Marine Life page 1
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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)

fish

Most fish are too heavy to float. Some sink to the ocean floor and live there. Other fish have a built-in swim-bladder (like a small gas filled ballon) inside. This helps them stay off the ground and up in the water. Still others, like sharks, must swim all the time to stay up, because they don't have a swim-bladder.

It is difficult to swim through water. Water is thicker than air. Fast fish have a fusiform body (shaped like a torpedo or rocket). Some fish are flat on both sides (laterally compressed). They can easily swim around coral reefs. The fish living on the bottom of the ocean are flat - both top and bottom. This helps them glide along the bottom. Fast moving fish have special features. Besides being shaped like a torpedo they can pull in fins not in use to reduce drag. They may also have a slimy mucous layer (like oil) that helps them glide through the water. Or they may have special skin control to reduce drag.

Fins

Fins are found in many places on a fish's body. There are side fins, dorsal (top and bottom) and caudel (tail) fins. These fins move the fish forward, help with turns and keeping balance.

The tail fin pushes the fish forward. Broad tail fins give a fast start. Long narrow tails are better for long distance swimming. 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. This pushes (propels) the fish forward.

Muscles

Fish use their muscles to move their bodies and fins. The larger white muscles are for speed, but they tire easily. The red muscles are for slow or regular movements. The fish can swim a long time with the red muscles. If the muscles need more oxygen the fish can open its mouth to let more water pass over its gills. The gills take oxygen from the water and give it to the muscles.

Cetaceans (Dolphins and Whales)

Dolphins and whales, like fish, spend their whole lives in the water. But, dolphins and whales are mammals. This means they are warm-blooded, have live births and nurse their young. It also means they must breathe air through their nose (blowhole).

dolphin

Dolphins and whales swim differently than fish. A fish's tail moves from side to side. A dolphin's tail moves up and down. The dolphin's tail is so powerful it can push the dolphin straight up out of the water.

Dolphins often push themselves out of the water (jump). The reason they do this is to take a breath of air. That way the dolphin does not need to slow down in the water.

Flying Fish

flying_fish

Flying fish do not really "fly". They glide across the surface of the water. They can glide very fast and very far through the air. As the fish leaves the water special fins are spread out that allows it to glide.

Rays

mantaray

Rays and skates live on the bottom of the ocean (they have no swim bladder). They use their fins in a different way than fish. Fish move their fins sideways. The ray moves its fins in an S-shaped wave, up and down, from the head to the tail.

Hydrofoils

sealion

Some water animals have flippers. Flippers can act like an airplane wing in the water. The sea turtle, sea lion and seal are examples of animals with flipppers. The movement of the flippers allows the animal to go up or down or forward in the water. Sea turtles and sea lions use their front flippers to move forward. Seals use their tail flippers to move forward.

Jet Propulsion

jellyfish

A few water-animals use jet propulsion to move around! The simplest example is the jellyfish. These animals fill their umbrella section with water and then push the water out. The jellyfish then moves in the opposite direction. But, there is no control over the direction. A squid does have control. The squid has an outside covering of muscle and is able to expell (shoot) water through a single siphon (pipe). The siphon can be moved to point in different directions. Some squid are able to reach speeds high enough to shoot them out of the water and onto the deck of a ship!

Several shelled animals such as scallops and clams also use jet propulsion to get away from enemies. To do this the animal must bring together its two shells, which forces water out sending it to safety.

clam

Click on the picture to see the clam move!

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