Amongst all the covid-19 reports and discussions, you might have missed that the Great Barrier Reef had experienced its third mass coral bleaching event in only 5 years. Preliminary findings indicate variable high bleaching across the Reef, with some offshore areas without any bleaching. The Great Barrier Reef Marine Park Authority conducted aerial surveys of 1,036 reefs to measure the extent and severity of the bleaching event. This concluded on 27 March 2020. A team at The Australian Research Council Centre of Excellence for Coral Reef Studies at James Cook University will undertake the analysis of the aerial imagery and survey footage collected to produce a report with the findings. Areas of mixed impact have had widespread and severe bleaching for the first time and areas that have been bleached in 2016, 2017 and 2020.
Once a full analysis is conducted, Oceans 2 Earth Volunteers will be sure to bring you all the updates and results to keep our readers informed about the health status of this World Heritage Site. In the meantime be sure to check out this marine conservation international volunteering opportunity, Oceans 2 Earth Volunteers Great Barrier Reef Marine Conservation project to see how you can have a direct impact while working as an in-water volunteer researcher on the Reef itself.
In last months’ edition of Marine Conservation Updates, we dove into the process of how corals are bleached, however, do you know what causes this bleaching of the corals and what some of the other threats to coral reefs are?
This week we are going to learn about the major stressors that threaten countless coral reefs around the world.
Climate Change
One of the biggest stressors to corals are increasing sea temperatures as a result of climate change. As we have just seen on the Great Barrier Reef in February/March 2020, corals cannot withstand the severe and intense temperature increases and as a result, expel the zooxanthellae (microscopic algae) and bleach. Even a rise in 1 degree Celsius over a four-week period can cause bleaching, however, this is dependent on the species as different coral species can tolerate varying ranges of sea temperatures.
Sunscreen
Chemicals like oxybenzone found in some non-reef-safe sunscreens and other skincare products have also proven to cause coral damage. An astonishing 14,000 tonnes of sunscreen seeps into the oceans each year! When the chemicals are absorbed by the corals the nanoparticles can cause damage to its DNA, disrupt reproduction and cause the corals to eventually bleach. In an effort to prevent this, some destinations around the world, like Hawaii and Palau, have banned the use of non-reef safe sunscreen products.
Ocean Acidification
The ocean is a ginormous carbon sink, one of the most important naturally occurring‘reservoirs’. What this means is that seawater can absorb and store carbon dioxide (CO2) found in the atmosphere. At least one-quarter of CO2 released from burning fossil fuels is dissolved into the ocean, up to 22 million tonnes per day.
There is a constant equilibrium of balance working, as more fossil fuels are burnt and levels of atmospheric carbon dioxide continue to increase, the ocean continues to dissolve more atmospheric CO2 to maintain the balance. However, the continued absorption of carbon is changing the chemistry of the oceans, with hydrogen ions becoming more abundant and reducing seawater pH levels. This makes the seawater become more acidic and for carbonate ions to decrease in concentration. This is the process of ocean acidification. Carbonate ions are essential for reef-building corals, molluscs, crustaceans and echinoderms and others that use calcium carbonate to produce their skeletons and shells.
With fewer carbonate ions, it is harder for reef-building corals to produce their skeletons (i.e. calcification), reducing growth rates, and making the coral structure weaker.
Using radiocarbon to determine the age of whale sharks…
On the topic of carbon being absorbed into the oceans, scientists from the Australian Institute of Marine Science have discovered a way of using carbon-14 to validate age estimations of one of the most beloved and largest fish in the sea, the whale shark.
Carbon-14, a radioactive isotope, was released in extremely high concentrations into the atmosphere as a by-product of nuclear bomb detonations during the cold war. Excess of this isotope was absorbed into the ocean and every living thing, including the cartilaginous skeletons of whale sharks. Growth bands on the whale sharks vertebrae are like tree-rings and can help to discern the age, however, the time each ring represents has not been accurately determined.
By comparing the levels of carbon-14 in the oceans during certain years with the amount of the carbon-14 isotope found in the vertebral growth bands of a whale shark, scientists have better accuracy in discerning their age. Mark Meeken from AIMS, said that it like a “time-stamp” on the vertebrae and he explained that it could be likely these animals could live for up to 100 years!
To conclude…
Who would have thought that the excessive amount of carbon-14 in the atmosphere, then absorbed into the ocean, might have assisted in age-determination of whale-sharks? It has also got me thinking that perhaps, in many years’ time, we might be able to trace the decreased levels carbon dioxide in the atmosphere in this last month, due to lack of traffic and industrial operations as a result of Covid-19, and use it as another “time stamp” for other species we don’t know much about.
Written by Megan Cundy, Oceans 2 Earth Volunteers Marine Conservation Advocate
