ParJodie L. Rummer, James Cook University; Bridie JM Allan; Charitha pattiaratchi, University of Western Australia; Ian A. Bouyoucos, James Cook University; Irfan Yulianto, IPB University et Mirjam van der Mheen, University of Western Australia
The Pacific is the deepest and largest ocean on the planet: it covers about a third of the earth's surface. Such a vast ocean can seem invincible. Yet over its entire extent - from Antarctica in the south to the Arctic in the north, and from Asia to Australia via the Americas - its fragile ecosystem is threatened.
In most cases, human activity is involved. We have systematically plundered the Pacific of its fish. It served us as a trash can: waste has been found into the Mariana Trench, 11 meters below the surface, the deepest place on Earth.
As we release CO2 in the atmosphere, the Pacific, like all other oceans, becomes more acidic. The fish lose their sight and smell; molluscs and other marine organisms struggle to develop their shells.
The oceans produce most of the oxygen we breathe. They regulate the climate, provide us with food, and enable millions of people to earn a living. They are also places of fun, relaxation and spiritual communion. A healthy Pacific therefore benefits everyone.
By understanding the threats to this precious ocean, we will certainly be in a better position to protect it.
The problem of plastic waste in the ocean has scientifically proven in the 1960s when two researchers discovered albatross carcasses littering the beaches of the Northwestern Hawaiian Islands in the North Pacific. Nearly three out of four albatross chicks who died before they could take flight had plastic in their stomachs.
Today, such debris is found in all of the major marine ecosystems on the planet. Their size ranges from a few nanometers to several meters depending on the location. A small part of this waste accumulates and forms gigantic floating “garbage vortices”. The Pacific Ocean is home to the largest of them.
Most of this debris from the land is transported by waterways. Twenty rivers and streams alone provide two-thirds of all plastic waste that ends up in the sea, and ten flow into the North Pacific. Every year, the Gyang-Tse River in China - which crosses Shanghai - discharges approximately 1,5 million tonnes debris in the Yellow Sea, an arm of the Pacific.
A fatal poison
Plastic waste in the oceans poses countless dangers to marine life. Animals become trapped by debris such as abandoned fishing nets, which injure them or cause them to drown.
Certain organisms, such as microalgae and invertebrates, can also stay in floating waste and travel long distances. They then leave their natural environment and risk colonizing other regions.
Of course, the health of wild animals is seriously affected by the ingestion of this debris, especially plastic microparticles of less than 5 millimeters. This plastic can clog the animal's mouth or collect in its stomach. He often dies after a long and painful agony.
Seabirds in particular often mistake floating plastic for food. A study of 2019 demonstrated that there was a 20% risk that a seabird would die after ingesting a single waste, and 100% after ingesting it 93.
Island countries on the front line
Plastic is extremely durable and can float great distances. In 2011, 5 million tonnes of waste ended up in the Pacific following the tsunami that hit the Japanese coast. Some debris crossed the entire ocean basin and finished their race on the North American coast.
Since the plastic floating offshore is mostly carried by surface ocean currents and winds, debris accumulates on the shores of islands encountered along the way. Kamilo Beach, at the southeastern tip of the Big Island of Hawaii, is considered one of the beaches most polluted in the world. Up to 20 tonnes of waste ends up there every year.
Likewise, on Henderson Island, an uninhabited atoll that is part of the Pitcairn Archipelago in the South Pacific, 18 tons of plastic have accumulated on a beach barely 2,5 km long. Thousands of waste run aground there daily.
Subtropical waste vortices
Plastic waste in the ocean knows different fates: some sink, others wash up on beaches; still others float on the surface, drifting with currents, winds and tides.
About 1% of this plastic accumulates and forms five subtropical "garbage vortices" in the open ocean. They form as a result of ocean circulation, driven by changes in wind fields and the Earth's rotation. There are two vortices of subtropical waste in the Pacific, one for each hemisphere.
The northern garbage pile divides into two vortices, one in the east between California and Hawaii; the other in the West, which extends eastward from Japan.
Ocean pollution, a shame for humanity
Discovered by Captain Charles Moore in the early 2000s, the eastern vortex is better known as the "plastic continent" because it is the largest, both in area (about 1,6 million square kilometers) and the amount of plastic that accumulates there. This waste plate can collect more than 100 kilos of debris per square kilometer.
The South Pacific waste vortex is located off Valparaiso, Chile, and extends west. Its plastic concentration is lower than that of the gigantic “continent” of the Northeast.
Abandoned fishing nets account for around 45% of the total waste weight of the “plastic continent”. Debris from the 2011 tsunami in Japan is also a major contributor (some 20% of the vortex).
Over time, the largest wastes degrade and fall apart. The resulting microparticles make up only 8% of the total weight of the Pacific 'plastic continent', but make up 94% of its 1,8 trillion pieces of plastic. In high concentrations, they can make the water cloudy.
