Oil Spills
Oil spills resulting from deliberate or accidental release of oils from ships or following a collision or grounding of vessels are one of the largest threats to reefs (GBRMPA, 2005.).
There are many ways in which the oil can come in contact with the reef after a spill. Floating oil may be deposited onto a reef as it becomes exposed at low tide, droplets of oil may be dispersed in the water column, or droplets adsorbed onto suspended solids in the water column may settle onto the reef (Teal and Howarth, 1984.).
Oiled coral which has been exposed at low tide (NOAA, 2005.).
When the oil comes in contact with the coral it can cause breakdown of the tissue and many other problems. Rinkevich and Loya (1979) for example, found that oil products could induce premature release of gonadal material and larvae, and reduce larval survival. Loya (1975) described that recolonisation of polluted reefs is slow as it disrupts reproduction and recruitment. These are just a few of the many effects it has on them.
The main factors influencing impact and recovery of coral reefs are as follows (IPIECA, 2006):
• The amount and type of oil spilled
• The degree of weathering of the oil prior to contact with corals
• The frequency of the contamination
• The presence of other factors, such as high sedimentation
• Physical factors such as storms, rainfall, currents and low tide
• The clean up operation
• The type of coral
• Seasonal factors such as mass spawning
Oil spills can be cleaned up via the use of chemical dispersants and skimmers. Dispersants are a mixture of surfactants and solvents that causes an oil slick to break into small droplets via dispersion (EHH, 2004.). Dispersants such as Ardrox 6120 have been known to inhibit fertilisation in the coral Acropora tenuis (Harrison, 1994.).
A good example of a successful clean up process using skimmers was in January 2006; when a tug boat collided with a bulk coal carrier on the edge of the Great Barrier Reef (ENS, 2006.). Over 25 metric tons of heavy fuel oil was spilled into the water. Four skimmer vessels were deployed to clean up the mess costing millions of dollars. This however was paid for by the ships owners; because of the international maritime law. Due to this quick clean up process the oil spill was contained before harming the reef.
