Living where land and water meet: Fiddler Crabs Lesson 5

Materials Prepare salt water by filling a pail with water, add drop of conditioner, add 2 pinches of Instant Ocean, stir 4 ½ cups of sand mixed with 4 ½ cups of humus, mix, remove sticks China marker Tape Tank with lid Water bowl Paper towel Hairgrass Cup with lid Ruler

Overview Review necessary elements of a habitat for Fiddler Crabs Create habitat Record living and nonliving elements in habitat Discuss how to take care of the Fiddler Crab Discuss feeding schedule Observe crabs and record questions

Background Along the shore of almost any body of seawater, you can spot a variety of crabs. Crabs are crustaceans, animals whose bodies are covered by hard shells, or exoskeletons. Crustaceans also include lobsters, crayfish, and shrimps. Crustaceans are a subgroup of larger group of animals known as arthropods – the most abundant macroscopic animals on Earth.

Crustaceans Crustaceans have segmented bodies and jointed appendages. An appendage is any part that extends out from an animal’s body, such as legs, feelers, and mouth parts. All crustaceans have armor-like exoskeletons with flexible joints. Muscles inside of and attached to the exoskeleton give these animals great strenth.

Fiddler Crab Most crabs live in or near the sea, either in shallow tidal mud flats or in the depths of the ocean. Most crabs breathe with gills. Lay eggs in a wet environment Cold blooded Metamorphosis in stages from egg to juvenile Can change color Around 4,500 kinds of crabs 62 kinds of Fiddler Crabs Indigenous to U.S. means can be found here

Body Structure 2 main parts Cephalothorax (head and thorax) abdomen Body covered by a shell called the carapace. Attached to the cephalothorax are 2 movable stalks that support the crab’s compound eyes. Eyes can see 360 degrees and can extend upward to see over small obstacles and to retract into a groove for protection. They can see stationary objects that are 65-100 feet away and moving figures that are 330 feet away. 2 pair of small antennae on the head – one for smell and the other for touch. Four pairs of walking legs and 2 pinchers connected to the cephalothorax. Walk sideways. The female has 2 small, equal sized claws, and the male has one large claw up to twice the size of the other claw. Use claws to feed and dig.

Behavior Semiterrestrial – living part time in water and part time on land Remain out of water by keeping a small amount of seawater in their gills. Must return periodically to the water to renew their water supply. If see bubbles while in the water, the crab is producing carbon dioxide as it breathes and fills its gills with seawater. During high tide, they stay in their burrows and emerge during low tide. Change colors – usually dark in sunlight and paler at night or when cloudy and at times will match color to environment. Male feeds only with the small claw but digs with both. Male uses its large claw to attract a female, discourage rivals, and defend territory. Because the claw is white and reflects sunlight, it can be seen at a great distance. If a large claw, which breaks easily, is lost, a new feeding claw will take its place and the new claw will grow to reach the size of the original large claw. Produces a squeaking sound, much like a cricket, by rubbing the surfaces of its big claw against its thorax.

Feeding Behavior Feed mainly at low tide. Known as “deposit feeders,” they roam the flats of much and sand, scooping up sand and soil that contain small particles of food, mainly bacteria and algae. Pushes sand and mud into its mouth with the small, spoon-like feeding claws. Layers of moving mouth parts open and close like elevator doors, and spoon-like hairs separate the tiny pieces of food from the sand and mud. After filtering out the food, it forms the sand and mud into little pellets and deposits them on the ground. They often feed on dead fish and other creatures.

Survival Behavior Hide among marsh plants and dig burrows for protection. Dig its burrow above the tide line. A burrow can be up to 2 feet deep. Burrow usually houses one crab at a time. To prevent water from entering its burrow, the fiddler lines the burrow with mud and plugs it up using the pellets at the burrow’s mouth. At the burrow’s deepest end, the fiddler digs another few inches, creating a horizontal tunnel. During both high tide and winter hibernation, the crab stays in the tunnel.

Life Cycle Mate in the spring. Male attracts female by waving its large claw or by drumming it against the ground at night. Each species has a specific wave pattern that females can recognize. Reddish, brown eggs that hatch in water. The newly hatched babies are microscopic and undergo a series of molts before becoming pea-sized juveniles. When young, they molt about once every 10 days; as adults, once or twice a year. The life span is around 2 years. After a molt, it has soft shell for about 30 minutes.

What would you like to know about the Fiddler Crabs?

Schedule Feeding Water Move habitat gently. Feed once a day at 7:40. Put food in water and on land. Remove old food before adding fresh food. Can also feed small pieces of apple, banana, or lettuce on the sand. Water Change the water once a week. Slowly lift the water bowl, dump the water, rinse the bowl, replace the bowl in the habitat, and refill water. Important not to spill water onto the sand. Move habitat gently.

Put plankton in water and on land. What happened when you put food in tank? Do the crabs respond to the food the same way the frogs do? How are the crab’s responses different?

Reading Selection Read Write 2 or 3 things you discovered about how people study dolphins. How is the animal research you are doing similar to the dolphin research being done at the research center? How is it different? How is your animal log similar to the data sheet the research center is using?

Extensions Research other kinds of crabs and create a display. Use a Venn diagram to compare the classroom habitat of the crab with its natural habitat. Feed the crabs a variety of foods to discover which the crabs prefer. Experiment with tuna flakes, shrimp pieces, green vegetables, and fruits. Crustaceans are a popular food source for humans. Research the nutritional value of crustaceans, as well as diverse ethnics dishes that use these animals.

The End!!!