Environmental Problems, Their Causes, and Sustainability 1

Figure 7-12 Natural capital:some components and interactionsin a coral reef ecosystem.When these organisms die,decomposers break down theirorganic matter into mineralsused by plants. Colored arrowsindicate transfers of matter andenergy between producers,primary consumers (herbivores),secondary (or higher-level) consumers(carnivores), and decomposers.Organisms are notdrawn to scale.Gray reef sharkGreen seaturtleBluetangsSea nettleFairy bassletParrot fishSergeant majorHard coralsAlgaeBrittle starBanded coralshrimpPhytoplanktonSymbioticalgaeConeyZooplanktonBlackcap bassletSpongesMorayeelBacteriaProducer toprimaryconsumerPrimary tosecondaryconsumerSecondary tohigher-levelconsumerAll consumersand producersto decomposersor nations have imposed restrictions on reef fishing orreduced inputs of nutrients and other pollutants, reefshave rebounded.Some 300 coral reefs in 65 countries are protectedas reserves or parks, and another 600 have been recommendedfor protection. But protecting reefs is difficultand expensive, and only half of the countries withcoral reefs have set aside reserves that receive someprotection from human activities.What Biological Zones Are Found in theOpen Sea? Where Is the Light?The open ocean consists of a brightly lit surface layer,a dimly lit middle layer, and a dark bottom zone.The sharp increase in water depth at the edge of thecontinental shelf separates the coastal zone from thevast volume of the ocean called the open sea. Primarilyon the basis of the penetration of sunlight, it isdivided into the three vertical zones shown in Figure7-6.The euphotic zone is the lighted upper zone wherefloating drifting phytoplankton carry out photosynthesis.Nutrient levels are low (except around upwellings),and levels of dissolved oxygen are high. Large, fastswimmingpredatory fish such as swordfish, sharks,and bluefin tuna populate this zone.The bathyal zone is the dimly lit middle zone thatdoes not contain photosynthesizing producers becauseof a lack of sunlight. Various types of zooplankton and136 CHAPTER 7 Aquatic Biodiversity