Oil spill in the Gulf of Mexico after the explosion of the Deepwater Horizon oil rig, 2010 © Flickr/NASA Goddard Photo and Video
Oil spills can have devastating impacts on coastal forests and mangroves. Mangroves are highly susceptible to oil exposure and can be affected in two main ways: from the physical effects of oiling and from the toxicological effects of the oil.
The physical effects of oiling (e.g. covering or blocking specialized tissues needed for respiration or salt management) may include either disruption or complete prevention of normal biological processes of exchange with the environment. When oil physically covers plants, animals and birds, they may die from suffocation, starvation, or other physical interference with normal physiological function.
Acute effects of oil (mortality) occur within six months of exposure and usually within a much shorter time frame (a few weeks). Visible signs of mangrove stress, including chlorosis, defoliation and death, often show within the first two weeks of a spill event. The tree may survive for a time only to succumb weeks or months later, or, depending on the severity of the damage, it may recover to produce new leaf growth. Seedlings and saplings, in particular, are susceptible to oil exposure. More subtle responses include branching of pneumatophores (breathing roots), germination failure, decreased canopy cover, increased rate of mutation, and increased sensitivity to other stressors.
Chronic oil impacts on mangroves include altered growth rates and reproductive timing or strategy and can be measured over long time periods, potentially a decade or decades. They may also exhibit morphological adaptations in order to survive the oiling such as the development of branched secondary pneumatophores in mangroves as a response to impairment of normal respiration.
Abiotic disturbances and their influence on forest health
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