Search

Increasing marine vessel traffic, and oil and gas exploration and development throughout the North Pacific basin brings increasing risks of oil spills. Recognizing the serious challenges presented to response authorities, this Special Issue was organized by the North Pacific Marine Science Organization to provide an introduction to the current state of scientific understanding regarding the environmental effects of oil spills. Because interactions of spilled oils with biota and their habitats are complex, the most serious environmental damages from these spills are not necessarily those of greatest immediate concern by the public. Our overarching goal for this Special Issue is to provide an efficient introduction to the most important ways that oil spills can harm biota, habitats, and ecosystems through invited, targeted mini-reviews augmented by original research articles. We provide a brief background on the challenges posed by large oil spills to response authorities, summarize findings from the articles published in this Special Issue, and highlight some key research needs.

The ecosystem response to the 1989 spill of oil from the Exxon Valdez into Prince William Sound, Alaska, shows that current practices for assessing ecological risks of oil in the oceans and, by extension, other toxic sources should be changed. Previously, it was assumed that impacts to populations derive almost exclusively from acute mortality. However, in the Alaskan coastal ecosystem, unexpected persistence of toxic subsurface oil and chronic exposures, even at sublethal levels, have continued to affect wildlife. Delayed population reductions and cascades of indirect effects postponed recovery. Development of ecosystem-based toxicology is required to understand and ultimately predict chronic, delayed, and indirect long-term risks and impacts.

Gulf menhaden ( Brevoortia patronus) exhibited unprecedented juvenile recruitment in 2010 during the year of the Deepwater Horizon well blowout, exceeding the prior 39-year mean by more than four standard deviations near the Mississippi River. Abundance of that cohort remained exceptionally high for two subsequent years as recruits moved into older age classes. Such changes in this dominant forage fish population can be most parsimoniously explained as consequences of release from predation. Contact with crude oil induced high mortality of piscivorous seabirds, bottlenose dolphin ( Tursiops truncatus), waders, and other fish-eating marsh birds, all of which are substantial consumers of Gulf menhaden. Diversions of fresh water from the Mississippi River to protect coastal marshes from oiling depressed salinities, impairing access to juvenile Gulf menhaden by aquatic predators that avoid low-salinity estuarine waters. These releases from predation led to an increase of Gulf menhaden biomass in 2011 to 2.4 million t, or more than twice the average biomass of 1.1 million t for the decade prior to 2010. Biomass increases of this magnitude in a major forage fish species suggest additional trophically linked effects at the population-, trophic-level and ecosystem scales, reflecting an heretofore little appreciated indirect effect that may be associated with major oil spills in highly productive marine waters. [ABSTRACT FROM AUTHOR]

Oil stranded by the 1989 Exxon Valdez spill has persisted in subsurface sediments of exposed shores for 16 years. With annualized loss rates declining from ∼68% yr-1 prior to 1992 to ∼4% yr-1 after 2001, weathering processes are retarded in both sediments and residual emulsified oil (‘oil mousse’), and retention of toxic polycyclic aromatic hydrocarbons is prolonged. The n-alkanes, typically very readily oxidized by microbes, instead remain abundant in many stranded emulsified oil samples from the Gulf of Alaska. They are less abundant in Prince William Sound samples, where stranded oil was less viscous. Our results indicate that, at some locations, remaining subsurface oil may persist for decades with little change. [ABSTRACT FROM AUTHOR]

We examined 32 shorelines selected at random in 2003 from shorelines in Herring Bay, Lower Pass, and Bay of Isles in Prince William Sound, Alaska, to examine the vertical distribution of oil remaining from the 1989 Exxon Valdez oil spill and to estimate the probability that sea otters and ducks would encounter oil while foraging there. On each shoreline, sampling was stratified by 1-m tide height intervals and randomly located 0.25 m² sampling quadrats were examined for evidence of surface and subsurface oil. Oil from the T/V Exxon Valdez was found on 14 shorelines, mainly in Herring Bay and Lower Pass, with an estimated 0.43 ha covered by surface oil and 1.52 ha containing subsurface oil. Surface and subsurface oil were most prevalent near the middle of the intertidal and had nearly symmetrical distributions with respect to tide height. Hence, about half the oil is in the biologically rich lower intertidal, where predators may encounter it while disturbing sediments in search of prey. The overall probability of encountering surface or subsurface oil is estimated as 0.0048, which is only slightly greater than our estimated probability of encountering subsurface oil in the lower intertidal of Herring Bay or Lower Pass. These encounter probabilities are sufficient to ensure that sea otters and ducks that routinely excavate sediments while foraging within the intertidal would likely encounter subsurface oil repeatedly during the course of a year. [ABSTRACT FROM AUTHOR]