Oil and Natural Gas - Energy Policy Analysis: A Conceptual Framework - page 77

rates, and increased susceptibility to disease and other histopathological disorders are examples of
the types of sublethal effects that may occur with exposure to petroleum hydrocarbons (Capuzzo
1987). Early developmental stages of species can be especially vulnerable, and several studies have
demonstrated that oil residuals in beach sediments may have significant toxic effects on fish eggs
and embryos (NRC 2003, 127-129). In addition to the incidence of tumors and other histopatho-
logical disorders, sublethal toxic effects of contaminants in marine organisms include impairment
of physiological processes that may alter the energy available for growth and reproduction and
may include direct genetic damage (Capuzzo 1987; Capuzzo, Moore, and Widdows 1988).
Marine birds and mammals can be affected by oil in the sea through several pathways:
As air-breathing organisms that obtain much or all of their food from beneath the surface of the
sea, marine birds and mammals must frequently pass through the water's surface. When floating
oil is present, they become fouled. Additionally, many species of birds frequent the intertidal
zone while foraging and resting, as do seals, sea lions, sea ducks, shorebirds, and sea otters.
While there, these warm-blooded vertebrates or their food may become coated with oil that has
come ashore. The presence of oil on the feathers of a seabird or the pelage of a marine mammal
can destroy the waterproofing and insulating characteristics of the feathers or fur and lead to
death from hypothermia. Seabirds and marine mammals may be poisoned when they ingest oil
while trying to remove it from their feathers or pelage, or when it adheres to food items. (NRC
2003, 132-133)
Marine mammals such as sea otters that depend on clean fur for insulation are vulnerable to
surface oiling (Geraci and St. Aubin 1990). If seabirds transfer oil from their feathers to the surface
of eggs during incubation, embryos may fail to develop. Oil may also reduce the distribution,
abundance, and availability of prey, indirectly reducing the survival or reproductive success of
marine birds and mammals (NRC 2003, 132-133). Ingestion of oil or oil-contaminated prey by
seabirds may compromise the ability of blood to carry oxygen, an effect that persists long after the
birds appear to have recovered from exposure (Fry and Addiego 1987). These effects on wildlife
may be exacerbated by stress from handling during oil cleaning (Briggs, Yoshida, and Gershwin
1996). A general rule of thumb among researchers is that the body count of birds recovered after
a spill represents about 10 percent of those actually killed by the spill (NRC 2003, 135), but there
is no way to verify this estimate. A variety of significant indirect, chronic, and delayed adverse
responses of various bird populations were chronicled after the Exxon Valdez oil spill of 1979
(136). Affected sea otter populations in Prince William Sound had not recovered from that spill as
recently as 1998 (Dean et al. 2000). Sublethal effects can be identified in marine birds and mam-
mals for many years after the acute effects of an oil spill have passed (NRC 2003, 138).
Effects of oiling on biogenically structured habitats may result from acute damage to coral
reefs, live-bottom habitats, mangrove swamps, salt marshes, oyster reefs, and seagrass and kelp
beds. Even though oil may not persist following a spill, the time required for recovery of damaged
populations of organisms that provide the physical structure of the habitat may be many years (NRC
2003, 141). Mixtures of dispersants and oil are more toxic to coral than oil by itself (Peters et al.
1997). Oil spills are known to cause severe and long-term damage to mangrove and salt marsh
ecosystems (Mille et al. 1998; Duke, Pinzon, and Prada 1997). Oil may persist in marsh sediments
for many years (Teal and Howarth 1984), and vegetation recovery times range from a few weeks
to decades (Hoff 1996). Oiling of mangroves can kill the plants and lead to unstable habitats and
sediment erosion (Garrity, Levings, and Burns 1994), producing long-term ecosystem change and
destroying the value of that habitat for nursery fish. These facts led the National Research Council