Air Pollution Stunts Coral Growth


Corals may be found in the oceans, but scientists say they are most sensitive to what exists above the surface.

Corals are living animals in the phylum Cnidaria, and they exist in the oceans as compact colonies. Corals are vital species as they secrete the chemical ‘calcium carbonate’, which builds up to form what we commonly recognize as coral reefs.

Coral reefs are visually stunning. They support a remarkable diversity of species in the oceans by providing irreplaceable food and habitat sources. Estimates suggest that reefs are home to a quarter of all marine species, despite only covering 1% of the Earth’s surface. In addition, they are important for humans as they support local fishing industries, enhance tourism and act as barriers to protect nearby shorelines.

Whilst the importance of reefs has long been recognised, corals are increasingly under threat.  In 2006, estimates suggested that around 20% of reefs had been completely destroyed in recent decades, with a further 20% or more severely degraded. They are vulnerable to ocean acidification resulting from warmer global temperatures, as this bleaches the reef. But disease can also destroy entire reefs once it takes hold. Not surprisingly, human activities are also having negative impacts, the most destructive being trampling and industrial fishing techniques.

Research published in the journal Nature Geoscience suggests that another factor may be contributing to coral decline.

The concentration of aerosols (air particles) in the atmosphere is increasing. Aerosols are composed of soot and sulphates from the burning of fossil fuels. As these build up in the air, they block incoming solar radiation and make clouds more reflective. This reduces the amount of sunlight available for photosynthesis in the corals, slowing down growth. In addition it also reduces the temperature of the ocean water. Both of these factors can slow coral growth.

Scientists looked at coral growth records in the Caribbean from 1880 to 2000, and found that changes in growth coincided with variations in aerosol emissions in this period. For example, the post WWII industrial expansion led to an increase in atmospheric aerosols, and this was followed by a decline in ocean temperatures during the 1960s and a slowing in coral growth. After 1970, clean air legislation reduced aerosol emissions, contributing to a rise in sea temperatures and increases in coral growth and bleaching.

The researchers suggest that these findings have implications for ensuring the future survival of coral reefs, as it may be that regional climate change from aerosol emissions is more influential than global warming as a whole. Geo-engineers will need to take this into account when introducing coral conservation projects.

  1. Kwiatkowski, L. et al. (2013) Caribbean coral growth influenced by anthropogenic aerosol emissions. Nature Geoscience. doi:10.1038/ngeo1780
  2. Reef Resilience

Photo credit: Sam and Ian / / CC BY-NC

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