Effects of Hypoxia, and the Balance between Enrichment, on Coastal Fishes and Fisheries Hypoxia and

A reduct ion in dissolved oxygen concentrat ion is one of the most important direct effects of nutrient over-enrichment of coastal waters on fishes. Because hypoxia can cause nlortality~ reduced growth rates, and altered distributions and behaviors o f fishes, as wel l as changes in the relative importance o f organisms andpathways of carbon f low within f o o d webs, hypoxia and anoxia can lead to large reductions in the abundance, diversity, and harvest of f ishes within af fected waters. Nutr ient enrichment , however, typically increases prey abundance in more highly oxygenated surface waters and beyond the boundaries of the hypoxic zone. Because o f this mosaic of high and low oxygen areas within a system~ not only the actual oxygen concentration of bottom waters, but the spatial arrangement, predictability, and persistence of highly oxygenated~ high productivity habitats~ and the ability of f ishes to locate and use those favorable habitats~ will de termine the ultimate effect of low oxygen on fish populat ions. Negative effects of hypoxia on fish, habitat, and f o o d webs potential ly nlake both fish populatiolts and entire systenls more susceptible to additional anthropogenic and natural s tmssors .