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Great Barrier Reef

How Coral Bleaching In The Great Barrier Reef Has Impacted Its Inhabitants

Climate Change has caused countless environments throughout the world to be destroyed, ecosystems to change, and species to face endangerment/extinction. The Great Barrier Reef in Australia has faced some of the greatest challenges throughout the past decade, and now, its enduring its third mass bleaching event within five years.

The last time the reef endured a mass bleaching event as intense as this one is gearing up to be, a third of all corals were killed, and fish populations declined rapidly, which also caused the specific ecosystems/species within the reef to change for the worse as well. A recent study wanted to analyze what actual effects these bleaching events have on the fish species that live among the coral reefs, as that could help us better prevent these types of things from occurring in other reefs around the world.

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The scientists behind the international study used something called “gene expression” as a tool to understand how well fish are able to handle hotter temperatures, which is an effect of coral bleaching. According to the study, gene expression is “the process where a gene is read by cell machinery and creates a product such as a protein, resulting in a physical trait.” Using this process, scientists were able to predict which fish species would specifically be the most at risk/affected by repeated heat waves that lead to bleaching. 

The study initially began in 2015 when the researchers collected liver biopsies from several species of coral reef fish after global ocean temperatures increased by 1 degree Celsius that year, however, at the time the team of scientists had no idea how different everything would look in just 5 years; in terms of coral bleaching, ocean temperatures/acidification, and climate change in general. 

It wasn’t until one year later that things took a turn for the worse. In 2016, Jodie Remmer, a lead author on the study, along with one other researcher on the project went to the Great Barrier Reef to work on a completely different project when they realized that the ocean temperature around them read as 33°C. This was absolutely shocking in the worst way possible, as 33°C was the same temperature that Remmer claims to have been used in a climate change simulation where scientists predicted what the world would look like, environment wise, by the year 2100, meaning climate change has intensified to a much more urgent level than anyone expected by 2016.

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After one week, Remmer claimed they watched entire patches of coral reef turn bone-white, as fish populations abandoned their homes in search of new resources for food. During that time, scientists collected genetic samples from a multitude of fish and coral species. What they were looking for is how these species “switched their genes on and off” based on environmental conditions. Some genes should always be on, and others should be regulated and used as a response to things like temperature stress (like during a bleaching event). 

The ability to turn these genes on and off is what gives all species the ability to maintain proper metabolic, respiratory, and immune responses to environmental changes. When this gene expression is compromised, so is the ability to survive, hence the massive decline in coral reef ecosystems/fish populations. 

“Our findings not only have implications for specific fish species, but for the whole ecosystem. So policymakers and the fishing industry should screen more species to predict which will be sensitive and which will tolerate warming waters and heatwaves. This is not a ‘one size fits all’ situation. Fish have been on the planet for more than 400 million years. Over time, they may adapt to rising temperatures or migrate to cooler waters. But, the three recent mass bleaching events are unprecedented in human history, and fish won’t have time to adapt,” Remmer stated. 

Remmer went on to say that her and her team’s goal has always been to protect the ocean and all of its inhabitants as much as possible. This new information and data isn’t very encouraging, however, it does give scientists and the government the sense of urgency they often need in order to justify a global response.