Environmental Problems, Their Causes, and Sustainability 1

G. H. Dermetrohas/T. C. CarmeraFigure 7-10 A developed barrier island: Ocean City, Maryland,host to 8 million visitors a year. Rising sea levels from globalwarming may put this and many other barrier islands under waterby the end of this century.risky to live in such places and hastens the destructionof their protective dune and vegetation systems.Some argue that people who choose to live inthese and other risky places should accept the full costof such risks. They should not expect taxpayers to supplementtheir high property insurance costs or helpthem rebuild houses lost in hurricanes or other naturaldisasters that are expected risks in such areas.What Are Coral Reefs? Aquatic Oasesof BiodiversityCoral reefs are biologically diverse and productiveecosystems that are increasingly stressed by humanactivities.Coral reefs (Figure 7-1 and photo on p. viii) form inclear, warm coastal waters of the tropics and subtropics(Figure 7-2). Coral reefs are ecologically complex interms of the many interactions among the diverseorganisms that live there as shown in Figure 7-12(p. 136).These reefs are vulnerable to damage because theygrow slowly and are disrupted easily. They also thriveonly in clear, warm, and fairly shallow water of constanthigh salinity. Corals can live only in water with atemperature of 18–30°C (64–86°F). Coral bleaching(Figure 7-1, right) can be triggered by an increase ofjust 1°C (1.8°F) above this maximum temperature.The biodiversity of coral reefs can be reduced bynatural disturbances such as severe storms, freshwaterfloods, and invasions of predatory fish. Butthroughout their long geologic history, coral reefshave been able to adapt to such natural environmentalchanges.Today the biggest threats to the survival and biodiversityof many of the world’s coral reefs comefrom sediment runoff and other human activities (Figure7-13, p. 137). Scientists are concerned that thesethreats are occurring so rapidly (over decades) andover such a wide area that many of the world’s coralreef systems may not have enough time to adapt.Good news. There is growing evidence that coralreefs can recover when given a chance. When localitiesOcean Beach Primary Dune Trough Secondary Dune Back Dune Bay orLagoonIntensive recreation,no buildingNo direct passageor buildingLimited No direct passagerecreation or buildingand walkwaysMost suitablefor developmentIntensiverecreationGrasses or shrubsTaller shrubsTaller shrubs and treesBay shoreNo fillingFigure 7-11 Natural capital: primary and secondary dunes on gently sloping sandy beaches help protectland from erosion by the sea. The roots of various grasses that colonize the dunes help hold the sand in place.Ideally, construction is allowed only behind the second strip of dunes, and walkways to the beach are built overthe dunes to keep them intact. This helps preserve barrier beaches and protect buildings from damage bywind, high tides, beach erosion, and flooding from storm surges. Such protection is rare because the shorttermeconomic value of oceanfront land is considered much higher than its long-term ecological value.http://biology.brookscole.com/miller14135