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Oil Spills and Corals Don’t Mix

by: Anna Kulow

Like tropical rainforests, coral reefs’ unparalleled biodiversity is of great economic and ecological importance. Among branching elkhorn coral and vibrantly-colored sponges is an ecosystem of macro- and microorganisms cycling nutrients, protecting shorelines, and producing natural products used in medicine. Reefs are crucial aspects of the economy – according to NOAA, reef tourism and recreation totals $9.6 billion dollars globally. However, these benefits are only realized if reefs are healthy. Unfortunately, marine scientists are witnessing a dramatic loss of coral reefs. According to a 2011 report by the World Resources Institute (WRI), 75% of the world’s coral reefs are at risk from local and global stresses. Ten percent of coral reefs have already been damaged beyond repair, and if humans continue with current management practices, WRI projects that 90% of coral reefs will be in danger by 2030, and all of them by 2050.

Elkhorn coral. Credit: NOAA
Elkhorn coral. Credit: NOAA

What is causing the destruction of coral reefs? In short, human activity. The reasons humans adversely affect coral reef health range from the straightforward physical destruction from tourism and trawling to the less understood consequences of warming oceans and ocean acidification resulting from man-made climate change.

Somewhere on that spectrum are the impacts of silent oil spills. Every year 500 million gallons of used petroleum lubricating oil enters the world’s oceans through routine ship maintenance and improper disposal of used oils. The U.S. Coast Guard estimates that sewage treatment plants discharge twice as much oil into coastal waters as do tanker accidents. In addition to hydrocarbons, lubricating oils and sewage contain chemical additives, heavy metals, and nutrients that pollute coastlines and disrupt the normal functioning of organisms and ecosystems.

For decades, marine ecologists have noted that chronic small oil spills into coastal waters pose a greater threat to coral ecosystems than infrequent large tanker spills. Consequences of chronic oil pollution include a complete lack of colonization by reef-building corals in areas chronically polluted by oil; decrease in colony viability; damage to the reproductive system of corals; lower life expectancy of coral larvae, called planulae, and abnormal behavioral responses of planulae and corals. Several studies have shown exposure to chronic low levels of common marine engine fuels and oils cause loss of zooxanthellae, the symbiotic algae living inside coral that provide a coral’s metabolic requirement through photosynthesis, leading to coral death. When coral experience chemical or physical stress, the zooxanthellae eject themselves from the coral, leaving the coral without the vital nutrients necessary to survive.

Coral reef ecosystems not only face threats from oil pollution directly, but indirectly as well. When used oil is collected, roughly 80% is burned as industrial fuel, releasing over 36 million metric tons of CO2 equivalents into the atmosphere each year. CO2 and its equivalents trap heat in Earth’s atmosphere, leading to increases in ocean temperatures globally. According to data published by the National Oceanic and Atmospheric Administration in 2015, sea surface temperatures have increased throughout the 20th century and continue to rise. In the past century, temperatures have risen an average of 0.13 degrees Fahrenheit per decade.

Even the smallest changes in water temperature can have detrimental consequences for coral reefs. When water temperatures warm even by only one degree Celsius, coral eject their symbiotic algae and can no longer meet their nutritional needs. Currently, the Great Barrier Reef is facing one of the most expansive bleaching events in history – only 7% of the reef remains unaffected. Warming ocean temperatures off the coast of Florida have been associated with an increase of white-band disease in elkhorn and staghorn coral. Furthermore, warming oceans can disrupt reproductive cycles for all reef inhabitants. A recent study from the University of Copenhagen noted that warmer waters in the Great Barrier Reef increased the frequency of coral spawning events. Many fish species rely on long-established coral spawning cycles for their own reproduction and a disruption in the cycle could result in a loss in productivity within the entire coral ecosystem.

Oil spill in Gulf of Mexico. Credit: UM Rosenstiel School
Oil spill in Gulf of Mexico. Credit: UM Rosenstiel School

There are alternatives to petroleum-based lubricating oils that show promise for the future of corals and other marine organisms. Companies such as California-based Biosynthetic Technologies are developing plant-based lubricating oils that meet or exceed the performance metrics of petroleum-based oils. In a 2004 study from the Australian Institute of Marine Science, researchers exposed adult coral and coral gametes to various concentrations of vegetable-derived lubricant and corresponding mineral-derived oils. They measured the loss of symbiotic algae as an indicator of toxicity and observed VDLs were significantly less toxic to adult coral than petroleum-based counterparts. In addition to being less toxic, a life cycle assessment of plant-based lubricants indicated that GHG emissions are 67.9-79.1% less than those from comparable mineral-based oils. A collective shift towards bio-based lubricants could slow the annual rise in atmospheric greenhouse gases and associated increases in global temperatures.

Coral reefs are ecologic treasures. They contain more biodiversity than any other ecosystem on the planet. Yet human activities threaten to cause irreversible destruction, creating underwater graveyards only hinting at once-vibrant communities full of incredible creatures. Switching to plant-derived oils, recycling and properly disposing of used oils, and maintaining vehicles and watercraft are steps we can take now to halt this damage and preserve coral reefs.

Anna Kulow is a freelance writer based in Solana Beach, Calif. This article is part of the Silent Oil Spills public awareness campaign.