First published: April 13 2018 https://rocean.com/blogs/rocean-blog/deadly-marine-heatwaves-and-coral-bleaching-on-the-rise
Deadly marine heatwaves are happening more often and lasting longer than ever before, a new study shows. As our oceans warm up, more and more marine animals are becoming the victims of detrimental human activities on earth. A new study by Eric Oliver from the University of Halifax and published in the journal Nature Communications found that heatwaves have increased by 54% between 1925 and 2016. The study based its research on satellite-derived temperature data.
As a result, marine ecosystems are experiencing on average 45 days of marine heatwaves per year. A phenomenon that harms biodiversity as well as fisheries and aquaculture.
On top of this, a second study published in the International Journal of Science found that a major underwater current in the Atlantic Ocean is the slowest it has been for 1,000 years. This particular current brings warm water from Ecuador to the North Atlantic and plays a crucial role in regulating weather patterns in Europe and the Americas.
The consequences of this phenomenon are yet to be fully known, but it is expected that disruptions in weather conditions will be one of them.
A rise of marine heatwaves
A marine heatwave is a prolonged period of unusually warm water, at a particular location. In the recent years, heatwaves have become more frequent and have increased in length of time, to the point of lasting sometimes over a year.
Where a heatwave on land stops as soon as the temperature lowers, a marine heatwave takes longer to cool down, even after temperatures have dropped. And just as a land heatwave is deadly, a marine heatwave counts its victims too. Whales, fish, sea lions, seabirds or corals, a rise of sea temperature affects all life under water.
Marine heatwaves affecting commercial fisheries
The rise of temperature in our oceans has commercial repercussions too. The study published in Nature Communications shows for example that heatwaves in the northwest Atlantic in 2012 has led to altered fishing practices and harvest patterns, price collapses of important fisheries and ultimately to intensified economic tensions between nations.
Between 2013 and 2015, marine heatwaves in the northeast Pacific also caused the closing of commercial and recreational fisheries, resulting in millions of dollars in losses among fishing industries, the study reports.
Increase in temperature leads corals to bleach and die
Global warming and human activity are directly tied to the increasing marine heatwaves. Around 95% of the solar radiation that gets trapped in the atmosphere is absorbed by the oceans. And where an unusual rise of temperature of the sea harms marine animals living there, corals are particularly affected by it.
In 2016, an intense marine heatwave in Australia led to an astronomic 90% of the Great Barrier Reef bleaching, and 70% of the shallow-water corals dying. The phenomenon directly led to the 2015/2016 El Niño, according to the study.Corals experience high stress when the temperature of the water, light or nutrients conditions change. As a result, they expel the symbiotic algae living in their tissues and turn white. While bleaching is not in itself deadly to corals, they become more susceptible to getting diseases and their mortality risks increase. The same phenomenon happens when the temperatures drop and become too cold.
When it comes to corals though, there is hope. In the recent years, scientists have discovered some corals species capable of surviving in high temperatures and surviving global warming, or at least for now.