Marine Invertebrates- the Blue Crab
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| Marine Invertebrates- The Blue Crab
Adapted from VIMS (Vickie Clark) and North Carolina State University Standards- Ocean Literacy The ocean and life in the ocean shape the features of the Earth The ocean makes Earth inhabitable The ocean supports a great diversity of life and ecosystems The ocean and humans are inextricably connected Performance Objectives Following completion of this lesson, students will be able to: Understand the life cycle, anatomy and general information of blue crabs Analyze data compiled of blue crab populations for each life stage Recognize how and why blue crabs migrate Research a different marine invertebrate to present and teach to the class Lesson Plan Concept Exploration Present the students with details of the blue crab including taxonomy, anatomy, habitat, reproduction, diet, threats, protection and economic importance. The blue crab, Callinectes sapidus, is a marine crustacean, also related to shrimp and lobsters. Their scientific name means a beautiful swimmer that tastes good! They are also sexually dimorphic, meaning you can tell if they are male or female from the outside of their body. Females have red-tipped claws, similar to how humans paint their fingernails, female blue crabs have painted red claws. Males have blue-tipped claws, which is how they got their name. If you notice, their shell is actually greenish brown, so they are actually named blue crabs for the males bright blue claws. Many states rely on blue crabs for food and jobs and are an economic importance, especially in the Chesapeake Bay area where 1/3 of the nation’s catch of blue crabs come from. In 2000, the bay’s harvest was valued at $55 million (www.chesapeakebay.net). You can also tell the difference between males and females based on their apron or abdomen. The male blue crabs have a t-shaped abdomen while females have a broad-shaped abdomen. Blue crabs, along with many other marine invertebrates, have a complex life cycle including multiple stages. Blue crabs have 4 life stages and are each unique in where they live, how they behave and what they eat. They grow and develop into these stages through molting. Before molting, a new shell is formed underneath the old exoskeleton, which then loosens and then is cast off. The larval and early juvenile stages need high salinity ocean water in order to grow and survive. As they get older, they move further into a low salinity, brackish estuary where they mate and the females return back to the ocean in order to release their eggs. Females carry the eggs on their apron, which looks like giant sponge, so they are called sponge crabs. Blue crabs extend along the Atlantic coast from Nova Scotia through South America. They are top predators in the estuary, as well as opportunistic and will basically eat whatever it comes across. This also means they will eat other blue crabs if they need to. Blue crabs survive about 1-3 years and can grow up to 9 inches from point to point. Because they are highly aggressive, they also have adapted the ability to release their claws. So, if two blue crabs are in a fight and a crab has ahold of the other crab by the claw, the crab can release his claw and run away. Later, they will regenerate a new one. The use chemoreception to find food and can survive out of water as long as the gills stay moist.
Concept Introduction. Set-up stations with pictures, slides or specimens of specific life stages of blue crabs (zoea, megalops, juvenile and adult). Split the class up into four groups. Have the students read the introduction to each life stage, view and draw the blue crab in the life stage and answer the questions. After they have visited each station, hand out the blue crab survey data and a map of Chesapeake Bay. Each group will analyze one data set. Each data set has thirteen data tables for each life stage. Have them indicate on the map which stations had the highest abundances of blue crabs and construct a hypothesis which relates the location of their crab life stage to specific variables such as salinity, season, etc. Concept Application The students will use my presentation as an example in order to research their own marine invertebrate species and present the background of the organism to the class and conduct a class activity such as a worksheet, diagram to color, lab, craft, etc. related to their class or phylum for the class to complete. Review/Evaluation Formative Assessment: Review their understanding of blue crabs through the blue crab life cycle worksheets and how they apply the information to develop their own hypotheses on the location of each life stage. Discuss the data with them and how it correlates with the blue crab migration. Summative Assessment: The students will present their own marine invertebrate “highlight” species and do a class activity. Their peers and I will evaluate their presentations based on content, creativity and knowledge of the material covered. They will turn in 5 questions from their presentation that I will turn into a cumulative test from all the students’ presentation. Therefore, the students are responsible for how well their classmates learn the material. Sources: http://www4.ncsu.edu/~dbeggles/bluecrabs/The%20Blue%20Crab%20Life%20Cycle.pdf http://web.vims.edu/bridge/index_archive1102.html?svr=www www.bluecrab.info www.chesapeakebay.net www.google.com/images 
Now, draw the abdomen (apron) of one of the live adult crabs and label if it is MALE or FEMALE Sex: _____________________ Chesapeake Bay Field Survey for Larval Callinectes sapidus, one season
Station #1: Mouth of Chesapeake Bay
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