Coral reefs are vibrant underwater ecosystems with intricate structures and diverse inhabitants. They serve as important marine habitats, supporting an estimated 25% of all marine species despite covering less than 1% of the ocean floor. Beyond their ecological significance, reefs provide substantial benefits to human populations, offering coastal protection by absorbing up to 97% of wave energy and supporting livelihoods through fisheries and tourism. These environments are delicate and face increasing pressures from human activities.
Ocean Warming and Coral Bleaching
Rising ocean temperatures, due to climate change, threaten coral reefs globally. Corals live in a mutually beneficial relationship with microscopic algae called zooxanthellae. These algae provide the coral with most of its energy through photosynthesis, also giving corals their vibrant colors.
When seawater temperatures rise above a certain threshold, this symbiotic relationship can break down. The stressed coral expels its zooxanthellae, causing the coral to turn white, a phenomenon known as coral bleaching. While bleached corals can sometimes recover if temperatures return to normal quickly, prolonged heat stress leaves them vulnerable to starvation, disease, and death. Mass bleaching events have become more frequent and widespread, affecting reefs and posing a serious challenge to their long-term survival.
Ocean Acidification
Ocean acidification is another human-induced change impacting coral reefs, linked to the increasing absorption of atmospheric carbon dioxide (CO2) by seawater. The ocean absorbs a significant portion of CO2 emissions, which then reacts with water to form carbonic acid, leading to a decrease in ocean pH. This change in water chemistry reduces the availability of carbonate ions, which are building blocks for corals and other calcifying organisms to form calcium carbonate skeletons.
The reduced availability of carbonate ions makes it more difficult for corals to build and maintain their skeletal structures, slowing their growth and making them more susceptible to erosion. If acidification becomes severe, existing coral skeletons can even begin to dissolve. This hinders reefs’ ability to grow and repair themselves after physical damage, compromising the structural integrity of the ecosystem.
Pollution and Nutrient Overload
Land-based pollution degrades coral reef environments. Runoff from agricultural areas, urban development, and industrial activities introduces sediments, nutrients, and chemicals into coastal waters. Excess nutrients, such as nitrogen and phosphorus from fertilizers and sewage, can lead to the rapid growth of algae. This algal overgrowth smothers corals by blocking sunlight and competing for space, disrupting the reef ecosystem’s delicate balance.
Sedimentation, caused by coastal development and deforestation, also directly harms corals by smothering them and interfering with their ability to feed and photosynthesize. Chemical pollutants, including heavy metals and pesticides, can impair coral growth, reproduction, and physiological processes. Plastic pollution and other marine debris contribute to reef degradation by entangling corals and blocking light.
Direct Physical Damage
Beyond environmental changes and pollution, human activities inflict direct physical damage on coral reefs. Careless boating practices, like dropping anchors or boat groundings, break and destroy coral colonies. Irresponsible tourism, including touching corals, standing on them, or collecting souvenirs, contributes to their degradation.
Destructive fishing methods pose a threat. Practices like dynamite fishing involve detonating explosives to stun or kill fish, but these blasts shatter the reef’s physical structure, creating rubble and destroying vast coral areas. Cyanide fishing, used for the aquarium trade, involves spraying poisons that can kill coral polyps and degrade reef habitats. Coastal development activities, such as dredging and construction, also cause direct physical harm to these fragile ecosystems.