Climate change is causing our reefs to disappear, but there is hope!
Coral reefs are found in 109 countries around the world. In the last few decades, coral colonies in 93 of them have experienced significant degradation. In fact, about a quarter of the world’s coral reefs are already considered to be damaged beyond repair. The loss of our coral reefs is truly a global problem because they:
- Cover just 1% of the ocean floor while supporting an estimated 25% of all marine life; that accounts for more than 4,000 species of fish, which means they’re responsible for the highest marine biodiversity in the ocean
- Drive tourism in over 100 countries around the world, providing millions of jobs and billions of dollars in income
- Act as natural breakwaters that help protect shoreline communities, coastal cities, and beaches from powerful waves produced by storms
- Feed entire communities of people across the globe, especially those living on islands
- Support human life by providing sources of medicine that are being used to treat cancer, arthritis, Alzheimer’s and other diseases
Corals (which are actually animals) have a symbiotic relationship with the microscopic marine algae (plants called zooxanthellae) living inside their tissue. The coral provides shelter for the algae and the algae provide oxygen, glucose, and amino acids that the coral needs to survive. The algae also give corals their gorgeous array of colors.
When corals become stressed, they expel the zooxanthellae which causes the coral to ghostly white in a process scientists call coral bleaching. A bleaching event doesn’t necessarily kill coral, though it can if the algae loss is prolonged and the stress isn’t alleviated. Coral that survives a bleaching event becomes weaker, struggles to grow and reproduce, and becomes more vulnerable to disease.
Mass coral bleaching events are occurring more often and the increased frequency is having a devastating and prolonged effect on the world’s coral reefs. The largest reef system in the world — the Great Barrier Reef — recently experienced a mass bleaching event that caused significant coral mortality in as much as 22% of the reef. Mass coral death has a ripple effect that impacts thousands of other marine species that rely on the coral community to survive — including humans.
What’s killing our corals: The impacts of climate change
Climate change is the largest contributor to coral bleaching because it introduces a variety of stressors that impact the long-term future of our coral reefs. These challenges include more frequent severe weather events, ocean acidification, and rising ocean temperatures and sea levels.
Rising ocean temperatures
The average global temperature has increased by almost 0.8°C since the 1880s. Around 90% of that excess heat is being absorbed by the ocean. Corals can experience stress after a one- or two-degree shift in temperature; prolonged heat stress increases the likelihood of mass coral bleaching, which leaves the corals more vulnerable to other threats.
Hard corals are reef-building corals. Massive reef structures like the Great Barrier Reef sit on a foundation made up of millions of hard corals. Their exoskeletons are almost stonelike because they’re composed of calcium carbonate, just like the shells of many mollusks. In order to build their exoskeletons, coral polyps must extract calcium from seawater — a process that requires a specific pH balance.
However, the ocean has absorbed about 30% of the additional carbon dioxide humans have introduced to the atmosphere since the late 1700s. Carbon dioxide reacts with seawater to form carbonic acid, which decreases the pH of seawater and changes the ocean’s chemistry. With fewer carbonate ions, it becomes more difficult for hard corals to grow and reinforce their exoskeletons. Weaker exoskeletons are more vulnerable to fracture during severe weather events.
More frequent severe weather events
Tropical cyclones have become more intense, more frequent, and can physically damage or destroy the reef structure. They can also reduce coral cover, alter species diversity, and affect reef productivity. The low pressure they generate can even decrease sea levels and leave some corals exposed.
Severe weather and extreme rainfall can also cause more freshwater and sediment to travel further away from the coast and onto the reef. Freshwater can change the ocean’s pH and decrease salinity, which can cause coral stress and lead to bleaching events. Increased turbidity (more sediment in the water) can block sunlight, affect coral growth, and limit shelter for other sea creatures who live on the Reef.
Coral reefs have a natural ability to withstand and recover quickly from the physical damage caused by storms and natural disasters. However, outside stressors like changing pH, salinity, and nutrient levels can weaken the reef and increase the time they need to recover. More frequent severe weather events increase damage while reducing the time corals have to recover.
Plastic pollution and poor water quality
Ocean plastic can abrade coral or tear its skin, allowing pathogens such as bacteria and other microorganisms to enter and a potentially deadly infection to start. Coastal development and land-based runoff from agricultural, industrial, and urban land uses are increasing the amount of sediment, nutrients, and contaminants entering the coastal waters where coral reefs grow.
Nutrient runoff has been linked to outbreaks of crown-of-thorns (COT) starfish in the Indo-Pacific region on reef systems like the Great Barrier Reef. In small numbers, these echinoderms benefit coral reefs by feeding on dominant hard coral species and maintaining biodiversity. However, population outbreaks of these starfish can have a devastating impact on the ecosystem.
Industrial fertilizers that leak into the ocean from mainland river systems can fuel enormous blooms of algae and phytoplankton, which COT starfish larvae feed on. Overfishing has also decimated their natural predators, which means more larvae are surviving into adulthood and preying on an unusually high number of hard corals. Crown-of-thorn starfish outbreaks can be especially destructive during coral bleaching events or when corals are already stressed.
Coral reefs can recover if we let them
Coral reefs are naturally resilient. By reducing threats and minimizing impacts, we can enable our coral reefs to recover naturally. Coral restoration projects help repopulate reef systems damaged by climate change by growing endangered and threatened coral species in land- or ocean-based nurseries and transplanting them to degraded coral colonies where they help restore the reef structure and bring biodiversity back to reef systems impacted by climate change.
One bracelet, two good deeds
We’re pulling one pound of trash from the ocean and donating $1 to SeaTrees by Sustainable Surf for every 4ocean Earth Day Bracelet sold this month. Our donation will be used to protect and restore coral reefs and other blue-carbon ecosystems like mangrove forests. This limited edition bracelet is only available April 2021 so don’t wait and add it to your collection today!