Concentration

Mass Coral Bleaching in Tropical Regions

Summary:

Coral bleaching has been receiving more attention since the first large spike of bleaching in 1997-98 (Brown, 1997). This event alone caused 90% coral mortality to 16% of the world’s reefs (Berkelmans, 1999). This large bleaching gained global attention and the causes for coral bleaching have been continually researched. Coral bleaching not only kills the coral but also affects the biodiversity in regions that heavily rely on large coral cover (Marshall et. al, 2006). As this issue has continued to worsen, the environmental effects have caused great concern. The bleaching severely affects the economies in tropical regions who rely on these large coral reefs for fisheries and tourism (Anthony, 2016). The main factors that have been found to affect coral bleaching is ocean acidification and rising ocean temperatures (Hoegh-Guldberg et al, 2007). This concentration seeks look at the two main causes of coral bleaching and look at current solutions being put in place and possible new solutions that can help mitigate coral bleaching.

To understand what causes coral bleaching, it’s important to first look at what is happening when coral bleaching occurs. Coral has a symbiotic relationship with Zooxanthellae, which is the main algae that lives in corals tissue, and it provided 90% of its energy requirements (Wooldridge, 2013). The coral gives the algae a protected environment as well as the compounds they need to photosynthesize. The algae provides food, energy and the vibrant pigmentation that coral often has (Marshall et. al, 2006). When the algae is not able to photosynthesize, the coral dies and therefore appears bleached as the algae and coral no longer have their symbiotic relationship. Once bleached the coral isn’t fully dead, it has the potential to regenerate. But, the time scale of bleaching is days to a week, whereas coral regeneration is weeks to months.

The causes of this bleaching have been studied in tropical regions all over the world. The first main cause of coral bleaching is ocean acidification (Anthony, 2016). Ocean acidification occurs because the ocean absorbs 26% of our CO2 emissions which have increased over the past 10 years. As more CO2 is absorbed into the ocean, the COS reacts with water and creates carbonic acid therefore raising the acidity of our ocean (Marshall et. al, 2006). Mainly, ocean acidification affects the calcium carbonate produced by dominant reef calcifiers (Pandolfi et. al, 2017). A study done at the University of Queensland, where they manipulated CO2 levels to stimulate the 3 projections of CO2 released by the Intergovernmental Panel on Climate Change, showed that CO2 is a large cause of coral bleaching as it erodes and effects their calcium structures (Anthony et. al, 2008). The rapidity of our growing CO2 emissions greatly affects the coral, as the rate at which change is occurring is critical to coral and ecosystem adaptation, and it is likely these projected changes by IPCC will exceed their capacity to adapt (Hoegh-Guldberg et. al, 2007). The other prominent cause of coral bleaching is rising ocean temperatures (Houghton, 2015). As ocean temperatures rise, the coral becomes stressed which causes sped up photosynthesis in the algae causing a buildup of oxygen free radicals which makes the coral eject the algae. Rising ocean temperatures was the leading cause of coral bleaching until ocean acidification became a more prominent overall issue, leading to further researched and tests. Ocean acidification coupled with rising ocean temperatures is one of the main causes of coral bleaching (Pandolfi et. al, 2017).

As more research is done on different coral reefs around the world, scientists, reef managers and policy makers are trying to find sustainable solutions to coral bleaching. Reaser et. al talks about one solution that is popular today, “[the] use of existing policy frameworks to implement the multiple conservation measures outlines in international coral reef initiatives…and develop and implement comprehensive local-to-national scale integrated marine and coastal area management plans” (Reaser, 2000). This type of solution, which tries to mix global and location solutions, seems good on paper but hard to actually put in place. Current research addresses the varying degree of coral reef tolerance to stressful impacts. More resilient reefs could suggest solutions that might apply more broadly. Another possible solution to be looked into is effective management regimes in local areas, as reefs tend to vary from place to place. It’s difficult to give a large, overarching solution to coral bleaching because each reef is different, and as of now they tend to dish out grand solutions that might only work for some reefs. While cutting our greenhouse gas emissions is imperative, there are other potential solutions to this issue. Further solutions can be found to potentially mitigate coral bleaching reef to reef.

