U.S. Navy Ship Salvage Manual Volume 6 - Oil Spill Response

S0300-A6-MAN-060ing or starvation may result from a contaminated food supply. Most seal populations are harmedmore by disturbance than by oil contamination. Observations have shown that seal pups handledor displaced by cleanup operations show a slower growth and higher mortality rates than undisturbedpups.2-4.10 Birds. Bird mortality from oil contamination is well documented and frequently used toillustrate the ecological impact of an oil spill. Birds that spend much of their time on or in thewater, such as ducks, penguins, auks, pelicans, etc., are the most vulnerable to oiling, but any birdthat nests or feeds in coastal regions may be impacted by oil after it has come ashore.Oil clogs the interstitial spaces of feathers causing them to mat together. The oiled, matted featherslose their insulating value and water repellency. As the feathers absorb water, the bird loosesbuoyancy. The bird must expend more energy than normal to stay afloat, move about and maintainbody temperature. At the same time, the bird may ingest oil and may not be able to find sufficientfood in its oiled environment. Drowning and hypothermia are principal causes of death ofoiled birds.Resident bird populations often leave areas contaminated by oil spills, possibly because of oilfumes and feeding difficulties. The effects of this displacement are not well known, but maycause increased mortality of young birds if the displacement occurs during winter or nesting season.Increased mortality of young birds or abandonment of eggs may result from oil contaminationof active nesting sites. Eggs can be lethally oiled by transfer of oil from the plumage of oiledadults. Minute amounts of oil can significantly reduce hatching success.2-4.11 Wetlands. Coastal and estuarine ecosystems, such as mangrove forests and salt marshes,are highly vulnerable to impact from oil spills in coastal waters. Several natural features of coastaland estuarine wetlands detract from their ability to assimilate spilled oil:• Networks of channels which transport oil deep into the vegetated coastal margin• Low wave energy, resulting in minimal natural dispersion by physical forces• Fine, highly organic, anaerobic sediments which entrap and hold oil for long periodsThe immediate effect of an oil spill in a marsh ecosystem is the destruction of invertebrates andthe above-ground portions of the marsh vegetation. Unless the marsh area is subjected to veryrapid erosion or physical disruption of surface sediments (such as may occur during cleanup operations),the underground rhizome system of the plants is likely to survive the oiling. Recovery ofthe plant community usually begins within one year and vegetative recovery is likely within threeto ten years. However, oily components will probably persist in fine-grained sediment for tenyears or more. Disruption by erosion or removal of sediments and the rhizome system by mechanicalremoval, in contrast, may result in long-term changes in the wetland ecology and prolong therecovery process. Marshes generally recover well from a single oil spillage or successive spillsprovided enough time has elapsed between spills.2-15