Analysis of Coral Bleaching Overtime

 Analysis of Coral Bleaching Overtime

Coral bleaching has become more widely known throughout the years because of its increasing effect on the health of our oceans. The article Global Analysis of Coral Bleaching Over the Past Two Decades published in the Nature Communications journal covers the history of coral bleaching and projections for the future. 

Stressful temperature changes associated with climate change have been known to cause coral bleaching and death. Bleaching patterns vary spatially and temporally, so this study examined coral in 3351 sites at 81 diff countries from 1998-2017 with a variety of environmental variables, including El Nino (a weather event that causes parts of the ocean to be warmer than usual). 

According to the data, bleaching was more common in areas with high intensity and frequency of temperature changes, and it was less common in areas with more sea surface temperature inconsistencies. Bleaching was also more common at tropical, mid-latitude sites, even though the thermal stress seen here is similar at equatorial sites. This suggests that genotypes more susceptible to bleaching have been weeded out at equatorial sites, or it suggests that there has been adaptation causing current corals to have a lower susceptibility to bleaching at equatorial sites.  

Hypotheses of why low latitudinal tropic corals bleached less: 

1. Geographic difference in species composition

2. More genotype diversity (include genotypes with lower levels of stress tolerance)

3. Some corals have already adapted to higher temperatures because of the higher temperatures at lower latitudes

It has been shown that there is a global correlation between lower bleaching rates and waters having a higher STT on a week by week scale. A small daily temperature range shows increased probability of bleaching. It is possible that having a greater STT reduced bleaching because corals that experience these fluctuations at local levels daily, weekly, or seasonally could have corals and coral symbionts more resistant to STT extremes. This could be because of acclimation and/or adaptation. 

This study shows how coral bleaching and its prevalence has changed over time. The best way to prevent bleaching is to reduce our carbon emissions and slow down climate change. Water has a high heat capacity, and while this means that it takes a long time for it to heat up, it also means it will take a long time for our oceans to cool back down. Rates of coral bleaching will only increase with time and at best stay stagnant if nothing is done to reverse climate change. 

This study also shows how different corals have already been affected by temperature changes and the resulting bleaching. If bleaching continues, life in our oceans will continue to change as the diversity of corals is essential to many organisms in the ocean. While some corals can survive these extreme temperatures, coral diversity is important for supporting biodiversity in our oceans. 

While there has been lots of research already conducted on coral bleaching, we still have so much to learn on what and why corals bleach and what we can do to prevent this to protect our oceans for the future.

                               Healthy Coral:                                 Bleached Coral:        

Frostenson, S., 2017. Experts: The Great Barrier Reef Cannot be Saved. [online] Vox. Available at: <https://www.vox.com/science-and-health/2017/4/18/15272634/catastrophic-coral-bleaching-great-barrier-reef-map> Accessed 7 October 2022

Works Cited:

Sully, S., Burkepile, D.E., Donovan, M.K. et al. A global analysis of coral bleaching over the past two decades. Nat Commun 10, 1264 (2019). https://doi.org/10.1038/s41467-019-09238-2