Oceans cover more than two thirds of the earth's surface, and they are very deep! Fish and other animals make their homes in all different parts of the ocean, even on the bottom, or sea floor. The ocean is also filled with lots of plants, which provide food, homes, and protection for ocean animals. A person who studies ocean life is called a marine biologist.
Microscopic plants and animals called plankton are very important in the ocean because they become food for a lot of animals. They drift along with the currents in the water and are eaten by fish, scallops, anemones, and others. Krill are small creatures that look like shrimp. They eat plankton and are eaten by larger animals, such as whales and birds.
Some creatures that live in the ocean use a special chemical reaction inside their bodies to create a glowing light. The light is called bioluminescence and happens when certain chemicals mix together, along with some oxygen from the water, in a particular part of the animal's body.
Because many bioluminescent animals live far down in the oceans where it is very dark (since sunlight cannot travel down that far through the water), the lights they make work sort of like a night light and help them see where they are going and to find food as well as other creatures to mate with. The anglerfish is an example of a deep sea creature that uses bioluminescence to find food. It has a glowing "lure" that extends from its head and dangles above its mouth. Other fish think the lure is food, but when they try to eat it, the anglerfish eats them instead! Here is a picture of an anglerfish: http://www.pbs.org/wgbh/nova/abyss/life/w57.html.
Fish have bones and are cold-blooded. (Cold-blooded means that their body temperature depends on the temperature of the water around them, unlike humans, who have a normal body temperature that stays at 98.6 degrees.) They breathe oxygen from the water through gills on the sides of their bodies. They cannot breathe air or live outside of water. Most fish are covered with small scales instead of skin. Fish use fins and a tail to swim around. Baby fish hatch from eggs. A person who studies fish is called an ichthyologist (say: ICK-THEE-ALL-O-JIST).
Most fish have a special part inside their bodies called a swim bladder. Air inside the swim bladder helps the fish float through the water. The fish can adjust how much air is in its swim bladder. If it wants to swim deeper, it lets some air out and if it wants to swim up towards the surface, it will let more air into its swim bladder.
Some animals that have the word "fish" in their names are not really fish. Some examples are cuttlefish (they are mollusks, see below), jellyfish (they are actually plankton), and starfish (they belong to a group called "echinoderms"). Can you think of any other animals that are called fish but do not have the things it takes to be a real fish?
Whales, dolphins, porpoises, walruses, manatees, dugongs, seals, and sea otters are all mammals that live in the ocean. Some, like seals and sea otters, can also live on land, but they spend most of their time underwater. These animals have lungs, are warm-blooded, give birth to live babies (they don't lay eggs) and nurse their babies, but they live in salt water instead of on dry land like most mammals. Since they have lungs, they need to breathe air instead of just getting oxygen from the water like fish and other ocean animals can. Instead of breathing air through their mouth or nose like we do though, a whale or dolphin uses a special hole on the back of its head called a blow hole to get air from above the surface of the water. Then it dives back down into the water and swims around for a few minutes before it needs to come up to breathe again. When it does, it breathes out the air through the blow hole and then breathes in more air so it can go back under the water again. When the air goes out of the blow hole, there is usually some water that squirts out with it, making a little spray at the surface (like the killer whale in the picture). Marine mammals also have some fur or hair, but sometimes it falls out by they time they become adults.
Most kinds of whales live in groups called pods. The pods are kind of like families. The older whales take care of the younger whales, which are called calves. Whales stay together in their pods for most of their life. Most kinds of whales live somewhere in the middle of the ocean so that they can quickly get to the surface since they need to go up for air a lot. There are two different types of whales - baleen whales and toothed whales:
Many marine mammals live in very cold water. They have blubber to insulate their bodies and keep them warm in the cold ocean waters. Blubber is a really thick layer of fat between the animal's skin and inside organs. It is very effective at keeping an animal warm. The gray whale's layer of blubber is about 10 inches thick! Do this experiment to find out how well blubber works.
Sharks look a lot like marine mammals, but they are actually fish! Unlike most fish though, sharks do not have bones. Their skeletons are made up of cartilage instead of bones. Cartilage is the same stuff that makes your ears and the tip of your nose have their shape and be a little bit flexible. Even though they don't have bones, sharks do have lots of other similarities to bony fish. They are cold-blooded and breathe through gills instead of through lungs. Sharks have gills on each side of their heads. As they swim, water passes over the gills and oxygen flows in from the water.
