marine science center case%study:range!expansion!of!blue

Marine Science Center

Case Study: Range Expansion of Blue Crabs Part 1-‐ Introduction of Blue Crab Blue crabs are a species of invertebrates that are found in salt marshes and other coastal estuaries. They are distinguished from other crabs by their winged-‐shaped carapace, which is olive-‐brownish in color. Their claws are blue, while mature females have red tips. Their back legs are shaped like paddles that make them efficient swimmers. The blue crab's scientific name, Callinectes sapidus, means "beautiful savory swimmer." Blue crabs are important predators that have a wide-‐ranging diet. They are considered omnivores, feeding on whatever they can find. Examples of their diet include mussels, snails, fish, plants, and smaller crabs, including smaller blue crabs. Blue crabs are one of the most important commercial fisheries for humans. Historically, the northern range of blue crabs has been the southern coast of Cape Cod. However, in recent years there have been sightings of blue crabs north of Cape Cod in the Gulf of Maine. There has also been a shift in the harvest of blue crabs. The graph on the left shows blue crab landings for states along the Atlantic Seaboard. The greatest landings have been historically south of Delaware. The graph on the right shows how landings have changed in these states over the last 35 years (positive slope shows an increase in landings while negative slope shows a decrease in landings).

Questions: 1. What are the factors that affect the distribution and abundance of marine organisms? Think about both physical (abiotic) and living (biotic) factors. 2. List the adaptations that allow blue crabs to survive in their habitat.

Credit: Tanya Rogers


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Blue Crab Landings (metric tons)


3. Interpret the graph shown above on the right. Which states have seen a decline in blue crab landings, and which states have seen in an increase in blue crab landings? 4. Based on the following two pieces of evidence, formulate a hypothesis why there has been a northern range expansion of the blue crab. Evidence 1:

Evidence 2:

Part 2-‐ Effect of the Expansion

The Gulf of Maine is the body of water that extends from Cape Cod to Nova Scotia. Since, 2004 this area has been one of the planet’s fastest warming bodies of water.

Blue crabs live in different environments depending on their life stage and there are lower temperature limits of each life stage. Currents transport blue crab larvae called zoea. Winter temperatures may affect the overwinter survival of adults and summer sea surface temperatures may affect the development of larvae.



Many marine species exhibit range expansion in response to environmental changes in their native habitats. As the oceans continue to warm as a result of climate change, marine species are shifting poleward. This has both ecological and economic implications. An effect of range expansion of marine organisms is the potential to disrupt existing food webs. Blue crabs have the potential to consume and outcompete native crabs and other organisms in the Gulf of Maine. One of the species that

occupies the same niche as blue crabs are green crabs, which share the same prey such as mussels. Green crabs are an invasive species from Europe that are now very abundant in the Gulf of Maine. Range shifts could also mean large economic implications for fishermen in the southern extent of blue crab’s native range. As these blue crabs move into northern waters, harvest numbers can be lower for fishermen in southern states. As they move into new areas they can have an impact on other harvestable species. Both blue crabs and green crabs can prey on economically important shellfish such as soft-‐shelled clams. Questions: 1. Looking at the diagram shown above, what is the food web relationship between blue crabs and green crabs? What do the arrows represent? 2. What is the net effect is of the possible established introduction of blue crabs into the Gulf of Maine on coastal food webs and fisheries?

Marine Science Center Researchers Studying Range Expansion Tanya Rogers Tanya is a Ph.D. student in the Kimbro lab at the MSC. She is interested in how and why species interactions vary across space and time, and what consequences this has in the context of environmental change, species losses, and species introductions. She is researching how blue crabs might impact salt marsh communities and green crab populations if they expand their range north of Cape Cod as the climate warms.


Case Study: Range Expansion of Blue Crabs Part 1 Questions

1. What are the factors that affect the distribution and abundance of marine organisms? Think about both physical (abiotic) and living (biotic) factors. __________________________________________________________________________________________ ______________________________________________________________________________________________________________________________________________________________________________________

2. List the adaptations that allow blue crabs to survive in their habitat. __________________________________________________________________________________________ ______________________________________________________________________________________________________________________________________________________________________________________

3. Interpret the graph shown above on the right. Which states have seen a decline in blue crab landings, and which states have seen in an increase in blue crab landings? __________________________________________________________________________________________ ______________________________________________________________________________________________________________________________________________________________________________________

4. Based on the following two pieces of evidence, formulate a hypothesis why there has been a northern range expansion of the blue crab. __________________________________________________________________________________________ ______________________________________________________________________________________________________________________________________________________________________________________ ___________________________________________________________________________________________

Part 2 Questions

1. Looking at the diagram shown above, what is the food web relationship between blue crabs and green crabs? What do the arrows represent? __________________________________________________________________________________________ ______________________________________________________________________________________________________________________________________________________________________________________ ___________________________________________________________________________________________

2. What is the net effect is of the possible established introduction of blue crabs into the Gulf of Maine on coastal food webs and fisheries? __________________________________________________________________________________________ ______________________________________________________________________________________________________________________________________________________________________________________ __________________________________________________________________________________________


marine science center case%study:range!expansion!of!blue

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