Environmental Problems, Their Causes, and Sustainability 1

BluegillWhite bassBrook troutWhite waterlilyBulrushMuskellungeRainbow troutRainbow darterWater lettuceBowfishWater hyacinthBladderwortLargemouth black bassBlack crappieWhite sturgeonAmerican smeltYellow perchVelvet cichlidWalleyed pikeEelgrassLongnose garDuckweedCommon piranhaCarpChannel catfishEgyptianwhite lotusAfrican lungfishFigure 13-3 Natural capital: freshwater biodiversity. Some inhabitants of freshwater rivers and lakes.examples. First, during the last century we lost abouthalf of the world’s coastal wetlands. This can decreasefish catches in coastal waters because coastal wetlandsand marshes provide essential spawning, feeding, andnursery areas for major commercial fish species.Second, more than one-fourth of the world’s diversecoral reefs have been severely damaged, mostlyby human activities (Figure 7-13, p. 137). By 2050 another70% of the world’s coral reefs may be severelydamaged or eliminated.Third, more than a third of the world’s originalmangrove forest swamps have disappeared, mostlybecause of clearing for coastal development, growingcrops, and aquaculture shrimp farms. Such activitiesthreaten many of the world’s remaining mangrovesystems.Fourth, many bottom habitats are being degradedand destroyed by dredging operations and trawlerboats, which like giant submerged bulldozers draghuge nets weighted down with heavy chains and steelplates over ocean bottoms to harvest bottom fish andshellfish. Each year thousands of trawlers scrape anddisturb an area of ocean bottom equal to the combinedsize of Brazil and India and about 150 times largerthan the area of forests clear-cut each year. Recovery inheavily trawled areas rarely is possible because of re-254 CHAPTER 13 Sustaining Aquatic Biodiversity