suggests potential changes in the size and taxonomic structure of the phytoplankton assemblage (Karentz et al., 1991).

The burning of fossil fuels and global agricultural practices have increased the amount of carbon dioxide, methane, and other gases in the atmosphere—such gases trap the heat radiating from the Earth, creating a "greenhouse effect." Continued increases in these gases have a strong potential to lead to global warming, and many scientists think that such warming has begun. A warming Earth could affect the sea, from the most inland marshes to the deepest oceans, in predicted ways that range from sea-level rise to modified patterns of rainfall and oceanic circulation (which, in turn, would affect nutrient supply and distribution). Increased sea water temperatures may alter the abundance, distribution, and reproduction of many coastal species (Ray et al., 1992), and may make northern regions more susceptible to invasions by warm temperate and subtropical species (Chapman, 1988).

As with all other environmental perturbations, there exists the potential for synergisms and cascading effects of global climate change that have not yet been considered, and which may interact with the other stresses reviewed here.



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