Sharks have several rows of sharp pointed teeth and powerful jaws to tear off big pieces of food, which they swallow whole. They don't even need to chew their food! Sometimes sharks lose teeth, but when they do, new ones grow in their place. Sharks have several rows of teeth. They eat bony fish, squid, marine mammals, and even sea turtles. They have an excellent sense of smell, which helps them find food. Many sharks eat near the surface of the water, but will also dive down deeper in search of food.
Not all sharks are large. Some only grow up to 7 inches long. However, most kinds of sharks grow to about 5-7 feet long, which is about the same height as an average adult. Not all sharks are dangerous to humans, either. There are over 350 kinds of sharks, but only about 25 of those have ever been known to attack humans. When sharks do attack people, it is probably because they mistake people for seals or other large ocean animals that they would like to eat. It is hard for them to tell what's what from below the surface of the water.
Baby sharks are called pups. Some pups grow inside their mothers like human babies do, but most hatch from eggs.
Rays are related to sharks and are also fish. They also have cartilage instead of bones. They look like flattened fish with eyes on top of their heads, gills underneath their bodies, and a long tail. Some rays like to live alone, but most of them live in large groups with other rays. Some kinds of rays have spines on their tails that have poison, which they use to stun or kill their prey. Some rays eat sort of like baleen whales - they filter small pieces of food out of the water. Like most ocean animals, their size can vary a lot. Some kinds of rays are tiny and some are really big. The largest rays are manta rays and can grow to be over 20 feet wide!
Mollusks are marine animals with soft bodies and no backbone. Animals like mollusks that do not have a backbone are called invertebrates. Animals that do have a backbone are called vertebrates. There is a lot of variety in the mollusk family. Some of them have a hard shell to cover and protect their soft bodies, but many do not. Did you know that clams and squids are related? They are both mollusks! Mollusks with shells, like clams, like to live in tide pools near the coast and larger ones with soft bodies, such as squid, live in the deep parts of the ocean. Here are some interesting things to know about several different mollusks:
Scallop - a small animal that lives between two identical shaped shells. Scallops, along with clams and oysters, are called bivalves. Scallops live on the ocean floor and move by quickly opening and closing their two shells with a thick muscle that works like a hinge to hold the shells together and allow them to open and close. When the shells come together, some water squirts out and the animal is propelled a little ways through the water. Most bivalves eat plankton and other tiny living things, like algae. Starfish and crabs often eat the soft bodies of scallops.
Conch (say: KONK) - this mollusk is called a gastropod and has a spiral-shaped shell and a soft foot. A conch looks similar to a snail and has tentacles to help it smell and feel. Its eyes protrude out from its head on two larger tentacles. It also has a claw-like foot it digs into the sand to propel itself forward and a very rough tongue for eating things that float in the water. Conch shells are used for many things, including musical instruments (sort of like a horn), decoration (they are very pretty), and even building materials!
Cuttlefish - these strange creatures have the amazing ability to instantly change the colors and patterns of their skin to blend in with their surroundings (they are related to the octopus, which can do this too!). Cuttlefish, along with octopi and squid, are called cephalopods. They are very fast swimmers and have multiple tentacles or arms that they use to catch and eat their food. These animals are meat-eaters and many of them use poison to kill their prey. Cuttlefish, octopi, and squid all have eight long arms. To learn more about cuttlefish, check out this website and click on "Launch Interactive" to find out about a cuttlefish's anatomy and how it works inside: http://www.pbs.org/wgbh/nova/camo/anatomy.html. Here are some videos of cuttlefish as well: http://www.arkive.org/common-cuttlefish/sepia-officinalis/video-10.html.
Giant Squid - some squid are small, but the giant squid, as its name tells us, is not a small one. This large creature can reach over 40 feet long and weigh about 1 ton (2,000 pounds), making it one of the largest ocean dwellers! Its main predator (an animal that hunts and eats it) is the sperm whale. A sperm whale might have to fight hard if it wants a giant squid for a meal though, because they are generally not much longer than the giant squid! Like other squid, the giant squid has eight arms and two very long tentacles with sharp barbs at the ends, which it uses to capture food. It likes to eat smaller squid and fish. Giant squid live very far down in the ocean and have big eyes to help them see.
Print this two-page coloring sheet and help kids cut and paste each animal onto the ocean page at the depth where it is most commonly found in the ocean. Talk about why each animal lives in that particular area. Encourage them to draw animals and plants to fill their ocean picture.
To view a printable version of this newsletter and the worksheet together, click here.