Coral reefs are built by tiny polyps that secrete calcium carbonate skeletons, forming complex three-dimensional structures. These ecosystems cover less than one percent of the ocean floor yet sustain an estimated 25 percent of all marine life. Coral harvesting occurs globally, driven by human demand for both living and skeletal material. This article details the techniques used to remove coral from the sea and the severe environmental consequences that follow.
Primary Drivers for Coral Removal
The demand for coral stems from several lucrative global markets requiring either the live organism or its calcium carbonate skeleton. The marine aquarium trade is a major driver, demanding live coral specimens for private and public display tanks. This market also fuels the collection of “live rock,” which is pieces of reef structure colonized by various organisms that provide biological filtration for aquariums.
Another significant motivation is the jewelry and curio market, which targets dead coral skeletons, including precious corals like red and black coral, for decorative items and souvenirs. These skeletal forms are often bleached, cleaned, and polished for sale. The third primary driver is the use of coral rock as a cheap source of aggregate, limestone, and building material in coastal regions. In some island nations, coral has historically been mined directly from the reef structure for use in road construction and cement production.
Destructive and Non-Destructive Harvesting Methods
Highly Destructive Methods
Blast fishing is a damaging method where fishermen use homemade explosives, often constructed from fertilizer or dynamite, to stun or kill large schools of fish. The shockwave from a single one-kilogram bomb can create a crater one to two meters in diameter, instantly pulverizing the hard calcium carbonate structure of the reef into unstable rubble. This destruction is indiscriminate, killing most non-target organisms and marine life within the blast radius.
Cyanide fishing, primarily for the live aquarium and food fish trades, severely impacts coral health. Divers squirt a solution containing sodium cyanide into reef crevices to stun the fish, making them easy to collect. The toxic compound is a respiratory poison that kills the coral polyps by inhibiting their mitochondrial activity. It is estimated that one square meter of coral is destroyed for every fish caught using this chemical method.
The physical removal of live rock for the aquarium trade or large-scale mining for building material is destructive. Collectors often use tools like crowbars, hammers, and chisels to manually break off large sections of the reef. This deliberate breakage fragments the reef, destroying habitat and leading to the localized collapse of the structural complexity that takes centuries to form.
Alternative Methods
Non-destructive harvesting methods are centered on sustainability and mitigation. These include collecting “corals of opportunity,” which are fragments naturally broken off by storms or wave action. This material is already detached and can be repurposed without damaging a healthy colony.
Coral mariculture or aquaculture involves cultivating coral in land-based or in-ocean nurseries. Small fragments are grown in controlled conditions until they are large enough to be sold, reducing pressure on wild populations. While often used for reef restoration, this practice also provides a source of genetically diverse and healthy specimens for the aquarium trade.
Immediate Localized Environmental Impact
The physical act of harvesting triggers an immediate and intense impact at the extraction site that affects the surrounding water quality and organisms. Physical breakage, especially from large-scale mining or blast fishing, creates massive sediment plumes of fine particulate matter. These clouds of suspended sediment travel outward, smothering coral polyps and other filter-feeding organisms like sponges and clams. Corals must expend significant energy to produce mucus to shed the suffocating sediment, which reduces their growth rate and leaves them vulnerable to disease.
The suspended particles also reduce light penetration, inhibiting the photosynthesis of the symbiotic algae, or zooxanthellae, that provide the coral with most of its energy. Furthermore, the sediment plumes can carry toxic heavy metals, such as copper and cobalt, that bioaccumulate in coral tissue, causing physiological stress and necrosis.
Cyanide and explosives cause mortality to non-target reef residents. The chemical poison kills invertebrates and small fish, while the shockwaves from blast fishing rupture the swim bladders and internal organs of marine life. This localized die-off severely depletes the genetic diversity and organism abundance within the harvest area.
Systemic and Long-Term Ecological Consequences
The localized physical destruction cascades into broader, long-term ecological consequences that affect entire regions. The loss of massive reef structures significantly reduces coastal defense, as healthy reefs absorb up to 97 percent of wave energy. This protective function is valued at approximately $9.0 billion annually worldwide, translating into increased coastal erosion and greater vulnerability to storm surges.
The destruction of the complex reef framework removes essential habitat and nursery grounds for commercially important fish species. Global reef fisheries are valued at an estimated $6.8 billion annually, and the long-term loss of fish stocks directly impacts food security and the livelihoods of millions of coastal residents. This habitat loss also causes a profound disruption of the reef’s food web. The removal of coral structure eliminates the shelter fish use to evade predators, leading to a breakdown in their natural predator-avoidance behavior.
The removal of high-trophic-level predators by fishing causes trophic downgrading, which shortens food chains and alters the ecosystem structure. Recovery is extremely slow, as blast-fished sites can remain as unstable rubble fields for decades or even centuries, preventing the settlement of new coral larvae.