Environmental Problems, Their Causes, and Sustainability 1

smaller fish, many of which migrate to the surface atnight to feed, populate this zone.The lowest zone, called the abyssal zone, is darkand very cold and has little dissolved oxygen. However,there are enough nutrients on the ocean floor tosupport about 98% of the species living in the ocean.Most organisms of the deep waters and oceanfloor get their food from showers of dead and decayingorganisms (detritus) drifting down from upper lightedlevels of the ocean. Some of these organisms, includingmany types of worms, are deposit feeders, which takemud into their guts and extract nutrients from it.Others such as oysters, clams, and sponges are filterfeeders, which pass water through or over their bodiesand extract nutrients from it. On parts of the dark,deep ocean floor near hydrothermal vents, scientistshave found communities of organisms where specializedbacteria use chemosynthesis to produce their ownfood and food for other organisms feeding on them.Average primary productivity and NPP per unit ofarea are quite low in the open sea except at an occasionalequatorial upwelling, where currents bring upnutrients from the ocean bottom. However, because theopen sea covers so much of the earth’s surface, it makesthe largest contribution to the earth’s overall NPP.Currently, about 40% of the world’s populationand more than half of the U.S. population live alongNatural Capital DegradationMarine EcosystemsHalf of coastal wetlands lost toagriculture and urbandevelopmentOver one-third of mangroveforests lost since 1980 toagriculture, development, andaquaculture shrimp farmsAbout 10% of world’s beacheseroding because of coastaldevelopment and rising sea levelOcean bottom habitats degradedby dredging and trawler fishingboatsOver 25% of coral reefs severelydamaged and 11% have beendestroyedFigure 7-14 Natural capital degradation: major humanimpacts on the world’s marine systems.Natural Capital DegradationOcean warmingSoil erosionCoral ReefsAlgae growth from fertilizer runoffMangrove destructionCoral reef bleachingRising sea levelsIncreased UV exposure from ozonedepletionUsing cyanide and dynamite toharvest coral reef fishCoral removal for building material,aquariums, and jeweleryDamage from anchors, ships, andtourist diversFigure 7-13 Natural capital degradation: major threats tocoral reefs.coasts or within 100 kilometers (62 miles) of a coast.Some 13 of the world’s 19 megacities with populationsof 10 million or more people are in coastal zones. By2030, at least 6.3 billion people—equal to the world’sentire population in 2003—are expected to live in ornear coastal zones. Figure 7-14 lists major human impactson marine systems. Explain how your lifestylecan contribute directly or indirectly to these impacts.7-3 FRESHWATER LIFE ZONESWhat Are Freshwater Life Zones? Lakes,Wetlands, RiversFreshwater ecosystems provide important ecologicaland economic services even though they cover lessthan 1% of the earth’s surface.Freshwater life zones occur where water with a dissolvedsalt concentration of less than 1% by volume accumulateson or flows through the surfaces of terrestrialbiomes. Examples are standing (lentic) bodies offreshwater such as lakes, ponds, and inland wetlandsand flowing (lotic) systems such as streams and rivers.Although freshwater systems cover less than 1% of theearth’s surface, they provide a number of importantecological and economic services (Figure 7-15, p. 138).http://biology.brookscole.com/miller14137