Part 7: How toxic is oil to coral?

Oil can kill corals, depending on species, life stage, and exposure. Branching corals, for example, are more sensitive to oil impacts than are massive or plate-like corals. The time of year when a spill occurs is critical, because coral reproduction and early life stages are particularly sensitive to oil.

How corals are exposed to oil also bears directly on how serious the impact will be. There are three primary modes of exposure for coral reefs in oil spills:

• Direct oil contact is possible when surface oil is deposited on intertidal corals.
  
• Oil entering the water column (if rough seas and a lighter, more soluble product are involved) can expose corals to harmful oil constituents.
  
• Subsurface oiling can occur when heavy oils weather, or mix with sediment material, and increase in density to the point where they actually sink. When this occurs, the potential for coral smothering is greatly increased.

Longer exposure to lower levels of oil may kill corals, as well as shorter exposure to higher concentrations. Chronic oil toxicity impedes coral reproduction, growth, behavior, and development. In addition, fish and invertebrates that live in and use the reef may also be impacted by oil.

For more information

Oil Spills in Coral Reefs: Planning and Response Considerations For more information about oil toxicity to corals, check Chapter 3 of this 2001 report, which summarizes relevant research for spill response decisionmakers.