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11.2 ECOSYSTEM RESPONSE 



The response of coastal ecosystems to rising sea level can be divided 

 into two components: 1) a vertical growth component, and 2) a horizontal 

 growth component. As sea level rises, an ecosystem capable of growing 

 vertically may stay in the same location. As marine conditions move 

 inland, landward horizontal movement is expected. Under some conditions, 

 seaward expansion of certain coastal systems may occur. For example, 

 intertidal ecosystems that are effective sediment traps, such as salt 

 marshes (Meade, 1982), may not only grow vertically, but may also expand 

 seaward if a large increase in suspended sediment accompanies rising sea 

 level (Frey and Basan, 1985). 



Availability of light is a major determinant of the productivity of 

 plankton and submerged coastal ecosystems, such as coral reefs, seagrasses, 

 and mudflats . As sea level rises , open water and submerged benthic 

 communities may not be as productive as they are today in relatively 

 Clearwater coastal zones. Increases in tidal range and wave energy may 

 cause an increase in turbidity from suspended sediments. Increased 

 turbidity will reduce the growth rate of light- limited seagrasses (Orth and 

 Moore, 1984; Keesecker, 1986). Intertidal marsh plants, however, may grow 

 better as a result of greater energy subsidies from greater water movement. 



The aerial extent of the intertidal zone depends on coastal topography 

 and tidal range. If land rises just inland of the present shoreline, the 

 aerial extent of the intertidal zone will be greatly reduced, unless tidal 

 range increases to compensate. Old shorelines occur just inland of the 

 existing shoreline along much of Florida's coast, for example (MacNeil, 

 1950). 



The organisms that occupy the four general types of coastal habitat 

 (open water, submerged bottom, intertidal zone, and supratidal zone) differ 

 depending on average conditions of salinity, water level, light, 

 temperature, dissolved oxygen, waves, and current (Remane and Schlieper, 

 1971) . Gradients of these factors intersect in coastal zones to give a 

 wide variety of microhabitats . Rising sea level should reposition these 

 gradients (Browder and Moore, 1981). 



At any one location, a succession of ecosystems should co-occur with 

 the changes caused by rising sea level. These changes would depend on the 



