The animals that eat primary consumers are called secondary consumers . Transfer of food in food chains is clearly inefficient . Long marine food chains that lead to higher trophic level consumers, such as tuna, utilize primary production hundreds of times less efficiently than short marine food chains , such as those that support anchovy or sardine. For more information check out the synopsis in our Book Galley . Pollution includes discharge of harmful waste, activities such as overfishing, construction of structures, and other harmful human activities that adversely affect ocean ecosystems by changing currents, distribution of dissolved substances or heat, or sediment transport patterns.
Eutrophication occurs when excessive nutrients are present as a result of sewage discharge.
Alterations of marine habitats by dams, bulkheads, levees, etc., can alter current patterns, affect sedimentation and prevent some sea life from migrating. Marine diversity is usually limited as a result. Most of the open ocean has low productivity, the exception being certain high latitude regions and the equatorial upwelling band across the eastern Pacific. High productivity in subtropical and tropical oceans is limited to areas of upwelling . These oscillations involve temperature changes in ocean water that in turn has an effect on upwelling.