Coral reefs need clean water to survive. Unfortunately, with 40% of the global human population currently residing along coastlines, one can imagine the severity of pollution problems of coastline waters. Pollution to coral reefs can be classified into 2 main groups: land-based and marine-based.
Sewage from an English seaside resort
Land-based sources of pollution can occur far inland and yet still have an impact on coastal waters and reefs. A shocking 80% of all marine pollution comes from land-based sources, such as agricultural and industrial runoff, deforestation and sewage. As coral reefs are in close proximity to land, this causes them to be especially vulnerable to land-based pollution.
Do you know how much fertilizers and pesticides we use on our crops each year worldwide? The number is skyrocketing high at more than 130million tons. Now, these pesticides and fertilizers from agriculture will get washed into water sources where they are then transferred to the coast. It is no wonder the extent of coral damage done to reefs. Add on to that, the effects of deforestation of overgrazing of livestock, where the sediments from soil get washed into the water sources, these exacerbate the problem of pollution.
Sediment plumes along coasts next to reefs.
All these sediments from deforestation and overgrazing activities will suffocate, weaken and kill the corals. At lower amounts, they will hinder the ability of zooxanthellae (the algae growing in coral reefs. For more information: An Introduction) to photosynthesize, thus slowing coral growth. As for the fertilizer runoff, the excess nutrients will cause phytoplankton bloom in the water, and block sunlight from reaching the corals, while also causing increased growth of algae and seaweeds that out-compete corals.
Oil spill
Marine-based sources of pollution can seriously undermine the health of coral reefs. Sources include commercial vessels and recreational vessels like cruise ships. These ships have discharge into the sea substances like fuel leakages and raw sewage. And we often also hear news about oil spills from commercial cargo ships – incidents which are extremely detrimental to coral reefs as corals that are exposed to oil experience tissue death, expulsion of zooxanthellae and other effects.
Pollution left behind by cruise ships.
Now, I’m sure plenty of us love to take cruise ships. Not that there is anything wrong in enjoyment, but it is definitely useful to know the effects of cruise ships on coral reefs. Cruise ships have been estimated to generate 70 times more solid waste than cargo ships. These recreational ships are actually a significant source of pollution in many areas.
Though there is an organization known as the International Convention for the Prevention of Pollution from Ships (MARPOL) who provides approved guidelines regulating the discharge of sewage and waste, their regulations are sadly met with ranging degrees of compliance by the cruise industry. Additionally, more direct physical damage from anchors, propellers or hull is another problem face by coral reefs. These can break or dislodge the corals. Such heavy damage can accumulate, and it can take the corals decades to recover from. Possibly, some of them will never ever recover as well, and we will have lost a valuable part of nature.
Spotlight on Southeast Asia:
The Food Agriculture Organization of the United Nations (FAO) estimates that the total amount of fertilizer used will increase 1% per year, and especially in developing countries like South Asia, it us expected to have the highest growth rates.
In Indonesia, a country well known for its land and marine biodiversity, there is a surge in people migrating from rural areas to coastal cities. This exerts pressure on the reefs. Out of all the pollution entering the reefs systems, untreated sewage is the worse. It is such a major problem that in the capital city, Jakarta, a biologist in 1993 had noted that all the coral reefs in Jakarta Bay were “functionally dead”. Indonesia also has one of the most intense clearing of tropical forests, a problem that contributes to coral reef damage.