SIDS and their coral reefs

The threatened reefs

The economy and culture of island people is closely tied to their relationship with the oceans.  Although that relationship has changed radically over the years, how island populations interact with their marine environment remains central to the future of island communities. That relationship is now threatened as sea levels rise, coastal zones are eroded and inundated, and increasingly violent storms appear to be conveyed by the oceans themselves.

Coral reefs have always protected and provided sustenance to tropical islands. The reefs dissipate the energy of strong waves and storm surges; they slow coastal currents that would erode and damage tropical beaches. They are the essential habitat and breeding ground for a multitude of marine species that have provided food to islands communities for millennia. Tropical islands and their coral reefs attract tens of thousands of visitors and bring prosperity to island communities that would struggle to develop without the lure of these natural features.

But these marine ecosystems are increasingly vulnerable, and the coral reefs around small islands are most at risk. The threats come from the islands communities themselves: overfishing and destructive fishing, unregulated coastal development including ports and marinas, coastal engineering, wastewater runoff from hotels and tourism infrastructure, erosion upstream in poorly managed watersheds, nutrient fertilizer runoff from unsustainable agriculture, marine based pollution from coastal shipping, and physical damage from anchors and boat groundings: all these activities damage and weaken coral reefs and reduce the ecosystem services they provide to coastal communities.

Coral bleaching

Climate change will worsen an already alarming situation. Coral cannot tolerate rising seawater temperatures: mass coral bleaching and mortality quickly follows higher ocean temperatures.

In 1998, a huge spike in sea surface temperatures killed 16% of the corals on reefs around the world.  Triggered by the El Nino of that year, it was declared the first major global bleaching event. The second global bleaching event in 2010 was once again caused by an El Nino event.

The third global bleaching event struck in October 2015, and became the longest and the most destructive on record up to that point in time. The El Nino of 2015 was once again the principal agent of the damage caused to the coral.

The image below shows a before and after photo of coral bleaching (left) and coral dying (right) at Lizard Island on the Great Barrier Reef off the coast of Australia in May 2016.

The bleaching of the Australian Great Barrier Reef continued into 2017—the first time that bleaching had occurred in consecutive years. Since it takes corals at least a decade to recover, mass bleaching events that occur every couple of years are likely to eventually kill the coral [1].

The increasing acidity of the oceans will reduce marine biodiversity and the rate of calcification of corals. Essentially, the reefs start to dissolve in the acidic waters. These changes will erode and damage the habitat for reef-based fisheries, increase the exposure of coastlines to waves and storms, and lessen the attraction of islands as destinations for international tourism.

A recent assessment of the threat to coral reefs conducted by the Washington-based World Resources Institute paints an alarming picture:

  • More than 60 percent of the world’s reefs are under immediate and direct threat from one or more local sources—such as overfishing, destructive fishing, coastal development, watershed-based pollution, and marine-based pollution.
  • Overfishing and destructive fishing (using explosives or poisons) is the most pervasive immediate threat, affecting more than 55 percent of the world’s reefs.  Coastal development and pollution from watersheds each threaten about 25% of reefs. Marine pollution and damage from ships is widely dispersed, threatening about 10 % of reefs.
  • Approximately 75% of the world’s coral reefs are rated as threatened when local threats are combined with thermal stress from rising surface water temperatures linked to the widespread weakening and mortality of corals due to mass coral bleaching.

The level of threat to the reefs in each of the SIDS regions is summarized below.

The Pacific region

 The Pacific region is the largest of the three regions and holds more than a quarter of the world’s coral reefs—most of which are found among the three major island groups of the western Pacific.  In the northwest, the Micronesia islands consists of several archipelagos dominated by coral atolls but including several volcanic islands. Most of the reefs in this region are fringing reefs and barrier formations including New Caledonia’s huge barrier reef which is over 1,300 km long.  The Polynesian islands occupy an extensive area in the central Pacific including Tonga, French Polynesia, Samoa, Niue, Tuvalu. Kiribati and Nauru.  Most of these islands are coral atolls interspersed with a few volcanic islands.

Papua New Guinea and the Solomon Islands comprise the eastern half of the Coral Triangle: a global biodiversity hotspot with more species of fish and corals than anywhere else on the planet. The islands and reefs to the east exhibit relatively low biodiversity, but provide habitat for large numbers of endemic species

More than any other region on the planet, the people of the western Pacific live in close proximity to the coastal marine environment and the coral reefs adjoining and protecting their islands. The reefs are the foundation of local fisheries, while in many areas reefs provide important quantities of exported seafood. Tourism across the region is the mainstay of many island economies—particularly for small islands where alternative livelihoods are limited.

Although large areas of the Pacific still have relatively healthy reefs with good coral cover, the situation is changing. Overfishing is common and is linked to growing coastal settlements not only around the larger islands but also in some of the smaller archipelagos in Micronesia. Watershed-based pollution on the higher-elevation islands affects a quarter of all reefs. In many areas, this is linked to clearing forests and erosion, but open-pit mining is also a significant source of sediments and pollution most notably copper and gold mining in Papua New Guinea and nickel mines in New Caledonia. Coastal development affects almost a fifth of all reefs most importantly in Fiji and Samoa.

