Coral bleaching occurs when coral polyps expel algae that live inside their tissues. Normally, coral polyps live in an endosymbiotic relationship with these algae, which are crucial for the health of the coral and the reef. The algae provides up to 90 percent of the coral’s energy.
Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically live in compact colonies of many identical individual polyps. Coral species include important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.
Sometimes called rainforests of the sea, shallow coral reefs form some of Earth’s most diverse ecosystems. They occupy less than 0.1% of the world’s ocean area yet they provide a home for at least 25% of all marine species including fish, mollusks, worms, crustaceans, etc. They are most commonly found at shallow depths in tropical waters, and are beautiful, brightly colored backgrounds of the marine world.
The stunning colors in corals come from marine algae called zooxanthellae, which live inside their tissues. These algae provide the corals with an easy food, which gives the corals energy, allowing them to grow and reproduce. Coral reefs are fragile, partly because they are sensitive to water conditions. When corals get stressed, from things such as heat or pollution, they react by expelling this algae, leaving a ghostly, transparent skeleton behind. This phenomenon is called ‘Coral bleaching.’
What causes coral bleaching?
1. Changes in water temperatures: When water is too warm, or too cold, corals become inhabitable for the algae (zooxanthellae) living in their tissues, causing the coral to turn completely white when the algae are expelled.
2. Changes in seawater chemistry: The altered state of the nutrients and chemicals in seawater due to pollution from waste water run-offs, seeps, cesspools, etc. can cause bleaching of corals.
3. Ocean acidification: Ocean Acidification is the decrease in the ocean water’s natural pH values due to over absorption of Carbon Dioxide emitted by human activities and industries. The lowered pH values in turn cause corals to lose their color.
Can corals recover from bleaching?
In some instances corals can recover from bleaching. If conditions return to normal, and stay that way corals can regain their algae, return to their bright colors and survive. It can take decades for coral reefs to fully recover from a bleaching event, as it leaves corals in a weakened state, worsening their struggle to regrow, reproduce and resist disease which eventually increases their risk of mortality. So it is vital that these events do not occur frequently.
What can we do
Human beings are incredible when we act together. If we take climate leadership then our coral reefs, and the thousands of species that rely on them, can rebuild and thrive for generations to come. Some everyday efforts that can be made to tackle this crisis efficiently:
1. Recycling and disposing trash properly can help minimize marine debris that harms the corals
2. Minimizing the use of fertilizers that harm water quality when washed into waterways that eventually end up in oceans.
3. Usage of environmentally-friendly modes of transportation will help reducing carbon footprints and the emission of greenhouse gases like carbon dioxide that accelerate ocean acidification.
If we lose coral reefs we also lose a vast number of fish and other animals that rely on them. This will have terrible consequences right up the food chain impacting larger creatures, like dolphins and sharks that rely on reef fish for their diet. Coral bleaching risks not just our oceans and wildlife, but the livelihood and food security of over half a billion people worldwide.
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