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The oceans are undergoing dramatic changes. We take a look at six of them.
According to the UN Food and Agriculture Organisation (FAO), around 80 million tons of fish are caught every year in seas and oceans. In 2011, 29% of the sea surface was overfished, and fish stocks consequently declined. The remaining 61% is at risk of heading the same way. Compare that with the start of the 1950s. At the time, the overfished and maximum-fished categories combined represented less than 5% of the total, compared to 90% today. In other words, only 10% is in a healthy state.
2. Degradation of coastal ecosystems
Coastal ecosystems such as mangroves, tidal swamps, and sea grass beds play an important role in the fight against climate change. They protect against storms and rising sea levels, and prevent erosion (loss of sand particles) on the coastline. These ecosystems also store considerable amounts of greenhouse gases, which acts as a brake on climate change. The total amounts of carbon captured in these coastal areas is up to 5 times higher than that of tropical forests. Moreover, they are the natural environment for numerous fish, which feed many coastal communities. And yet, despite these advantages, these ecosystems are among the most endangered on Earth. According to the Blue Carbon Initiative, which is partly coordinated by the UN Educational, Scientific and Cultural Organization (UNESCO), between 340,000 and 980,000 hectares are destroyed every year.
The total amounts of carbon captured in the coastal areas is up to 5 times higher than that of tropical forests. © IRD/Jean-Michel Boré
According to UNESCO, 80% of sea pollution comes from the mainland. Examples include sewage water and artificial fertiliser, which bring huge amounts of nutrients into the seas. This excess of nutrients leads to algae growth. Algae then consume so much of the oxygen from the water that more and more areas hardly contain any oxygen. Marine life then gives up on a massive scale. A good example is the Gulf of Mexico, into which the Mississippi flows. There is now a dead zone of around 13,000 km². There are currently almost 500 similar dead zones around the world, with a total area of 245,000 km². This roughly equates to the area of the United Kingdom.
In December 2016, the United Nations published the 'Marine Debris' report. It revealed that the number of species which suffer damage as a result of marine waste has risen from 663 to 817 since 2012. Species including fish, birds, reptiles and mammals all suffer as a result of pollution. According to the researchers, 40% of cetaceans and 44% of marine birds ingest this waste. 80% of marine waste consists of plastic (see inset).
In 2016, the Ellen MacArthur Foundation gave another shocking warning. If we do not alter our current habits, there will be more plastic in the seas than fish by 2050.
On top of this is the fact that plastics contain toxic substances, including plasticisers and dyes. Plastic waste also absorbs numerous toxic substances including PCBs, DDT and PAKs. According to environmental toxicologist Colin Janssen from UGent, shellfish in the North Sea contain so much plastic that we eat up to 11,000 plastic particles every year.
There are many other forms of pollution in the oceans. For example, oil, radioactive substances, heavy metals and other toxins, and pollution which comes via the atmosphere.
Since humans burn significant amounts of fossil fuels, more and more CO2 is released into the atmosphere. According to the UN, oceans absorb around 26% of this. However, if CO2 dissolves in sea water, 'dihydrogen carbonate' is formed, otherwise known as carbonic acid. The result: since the start of the Industrial Revolution, the oceans have become 30% more acidic. As a consequence many organisms in the oceans need to use more energy constructing their shells and other structures. More and more zones will become uninhabitable for these organisms, due to acidification alone.
The UN warns that within several decades, coral will no longer be able to grow in tropical oceans. Nonetheless, coral reefs are the nurseries of the oceans, and hotspots for biodiversity.
5. Less oxygen
The large amounts of nutrients, including artificial fertiliser, which flow into the oceans, result in oxygen-deficient dead zones, especially in coastal areas. But the warming of the oceans by climate change will result in further oxygen depletion in the oceans. A study in the scientific journal Nature, published in 2017, revealed that the oxygen content of seas has decreased by 2% over the last 50 years. And a 2010 investigation, published in the Annual Review of Marine Science, predicts a decrease of up to 7% in the quantity of oxygen in the oceans over the next 100 years.
Volgens UNESCO maken oceanen 90% van het gebied uit waar leven op onze planeet mogelijk is. Er komen dan ook heel veel soorten voor. We vinden er het grootste dier op aarde: de blauwe vinvis. Maar ook treffen we daar miniscule organismen aan zoals fytoplankton, dat instaat voor 50% van de zuurstof in de atmosfeer en de basis vormt van de voedselketen in oceanen.
De vele problemen waarmee oceanen kampen (overbevissing, degradatie van kustecosystemen, vervuiling, verzuring, dalend zuurstofgehalte,...) hebben een nefaste invloed op de biodiversiteit. Alsof dat nog niet genoeg is, dienen andere gevaren zich intussen aan. Zones die tot nu toe redelijk onaangetast zijn gebleven, komen in gevaar door technologische vernieuwingen die diepzeemijnbouw mogelijk maken, net als intensievere vismethodes, en het alsmaar dieper boren naar olie en gas. Tegen 2100 zal meer dan de helft van de soorten in zee op de rand van uitsterven staan als we verder doen zoals vandaag, waarschuwt UNESCO.
Oceans are an important source of nutrition, especially for people in the poorest countries. According to the UN, 540 million people, or 8% of the global population, make their living from fishing and aquaculture, and fish is the most important source of animal protein for at least 1 billion people.
The numerous dangers which currently threaten oceans, also threaten these sources of nutrition and income. The degradation of oceans also reduces the possibilities for recreation and tourism. It also threatens human health, due to the increasing amounts of toxins in marine organisms. These developments could lead to more poverty, hunger, conflicts and even war.
Rays of hope
Fortunately, despite the numerous dangers which threaten the oceans, there are also countless initiatives intended to turn the tide. 12.7% of the marine areas which extend from individual littoral states (between 0 and 200 nautical miles) is already protected. The EU is working towards sustainable fisheries in 'as many waters as possible'. Furthermore, in December 2016, the EU and the UN agreed to cooperate in several areas including ocean pollution. The international 'Our Ocean Conference' was also held in 2016, in Washington. 5.3 billion dollars was pledged for protecting the oceans. Similar conferences are planned within the EU in 2017, and in 2018 in Indonesia. And don't forget: in June 2017, the international community turned its attention to the UN Conference on SDG14 in New York, the Sustainable Development Goal to protect the oceans. Belgium has been actively participating.
What kind of waste do we find on our beaches?
Every year, Ocean Conservancy organises an International Coastal Cleanup: beaches are cleaned up in the participating countries. In 2015, almost 800,000 volunteers collected around 8 million kilograms of waste. This included rubbish which had washed up on the beach, and which had been left by beach-goers or thrown into the sea. You can find the Top 10 of the collected items below. The message is clear: take care of our oceans, don't leave waste behind on our beaches!
*Based on the number of items which were collected during the International Coastal Cleanup 2015.