term exposure to low concentrations of diesel oil coincided with depuration of aromatic hydrocarbons (Widdows et al., 1987). Donkin et al. (1990) suggested that reductions in scope for growth in M. edulis were related to the accumulation of two- and three-ring aromatic hydrocarbons, as these compounds induced a narcotizing effect on ciliary feeding mechanisms.

Krebs and Burns (1977) observed long-term reductions in recruitment and over-wintering mortality in the fiddler crab Uca pugnax for seven years following the spill of No. 2 fuel oil from the barge Florida. Recovery of crab populations was correlated with the disappearance of naphthalenes and alkylated naphthalenes from contaminated sediments. Similar patterns of long-term changes in recruitment and density of benthic fauna have been observed at sites of other oil spills and in experimental mesocosms (Cabioch et al., 1980; Grassle et al., 1981; Oviatt et al., 1982; Elmgren et al., 1983). Ho et al. (1999) compared the toxicity to the amphipod Ampelisca abdita and chemistry of spilled No. 2 fuel oil in subtidal sediment samples for nine months following the spill from the barge North Cape (Box 4-1). Toxicity to the amphipods decreased as the PAH concentration in sediments decreased over the first six months post-spill (Figure 5-3).

The persistence of PAH in sediments, especially in urban areas with multiple sources of hydrocarbon inputs, is an example of chronic persistence and toxicity beyond the observations made following oil spills (Box 5-3). Meador et al. (1995) reviewed the processes controlling the uptake and persistence of PAH in marine organisms, especially under chronic exposure conditions, highlighting differential mechanisms of uptake, tissue distribution, and elimination. Transfer of contaminants to marine biota and the human consumer and toxicological effects on the ecosystem are dependent on the availability and persistence of these contaminants within benthic environments. The bioaccumulation of

FIGURE 5-3 Amphipod mortality and PAH concentrations in sediments after the North Cape oil spill off Cape Cod, Massachusetts, January 19, 1996 (modified from Ho et al., 1999, Marine Pollution Bulletin).

lipophilic organic contaminants is influenced by chemical factors such as solubility and particle adsorption-desorption kinetics of specific compounds and biological factors such as the transfer of compounds through food chains, the amount of body lipid in exposed organisms, and metabolic transformations. The incidence of tumors and other histopathological disorders in bottom-dwelling fish and shellfish from contaminated coastal areas has suggested a possible link between levels of lipophilic organic contaminants (such as PAH) and the increased incidence of histopathological conditions (Neff and Haensly, 1982; Berthou et al., 1987; Varanasi et al., 1987; Gardner and Pruell, 1988; Moore et al, 1994; McDowell and Shea, 1997).

In addition to possible histopathological damage, sublethal toxic effects of contaminants in marine organisms include impairment of physiological processes that may alter the energy available for growth and reproduction and other effects on reproductive and developmental processes including direct genetic damage (Capuzzo, 1987; Capuzzo et al., 1988). Chronic exposure to chemical contaminants can result in alterations in reproductive and developmental potential of populations of marine organisms, resulting in possible changes in population structure and dynamics. It is difficult to ascertain, however, the relationship between chronic responses of organisms to contaminants and large-scale alterations in the functioning of marine ecosystems or the sustainable yield of harvestable species. Cairns (1983) argued that our ability to detect toxic effects at higher levels of biological organization is limited by the lack of reliable predictive tests at population, community, and ecosystem levels. Much research effort is needed in these areas before environmental hazards as a result of contaminant inputs can be addressed adequately. Koojiman and Metz (1984) suggested that the sublethal effects of contaminant exposure should be interpreted in light of the survival probabilities and reproductive success of populations, thus bridging the gap between individual and population responses. Although a wide range of sublethal stress indices have been proposed for evaluation of chronic responses of organisms to contaminants, few have been linked to the survival potential of the individual organism or the reproductive potential of the population. Rice et al. (2001) reviewed studies on the long-term effects of the Exxon Valdez oil spill on pink salmon, specifically addressing differential effects of low concentrations of oil on specific life history stages. Their results illustrate the complexity of assessing population-level impacts from persistent hydrocarbon residues, even at very low concentrations.

Putative damage to pink salmon as a result of the Exxon Valdez oil spill has been controversial (e.g., Rice et al., 2001). Much of this controversy has focused on the potential damage to embryos incubating in the mouths of streams that were oiled. The potential damage to resident fish embryos in these oiled redds may be long lasting and serious. For example, contrasts between oiled and unoiled streams around

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