Lesson 5

1. Living where land and water meet: Fiddler Crabs Lesson 5

2. 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

3. 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

4. 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.

5. 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.

6. 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

7. 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.

8. 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.

9. 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.

10. 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.

11. 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.

13. What would you like to know about the Fiddler Crabs?

14. Schedule • Feeding • 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.

17. 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?

18. 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? • How is it different?

21. 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.

22. The End!!!