Environmental Problems, Their Causes, and Sustainability 1

The dominant organisms in mangrove forestswamps are trees that can grow in salt water. Thesetrees have extensive roots that extend above the water,where they can obtain oxygen and provide support forthe plant. These nutrient-rich forests are found in shelteredregions along tropical coasts (Figure 7-2).Because ocean waves do not reach these saltwaterecosystems, they collect mud and anaerobic sediment.The constant water movement in estuaries andtheir associated coastal wetlands stirs up the nutrientrichsilt, making it available to producers. Thesesystems filter toxic pollutants, excess plant nutrients,sediments, and other pollutants. They reduce stormdamage by absorbing waves and storing excess waterproduced by storms. And they provide food, habitats,and nursery sites for a variety of aquatic species.Bad news. We are degrading or destroying some ofthe ecological services that these important ecosystemsprovide at no cost. Researchers estimate thatmore than a third of the world’s mangrove forestshave been destroyed—mostly for developing aquacultureshrimp farms, growing crops, and coastal developmentprojects.What Niches Do Rocky and Sandy ShoresProvide? Hold On, Dig In, or Hang Outin a ShellOrganisms in coastal areas experiencing daily low andhigh tides have evolved a number of ways to surviveunder harsh and changing conditions.The area of shoreline between low and high tides iscalled the intertidal zone. This is not an easy place tolive. Its organisms must be able to avoid being sweptaway or crushed by waves, and avoid or cope with beingimmersed during high tides and left high and dry(and much hotter) at low tides. They must also survivechanging levels of salinity when heavy rains dilute saltwater. To deal with such stresses, most intertidal organismshold on to something, dig in, or hide in protectiveshells.Some coasts have steep rocky shores pounded bywaves. The numerous pools and other niches in the intertidalzone of rocky shores contain a great variety ofspecies with different niches as shown in the top partof Figure 7-9 (p. 134).Other coasts have gently sloping barrier beaches, orsandy shores, with niches for different marine organismsas shown in the bottom portion of Figure 7-9.Most of them are hidden from view and survive byburrowing, digging, and tunneling in the sand. Thesesandy beaches and their adjoining coastal wetlandsare also home to a variety of shorebirds that feed inspecialized niches on crustaceans, insects, and otherorganisms (Figure 5-5, p. 92).What Are Barrier Islands? Natural Protectorsof the ShoreNarrow islands off some shores help protect coastalzones from storm waves, but developing these islandsreduces this natural protection and makes them riskyplaces to live.Barrier islands are low, narrow, sandy islands that formoffshore from a coastline. Most run parallel to the shore.They are found along some coasts such as most of NorthAmerica’s Atlantic and Gulf coasts. These islands helpprotect the mainland, estuaries, and coastal wetlandsfrom the onslaught of approaching storm waves.These beautiful but very limited pieces of real estateare prime targets for real estate development. Almostone-fourth of the area of barrier islands in theUnited States has been developed.Living on these islands can be risky. Sooner orlater, many of the structures humans build on lowlyingbarrier islands (Figure 7-10, p. 135), such asAtlantic City, New Jersey, and Miami Beach, Florida,are damaged or destroyed by flooding, severe beacherosion, or major storms (including hurricanes).Their low-lying beaches are constantly shifting,with gentle waves building them up and storms flatteningand eroding them. Currents running parallel tothe beaches constantly take sand from one area anddeposit it in another. Some beach communities spendlots of money to replace the eroded sand. But sooner orlater nature moves it somewhere else.Figure 7-11 (p. 135) shows that undisturbedbeaches on typical barrier islands have one or morerows of natural sand dunes with the sand held in placeby the roots of grasses. These dunes serve as the firstline of defense against the ravages of the sea at no cost.If we left it that way and built behind the second set ofdunes, these beaches would be safer places for peopleand many of the populations of natural organisms thatlive there. Mainland coastal cities, beaches, and undisturbedsalt marshes and estuaries behind these protectiveislands would also be safer from damage.But this real estate is so scarce and valuable thatdevelopers want to cover it with buildings and roads.In doing this, they are rarely required to take into accountthe storm protection and other free ecologicalservices the protective dunes provide. Thus the firstthing most coastal developers do is to remove the protectivedunes or build behind the first set of dunes.This means that large storms can flood and even sweepaway seaside buildings and severely erode the sandybeaches. Then we call these human-influenced eventsnatural disasters.Governments often provide owners with fairlycheap property insurance, funds for replenishingeroded sand, and grants and low-cost loans to rebuildafter damaging storms. This makes it less financiallyhttp://biology.brookscole.com/miller14133