Threats to
marine ecosystems
Threats to
marine ecosystems
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Marine ecosystems support marine life as well as our jobs, our hobbies, our food, our oxygen.

Each ecosystem is composed of different species, in different types of habitats. There are many ways in which humans exploit these marine environments and cause massive damage to these fragile ecosystems.

Understanding how ecosystems are affected by our activities is essential to know how to reduce our impact and adapt our behavior accordingly. Taking an interest in our impact on ecosystems and the consequences for us is a key step in protecting marine life.

Plastic pollution

Every minute, 15 tonnes of plastic waste are dumped into the oceans, so 8 million tonnes each year. It is urgent to act now!

Pollution of ecosystems by plastics is a problem of great complexity and scientists are not yet able to fully assess its consequences on the balance of ecosystems and on the health of consumers. The social and economic impacts are also considerable. A commitment from the public authorities is necessary to improve the management of municipal waste. Everyone’s awareness and commitment are also essential.

The first and most direct effect of this pollution is the imprisonment of animals in driftnets or large debris. It is a major cause of mortality for marine mammals, turtles and birds.

A second direct effect is ingestion. We now admit that this concerns the entire food chain of the marine ecosystem. There is a continuum of plastic debris sizes, from several centimeters to a micron (thousandth of a millimeter) or even a nanometer (millionth of a millimeter).

Each size of marine organism in the food chain corresponds to a size of debris that risks being ingested. After ingestion, plastic accumulates in the digestive system of animals, which then eat less and eventually die.

A large number of organisms, some of which can be invasive, agglutinate on plastics and are transported with them by the flow of currents, over thousands of kilometers and this for several decades. It is a real danger for the balance of ecosystems.

The organisms associated with plastic are as diverse as fish, algae, shells, etc. They may be visible to the naked eye or microscopic in size. In addition, it has been shown that the bacteria that grow on plastics in gyres are different from natural bacteria found in the marine environment. Some could be potentially pathogenic.

Plastic debris represents chemical pollution for several reasons. They contain compounds that can be chemically transferred to marine organisms during ingestion (they are said to be bio-available). Some of these molecules are potentially toxic and can accumulate in the body (they are bioaccumulative). In addition, during the aging of plastic in the environment, chemical compounds incorporated during its manufacture (mainly additives) can be released into the environment or when they are ingested by organisms.

Plastics are also vectors of persistent organic pollutants. Certain plastics thus have the capacity to concentrate pollutants present in the environment during their long stays in rivers and oceans. Plastics can thus multiply the initial concentration of these molecules by a factor of up to 100,000. These molecules are also likely to bio-accumulate in living organisms, and to concentrate along the food chain.

Oil spills

This type of industrial and ecological disaster generally occurs after the sinking of an oil tanker, an accident on an oil platform in the open sea or a wild degassing. The hydrocarbons released into the water then float on the surface and spread over large areas before reaching the coast.

Oil spills are dangerous for the marine environment, greatly disrupting marine flora and fauna, with:

Through the asphyxiation of the environment, then the destruction of the seabed and the habitat of many animals. Flora and fauna of the coastal land areas are also affected.

In particular, filtering animals will bio-accumulate a fraction of the elements (petroleum), these products will contaminate the entire food web.

Atlantic cod (Gadus morhua) exhibit significant changes in the composition of their plasma proteins following an exposure to small doses of oil in water. The study of these proteins suggests that this oil has effects on the immune system, fertility, bone resorption, fatty acid metabolism and increased oxidative stress, with also cell mobility disorders and an increase the level of proteins associated with apoptosis.


Current estimates indicate that overfishing has affected more than 85% of the world’s fishery resources and that most fisheries are exploited far beyond their sustainable capacity.

Although this is about to have long-term effects on human consumption, there are also a number of other effects, such as:

Sharks and tuna are particularly sensitive to overfishing. When removed from their living areas, sea creatures along the food chain are negatively impacted. Populations can grow and the role these large creatures play – from what they eat to the decomposition of their bodies – has potentially life-threatening effects on ocean ecosystems.

