Oil spilled from ships or other sources into the marine environment often occurs in close proximity to coastlines, and oil frequently accumulates in coastal habitats. As a consequence, a rich, albeit occasionally controversial, body of literature describes a broad range of effects of spilled oil across several habitats, communities, and species in coastal environments. This statement is not to imply that spilled oil has less of an effect in pelagic marine ecosystems, but rather that marine spills occurring offshore may be less likely to be detected, and associated effects are more difficult to monitor, evaluate, and quantify (Peterson et al., 2012). As a result, we have a much greater awareness of coastal pollution, which speaks to our need to improve our capacities in understanding the ecology of the open oceans. Conservation of coastal ecosystems and assessment of risks associated with oil spills can be facilitated through a better understanding of processes leading to direct and indirect responses of species and systems to oil exposure.
It is also important to recognize that oil spilled from ships represents only ~9% of the nearly 700 000 barrels of petroleum that enter waters of North America annually from anthropogenic sources (NRC, 2003). The immediate effects of large spills can be defined as acute, due to the obvious and dramatic effects that are observed. In contrast, the remaining 625 000 barrels that are released each year can be thought of as chronic non-point pollution, resulting from oil entering the coastal ocean as runoff in a more consistent but much less conspicuous rate. In this chapter, we primarily address the effects of large oil spills that occur near coastlines and consider their potential for both acute and chronic effects on coastal communities. As described below, in some instances, the effects from chronic exposure may meet or exceed the more evident acute effects from large spills. Consequently, although quantifying chronic effects from low exposure rates can be challenging and time-consuming, the results of such efforts provide insights into the understudied effects of chronic non-point oil pollution.