Coral reefs are degraded by an accumulation of stress from human activities. Overfishing, pollution and coastal development are high on the list of factors in chronic stress. Some coral reefs are covered with sand and sediments. Others are dredged or blasted for their limestone or to improve access and safety of navigation. In addition to this, the overall long-term changes (higher sea temperatures and CO2 levels), storms, earthquakes and volcanic eruptions also affect coral reefs.
Increasing demand for fish has led to the overfishing of reef species. Overfishing of certain species can easily affect the ecological balance and biodiversity of the reef. For example, overfishing of herbivorous fish can lead to high levels of algal growth that can quickly suffocate corals.
DESTRUCTIVE FISHING METHODS
Dynamite fishing and cyanide make the fish easier to catch. These practices do not target species, they destroy everything where they are applied. Damage on the coral reef affects the entire reef ecosystem, and thus has an immediate impact on the livelihood of fishermen and their families in these areas.
Tourism generates large amounts of money for the host country. Unregulated tourism can cause damage to the surrounding environment because of negligent divers, misplaced boat anchors and hotels discharging untreated wastewater (polluting water, creating sedimentation, whilst also encouraging the growth of algae that disturb corals).
Coral reefs need water that is low in minerals to develop. Pollution from land-based human activities, when transported by river flows into coastal waters can damage coral reefs.
It is estimated that nearly 2 million people worldwide have an aquarium. The vast majority of aquariums are constituted of species caught in the wild. The threats brought about by this trade include the use of cyanide for the collection of fish, overly targeted organisms and high levels of mortality due to different maintenance and shipping practices.
Coral bleaching occurs when the symbiosis between corals and their symbiotic zooxanthellae (algae) stops, resulting in the loss of these microalgae and the rapid bleaching of the coral host (hence the term “bleaching”). This is a stress response from the coral host which can be caused by various factors. The most common and most serious cases are caused by an increase of the surface’s temperature.
RISING OCEAN TEMPERATURE
If the ocean surface temperatures continue to rise, the frequency and severity of coral bleaching will also increase, possibly affecting the ability of coral reefs, as we have known them, to adapt and provide most services we ask them.
This is the name given to the decreasing pH of ocean water caused by the absorption of carbon dioxide from the atmosphere. Although the natural absorption of CO2 by the world’s oceans helps mitigate the climatic effects of CO2 emissions, the resulting decrease in pH (i.e. making water acid) will have negative consequences, especially for oceanic calcifying organisms such as coral reefs.
Rising sea level
Observations since 1961 show that the average temperature of the ocean on a global scale has increased, even at depths of 3000 m (IPCC report), and that the ocean has absorbed more than 80% of the increase in heat. This temperature increase causes rising sea levels and creates problems for low-lying countries.
Over the past 10 years, the incidence of diseases developed in corals appear to have increased dramatically, contributing to the deterioration of coral reef communities worldwide.
Species that have been moved intentionally or not, due to human activity, in areas where they do not coexist naturally are called “invasive species”. Often natural controls such as predators and parasites of invasive species are lacking. These invasive species can therefore multiply and change rapidly. The damage caused by these species can be devastating: altered ecosystem dynamics, biodiversity loss, reduced resilience of ecosystems and loss of resources.