The disappearance of predators (and therefore the increase in marine populations) ultimately leads to considerable damage to coral reefs and other elements of the ocean ecosystem. Reefs are essential to marine life, and once damaged, it is difficult to repair the damage, if at all.

Algae are essential for the development of marine life. However, if they invade the marine environment, they can affect fish, reefs, etc.

The tuna vessels are known to fish young tuna but also other species. These fish are then thrown back into the sea, but often already dying or dead. With this practice, wild fish are threatened.

A number of human communities around the world depend on fish as their main food resource. The growth of overfishing has seriously threatened these communities, often located in developing countries. Without the opportunity to catch their food, their populations are threatened.

Many of these communities that depend on fish for food also rely on low-activity fishing industries for economic viability. These enterprises, unlike large-scale fishing enterprises, generally do much less damage to marine life because they are much smaller. However, when these communities cannot access food or financial support, they may face problems in the future.

Habitat destruction

Destruction of habitats in the marine environment by coastal development is underestimated.

Each construction won on the sea destroys an underwater habitat by covering or damming. A high density of works won over the sea on small shallow areas represents a quantitatively major damage to underwater environments. This destruction is irreversible.

Evaluating the negative effects of constructions on the sea on marine ecosystems is often seen as an hostile approach. As a result, few studies deal with this conflicting and politically sensitive topic, few financial and human commitments are devoted to this subject. Thus, taking into account the impacts caused by developments gained on the sea is neglected.

Coastal developments destroy the richest marine habitats. Covering marine space (which has become terrestrial) completely destroy bodies of water and disrupt environmental conditions. The coastal natural space is thus reduced each time.

It is the addition of all the works built on the sea that should be considered to assess their overall impact. This accumulation corresponds to the destruction of underwater habitats that can be estimated on the scale of geographic or administrative (state, region, department or municipality) or natural (rocky coast, alluvial coast …). Each additional structure will increase the rate of littoral marine space destroyed.


Eutrophication is the process by which nutrients accumulate in a habitat.

Eutrophication of aquatic environments is an environmental imbalance caused by the increase in the concentration of nitrogen and phosphorus in the environment. Too much nitrogen and phosphorus in the water causes algae to grow faster than ecosystems can handle. Significant increases in algae harm water quality, food resources and habitats, and decrease the oxygen that fish and other aquatic life need to survive. Large growths of algae are called algal blooms and they can severely reduce or eliminate oxygen in the water, leading to illnesses in fish and the death of large numbers of fish. Some algal blooms are harmful to humans because they produce elevated toxins and bacterial growth that can make people sick if they come into contact with polluted water, consume tainted fish or shellfish, or drink contaminated water.

Ocean acidification

CO2 or carbon dioxide is not only responsible for global warming. In fact, not all of the CO2 we emit from burning oil, coal or gas stays in the atmosphere. A significant part (25%) is absorbed by the oceans. For the planet’s climate it’s pretty good.

Without the oceans, global warming would be even more significant. But the role of shock absorbers played by the world’s seas comes at a price. It is precisely the absorption of these phenomenal amounts of CO2 by the oceans that causes their acidification. Since the start of industrial development, the acidity of the oceans has increased by almost 30%.

The first to suffer from ocean acidification are organisms with calcareous skeletons or shells, in particular corals and molluscs such as mussels or oysters. In more acidic water, these organisms have a harder time making their calcareous shell or skeleton.

Fish would also be affected, first indirectly. When a part of an ecosystem is affected, it has repercussions on the whole system. For example, the degradation of coral reefs will affect the species that shelter there. But the fish are also directly affected. Studies indicate that the acidification of oceans would have effects on the physiology of certain fish and in particular on their sensory system. This would make them unable to detect the presence of a predator.

How to contribute at your own scale?