Some causes of coral reef degradation

Coral reefs are the ocean's most diverse ecosystem and one of the most diverse on our planet. Coral reefs make up less than 1% of the ocean, but 25% of all marine life lives there, often likened to undersea rainforests. Corals are the main components that make up coral reefs.

There are many types of coral such as brain coral, branch coral, etc. Some soft corals include fan coral and sea pens (looks like a feather pen). In the ocean world, coral reefs are like miniature cities of marine species, housing and providing food for about 4000 species of fish, 800 species of coral and hundreds of other sea creatures. Coral reefs are one of the unique marine ecosystems of Vietnam, which have a very high level of biodiversity and interesting landscapes. Vietnam's coral reefs are widely distributed from North to South with an area of more than 1100km2, the largest coral area and the largest biodiversity recorded in the central and southern seas. Coral in Vietnam is very diverse, with about 400 species of hard corals belonging to 79 genera. The coral biome in Vietnam is completely comparable to the most diverse coral areas in the world.

In general, coral reef ecosystems have a very complex structure and are very sensitive to environmental threats. When corals are young, they can easily become prey for many marine animals. Once skeletons have developed, they are no longer a delicacy for these animals, however, there are also some fish, sea worms, snails and starfish that prey on adult corals. In particular, in many waters of the Pacific Ocean, starfish are extremely active coral hunters.

One of the biggest threats to corals is discoloration (loss of pigment) or bleaching.This phenomenon occurs when the surface sea temperature increases, affecting the life of zooxanthellae algae symbiotic with corals. Sea water temperature above 30oC can cause bleaching. Prolonged bleaching can kill coral communities or make them vulnerable to other threats. In recent years, many tropical coral reefs have degraded due to coral bleaching or dying. Ocean acidification – seawater increasing acidity – also makes it difficult for corals to form a calcium carbonate skeleton. If acidification occurs at a faster rate, the already formed bone structures of coral reefs may also be disrupted.

However, the direct impact of coral reef degradation is human activities. Recent studies show that coral reefs in many areas of Vietnam are deteriorating due to both natural and man-made impacts, mainly coral exploitation, overfishing, tourism, leveling, dredging, etc. in areas with coral reefs. These agents also reduce the ability of corals to adapt and withstand the effects of climate change such as increasing sea temperature, ocean acidification. Deforestation also erodes the soil, which carries water to the sea and forms sediment that coats coral reefs.

The degradation of coral reefs in the bay has many causes such as destructive mining with explosives, cyanide (now no longer); environmental pollution (tourism activities, waste discharge, aquaculture ...) changes living conditions, occurrence of diseased corals, explosion of coral-eating organisms (thorn starfish) and favorable phenomena local nutrition (eutrophication); coral bleaching and natural disasters (storms, floods). The loss of coral reef area is mainly due to the process of leveling, building tourist infrastructure and living in coastal and island areas.The leveling not only destroys the area of coral reefs but also brings the amount of sediment to the sea, causing deposition on the surface of the reef, causing coral death, causing degradation of other reef areas.

Recently, the Institute of Oceanography has experimented with coral restoration in Nha Trang Bay, has identified 9 species of hard corals that are able to recover with survival rates of over 60%, average growth rates from 0 ,4 -6.5mm/month.This result brings certain effects, contributing to minimizing adverse impacts on coral reefs, improving reef areas by increasing coral cover, increasing sustainable clinging prices for coral regeneration and create a stable environment for the development of reef biomes. However, compared with other restoration areas in Vietnam's waters such as Ly Son, Binh Dinh, and Con Dao, the survival rate of restored corals in Nha Trang Bay is not high. Several causes have been identified such as coral predators, spatial competition between species, environmental quality changes due to indirect human activities and other factors such as dynamical regimes.

Marine protected areas play a very important role in protecting corals, the most important of which is having a healthy fish community and ensuring clean sea water for coral growth. Fish are important to coral reefs, especially the fish that eat seaweed and keep the seaweed from growing on the coral, as are herbivorous fish that also make the spiny starfish unable to survive, grow and eat corals. Strictly protected reef areas often have healthier coral communities and are more resilient to disasters. Clean water is also important for coral survival. Wastewater from the mainland through rivers flows into the sea carrying mud and nutrients accelerates the growth of algae and some coral predators. Therefore, effective land use, avoiding excessive use of chemical fertilizers and limiting erosion caused by deforestation and construction also reduce the amount of water carrying a lot of sediment into coral seas. In the long run, however, the future of coral reefs will depend on reducing carbon dioxide (CO2) emissions. In the atmosphere, CO2 produced by burning fossil fuels has been heating the oceans, leading to coral bleaching and changing the acidity of the water.

Image of corals planted and restored at Cu Lao Cham Marine Protected Area, Quang Nam in 2015 by the scientific staff of the Department of Aquatic Resources, Institute of Oceanography

Translated by Phuong Ha
Link to Vietnamese version

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