What are the biggest threats to reefs?

Coral outcrop on Flynn Reef at The Great Barrier Reef. Photo credit: Toby Hudson.
Coral outcrop on Flynn Reef at The Great Barrier Reef. Photo credit: Toby Hudson.

By Emma Corradini

Though coral reefs protect an estimated 25 percent of all marine life, these habitats are constantly under threat from various species and conditions. Reefs are home to countless species of animals and can become huge structures, such as the Great Barrier Reef which is larger than 65 million NFL football fields, but are these massive homes are constructed by small by small coral polyp animals that produce a calcium carbonate (limestone) shell. As these animals die, their shell becomes part of the coral structure, giving future generations of coral polyps room to grow. The reefs would continually expand, generations of coral polyps growing on top of the shells of their predecessors, except for the intervention of humans and other problems that kill the growing coral.

Some of the biggest threats to coral reefs include:

For example, fishing with cyanide and dynamite stun fish but kills the coral. These practices are more common to Indo-Pacific coral reefs to supply the aquarium trade and the Hong Kong, Singapore and Chinese restaurant trade.

When too many of a certain species is removed the cascading negative effect ripples throughout the food chain. For example, in the Great Barrier Reef (Australia) the Crown of Thorns Starfish consumes large amounts of coral and reduces coral cover when it’s natural predators are over-fished.

Many toxins that are dumped into the ocean have harmful results on coral reefs. For example, sewage and fertilizers that end up in the ocean have a huge negative impact, particularly ones high in nitrogen, which offsets the ocean’s balance and can lead to the excessive growth of algae and other unwanted species. All coastal reefs are vulnerable to this, but especially ones near developing areas like in South-East Asia.

When sediment coats the coral, algae is unable to photosynthesize. Coastal industrial activity, deforestation, and destruction of mangroves (forests in tropical coastal areas) all contribute to excessive sedimentation.

Reefs are threatened by climate change in two ways: bleaching and acidity.Rising temperatures cause bleaching (algae die or are expelled) and rising acidity due to absorbed carbon dioxide weakens the calcium carbonate structures. A global bleaching event hit oceans in 2015 and is set to continue for at least a year.

Unaware or uncaring about how delicate coral reefs are and how long they take to grow back, humans can be one of the most destructive forces on coral reefs. Swimmers standing on reefs can crush structures that took hundreds of years to create. Removing coral structures for souvenirs or to use in home aquariums are equally catastrophic.