Threats to Coral Reefs

If we are to be able to protect coral reef systems it is very important to know what kind of threats corals are dealing with right now!
We can divide these threats in three groups: abiotic threats, biological threats and anthropogenic threats. So let’s take a look…

Abiotic threats to Coral Reefs

Abiotic threats are caused by physical or chemical factors that  affect living organisms and the functioning of an ecosystem. For instance in reef systems temperature, light, pH and salinity but also things like chemical components in soil and water.
A current and widely known result of changes in physical factors is coral bleaching. Coral bleaching happens when corals lose their vibrant colors and turn white.

But there’s a lot more to it than that. Coral are bright and colorful because of microscopic algae called zooxanthellae. The zooxanthellae live within the coral in a mutually beneficial relationship, each helping the other survive. But when the ocean environment changes, particularly to an increase in temperature, the coral is put under stress and expels the algae. When the algae is expelled, the coral’s colors fade until it looks like it’s been bleached. If the temperature stays high, the coral won’t let the algae back, and the coral will die. The leading cause of coral bleaching is climate change. A warming planet means a warming ocean, and a small change in water temperature—as little as 2 degrees Fahrenheit—can cause coral to drive out algae. Coral may bleach for other reasons, like extremely low tides, pollution, too much sunlight, change in pH. 

Other abiotic threats can be the wind, weather and the waves that cause the physical damage of coral reefs. Turbidity can cause a lack of sunlight for the corals, this makes the corals unable to perform photosynthesis. Other things that may cause stress to the corals are a change in sediment levels, pressure, salinity, current, ocean depth and nutrients.

bleached coral
bleached coral costa rica

Biotic threats to Coral Reefs

Biotic threats are caused by the living components of an ecosystem, for instance the fishes, invertebrates and competing corals. They are mostly natural interactions between corals, parasites, predators, or coral disease. They can also be non natural threats, like invasive parasites, predators and coral diseases that have been introduced to a coral ecosystem.

Anthropogenic threats to Coral Reefs

Anthropogenic threats are threats caused by humans. Humans may also be indirectly responsible for many biotic and abiotic threats; like ocean warming and the introduction of non-native species in many ecosystems all round the globe.
Most coral reefs occur in shallow water near shore. As a result, they are particularly vulnerable to the effects of human activities. This is both through direct exploitation of reef resources, and through indirect impacts from adjacent human activities on land and in the coastal zone. Many of the human activities that degrade coral reefs are inextricably woven into the social, cultural, and economic fabric of regional coastal communities. 

Pollution, overfishing, destructive fishing practices such as using dynamite or cyanide, collecting live corals for the aquarium market, mining coral for building materials, and a warming climate are some of the many ways that people damage reefs all around the world every day. 

One of the most significant threats to reefs is pollution. Land-based runoff and pollutant discharges can result from dredging, coastal development, agricultural and deforestation activities, and sewage treatment plant operations. This runoff may contain sediments, nutrients, chemicals, insecticides, oil, and debris.

When some pollutants enter the water, nutrient levels can increase, promoting the rapid growth of algae and other organisms that can smother corals.

Coral reefs also are affected by leaking fuels, anti-fouling paints and coatings, and other chemicals that enter the water. Petroleum spills do not always appear to affect corals directly because the oil usually stays near the surface of the water, and much of it evaporates into the atmosphere within days. However, if an oil spill occurs while corals are spawning, the eggs and sperm can be damaged as they float near the surface before they fertilize and settle. So, in addition to compromising water quality, oil pollution can disrupt the reproductive success of corals, making them vulnerable to other types of disturbances.

Ocean acidification is mainly caused by increased levels of carbon dioxide gas in the atmosphere dissolving into the ocean. This leads to a lowering of the water’s pH, making the ocean more acidic. This in turn causes the hard limestone skeletons of coral to become weaker and in some areas the reef is crumbling away.

Many factors contribute to rising carbon dioxide levels. Currently, the burning of fossil fuels such as coal, oil and gas for human industry is one of the major causes.

diseased coral

In many areas, coral reefs are destroyed when coral heads and brightly-colored reef fishes are collected. They are sold for the aquarium and jewelry trade. Careless or untrained divers can trample fragile corals, and many fishing techniques can be destructive. In blast fishing, dynamite or other heavy explosives are detonated to startle fish out of hiding places.

This practice indiscriminately kills other species and can demolish or stress corals so much that they expel their zooxanthellae. As a result, large sections of reefs can be destroyed. Cyanide fishing involves spraying or dumping cyanide onto reefs to stun and capture live fish. This can kill coral polyps and degrades the reef habitat. More than 40 countries are affected by blast fishing, and more than 15 countries have reported cyanide fishing activities.

Other damaging fishing techniques include deep water trawling. This involves dragging a fishing net along the sea bottom. There is also muro-ami netting, in which reefs are pounded with weighted bags to startle fish out of crevices. Often, fishing nets left as debris can be problematic in areas of wave disturbance. In shallow water, live corals become entangled in these nets and are torn away from their bases. In addition anchors dropped from fishing vessels onto reefs can break and destroy coral colonies.

What can we do to stop threats to coral reefs?

Without a doubt, at this time, humans are causing the most threats to coral reef systems. Coral have thrived on earth for it is thought to be over 500 million years. Humans have been around for the last 200,000 years. With industrialization and the greed in recent decades, there is a real possibility that we could wipe them out in the next 50 years.
Coral restoration projects can only do so much. We all need to make positive changes in our lifestyles to help coral reefs. If we can slow climate change, reduce C02 emissions, and choose to spend money on sustainably produced products, we might be able to make a difference!

So next time you turn off a light or walk to work, remember you are helping coral reefs!

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sebastiaan marine conservation intern

Sebastiaan Moesbergen joins us from the Netherlands. He is currently studying applied Biology at University and has been enrolled in our internship program since the beginning of March. As part of his internship he is assisting us with research and investigation and has been spearheading our spotlight on coral articles. Thank you Sebastian!