In Papua New Guinea, sedimentation and pollution from inland areas are a threat to reefs. Natural phenomena have affected some islands, including outbreaks of Crown of Thorn Starfish (COTS) in Papua New Guinea, the Cook Islands, and French Polynesia. Coral bleaching events have been widespread: in Palau in 1998 and 2010, and around Kiribati in 2002 and 2005–caused by elevated sea surface temperatures across wide areas of Micronesia in late 2010. In the eastern Pacific, the threats to reefs are more variable but they include the earliest recorded mass bleaching and coral mortality which occurred in 1982-3.

Climate change impacts are projected to increase the proportion of threatened reefs up to 90 percent by 2030.  Around Papua New Guinea, the Solomon Islands, and Vanuatu, the combined effects of acidification with thermal stress will push many reefs into the very high or critical threat categories.

The Caribbean region

The Caribbean region includes about 10 percent of the world’s coral reefs.  Reef types include fringing and bank reefs as well as several barrier systems most notably around Cuba and along the coast of Belize. The Bahamas group, including the Turks and Caicos Islands, is a large system of shallow banks with reefs at their outer edges. The most northern reefs are around Bermuda—warmed by the Gulf Stream.

The diversity of reef species is relatively low. While there are more than 750 species of reef building corals across the Indian and Pacific Oceans, the Caribbean hosts less than 65.  However, these species are unique with over 90 percent of fish, corals, and crustaceans found nowhere else.

The Caribbean region is densely populated: the SIDS islands support a total population of over 40 million. Although many islands are relatively wealthy, there remains a heavy dependence on the reefs for food and tourism. In many of the poorer islands, tourism has long surpassed agriculture’s and industry’s contribution to GDP.  Even in places where tourism is less intense, the reefs play an important supporting role: providing food, protecting coastlines, and providing sand for beaches.

The region is exposed to regular and intense tropical storms and numerous coastal settlements are protected by barriers of coral reefs—which break waves for offshore and reduce the effects of coastal flooding and erosion.

The reefs in the Caribbean have been in decline for several decades.  Since the 1980s a major cause of damaged reefs has been the impact of diseases particularly those affecting long-spined sea urchins and many coral species. Urchins are important herbivores: feeding on reef algae which would otherwise smother coral. This role is even more important in areas where overfishing has depleted herbivore fish. Disease has also killed off extensive areas of elk-horn and stag-horn corals—once widespread in the Caribbean and important reef-building corals. The causes are poorly understood, but anthropogenic stresses such as pollution are thought to be an important factor. Overfishing is endemic, and the reefs have some of the lowest biomass values anywhere in the world. Groupers and snappers are rare, and fishers have moved down the food chain taking increasing numbers of the herbivores that keep coral healthy.

Reefs have survived overfishing, but the combination of overfishing, pollution, and bleaching has been devastating for Jamaica, Haiti, and many of the islands in the Lesser Antilles. The 2005 bleaching event in the US Virgin Islands was followed by outbreaks of disease that led to further losses of coral. Tropical storms and hurricanes also damage reefs. Twelve hurricanes and eight tropical storms hit the northern Caribbean between 2004 and 2007. The loss of living coral in the Caribbean has led to a weakening of the structure of many reefs—further reducing biodiversity and productivity.

More than 75% of the reefs in the Caribbean are threatened, with more than half in the high and very high threat categories. Overfishing is the predominant threat, followed by coastal development and watershed-based pollution—the latter threatening at least a quarter of the reefs. Only the more remote reefs are better protected: those around the smaller islands of the Bahamas and the coastal systems of the south-western Caribbean.

Overfishing can also fatally damage a coral reef. When overfishing is combined with higher seawater temperatures, corals have little chance of recovering.

Haiti is an extreme example of the impact of overfishing on the marine environment.  For instance, Reef Check surveys conducted in 2014 showed that the reefs of Haiti are the most overfished and destabilized in the world. Many reefs in Haiti resemble ghost towns–with algal dominated reefs and only a few tiny fish.

The image above shows a typical former coral reef at La Gonave in Haiti–overfished to the point where it has become an algal dominated reef with a few stubs of coral surviving but no fish. [2]

The Indian Ocean Region

The SIDS in this region are the Comoros islands, the Seychelles, Mauritius, and the Maldives. In the Maldives, the islands are built from reefs and the people depend heavily on fishing and tourism.  Reef-based tourism is a mainstay of the island economies.

The devastating bleaching event of 1998 hit this region harder than any other. In the Maldives and the Seychelles more than 80 percent of coral suffered complete mortality. Further bleaching occurred in 2001 and 2005, although many reefs recovered. More than 65 percent of reefs in the Indian Ocean are at risk from local threats, with one third rated at high or very high risk. The risk is high along the mainland shores.

The single biggest threat is overfishing: which affects at least 60 percent of coral reefs. Dynamite fishing is also a problem—but occurring mainly along the coast of Tanzania. The threat in the Maldives has intensified due to overfishing—probably linked to the increase in population.  Although fishing in the Maldives targets deep-water species such as a tuna, they still depend on bait fish caught on the reefs.




For a deeper dive…

[1] See : Great Barrier Reef hit by bleaching for the second year in a row,  You can find the article here

[2] See the website for ReefCheck International and their international programs here

[3] For more information on the worsening global situation, go to the World Resources Institute website.  WRI has published several excellent reports on the health of the coral reefs across the world.  See the WRI website here