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FUTURE DIRECTIONS IN OCEAN SCIENCES 101 



glaciers, the volume of fresh water that enters polar waters (e.g., 

 the Gulf of Alaska) is likely to increase substantially. The input 

 of fresh water can be critical to coastal currents, as seen by the 

 effects of the Mississippi and St. Lawrence rivers. Changes in 

 precipitation (temporal and spatial) and the amount of ice melt 

 could shift the direction and change the magnitude of coastal 

 currents. Such physical changes will affect fish populations by 

 affecting transport of eggs and larvae. 



The effects of El Nino events on eastern boundary current 

 ecosystems in the Pacific Ocean could serve as a model of the 

 possible effects of global warming (McGowan, 1990) in terms of 

 decreased primary and secondary production. In addition, an in- 

 creased temperature differential between land and ocean could 

 enhance coastal winds and hence wind-induced transport of sur- 

 face water away from the shore, reducing the reproductive success 

 of species that spawn offshore but rely on coastal habitats later in 

 their life cycles. Stronger winds would also increase turbulence 

 in the surface mixed layer, dispersing patches of planktonic food, 

 and thereby making the food less available for fish. 



The third example involves the impacts of a changing sea level. 

 If sea level rises at a rate of 1 to 3 millimeters per year over the 

 coming 50 to 100 years, profound impacts on nearshore habitats 

 would result. In areas with broad, flat coastal plains, the width of 

 the inner continental shelf may be expected to increase greatly. 

 This change would wipe out many coastal habitats. In addition, 

 distribution of the wave energy over a wider continental shelf 

 may substantially modify the transport of planktonic organisms 

 to shore, affecting the success of larval recruitment and the tran- 

 sition of organisms from larval to juvenile stages. 



Other Anthropogenic Influences 



Other human-induced environmental changes also affect ma- 

 rine populations, although they vary regionally and their extent is 

 disputed. For example, McGowan (1990) reported no detectable 

 change of pelagic species or of ecosystem structure in the Califor- 

 nia Current ecosystem despite extensive harvesting (fishing) of 

 top predators and vastly increased inputs of pollutants. In con- 

 trast, the Baltic Sea ecosystem has changed significantly in the 

 past 50 years in response to eutrophication (Kullenberg, 1986). 



The incidence of unusual, and sometimes harmful, phytoplankton 

 blooms is increasing in coastal waters around the world. The 

 evidence is particularly compelling in European and Japanese wa- 



