that helps the fish get off the ground and up in the water. Some fast-moving fish and sharks do not have a swim bladder and therefore must keep moving or they will sink. Water is about 800 times denser (thicker) than air and has a high viscosity. Viscosity tells how much drag or resistance there is to a moving body. There are two kinds of drag: water pressure drag and body friction drag. To overcome water pressure drag, fish have streamlined bodies that move through the water with the least possible resistance. Fish bodies come in a variety of shapes and sizes:
Some of the fastest fish in the ocean are tuna, mackerel and jacks. They have the fusiform shape. Coral reef fish have laterally compressed bodies that enable them to move in and around coral. Fish living on the ocean floor are dorsoventrally flattened. Fast swimming fish often have special features to improve their streamlining (low drag). This includes fins that can be tucked away in special grooves when moving quickly. As the fish moves, water flows over its body. This flow can be classified as laminar (smooth), turbulent (irregular) and transitional (changing). Laminar flow causes the least amount of drag and turbulent flow causes the most drag. Streamlining the bodyshape promotes (increases) laminar flow. Fish have several different ways of dealing with friction drag:
Barracuda secrete (release) slimy mucous from glands under their skin. This reduces drag by 60%! Sharks have denticles on their skin that cause the water to form a thin film that reduces drag in much the same way as the slimy mucous. Dolphins and whales have the ability to adjust their skin tension (pressure) to reduce drag. As a result all of these fish are fast swimmers. The fins of fish are crucial (very important) for swimming through the water. Fins consist of a fan of skin supported by skeletal rays. Muscles attached to these rays allow the fins to be moved side to side as well as along the body causing waves to travel the length of the fin moving the fish forward. Reverse these waves and the fish can also swim backwards! Fins are found in many places on the body of the fish. Paired fins are on the sides of the body sometimes near the head or further back on the body. Dorsal fins are found on the back or underside of all fish. The caudal or tail fin is at the back of the fish. These fins, working together, allow the fish to move forward, make turns and maintain balance. The caudal, or tail fin, is the main source of propulsion (push forward)for most fish. A broad (wide) tail is good for fast starts. Long narrow tails are better for long-distance swimmers. Some fish have an uneven (heterocercal) tail where the spinal column extends into the large lobe (rounded part) of the fin. This is often found in sharks and other fish without a swim bladder because the upper lobe gives an upward thrust to help keep the fish horizontal in addition to forward thrust. Many fish have an even (homocercal) tail with both lobes symmetrical (the same). This type of tail produces only forward thrust without the added upward thrust. The broad tail of the grouper allows it to accelerate quickly. The fast swimming tuna has a crescent shaped tail (thin, curved) with a narrow base that acts as a hydrofoil (lifting up), so that drag is minimal (very little). When most fish swim, they undulate (bend) their bodies in an S-shaped wave. This wave motion begins at the head and travels down the body toward the tail. The body and tail movements create a backward movement of water which propels the fish forward. The fish also uses its muscles as a major source of propulsion power. The muscles along the fish's side are its strongest and are what contract and expand in waves as it swims. With the tail movements this undulation moves the fish forward as it bends back and forth in the water. The muscles have different colors depending on where they are located and how they are used. The white muscles are the larger group found throughout most of the body. These "fast" muscles are used for powerful bursts of speed, but they tire quickly. The red muscles are usually found just beneath the skin and are slow and virtually inexhaustible (cannot be used up). These muscles are used to provide long-term power for slow, cruising speeds. The red muscles require more oxygen, so, fast-moving fish like tuna have a high oxygen demand (need). This is met by swimming with its mouth open so that large quantities of oxygen-carrying water can pass its gills. The fish's skeleton is quite strong and flexible for the many contracting muscles. The backbone extends from the head to the tail and has many interlocking vertebrae that allow side to side movement. Cetaceans (Dolphins and Whales) Dolphins and whales, like fish, spend their whole lives in the water. However, unlike fish, they are mammals. This means that they are warm-blooded, they have live births, they nurse their young and they need to breathe air. A big difference between fish and dolphins is that a fish's tail moves from side to side and a dolphin's moves up and down. The dolphin's tail movements are so powerful that they can even push the dolphin straight up out of the water.
As mentioned earlier, dolphins and whales are mammals and therefore need to breathe air. Their nose, located at the top of the head, is called a blowhole. When the animal needs to breathe, it swims up to the surface of the water, opens its blowhole and takes a breath. When the dolphin breaks the surface, It creates a wake that acts as a strong drag force and slows it down. The dolphin faces much less drag when it is completely submerged. Therefore, when a dolphin is traveling at high speeds, it will jump clear out of the water in order to get the necessary breath of air. This greatly reduces the amount of time spent fighting the pull of the wake and does not slow the dolphin down. Flying Fish
Flying fish do not actually fly, instead they glide across the surface of the water. Some flying fish have been seen at heights of 36 feet above the water's surface. A flying fish may soar at speeds of up to 35 miles an hour for distances of 250 yards or more in a single glide! In order to get out of the water, the fish gathers speed swimming toward the surface. As it leaves the water, the pectoral and pelvic fins are extended, providing enough lift for the fish to completely clear the water. As the fish returns to the surface, its tail moves quickly from side to side, allowing the fish to take-off again. Rays
Animals like rays and skates use their pectoral fins to move through the water but in a very different way. Instead of moving them horizontally (sideways) like a fish, a ray moves its pectoral fins vertically in an S-shaped wave, beginning at the side of the head and moving toward the base of the tail. They are able to change the pitch of the fin in order to get the most efficiency during the upbeats as well as the down beats of the fin. Rays do not have a swim bladder and spend most of their time lying on the ocean floor. Hydrofoils
Many animals swim through the water using their flippers as hydrofoils. A sea turtle's flipper resembles (looks like) an airplane wing and is subjected to the same types of forces when the animal is swimming. As the turtle's flipper strokes downward, the leading edge is tilted slightly forward about 25 degrees, creating lift and propulsion. When the flipper comes back up, the lift is cancelled and the turtle is propelled forward. Sea lions also use their flippers as hydrofoils. Their long front flippers are used to pull them through the water, while their smaller hind flippers are used for steering. Seals, on the other hand do not have large, well-developed front flippers and use vertical movement of their hind flippers and tail to propel themselves through the water. Jet Propulsion
A more complex (more parts) animal using jet propulsion is the squid. Some squid are able to reach speeds high enough to shoot them out of the water and onto the decks of passing ships! The squid has a muscular mantle (outer covering) which, when expanded, fills with water. When these muscles contract, water is expelled through a single siphon and the squid is propelled in the opposite direction. The squid can control its direction by rotating (moving) the siphon. Often the expulsion of water is accompanied by a puff of dark ink from the squid's ink sac in order to deter (cause fear or doubt) predators from following. Several species of bivalves (two-shelled animals) such as scallops also use jet propulsion to get away from enemies, such as a predatory sea star. To do this the scallop must contract (bring together) its two shells, which forces water out sending the scallop to safety. This is very exhausting and cannot be repeated often. Luckily, the scallop's predators are slow moving! Clams also use jet propulsion to move.
Click on the picture to see the clam move!
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