Addition and redistribution of chemical substances

The most recent review of ocean pollution concluded that most coastal areas arc contaminated, some extensively, but that the open occan is relatively unimpacted (GESAMP 1990). Despite apparent freedom from human impact, even distant oceanic ecosystems have traces of human activities (Flegal et al. 1993); no oceanic system is free from human influence. Pollution has impacted open-ocean systems through chemical discharges, toxic inputs (oil spills, ocean dumping of PCBs, heavy metals, pseudohor-mones), and alteration of nutrient regimes (Tanabe et al. 1984; Young et al. 1985; Tanabe 1988; Cox 1993; Suchanek 1993, 1994). Atmospheric pollution has been detected on the deep-sea floor (La Flamme and Hites 1978; Takada et al. 1994). Plastic products and monofilament "ghost" drift nets are among the more persistent forms of human-caused hazards that kill substantial amounts of oceanic life (Shomura and Godfrey 1990). Oil input into marine systems may be as high as 8.8 x 106 metric tons per year (NRC 1985). This sort of pollution is currently thought to be a coastal phenom enon, but this idea is almost certainly a product of ignorancc. Our knowledge of the "natural" levels of open-ocean water quality is so patchy that almost any change in water quality from anthropogenic causes would go unnoticed. The pervasive nature of chemical pollution suggests that open-ocean organisms and ecosystems are likely to experience the same kinds of disruption as coastal systems, although on a longer time scale, with the exception of acute local impacts from leakage of oil or other contaminants at depth. The biomagnification of toxins up through the food web could lead to significant changes in community structure if the larger apex organisms are negatively affected (Tanabc et al. 1984; Tanabe 1988; Addison 1989). These changes in community structure could have ramifications through changes to the food web, microbial loops, nutrient pools and feedback to the atmosphere.

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