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Ocean Acification and Coral Bleaching

This map shows various projections for coral reefs in Hawaiʻi under two Representitive Concentration Pathways (RCPs), 4.5, which is a moderate reduction scenario (meaning reduced CO2 emissions), and RCP 8.5, which is a business as usual scenario (meaning continued rates of CO2 emissions).  The top panels indicate the year in which coral bleaching will occur annually, mainly due to increasing ocean temperatures.  The reef ecosystem has a difficult time recovering when bleaching events are annual.  The middle panels show the percent reduction in omega aragonite from 2006 until the year annual bleaching occurs.  Omega aragonite is decreasing because of CO2 absorbed by the ocean, in a process known as ocean acidification.  In any omega aragonite saturation state below 4, calcifying organisms, such as coral, have a harder time building their skeletons.  This study has found that by the year annual bleaching occurs, the omega aragonite levels will be under 4 at every reef around the world, including Hawai’i.  The bottom panel takes into account both coral bleaching and ocean acidification to predict the reduction in coral growth rate from 2006 until the year shown in the top panel.  The percent reduction values are somewhat arbitrary without more context, but growth reductions in the range of 6-9% is predicted for Kona.  Projections of bleaching and ocean acidification impacts were obtained from van Hooidonk et al. (2014). 

van Hooidonk, R. J., Maynard, J. A., Manzello, D., & Planes, S. (2014). Opposite latitudinal gradients in projected ocean acidification and bleaching impacts on coral reefs. Global Change Biology, 103–112. doi:10.1111/gcb.12394

 

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