Table of Contents
Teaching Tip: Along the Shore
Are you taking a trip to the beach this summer? If so, here are ideas on how to use some of that time in a shoreside science study. You can modify your study based on whether your beach is sandy or rocky, as each one offers a different aspect of shore life.
For an in-depth study, bring along a magnifying glass (or low-power field microscope), gloves, containers, and a notebook for recording your observations. Use paints, crayons, markers, or colored pencils to combine art with the science lesson and capture some of the color of the seashore. And if you're at a rocky beach, you might want to bring along a small water net for fishing specimens out of tide pools.
Using the magnifying glass or low-power microscope, look at a sample of ocean water for tiny creatures and plants. You'll probably see a variety of marine diatoms and dinoflagellates (very small algae) and protozoans (one-celled organisms). You could also take a sample of water home, and look at it under a high-power microscope, using a concave slide, to see greater cell detail.
Birds are an easy part of shore life to observe. Look at the birds on the beach and in the water. What do their bills look like? What about their feet? How do they get their food? If you have a field guide for identifying birds, see if you can figure out which species each one you spot belongs to. It might be helpful to have your children 'classify' different sea birds--what characteristics would they use to decide how to group them?
On sandy beaches, look for tracks, insect life, burrowing animals such as clams, bristle worms, or sand crabs, and jellyfish and seaweed that have been stranded on the shore.
On rocky beaches, the shore 'anatomy' is very different. You might see plants growing on rocks, tide pools with water plants and animals, and even limpets clinging to the sides of rocks. Look for mussels, rock and hermit crabs, clusters of anemone, and perhaps even starfish and coral in a tide pool.
If you're at a sandy beach and you don't mind the risk of coming home with a carful of 'treasures', let your kids collect driftwood pieces, crab shells, sea sponges, and other interesting specimens that catch their eyes. Try a family scavenger hunt with lists you've prepared-- draw pictures for very young children, or perhaps only write out scientific class or family names to challenge older children. When you're finished, draw some of the specimens in a notebook. At a rocky beach, you should be more selective in what you pick up. It's usually a good idea to wear gloves when picking up a specimen--some organisms can sting.
The fun doesn't have to stop when you leave; in addition to shells, there's usually algae (seaweed) along the beach, that can be brought home and preserved by pressing it. If it's not already wet, dip the specimen in water, then arrange it on a piece of paper with a sheet of waxed paper underneath. Cover with a piece of paper and another sheet of waxed paper over that, then press the whole set of papers and specimen between several heavy books. You'll need to let your algae specimen dry for several days at least before it's ready to remove from the 'press'. Frame the specimen, or paste it into a notebook with its scientific and common names.
Teaching Tip: Shells
All the shells you might find along a beach (other than crab and other crustacean shells) are from sea creatures called mollusks. The mollusk phylum includes species in vastly different classes, ranging from squids to scallops to sea snails.
What do these species have in common? Mollusks' bodies are divided into three parts: the head, foot, and visceral mass. The head contains the mouth, except in the bivalve class where the head is not distinct. The foot is usually used for crawling, swimming, or burrowing. The visceral mass contains the digestive, reproductive, circulative, respiratory, and excretory organs.
Mollusks have exoskeletons, meaning that their 'skeleton'--the hard part of them--is on the outside. Most mollusks have calcareous (limestone) exoskeletons, which could end up in your shell collection if they wash up on the shore.
The best-known shells come from the gastropod and bivalve classes. Gastropods--snails and slugs--aren't usually impressive on land. Many marine snails have beautiful shells, however, and not just in the shape you might expect. Maybe you've heard of periwinkles, conchs, murex, whelks, and cowries; these all come from sea snails! 'Sea slugs', because they don't have shells, are called nudibranches. The name gastropod means 'stomach-foot'--the belly of this mollusk rests on its foot.
Bivalves have halved shells, that are hinged together. The two halves are held closed by muscle, and only open when that muscle is relaxed. Usually bivalves have a hatchet-like foot that they use for digging. Water is siphoned into the bivalve, where mucus traps tiny food particles that the animal can eat. Clams, scallops, mussels, oysters, and cockles are all bivalves. So, oddly enough, are shipworms-- the 'termites of the sea', worm-like animals that bore into wood.
Squids, octopi, and nautiluses belong to the cephalapod class. The name cephalopod means 'head-foot'--the head and foot are indistinguishably merged. A cephalopod moves by 'jet propulsion'--it is propelled forward by expelling water forcefully through a siphon by its mouth.
The other, less common classes of mollusks are Monoplacophora, Polyplacophora (which includes chitons), Scaphopoda, and Aplacophora.
Often, the shells you pick up on the beach still have their 'owner' inside--if the mollusk died, the shell might be inhabited by a hermit crab. If you'll be in the area for a while, you can let your shells sit for a few hours in a pan or bucket of seawater before taking them home, to be sure you're not getting any live ones.
Teaching Tip: Fish
Did you know sharks and stingrays are fish? They differ in a few ways from tuna, clownfish, and other typical fish you might find in the ocean, though: while the latter are bony fish, sharks, rays, chimaeras, lampreys, and hagfish are cartilaginous fish. Bony fish are so named because they have internal skeletons which are partly or wholly made of bone. Cartilaginous fish, however, have skeletons made of cartilage, a tough, flexible tissue.
Fish have vital organs--such as a heart--like other vertebrates, but have fins instead of legs and gills instead of lungs. Bony fish have a gill cover, called an operculum; sharks and other cartilaginous fish (except chimaeras) do not have gill covers. Oxygen from the water comes in through the gills and is brought into contact with the fish's blood and circulated throughout the body.
