especially following oil spills that contaminate highly productive coastal waters.
Waves may disperse oil slicks into the water column, presenting contact and ingestion hazards for fish and suspension-feeding organisms. However, most oils are buoyant and rarely penetrate more than a few tens of meters into the water column and tend to return to the sea surface in calmer seas. Volatile components of oil present inhalation hazards for seabirds, turtles, and marine mammals that may lead to death. Oil driven toward shorelines presents contact or smothering hazards for organisms that inhabit or traverse the intertidal zone, which may lead to ingestion of oil or asphyxiation.
In contrast, oil spills rarely lead to mass mortalities of fish or other organisms that inhabit subsurface waters. This is primarily because most components of oil do not readily dissolve into water, and those components that do dissolve usually are rapidly diluted to concentrations below acute toxicity thresholds. This rapid dilution results from dissolution of oil components from oil slicks that are typically less than 1 millimeter thick, into mixed water column layers that are typically tens of meters or more in thickness, indicating dilution factors on the order of 10,000 or more that are attained relatively rapidly. However, even diluted oil components can lead to a variety of adverse sublethal effects on marine organisms.
In unusual cases, such as the 2010 DWH blowout in the northern Gulf of Mexico, oil may combine with sediment or other organic material and sink to the seafloor, where it accumulates and presents a contact and ingestion hazard to benthic organisms.
The harmful effects of oil may go beyond the effects on an individual organism or species. Exposure to oil can launch a cascade of effects through different trophic levels within an ecosystem. For example, oiling can affect habitat quality, thereby reducing the availability of prey (see Figure 14). Food webs can also be disrupted if predators are