These exercises were created by Dr. Karen Grove (© 1998 Grove) for use in the Introduction to Oceanography course offered by the Department of Geosciences at San Francisco State University. Other educators are welcome to use these exercises in their own classes. Please send comments to Course home page: Commercial use is prohibited.

VOYAGE 10: Design a Critter

Don't forget to check out the course web site where you can obtain preparatory information before each class and summaries that are posted after the class meets. Click here to bring up a new browser window with the course site. You can also use this site to display the text and images part of the voyage on a second window so that you don't have to print anything.


This voyage is different than the others. Rather than submitting your answers online, you should submit your assignment in class (due in class on Thursday, 6 December or earlier). THE CRITTER DESIGN IS WORTH THE VOYAGE TOTAL OF 10 POINTS.

For this "Design a Critter" section, choose one of the life environments illustrated in Figure 1. Choose either the benthic realm (organisms that live on the ocean bottom) or the pelagic realm (organisms that live in the water). Then choose a
subdivision of that realm, such as the intertidal zone (benthic), photic (pelagic), bathyal, abyssal, or hadal. Consider characteristics of the environment such as density, light, food sources, and nutrients; and features your organism would need to function well in that environment. Voyage 9 are provided here to help you with the different environments. Chapter 12 in the textbook also has information about the various life environments and their characteristics.

Then design an organism (plant or animal) that would be well adapted to living in that environment. You may look at Chapters 13 and 14 in the textbook, where examples of already-living organisms may spark your creativity. Please use one full sheet of paper, with a drawing of your organism that has its parts labelled and explained. That is, for what aspect of the organism's lifestyle (for example, eating, procreating, avoiding predators) is each part designed. Be sure to list the environment you have chosen and how your critter has adapted to this environment.

Life environments

The physical and chemical structure of the ocean that we have discussed in class provides habitats that marine organisms depend on. Variations in such factors as temperature, light, and nutrient concentration create distinct conditions to which organisms have adapted. For example, the planktonic seaweed in the Sargasso Sea grows slowly and lives a long time, an adaptation to low nutrient concentrations. Fish that live at deeper levels of the ocean have developed bioluminescence and photic organs that help them to cope with low-light conditions. For more information about the characteristics of different life environments, see pages 231-238 in the textbook.

Figure 1. Divisions of the marine environment. The two large divisions are the benthic realm (organisms that live on the seafloor) and the pelagic realm (organisms that live in the water). The benthic and pelagic environments are subdivided into zones based on depth. From deepest to shallowest, the zones are hadal, abyssal and bathyal zones. In the pelagic environment, the shallowest zone is called the photic or surface zone. In the benthic environment, the shallowest zones are called the intertidal and subtidal zones.

NOTE: this diagram has a large amount of vertical exaggeration (slopes look MUCH steeper than they really are).

Figure 2. General characteristics of the marine environment.

Figure 3. This diagram shows some of the physical and chemical conditions that change with depth in the ocean. The first panel shows variation in density with depth. This density change is a function of temperature, which decreases downward in the ocean. Panels 2, 3, and 4 all show variation in nitrates, phosphates, and silicates, which are nutrients essential for plant growth. The fifth panel shows variation in dissolved oxygen, which is supplied to the ocean from the atmosphere and by plant photosynthesis.

Note that the vertical axis in all graphs is depth (deeper toward bottom of graph) and that the horizontal axis in all graphs is concentration, accept panel one, which is density. In all graphs, concentration or density increases toward the right side of the graph. These characteristics are not uniform throughout the ocean, but these graphs represent common conditions.


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