Usually bony fish have two dorsal fins along their backs, a caudal fin on their tails, and an anal fin on the their bellies near their tail. They also have a pectoral fin on each side (roughly where a shoulder would be) and a pair of pelvic fins on their bellies below the pectoral fins, which are used for steering and balance. Sharks have similar fins, designed to make them powerful swimmers.
Bony fish reproduce by external fertilization: the female's spawn is fertilized by sperm and hatches into fry, or young fish. Sharks, on the other hand, have complex reproductive systems--they reproduce by internal fertilization and some shark species, as well as manta rays, give live birth.
Besides their reputation, sharks have some unusual features: in addition to having a flexible jaw, they have teeth that are constantly falling out and being replaced. They also have a stomach that expands to hold what they've eaten! Sharks are nearsighted, but have a very sharp sense of smell, which is why the smell of blood can so excite them.
Rays, skates, and sawfish--generally grouped together as rays--breathe through openings called spiracles that are located behind their eyes. Stingrays, as their name implies, can be very harmful to people; but giant manta rays (or devilfish) are a minimum threat to anything bigger than a shrimp or small fish, even though they can weigh up to 3,000 pounds!
Rays look downright nice compared to the other group of cartilaginous fish. Lampreys and hagfish, who belong to a separate division of cartilaginous fish, do not have jaws. Lampreys are parasites--they live off of larger animals--and hagfish are scavengers, eating dead organisms.
If you want to get some hands-on experience while learning more about fish, we recommend dissecting a perch and dogfish. The perch is typical of bony fish and the dogfish, a small shark, is typical of cartilaginous fish.
Teaching Tip: Sea Animal Defenses
God has made some marine creatures with extra-special defense responses, enabling them to scare away or escape from predators. Here are some fish, mollusks, and echinoderms with amazing built-in defenses.
The surgeonfish has a razor-sharp retractable spine on either side of its tail that it pops out when it's in danger. The porcupinefish, another spiny fish, can inflate its body by swallowing water. This causes the short spines that usually lay flat along its body to erect and stand out like the spines of a porcupine.
Scallops can escape from one of their predators, starfish, by sending out a stream of water that shoots them out the surprised starfish's grasp. Starfish also have a unique defense: they can regenerate (grow back) lost arms. They can also asexually reproduce themselves: if a starfish is cut in half down its middle, each piece can grow into a whole starfish. This once caused a real problem for fishermen who would cut starfish in half and then throw the pieces back into the ocean, in an effort to keep them from preying on oysters.
Squids, octopuses, and cuttlefish have an ink sack near the end of their digestive tract, that they can use as a defense. Squids discharge the contents of the sack and then turn a pale color, confusing the predator that was chasing them. Octopuses can change color and skin texture to match their surroundings. And some have two autotomizable arms that can 'self-cut'. The segments that are ejected from the arm expand after they're cut off, confusing the predator. Later, replacement segments grow on the special arms.
Although you won't be able to see any of its regenerative properties in action, we suggest you dissect a starfish specimen for hands-on study.
Habitat Quick Profile: Kelp Forest
Kelp, a brown algae, grows in cold ocean water (such as the Pacific and Atlantic) where there is a depth of about 60-100 feet. Places where the kelp grows to be less tall are called kelp beds. Giant kelp grows up to the surface, where it forms a canopy; palm kelp grows at the bottom where it still receives enough light for photosynthesis. Red algae grows along the ocean floor, where anemones, sponges, abalone, and sea urchins can also be found.
Sea otters and sea lions both like kelp forests. Sea otters are an important part of this habitat, because they eat sea urchins, which can destroy the kelp if they don't have predators. Since sea otters lack insulating blubber, they have to eat almost constantly--they need to eat up to 25% of their body weight every day! In addition to sea urchins, they eat abalone (a gastropod) and sometimes fish.
Killer Octopus? The tiny blue-ringed octopus--no more than a few inches long even with its tentacles--has a sharp beak that can bite through a wet suit. It's also poisonous; and unless a bitten person receives treatment until the venom has worked itself of the body, it's fatal.
Whoa, big guy! Leatherback sea turtles, who hatch at about 2-1/2 inches long, reach adult sizes of 4-8 feet and a weight of 700-2,000 pounds. This makes them the largest living turtles! They're called leatherbacks because of their rubbery (rather than bony) shells. Leatherback turtles can maintain a core body temperature that is higher than the water around them, enabling them to swim in cold oceans where other marine reptiles can't survive. These turtles feed on jellyfish, and were created with special spines in their esophagi to help them swallow their slippery meals.
The Scientific Speaker
Sea comes from an Old English word and can refer to a landlocked body of salt water or sometimes fresh water, as well as to a tract of water within the ocean (like the Mediterranean) or as a synonym for ocean.
Ocean comes from a Middle English word, which came from the Latin oceanus; the Latin was derived from a Greek god's name, mentioned by Homer in the Odyssey. 'Ocean' can refer to the whole connected body of salt water on the earth (covering about 70% of it!) or to tracts of water such as the five oceans.
A malacologist studies mollusks, an ichthyologists studies fish, and a phycologist (also known as an algologist) studies algae. (For the name of the branch of science dealing with that subject, take off the -ist ending and add -y.)
The upper part of a turtle's shell is called a carapace and is made up of horny plates called scutes. The bottom part of the shell is called a plastron.
Click here to view great photo images of NW African shells.
For an online world map that allows you to view all the oceans and other main bodies of water, visit this site.