It is estimated that each year up to 15 million tonnes of plastic waste is discharged into the ocean from ribs and rivers. This quantity should double by 2025, as the production of plastic continues to increase.
Urgent action is therefore needed to stem this flow of waste, including taking measures to collect and remove plastic from the water, but also - and this is crucial - to stop producing so much.
Breathless fishing grounds
The Pacific, the largest and deepest of all oceans, logically has the largest fishing grounds in the world. For thousands of years, people have lived there from the content of their nets ...
But all over the world, fishing campaigns are depleting fish populations because they don't give them time to rebuild. This overfishing is considered one of the most serious threats to the oceans.
Humanity takes about 80 million tonnes of marine animals every year. In 2019, leading scientists around the world said that of all the dangers threatening marine biodiversity, fishing is the one that causes the most damage. According to their estimates, 33% of fish species are overexploited, 60% are fished to the maximum viable level, and only 7% are underexploited.
Declining fish populations is not just a problem for mankind. Fish play an important role in marine ecosystems and constitute an essential link in the complex food chains of the oceans.
"Like a fish in water" ... an expression that has lived
Overfishing occurs when humanity exploits fishery resources beyond their maximum limit, called " maximum sustainable yield ". Fishing beyond this limit causes populations to decline, upsets the balance of the food chain, degrades habitats and creates a scarcity of food resources for humanity.
The Pacific Ocean is home to huge tuna fisheries, which each year provide nearly 65% stocks globally. But the long-term survival of many tuna populations is threatened.
A study published in 2013 shows that the number of bluefin tuna - a very popular fish, used in particular for making sushi - has decreased by more than 96% in the North Pacific.
Along the west coast of Canada, the Pacific salmon populations have been declining rapidly since the early 1990s, in part due to this overfishing. As to Japan, it has recently been severely criticized for proposing to increase fishing quotas for Pacific bluefin tuna, a species which is said to number only 4,5% of its original population.
According to specialists, overfishing is also a problem in Australia. In 2018, for example, studies showed that large fish species were declining rapidly in territorial waters due to overfishing. In areas open to fishing, exploited populations decreased by 33% on average in a decade, from 2005 to 2015.
The reasons for overfishing
There are many reasons for overfishing and the lack of control over this practice. These include:
- La poverty fishermen from developing countries.
- The subsidies granted to the fishing sector, which allows large fleets to navigate the waters of developing countries and compete with small-scale fishermen; they keep a struggling industry afloat.
- Poor management fishing grounds and communities.
- Frequent non-compliance of fishing regulations due to lack of investment by local authorities.
Take the example of Indonesia, which lies between the Pacific and the Indian Ocean. It's the third largest producer in the world of wild fish after China and Peru. About 60% of the catch is made by small-scale fishermen, many of whom come from poor communities in coastal regions.
Overfishing was first reported there in the 1970s. A presidential decree followed in 1980, banning trawl fishing off the islands of Java and Sumatra. Even so, overfishing continued into the 1990s and persists today. Species affected include coral reef fish, lobsters, shrimp, crabs and squid.
The case of Indonesia shows that there is no simple solution to this situation. In 2017, the Indonesian government released a new supposed to keep fishing at a sustainable level of 12,5 million tonnes per year. Yet in many areas overfishing has persisted, mainly due to unclear regulations and a lack of enforcement at the local level.
This enforcement is particularly complicated because almost all small Indonesian fishing vessels are under the control of the provincial authorities. This reveals the need to improve cooperation between different levels of government in the fight against overfishing.
What can we do ?
To avoid overfishing, governments should first work to address issues of poverty and access to education in small fishing communities. This may involve finding another means of livelihood for them. In the village of Oslob, in the Philippines, for example, former fishermen converted into tourism : They bait whale sharks with krill to attract them closer to the shore, so that tourists can swim with them.
Tackling overfishing in the Pacific also requires cooperation among nations to monitor fishing practices and enforce regulations.
The global network of marine protected areas must also be extended and strengthened to preserve marine life. Today, less than 3% of the oceans are highly protected areas where all fishing is prohibited. In Australia, many marine reserves are small in size and are found in areas with low minimal economic interest for fishermen.
THEdepletion of fishing grounds around the world shows how vulnerable ocean life is. It is clear that humanity is exploiting these resources beyond their limit. Billions of people rely on fish for a source of protein and for a living. But if overfishing continues, it is not only the oceans that will suffer, but also its main stakeholders.
The danger of acidic oceans
The tropical and subtropical waters of the Pacific Ocean are home to more than 75% of the world's coral reefs, including the Great Barrier Reef and more isolated reefs in the Coral Triangle, such as those in Indonesia and Papua New Guinea.