 

Questions:

Descriptive: Given current trends in tropical ocean temperature and pH, where and how frequently do we expect coral bleaching in the future?

What might be major surprises and factors of coral bleaching in the future?

Explanatory: As ocean acidification affects calcification and rising temperatures affect the photosynthesis of coral, how do these two factors affect coral reef in different tropical locations?

As more causes for coral bleaching are being researched (such as the effect of sunscreen on coral bleaching), are creating solutions to these currently smaller issues effective at mitigating coral bleaching?

Evaluative: How does coral bleaching directly affect local coastal communities and their economies?

Does coral bleaching negatively affect coastal communities enough, compared to other issues, so they want to find solutions?

Does coral bleaching affect the global community enough so that people will feel the need to make changes in order to mitigate coral bleaching?

What marine species are directly affected by coral bleaching, and which species are more resilient?

Instrumental: How can human needs for coral reefs help push for more protective and aggressive initiatives?

How can further research on how different coral species respond to rising temperatures and ocean acidification help produce further solutions for coral bleaching?

How reliable of a solution is looking to the global community to help mitigate our greenhouse gas emissions in order to reduce coral bleaching?

Sources:

Sources:

Anthony, K. R. N., D. I. Kline, G. Diaz-Pulido, S. Dove, and O. Hoegh-Guldberg. “Ocean Acidification Causes Bleaching and Productivity Loss in Coral Reef Builders.” Proceedings of the National Academy of Sciences 105, no. 45 (November 11, 2008): 17442–46. https://doi.org/10.1073/pnas.0804478105.

Anthony, Kenneth R.N. “Coral Reefs Under Climate Change and Ocean Acidification: Challenges and Opportunities for Management and Policy.” Annual Review of Environment and Resources 41, no. 1 (2016): 59–81. https://doi.org/10.1146/annurev-environ-110615-085610.

Berkelmans, R, and J K Oliver. “Large-Scale Bleaching of Corals on the Great Barrier Reef,” n.d., 6. (1999).

Brown, Barbara E. “Coral bleaching: causes and consequences.” Coral reefs 16, no. 1 (1997): S129-S138.

Hoegh-Guldberg, O., P. J. Mumby, A. J. Hooten, R. S. Steneck, P. Greenfield, E. Gomez, C. D. Harvell, et al. “Coral Reefs Under Rapid Climate Change and Ocean Acidification.” Science 318, no. 5857 (December 14, 2007): 1737–42. https://doi.org/10.1126/science.1152509.

Houghton, John T. “Global Warming and Climate Change.” Global Warming 5 (2015): 1-9. doi:10.1017/cbo9781139164252.003.

Marshall, Paul, Great barrier reef marine park authority, Heidi Schuttenberg, Jordan West, and Union mondiale pour la nature. A Reef Manager’s Guide to Coral Bleaching. Townsville (Australia): Great Barrier Reef Marine Park Authority, 2006.

Pandolfi, John M., Sean R. Connolly, Dustin J. Marshall, and Anne L. Cohen. “Projecting coral reef futures under global warming and ocean acidification.” science 333, no. 6041 (2011): 418-422.

Reaser, Jamie K., Rafe Pomerance, and Peter O. Thomas. “Coral bleaching and global climate change: scientific findings and policy recommendations.” Conservation Biology 14, no. 5 (2000): 1500-1511.

Wooldridge, Scott A. “Breakdown of the coral-algae symbiosis: towards formalising a linkage between warm-water bleaching thresholds and the growth rate of the intracellular zooxanthellae.” Biogeosciences 10, no. 3 (2013): 1647-1658.