Herbivory And Its Effects On Brown Algae Seaweed

Seaweed serves as a primary food source for a number of marine herbivores. Various fish, sea urchins, gastropods, and crabs, as well as smaller herbivores such as amphipods, isopods, and polychaetes all eat the plants. In many aquatic habitats, this consumption is intense, and has been going on throughout most of evolutionary history. Consequently, in response to these pressures many seaweeds have evolved elaborate defense mechanisms. In the first of three articles which will be presented, Duffy and Hay (1990) describe the different protective strategies employed by marine plants. Of these, perhaps the most common are the chemical defense mechanisms. Such defense systems are generally most elaborate among tropical seaweeds. However, in tropical plants certain strategies are also conspicuously absent. For example, the article by Steinberg et al. (1991) notes that tropical brown algae produce very low levels of protective polyphenolic compounds. The paper also gives several possible explanations for this observation. A third article by Tugwell and Branch (1992), however, may provide the answer. It suggests that many fish species have evolved countermeasures to the polyphenolics. Thus, it may be that the compounds offer no survival advantage against tropical fish. Since most defensive measures also involve some inherent cost to the organism, the production of polyphenolics by tropical seaweeds has subsequently been selected

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henolics. The exact functions that some of these chemicals perform remain largely unknown (1:370). According to Duffy and Hay (1990), however, it has been found that several terpenoid compounds decrease the overall herbivore damage experienced by seaweeds. The polyphenolics are another important chemical defense. In coral reef environments, there tends to be a greater variety of potential enemies. Consequently, seaweeds which occur in these habitats sometimes possess integrated defenses. Such integration may involve the coordination of structural, chemical, and nutritional characteristics in order to ensure survival. For example, the tropical green alga, Halimeda, protects itself by combining both heavy calcification and chemical defenses; each of these defenses will vary according to grazing pressures (1:373). Although the armament employed by seaweeds against herbivores is impressive, it does not come without some cost to the plant itself. In fact, in areas with lower rates of herbivory, plants with elaborate defense mechanisms actually seem to be selected against. The problem with analyzing the costs of protection, however, relate to measurement of those costs. Obviously, algae that grow in physically stressful env
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Some common words found in the essay are:
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Approximate Word count = 2128
Approximate Pages = 9 (250 words per page)