Coral Reef Ecosystems Under Global Threat

According to the World Wildlife Fund roughly one-quarter of coral reefs worldwide are already considered damaged beyond repair, with another two-thirds under serious threat.

Major threats to coral reefs and their habitats include:

Climate change

Corals cannot survive if the water is too acid or the temperature is too high. Global warming has already led to increased levels of coral bleaching, and this is predicted to increase in frequency and severity in the coming decades. Such bleaching events may be the final nail in the coffin for already stressed coral reefs and reef ecosystems.

Destructive fishing practices

These include cyanide fishing, blast or dynamite fishing, bottom trawling, and muro-ami (banging on the reef with sticks). Bottom-trawling is one of the greatest threats to cold-water coral reefs.

Overfishing

This affects the ecological balance of coral reef communities, warping the food chain and causing effects far beyond the directly overfished population.

Careless tourism

Careless boating, diving, snorkeling, and fishing happens around the world, with people touching reefs, stirring up sediment, collecting coral, and dropping anchors on reefs. Some tourist resorts and infrastructure have been built directly on top of reefs, and some resorts empty their sewage or other wastes directly into water surrounding coral reefs.

Pollution

Urban and industrial waste, sewage, agrochemicals, and oil pollution are poisoning reefs. These toxins are dumped directly into the ocean or carried by river systems from sources upstream. Some pollutants, such as sewage and runoff from farming, increase the level of nitrogen in seawater, causing an overgrowth of algae, which ‘smothers’ reefs by cutting off their sunlight.

Sedimentation

Erosion caused by construction (both along coasts and inland), mining, logging, and farming is leading to increased sediment in rivers. This ends up in the ocean, where it can ‘smother’ corals by depriving them of the light needed to survive. The destruction of mangrove forests, which normally trap large amounts of sediment, is exacerbating the problem.

Coral mining

Live coral is removed from reefs for use as bricks, road-fill, or cement for new buildings. Corals are also sold as souvenirs to tourists and to exporters who don’t know or don’t care about the longer term damage done.

Reports

In Australia, the iconic Great Barrier Reef’s long-term outlook has been downgraded in a grim new report by The Great Barrier Reef Marine Park Authority that warned businesses to “prepare for change” and changed the reef’s overall outlook from “poor” to “very poor”.

The Outlook Report 2019 noted the region had deteriorated since 2009, when it was considered to be at a “crossroads between a positive, well-managed future and a less certain one”. In 2014 it was seen as an “icon under pressure”, but this year, the report noted “Australia is caring for a changed and less resilient reef”. The report said without extra local, national and global action on the greatest threats, the overall outlook for the reef’s ecosystem would remain “very poor”.

While climate change was identified as the most significant threat to the region’s long-term outlook, poor water quality also continued to affect many areas and there has only been a slow improvement in pollution from agricultural land practices. Gradual sea temperature increase and extremes, such as marine heatwaves have caused mass bleaching events in 2016 and 2017 which have damaged coral and impacted fish communities. Some coral reef habitats in the region have been downgraded from “poor” to “very poor” due to record-breaking sea surface temperatures.