activities, spills and accidental losses of cargoes, and through atmospheric deposition of particulate materials. Halogenated hydrocarbons (pesticides, herbicides, and plastic compounds such as polychlorinated biphenols [PCBs]), heavy metals, petroleum products (including compounds such as polycyclic aromatic hydrocarbons [PAHs]), fertilizers (nitrogenous and phosphorous compounds), mining wastes, fuel ash, and radioactive materials are among the primary marine pollutants (Hughes and Goodall, 1992). An increased incidence of tumors and diseases in fish is one of the many consequences of contamination of estuarine and coastal environments by this broad range of pollutants (Myers et al., 1991; McCain et al., 1992; Vethaak and Rheinaldt, 1992).

Coastal eutrophication—nutrient enrichment from agricultural, sewage, and urban sources—has had severe impacts in shallow shelf areas and enclosed estuaries and bays worldwide (Nixon et al., 1986; Mannion, 1992; Turner and Rabalais, 1994). Macroalgal and phytoplankton blooms are frequent results which, in turn, often create conditions of hypoxia (low oxygen concentrations) and anoxia (no oxygen). Extensive invertebrate and fish mortalities may ensue (Norse, 1993). In particular, eutrophication has been linked to a more common occurrence of blooms of toxic algae (Hallegraeff, 1993; Smayda and Shimizu, 1993; Anderson, 1994).

Alterations in Physical Habitat

Coastal zones around the world have undergone significant physical alterations. In many regions large portions of salt marshes have been removed by dredging, filling, and diking to create dry land (Chabreck, 1988). Such activities are manifested today in tropical estuaries through the removal of mangrove communities for shrimp pond aquaculture (Robertson and Alongi, 1992; Norse, 1993). Long stretches of coastline in many regions of the world have been impacted by the emplacement of seawalls, jetties, groins, railroads, and other artificial structures that have altered natural patterns of sedimentation, erosion, and water flow. Mining has directly impacted intertidal and nearshore habitats and is a potential source of stress to the biodiversity of the deep sea. Upland and coastal mining, agriculture, and deforestation have caused extensive land erosion and the subsequent deposition of sediment, at times meters thick, in intertidal and shallow-water systems. In fact, sedimentation has become the major threat to certain coral reefs.

Other coastal habitats have been extensively altered through dredging (e.g., for ship channels) and by commercial dragging of the bottom in nearshore habitats for fish, clams, sea urchins, and other commercial targets (Matishov and Pavlova, 1994). Indeed, trawling and dredging on the seafloor are important indirect effects of fisheries operations. Recent surveys have revealed particularly profound impacts in the Gulf of Maine (Witman and Sebens, 1992; Watling and Langton, 1994) and elsewhere such as the North Sea (de Groot, 1984; see general

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