This section contains general descriptions of marine trophic levels, food chains, and food webs, as well as a description of two general marine environments: benthic or demersal (associated with the seafloor) and pelagic (the water column and open ocean). A broad description of the types of marine organisms found within these environments is provided, as well as a description of organisms important to fisheries. Protected species are also described in this section. This section is intended to provide background information on the ecosystem and ecosystem concepts that must be considered when managing the fisheries of American Samoa. 3.3.1 Marine Food Chains, Trophic Levels, and Food Webs Food chains are often thought of as a linear representation of the basic flow of organic matter and energy through a series of organisms. Food chains in marine environments are normally segmented into six trophic levels: primary producers, primary consumers, secondary consumers, tertiary consumers, quaternary consumers, and decomposers. Generally, primary producers in the marine ecosystems are organisms that fix inorganic carbon into organic carbon compounds using external sources of energy (i.e., sunlight). Such organisms include single-celled phytoplankton, bottom-dwelling algae, macroalgae (e.g., sea weeds), and vascular plants (e.g., kelp). All of these organisms share common cellular structures called “chloroplasts,� which contain chlorophyll. Chlorophyll is a pigment that absorbs the energy of light to drive the biochemical process of photosynthesis. Photosynthesis results in the transformation of inorganic carbon into organic carbon such as carbohydrates, which are used for cellular growth. Primary consumers in the marine environment are organisms that feed on primary producers, and depending on the environment (i.e., pelagic vs. benthic) include zooplankton, corals, sponges, many fish, sea turtles, and other herbivorous organisms. Secondary, tertiary, and quaternary consumers in the marine environment are organisms that feed on primary or higher level consumers and include fish, mollusks, crustaceans, mammals, and other carnivorous and omnivorous organisms. Decomposers live off dead plants and animals, and are essential in food chains as they break down organic matter and make it available for primary producers (Valiela 2003). Marine food webs are complex representations of overall patterns of feeding among organisms, but generally they are unable to reflect the true complexity of the relationships between organisms, so they must be thought of as simplified representations. An example of a marine food web applicable to the Western Pacific is presented in Figure 9. The openness of marine ecosystems, lack of specialists, long life spans, and large size changes and food preferences across the life histories of many marine species make marine food webs more complex than their terrestrial and freshwater counterparts (Link 2002). Nevertheless, food webs are an important tool in understanding ecological relationships among organisms.
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