Offshore drilling requires the construction of significant onshore infrastructure such as new roads, pipelines, and processing facilities, which are often built on formerly pristine beaches. Thanks in part to drilling operations, Louisiana is losing roughly 24 square miles of coastal wetlands each year, eating away at natural storm barriers and increasing the risks of storm damage, including damage from oil spills. When companies dredged canals, they dumped the soil they removed alongside, creating “spoil levees” that could rise higher than 10 feet and twice as wide. The weight of the spoil on the soft, moist delta caused the adjacent marshes to sink. In locations of intense dredging, spoil levees impounded acres of wetlands. The levees also impede the flow of water and sediments over wetlands during storm tides.If there were 10,000 miles of canals, there were 20,000 miles of levees. Researchers estimate that canals and levees eliminated or covered 8 million acres of wetlands.
Oil has the potential to persist in the environment long after a spill event and has been detected in sediment 30 years after a spill, especially in areas sheltered from weathering processes, such as the subsurface sediments under gravel shorelines, and in some soft substrates. Oil spills may cause shifts in population structure, species abundance and diversity, and distribution. Habitat loss and the loss of prey items also have the potential to affect fish and wildlife populations. Different animal classifications are affected in different ways by oil. Oil can be directly toxic to marine invertebrates or impact them through physical smothering, altering metabolic and feeding rates, and altering shell formation. Fish can be impacted directly through uptake by the gills, ingestion of oil or oiled prey, effects on eggs and larval survival, or changes in the ecosystem that support the fish. Physical contact with oil destroys the insulation value of fur and feathers, causing birds and fur-bearing mammals to die of hypothermia.
Oil causes harm to wildlife through physical contact, ingestion, inhalation and absorption. Floating oil can contaminate plankton, which includes algae, fish eggs, and the larvae of various invertebrates. Fish that feed on these organisms can subsequently become contaminated. Larger animals in the food chain, including bigger fish, birds, terrestrial mammals, and even humans may then consume contaminated organisms.
Initially, oil has the greatest impacts on species that utilize the water surface, such as waterfowl and sea otters, and species that inhabit the nearshore environment. Although oil causes immediate effects throughout the entire spill site, it is the external effects of oil on larger wildlife species that are often immediately apparent. Marine algae and seaweed responds variably to oil, and oil spills may result in die-offs for some species.