New Caledonia Barrier Reef

• Category: Marine and Oceanic Biomes.
• Geographic Location: Oceania.
• Summary: This large reef supports a diverse marine ecosystem but is vulnerable to the effects of mining, destruction of surrounding mangrove forests, overfishing, and climate change.

The New Caledonia Barrier Reef is located in New Caledonia in the South Pacific near Australia’s eastern coast, and surrounds Grande Terre, New Caledonia’s largest island. This barrier reef is the second-longest double-barrier coral reef in the world, after Australia’s Great Barrier Reef. It surrounds a 9,300-square-mile (24,000-square-kilometer) lagoon that is 82 feet (25 meters) deep. The reef is located approximately 19 miles (30 kilometers) from the shore.

New Caledonia has a temperate climate. The average temperature is 75 F (24 C) during the winter and 59 F (15 C) at night, although during the hot season, temperatures range from 79 to 86 F (26 to 30 C). The cyclone season is from January to March.

Biodiversity

The islands of New Caledonia were formerly a part of the Gondwana supercontinent and, as a result, the reef is populated with many ancient species, including varieties of sponge and mollusk. Also making a home in the reef are algae, plankton, crustaceans, cetaceans, sharks, and other fish. Seagrass beds comprise one-third of the reef, providing nesting and feeding grounds for several species of endangered turtles and the largest dugong population in the world.

The soils of the islands are heavily laden with nickel and magnesium, and mining on the islands causes sedimentation, which clouds the water and can bury the reefs, posing a serious threat to the ecosystems they support. Sedimentation also is caused by damage to the mangrove forests, which not only prevent soil erosion in the archipelago but also serve as a breeding ground for many fish, and filter out coastal pollution.

The barrier reef comprises more than 300 species of coral, which are supported by their symbiotic relationship with the photosynthetic algae called zooxanthellae. Elevated sea-surface temperatures in 1998 resulting from the El Niño weather pattern caused coral bleaching, which caused zooxanthellae to be expelled from the corals here.

Scientists warn that global warming will affect the growth of the corals because of the predicted increase in both sea-surface temperature and salinity. The coral is also threatened by infestations of the carnivorous crown-of-thorns starfish, which feeds on polyps, and eutrophication due to shrimp and oyster aquaculture on the islands.

More than 350 species of algae are present in the barrier reef, including phytoplankton, on which coral can feed. Also feeding on algae are the Horse Hoof clam (Hippopus hippopus), and the critically endangered giant clam (Tridacna gigas), which live among broken coral and are supported by symbiosis with zooxanthellae. Cyanobacteria, which can exist in symbiosis with coral, is also present on the reef. Though helpful because of their ability to fix nitrogen, some cyanobacteria secrete harmful toxins or form suffocating blooms, especially close to aquaculture farms that flood the waters with bloom-promoting nutrients. Small crustaceans known as copepods feed on such bacteria and possibly keep their populations in check.

The reef supports a wider benthic (bottom-dwelling) community of 600 sponge, 5,500 mollusk, and 5,000 crustacean species, as well as species of worms, arachnids, and scorpions; all of these invertebrates supplying food to the fish population here.

There are more than 2,300 species of fish, over 100 of which are endemic (found nowhere else) to the reef, including the Erythrocles taeniatus, Gymnocranius oblongus, and Scolopsis lacrima. More than half of the reef's fish are small, measuring less than 6 inches (15 centimeters). The most common species belong to the gobies, wrasses, damselfish, and cardinalfish groups.

Notable commercial fish types include emperor and goatfish, which feed on benthic species such as worms, crustaceans, and mollusks. Snapper and wrasse are known to feed on other invertebrates, as well as small fish. Parrotfish, a type of wrasse, feeds on the coral polyps themselves, breaking down their skeletons and excreting them as sand, as well as preventing overgrowth of potentially polyp-choking algae. Some species of butterfly fish live almost exclusively on specific polyp species, and their survival is thought to be completely dependent on the survival of the coral they feed on.

New species of fish and invertebrates are being documented continuously, including a new species of extremely rare amphipod (Didymochelia ledoyerisp), and a Palaemonidae shrimp (Brachycarpus crosnieri).

Seagrass covers a considerable 347 square miles (900 square kilometers) of the 5,513-square-mile (14,280-square-kilometer) reef area. The seagrass meadows are spawning areas for fish and invertebrates, as well as feeding grounds for dugongs and marine turtles, which generally subsist on seagrass. Seagrass productivity is actually increased by such grazing because it prevents overgrowth that promotes sedimentation and obscures light.

