12.15.2: Chapter Questions
- Page ID
- 50287
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- Why is it necessary to have primary producers, animals, and decomposers in a marine ecosystem?
- What is metagenomics and how can it be applied to oceanic studies? What type of genetic material is typically extracted in metagenomic studies?
- Dissolved oxygen concentration varies substantially with depth. Describe and explain the distribution of dissolved oxygen in the deep ocean.
- Why is nitrogen generally the limiting nutrient in the oceans? List the sources of biologically available nitrogen in the photic zone.
- Of all the organic carbon in the oceans, 99% is in nonliving particulate or dissolved form. Why?
- Why are most of the world’s major fisheries in coastal waters? Why are many major fisheries off the west coasts of the continents? Why are the waters around Antarctica highly productive?
- List and describe the principal differences between the pelagic and benthic environments. Why are the boundaries between zones of the benthic and pelagic environments defined by depth ranges?
- At what depths in the pelagic and benthic environments would you expect to find substantial variation in the species composition of the fauna and flora between tropical, mid-, and high latitudes? Why?
- Describe the major types of plankton.
- Why are phytoplankton small?
- List the major categories of organisms that constitute the nekton. What are the principal distinguishing characteristics of each category?
Critical Thinking Questions
- Very high productivity is found in the circumpolar ocean around Antarctica. This is also the region most often under the hole in the ozone.
(a) Does the high productivity indicate that the ozone hole does not have a significant adverse effect on the ocean ecosystem? Explain why or why not.
(b) What other information did you use to reach your answer?
(c) What other studies or data would you like to have to make sure that your answer is correct? - The enhanced greenhouse effect is expected to cause climate changes that will lead to warming of the mixed layer of the oceans by several degrees.
(a) Hypothesize how this change might affect winds, the characteristics of the pycnocline, and ocean currents.
(b) Would these changes affect the amount of nutrients available to phytoplankton? If so, how?
(c) What is one possible way that some phytoplankton can adapt to changes in nutrients? - A number of years ago it was suggested that nuclear reactors should be placed on the seafloor in tropical deep-water areas and other areas of the oceans where the primary production in the mixed layer is nutrient-limited. The intention was that the heat generated by the reactor would cause artificial convection-driven upwelling, increase the supply of nutrients to the mixed layer, and increase primary production.
(a) Would this proposal work? If not, why not?
(b) If so, can you suggest reasons (other than the potential for the release of radioactivity) to explain why the idea was not adopted? - If you measured the dissolved oxygen concentration carefully in the photic zone during a spring bloom of phytoplankton, describe how you would expect it to change over 24 h and why. Would the changes in concentration during the 24 h be different at different depths within the photic zone? If so, describe how and why.
- Pelagic food chains that lead to large predatory fishes in the deep oceans far from land tend to be much longer than in coastal regions. What might account for this difference?
- What is a detritus-based food web? Would you expect detritus based food chains that lead to large fishes that feed on benthic animals to be longer than the pelagic food chains in the overlying water that lead to large carnivorous fishes? Why? Would your answer be different for coastal and deep-ocean regions? Why?
- Many fewer species of reptiles and mammals live in the oceans than on land, and many more species of fishes and invertebrates live in the oceans than live on land and in freshwater. What do you think are the reasons for these differences?