Photo: / Papahānaumokuākea Marine National Monument CC BY NC ND

Threats to coral reefs

The greenhouse effect, global warming, local pollution and implications for coral reefs described in a regional overview.

The Great Barrier Reef off eastern Australia has lost more than half its coral cover in the past 30 years, and the Marine Park Authority sees climate change as the most serious threat to the reef. Almost half of this loss is attributed to foraging by the crown-of-thorns starfish, possibly triggered by nutrient-rich run-off from farms. New practices to reduce run-off and erosion and improve farm productivity are being tested. The cuts to pollution needed for the reef’s survival need to be scaled up and include all catchments running into the reef’s waters, encompassing millions of hectares. The major threat to this objective is the plan to build industrial developments along the entire coastline, which will allow some 100 million tonnes of dredge spoil to be dumped into the shallow coastal waters.

However, public support has recently resulted in a ban on dumping the spoil, but increased shipping traffic, dredging, dumping for port maintenance and other causes of coastal habitat destruction are still significant problems.

The Mesoamerican Barrier Reef (Belize Coral Reef) is the second-largest coral reef system in the world and the largest in the northern hemisphere. It was listed as a World Heritage Site by UNESCO in 1996. It contains more than 100 species of corals. Its most widespread reef is the one off Belize, but both the coasts of the Greater and Lesser Antilles and the waters off Florida include coral reefs. Although less affected by the extreme weather conditions in 1997–98, some coral species were almost eradicated locally in 1998-99.

The Florida Coral Reef is the third-largest barrier reef system in the world and the only coral barrier reef in the continental United States. This reef consists of two ridges separated by the Hawk Channel. More than 40 species of coral live on this reef and species diversity is comparable to that of the reefs in the Caribbean Sea, even though it extends close to the northern limit for tropical corals. The first recorded bleaching incident on the Florida reefs was in 1973, and in recent decades incidents of bleaching have become more frequent.

The so-called Coral Triangle covers an area of ocean including the states and islands of Indonesia, Malaysia, the Philippines, New Guinea, Solomon Islands and Timor. This area is probably the richest area in the world in marine resources. More than 120 million people depend on these resources for their income and livelihood, and fish is of course the major source of protein in local diets. Fisheries exports, including more than a fourth of the global tuna catch and coral reef fish, amount to some US$ 1 billion annually. In addition to this lucrative trade income some parts of the region attracts tens of millions of visitors annually, and this nature-based tourism is estimated to be worth at least ten times as much as the income from fisheries.

In 2009 the six coral triangle countries established an initiative of cooperation to sustainably manage their natural marine sources for future generations. To address all these factors ecosystem-based fisheries management will be applied, threatened marine species will be protected and climate change matters will be addressed. Some of the basic activities addressed will be to enlarge the small existing protected areas and stimulate development of community-based natural resource management, thus conserving and sustainably using marine resources.

The so-called cold-water stone corals that build deep-water reefs in temperate waters do not rely on symbiosis with zooxanthels, which is why they can be found at greater depths. Obviously, there is still no indication of coral bleaching among those corals. On the other hand, deep-water trawl fishing may cause mechanical damage to the cold-water reefs, so human activities are already affecting the reef structures in northern waters.

There are also biological threats to coral reefs. A starfish called the crown-of-thorns has recently been found to eat coral polyps leaving only the skeleton behind. It is not known why this aggressive behaviour has increased. Another human activity causing destruction of coral reefs is by dynamite fishing and collection of corals to sell to tourists, and tourism itself may also cause severe mechanical damage to the reefs.

Coastal agriculture, development and shipping, deforestation and increased unsustainable fishing are all important vectors in this degradation of the coral reefs.

Some 850 million people in the tropical regions around the globe benefit directly from the social and economic services provided by coral reefs. The projected degradation will obviously affect both the reefs and the communities they sustain.

Another way of measuring effects on coral reefs is by referring to the Living Planet Index database (WWF, 2015) which covers 930 fish species, 352 of which are classified as reef associated. This index has declined 34 per cent between 1979 and 2010. While overexploitation is listed as the primary threat, climate change is also identified as a significant threat.

It is fair to say that the Coral Triangle is the world’s centre of marine life, but in the last few decades more than 40 per cent of the region’s coral reefs and mangroves have been destroyed. The reasons for these threats are population growth, economic development, pollution and damage from agriculture, shipping installations and unsustainable fishing.

These basic threats are compounded by increasing ocean temperatures.

Lennart Nyman

Lennart Nyman is a scientist and environmentalist from Sweden who has worked for some 50 years studying various aspects of marine, freshwater and terrestrial ecosystems worldwide.
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