Notable turtle species of the New Caledonia Barrier Reef biome include the hawksbill turtle, which feeds on sea sponges living in the reef; green sea turtle, which uses the region as an important nesting site; the invertebrate-eating loggerhead turtle; and leatherback turtle, which feeds almost exclusively on jellyfish, keeping their populations in check. Many of these turtles are prey only to sharks, although human pilfering of their nests for eggs and hunting for turtle meat has had dire effects on their populations.

A number of seabirds breed in the area surrounding the reef. They include: both the lesser and brown noddy; the red-footed booby, which dives into shallow water to catch small fish and squid living among the reef; and the sooty tern, known to breed on coral islands and pick fish. Large marine mammals such as blue fin and the sei whales have been known to pass through the reef.

Environmental Concerns

While the coral reefs of the Lagoons of New Caledonia have experienced less coral bleaching than many of the world’s reefs, nearly 25 percent of the region's coral is deteriorating due to climate change. Soil erosion, overfishing, warmer water, and extreme weather have all impacted the reefs. Other threats include erosion during cyclone flood surges from nickel mining and bushfires; heavy sedimentation in lagoon areas resulting from the destruction of sediment-retaining mangroves; coastal development; industrial, domestic, and marine pollution; small-scale infestations of the coral-feeding crown-of-thorns starfish; and climate change. The New Caledonian government established the Natural Park of the Coral Sea in 2014. This designation encompasses the economic zone and is meant to protect the ecosystem. Six lagoons and coral reefs are United Nations Educational, Scientific, and Cultural Organization (UNESCO) World Heritage Sites.

Climate change poses numerous and varied threats to the barrier reefs, from warming temperatures that affect the chemical and species balance of the ecosystems, to greater incidence of droughts that could damage subsistence agriculture and livestock farming, leading to heavier fertilizer use and harsher runoff into the sea. More severe cyclone activity could directly damage coral structures, and degrade habitat complexity.

In 2024, the Great Barrier Reef Foundation launched the Global Resilient Reefs Initiative (RRI) to maintain the world’s coral reefs and help them adapt to climate change. New Caledonia’s reefs were chosen as one of the RRI’s first sites (along with the Belize Barrier Reef, Australia’s Ningaloo Coast, and the Rock Island Southern Lagoon in Palau). The RRI partnered with the local New Caledonian Biodiversity Agency (ANCB) to create plans and implement projects that support the local community's fight against climate change and assess and improve reef resiliency.

Bibliography

Charpy, L. et al. “Cyanobacteria in Coral Reef Ecosystems: A Review.” Journal of Marine Biology, 2012, doi.org/10.1155/2012/259571. Accessed 10 Dec. 2024.

Chevillon, Christophe. "New Caledonia's Marine Ecosystem, among the Healthiest on Earth, Deserves Stronger Protection." Pew Charitable Trusts, 4 June 2021, www.pewtrusts.org/en/research-and-analysis/articles/2021/06/01/new-caledonia-marine-ecosystem-among-the-healthiest-on-earth-deserves-stronger-protection. Accessed 10 Dec. 2024.

"Helping New Caledonia’s Coral Reefs Survive Climate Change." Great Barrier Reef Foundation, 15 Feb. 2024, www.barrierreef.org/news/news/helping-new-caledonia-s-coral-reefs-survive-climate-change. Accessed 10 Dec. 2024.

“Lagoons of New Caledonia: Reef Diversity and Associated Ecosystems.” United Nations Educational, Scientific, and Cultural Organization, . Accessed 10 Dec. 2024.

"New Caledonia Launches Its First Reef Resilience Strategy." United Nations Educational, Scientific, and Cultural Organization, 20 Feb. 2024, whc.unesco.org/en/news/2658. Accessed 10 Dec. 2024.

Payri, Claude E., et al. “Vulnerability of Mangroves, Seagrasses and Intertidal Flats in the Tropical Pacific to Climate Change." Vulnerability of Tropical Pacific Fisheries and Aquaculture to Climate Change, edited by Johann D. Bell, et al., Secretariat of the Pacific Community, 2011.

"Reefs of New Caledonia." NASA Earth Observatory, earthobservatory.nasa.gov/images/149880/reefs-of-new-caledonia. Accessed 10 Dec. 2024.