13.7.2: Chapter Questions

Study Questions

1. What characteristics of the coastal oceans make them different from the deep oceans?
2. How does coastal upwelling occur? How could you tell whether upwelling is likely in waters off a particular coast without making any direct observations of the oceans?
3. Describe the circulation in coastal upwelling zones. How do organisms take advantage of this circulation?
4. What are the sources of nutrients to the coastal photic zone? Discuss their distribution in the oceans.
5. Why are there seasonal cycles in populations of marine organisms in mid-latitudes and polar regions? Why is there little or no seasonality in tropical regions?
6. Why does primary production slow during midsummer in mid-latitudes, and why is there sometimes a fall bloom?
7. Why is there a succession of dominant phytoplankton species during a typical seasonal cycle? Why are diatoms usually replaced by flagellates during this succession?
8. What are the relative magnitudes of fish biomass and production in the deep oceans and coastal regions? Why are these not proportional to the relative areas of these regions?
9. What are the major types of estuarine circulation? Why do they occur in different estuaries?
10. If you were in Australia and operating a boat that had only a weak engine, on which side of an estuary would you choose to travel out to the ocean, and on which side would you choose to return? Why?
11. Why are estuaries stressful environments for marine organisms?

Critical Thinking Questions

1. Some areas of the coastal oceans have lower oxygen concentrations and a greater probability of developing periodic anoxia in the lower part of the water column than other areas. List and explain the factors that make some coastal areas more susceptible to anoxia than others.
2. Describe what would happen to the low-density organic particles in sewage if they were discharged to the surface layer at the center of a partially mixed estuary. Would the fate of these particles be different if they were discharged to the lower layer? If so, how?
3. It has been suggested that, if the Earth’s climate does warm by several degrees, the seasonal cycle of primary production may be disrupted more in polar coastal regions than anywhere else on the Earth. Do you agree or disagree with this prediction? Explain the reasons for your answer.
4. Is it likely that a global climate change in which the Earth’s atmosphere warms by several degrees will alter the frequency or intensity of dinoflagellate blooms? Why? Is it likely that the frequency and geographic extent of periodic anoxia in coastal waters will change? If so, how and why?
5. Many marine species are overfished. The current method of managing fisheries is to restrict the total catch of individual species to below the maximum sustainable yield of that species. However, this approach does not prevent adverse effects on other species that may depend on the targeted species for food. For example, it is hypothesized that Pribilof seal populations in the Bering Sea are declining because the fish species that they consume are being heavily fished, reducing the seals’ food supply. A new approach to fishery management is developing in which ocean ecosystems are managed as a whole. For example, the growing fishery for krill in the Southern Ocean is managed by an ecosystem-based international treaty. Krill are the food supply on which a number of whale and seal species are dependent. Populations of these whale and seal species were drastically reduced by hunting in the first half of the twentieth century and have not yet recovered. Populations of penguin species that also rely on krill have increased to take advantage of the food previously eaten by whales and seals. If the krill fishery is to produce close to its maximum sustainable yield and contribute significantly to the solution of world hunger and protein deficiency, the whale and seal populations will never recover to their previous population levels, and it may be necessary to reduce penguin populations to protect whales and seals from renewed decline.
   (a) Do you think that marine ecosystems and fishing should be managed in this way? Explain your reasons.
   (b) What alternatives would you propose to solve the world hunger problem?
6. A swarm of locusts threatens the crops of a large area of North Africa. Should the locusts be eradicated to protect the food? A growing population of fur seals threatens to consume a growing percentage of fish from a regional fishery where the human population depends heavily on seafood. If the fish populations are not to crash from overfishing, the catch must be reduced, creating high prices and market shortages, or the fur seal population must be controlled. Would you kill seals to keep the population from growing so large as to damage the fishery? Did you have different reactions to these two scenarios? If so, why?