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Destruction of Coral reef

Climate change has affected the tropical reef ecosystem, and the people who depend on them dramatically (Hughes et al, 2017). Since the early 1980s, rising sea temperature has caused miraculous mass bleaching of corals (Hughes et al, 2017). Mass bleaching start off when marine water is too warm and disturbs the symbiotic relationship between corals and algal guest, causing coral to loose color (Hughes et al, 2017). Although, bleached coral is not dead and can survive the bleaching period, but when the corals experience more stress, they can expire (Hughes et al, 2017). The three big bleaching episodes that occur in the Great Barrier Reef, Australia were in 1998, 2002 and 2016. The initial bleaching of coral in 1998 happened mainly in central and southern regions (Hughes et al, 2017). In 2002, bleaching was more extensive and affected the reef in the central region, which was unaffected in 1998 (Hughes et al, 2017). In 2016, bleaching was more extensive and harsh than 1998 & 2002 (Hughes et al, 2017). In 2016, the bleaching of coral was four times higher than the one in 1998 & 2002 (Hughes et al, 2017). The regular increasing of extensive bleaching enclose the hidden information about the climate change that how climate warming has kick started bleaching episode and conversely demise of the coral reef. Coral reef bleaching exhibits a fractional impact of global warming. Other massive impacts of global warming on coral reef include CO2 and natural phenomena.

Rising CO2 and El Nino impact on coral reef.

Just like coral bleaching, rising CO2 level in the atmosphere creates risk for the coral reef in the ocean. Ocean is the second biggest reservoir of carbon dioxide and considerable uptake in CO2 can create major complication in the ocean. Prior to industrial revolution, atmospheric CO2 has risen from ~280ppm to ~387ppm today.  Mortality of coral reef starts when atmospheric C02 level exceeds ~320ppm (Veron J et al, 2009). When CO2 level exceed ~320ppm, water becomes warm causing destruction in a form of El nino and cyclone world wide (Veron J et al, 2017). Today's CO2 level is ~387ppm which is allowing a lag time of 10 years for sea temperature respond, most of the coral reef's are on the verge of declining tremendously (Veron J et al, 2017). Increase in CO2 level drastically will force the return of El Nino events in every 4 to 7 years (Veron J et al, 2017). Increase in CO2 will also bring down the quality of ocean water and hence will become less suitable for the species living in the ocean (Veron J et al, 2017). If CO2 level made it to ~450ppm in the ocean (predicted by 2030-2040), coral reef will rapidly decline worldwide from the different sources of mass bleaching and ocean acidification (Veron J et al, 2017). If the CO2 level further accelerate and reaches ~600ppm, the reef will destroyed the geologic structure and the marine organism population will be restricted to refuge only (Veron J et al, 2017). Overall increasing CO2 will severely impact the coral reef in the upcoming decades and the coral will be in increasing acidification stress (Veron J et al, 2017)

One more concern that arises from increase in CO2 is the saturation of aragonite in ocean water. Aragonite is a calcium carbonate form naturally in all mollusk shell (Veron J et al, 2017). The saturation level of aragonite in the ocean has fallen greatly in the last century (from 4.6 to 4.0) and will continue to fall if CO2 rises further (Veron J et al, 2017). Increase in CO2 and warm water give rise to natural phenomena such as cyclone, hurricanes and typhoon, which can wipe of corals in no time. Knowing the correlation between cyclone and global warming will further enhance are learning about coral reef. 

Scientist believe that the rapid decrease in the population of coral (About 97%) drive from the unexpected El Nino events (Claar et al, 2018). El Nino drives mainly because of increases sea surface temperature (Claar et al, 2018) and short term El Nino and La Nina events have caused mass bleaching of coral in tropical pacific region (Claar et al, 2018). Notable examples include 95% of coral destruction in some location in Eastern Pacific and almost 100% mortality in some sites by Indonesia (Claar et al, 2018). Understanding how El Nino and La Nino events impacts the coral is essential for developing planning for coral reef conservation, which is important for biodiversity of the animals living by the coral, but also for the human beings in particular (Claar et al, 2018).