Coral reefs are hit hard by climate change. There is a lot of talk about the damage caused to these ecosystems by the coral bleaching but another insidious phenomenon, ocean acidification, also threatens the survival of reefs.
This acidification most notably affects shallow waters, and the subarctic Pacific region is there. particularly vulnerable.
Coral reefs cover less than 0,5% of the planet's surface, but it is estimated that they are home to 25% of all marine species. Due to ocean acidification and other threats, these incredibly biodiverse “submarine rainforests” are among the most threatened ecosystems.
A chemical reaction
Ocean acidification causes seawater pH to drop as it absorbs CO2 of the atmosphere.
The oceans absorb up to 30% of CO2 atmospheric, resulting in chemical reaction during which the concentrations of carbonate ions decrease, while the concentrations of hydrogen ions increase. This change makes the water more acidic.
Since the Industrial Revolution, the pH of the oceans has fallen by 0,1 unit. It may sound insignificant, but it does mean that ocean acidity has increased by around 28% since the middle of the XIXe century. The Intergovernmental Panel on Climate Change (IPCC) believes that this acidification accelerates.
Why is acidification dangerous?
Carbonate ions serve as building bricks for coral structures and agencies who make shells. A drop in the concentration of carbonate ions therefore has unfortunate consequences for marine life.
Studies have shown that in more acidic waters the mollusks have trouble make and repair their shell. Their growth is also affected, as well as their metabolismTheir reproduction et their immune system. They also show abnormal behavior. Scientists have thus exposed sea hares (a species of slug) in French Polynesia to a simulated ocean acidification, and found that they were less successful in finding food and making poorer decisions.
Ocean acidification is also a problem for fish. Numerous studies show that a level of CO2 high can disrupt their smellTheir view and their hearing. It can also affect their coping mechanisms, such as their ability to apprendre, avoid predators and choose one suitable habitat.
The winners and the losers
Des different oceans of the planet, Pacific and Indian Ocean have experienced record acidification since 1991. This suggests that their marine biodiversity may be the most vulnerable.
This acidification does not affect all species in the same way and its effects may vary over the life of the organism concerned. It is therefore crucial to do more research to identify future winners and losers, thanks to hereditary traits, for example, which can increase the chances of survival and reproduction of an organism under conditions of increased acidity. The populations that do the best could adapt, while the less efficient would be subject to management and conservation measures.
One of the winners may well be the Ocellated Sculpin, a species endemic to the Great Barrier Reef, which thrives in the shallow waters around coral reefs. Research suggests that simulating ocean acidifying conditions has no impact on the early stages of growth, development and survival of embryos and newborns, nor on the foraging or metabolic performance adults.
But the acidification of the ocean risks leaving other species of the Great Barrier behind. Studying the Pacific Clownfish - a species made famous by the Disney animated film The world of Nemo - the researchers thus observed that they suffered from multiple sensory alterations under conditions simulating the acidification of the ocean. These alterations ranged from difficulties to smell the smells and hear to find their way back to the inability to distinguish a species harmless an predator.
It is not too late
More than one half a billion people depend on coral reefs for food, income and protection from storms and coastal erosion. The reefs create jobs - in the tourism and fishing sectors in particular - and are places of recreation. Globally, this sector brings in $ 11,9 trillion per year. It should also be noted that coral reefs have deep cultural and spiritual significance for many indigenous peoples.
Ocean acidification is not the only threat to these reefs. With climate change, the rate of ocean warming has doubled since the 1990s. The Great Barrier Reef, for example, has warmed by 0,8 ° C since the industrial revolution. Since five years, this warming caused two consecutive and devastating episodes of coral bleaching. The consequences of warming seas are amplified by their acidification.
Reducing greenhouse gas emissions must become an international mission. The Covid-19 slowed down our activities and our movements around the world, showing that it was possible to drastically reduce our production of CO2. If we manage to achieve the most ambitious goals of theparis agreement, by limiting the global temperature increase to less than 1,5 ° C, the decrease in the pH of the Pacific Ocean will be much less.
However, it will be necessary to reduce CO emissions2 much more drastically (-45% over a decade) to ensure that global warming does not exceed the threshold of 1,5 ° C. This will give us hope that coral reefs in the Pacific, and around the world, will not be doomed.
It is obvious that the decisions we make today will affect the oceans of tomorrow.
Translated from English by Iris Le Guinio for Fast ForWord
Jodie L. Rummer, Associate Professor & Principal Research Fellow, James Cook University; Bridie JM Allan, Lecturer / researcher; Charitha pattiaratchi, Professor of Coastal Oceanography, University of Western Australia; Ian A. Bouyoucos, Postdoctoral fellow, James Cook University; Irfan Yulianto, Lecturer of Fisheries Resources Utilization, IPB University et Mirjam van der Mheen, Fellow, University of Western Australia
Featured image credits: Shutterstock