Invasive Species Case Study:
The Chinese mitten crab in San Francisco Bay*
The flow of goods in and out of Bay Area ports is a vital part of the region's economy. However, the ships bringing these goods also discharge ballast water containing exotic, and unwelcome, marine life into San Francisco Bay. In June 1999, the Port of Oakland became the first major US West Coast port to take action against this threat by restricting the discharge of ballast water.
Ballast water is used by ships to provide stability and make the vessels easier to handle. The need for ballast water varies by type of ship, and with differing cargo and sea conditions. Ballast water is often taken on in a port or coastal region, where the water contains many organisms. It may be released at sea, along a coast or in another port. If conditions are right, the "kidnapped" organisms may find a new ecosystem in which to flourish.
The Chinese mitten crab (Eriocheir sinensis) is a native of China and Korea. Pathways of introduction into new biogeographic regions include the live seafood trade, release via ballast water, and ship hull fouling. The Chinese mitten crab has become a well-known and unwelcome resident of San Francisco Bay and its tributaries with the population increasing in number and distribution since its first capture by commercial fishermen in 1992.
General: all groups have the same questions:
1. Compare the terms ecosystem, community, species, and population as they relate to ecology.
2. What is the difference between exponential and logistic growth? What are some density-dependent factors that keep populations from growing exponentially indefinitely? What are some density-independent factors?
3. What is an ecological niche? What happens when two species have identical niches? How does the fundamental niche differ from the realized niche?
4. Explain an example of resource partitioning, and explain how natural selection can lead to character displacement.
5. Describe an example of each of the three types of symbiosis discussed in your text.
6. Explain how energy moves through the living components of an ecosystem (starting with primary productivity and including a discussion of food webs and ecological pyramids).
7. Explain how water, carbon, and nitrogen cycle through ecosystems, and give at least one example for each of how human activities can alter the cycle.
8. Seven different biomes are described in your textbook. If you were in charge of global ecosystem conservation but were told you had to focus all of your resources on preserving two of the seven types of biospheres, which would you choose, and why?
Specific Questions to this case study:
1. Discuss the negative effects of the Chinese mitten crab has had on the San Francisco Bay.
2. Discuss how the Chinese mitten crab population could be brought under control.
3. Is there a difference between "invasive species" and "exotic species"?
4. Describe the characteristics of invasive species that increase their success in new environments. Why has the Chinese mitten crab been so successful in SF Bay?
5. Describe the effect of invasive species on community structure.
6. What are the economic impacts of the Chinese mitten crab on fishing in SF Bay. What agencies should be responsible for regulating and controlling invasive species? Who should pay these costs?
7. What is meant by the term “biodiversity”? Defend or dispute the statement "Exotics increase the biodiversity of an area."
8. How might the effects of global warming alter the success or failure of invasive species in colonizing new habitats? Would this affect the Chinese mitten crab?
*adapted from an article in Bay Area Monitor ~ March/April 2000
Stopping the Flow: Ballast Water and Invasive Species