Coral reefs are being degraded by an accumulation of stresses arising from human activities and changes in the natural environment. Increased emissions of CO2 as a result of human activities have contributed to the warming of the earth’s surface; this includes the temperature of the world’s oceans, which is having a devastating effect.
How are we damaging coral reefs?
Increasing demand for fish, for coastal populations, export and the tourist industry has resulted in over fishing of many reef species with a decline in stocks. In addition, Over-fishing of certain species on or adjacent to coral reefs can affect the reef’s ecological balance and biodiversity. For example, over-fishing of herbivorous fish can also lead to high levels of algal growth. From subsistence level fishing to the live fish trade, better fisheries management is needed. The aquarium trade is a $4-5 billion industry, and the great majority of marine aquaria are stocked with species caught from the wild. Threats from the trade include the use of cyanide in collection, over-harvesting of target organisms and high levels of mortality associated with poor husbandry practices and insensitive shipping. Where poorly managed, the trade has a significant impact on reefs and so, for example, Hawaii has passed a legislative bill to ban the trade in aquarium fish. To learn more about the effects of overfishing, visit: https://oceanservice.noaa.gov/facts/coral-overfishing.html
Destructive fishing methods
Fishing with dynamite, cyanide and other damaging methods causes coral breakage that damages the reef as a whole and contributes to unsustainable fisheries. Dynamite and cyanide stun the fish, making them easier to catch. Damaging the coral reef habitat on which the fish rely will also reduce the productivity of the area, with further impacts on the livelihoods of fishermen.
The tourist and leisure industries generate vast amounts of income in coastal countries. Where unregulated, recreational activities cause damage to the very environment upon which the industries depend. Physical damage to the coral reefs can occur through contact from careless swimmers, divers, and poorly placed boat anchors.
Coastal populations have some of the fastest rates of growth in tropical countries and the associated development has a range of negative impacts on coral reefs. Airports and buildings are often built on land reclaimed from the sea. Sensitive habitats can be destroyed or disturbed by the dredging of deep-water channels or marinas, and through the dumping of waste materials.
Coral reefs need clean water to thrive. From litter to waste oil, pollution is damaging reefs worldwide. Pollution from human activities inland can damage coral reefs when transported by rivers into coastal waters and hotels and resorts often discharge untreated sewage and wastewater into the ocean. Where land development alters the natural flow of water, greater amounts of fresh water, nutrients and sediment can reach the reefs causing further degradation. For example, once prolific mangrove forests, which absorb massive amounts of nutrients and sediment from runoff caused by farming and construction, have been destroyed. Corals require waters with low nutrient content, and the addition of nutrients favors species that disrupt the balance of the reef communities. Nutrient-rich water causes phytoplankton to thrive in coastal areas, often causing algal blooms. It also encourages the growth of algae, which compete with corals for space on the reef.
How are corals affected by climate change?
Coral bleaching occurs when the symbiosis between corals and their symbiotic zooxanthellae (tiny algae) breaks down, resulting in the loss of the algae and a rapid whitening of the coral (thus the term “bleaching”). This is a stress response by the coral host that can be caused by various factors, but more severe and frequent cases are being caused by a rise in sea surface temperature (SSTs). If the temperature decreases, the stressed coral can recover; if it persists, the affected colony can die. Coral bleaching is now a global phenomenon, and events are increasing in frequency and intensity.
This is the name given to the ongoing decrease in the pH of the Earth’s oceans, caused by their uptake of anthropogenic CO2 from the atmosphere. Although the natural absorption of CO2 by the world’s oceans helps mitigate the climatic effects of anthropogenic emissions of CO2, it is believed that the resulting decrease in pH, (i.e. making the water acidic), will have negative consequences, primarily for oceanic calcifying organisms such as coral reefs.
What else is damaging coral reefs?
The frequency of coral disease appears to have increased dramatically, contributing to the deterioration of coral reef communities around the globe. Most diseases occur in response to the onset of bacteria, fungi, and viruses. However, natural events and human-caused activities may exacerbate reef-forming corals’ susceptibility to waterborne pathogens. More information is needed to identify the mechanisms by which most diseases kill their hosts, and how they are transmitted. The onset of coral disease has been shown to spread following coral bleaching events, so the evidence of a connection between warmer-than-normal water and coral disease is growing stronger. There is also evidence to indicate that low water quality increases incidence. It is critical that governments and managers continue their efforts to reduce (or stop) the effects of other major reef threats (sediments, pesticides, nutrients, over-fishing, etc.) while this scientific information is gathered, if we are to give coral reefs a fighting chance of survival.
Alien invasive species
Species that, as a result of human activity, have been moved, intentionally or unintentionally, into areas where they do not occur naturally are called “introduced species” or “alien species”. In some cases where natural controls such as predators or parasites of an introduced species are lacking, the species may multiply rapidly, taking over its new environment, often drastically altering the ecosystem and out-competing local organisms. The damage caused by invasive species can be devastating, through alteration of ecosystem dynamics, biodiversity loss, reduction of the resilience of ecosystems, and loss of resources, with environmental, economic as well as socio-cultural impacts.
- To learn more about the effects of climate change on coral reefs, visit: https://oceanservice.noaa.gov/facts/coralreef-climate.html
- To learn more about ocean acidification, visit: https://oceanservice.noaa.gov/facts/acidification.html
- To learn more about ocean acidification, visit: https://oceanservice.noaa.gov/facts/coral_bleach.html
- To learn more about the effects of overfishing, visit: https://oceanservice.noaa.gov/facts/coral-overfishing.html
- What is coral bleaching?: http://coralreefs.org/wp-content/uploads/2014/03/ISRS-Consensus-Statement-on-Coral-Bleaching-Climate-Change-FINAL-14Oct2015-HR.pdf