Who are the sea watchers?

Common Dolphin (‘Delphinus delphis’). Paloma Carrasco, @palodelmar, Author provided

The ocean serves as a sink for many of the chemicals that are released into the environment. These polluting substances can arrive naturally or through anthropogenic activities such as livestock, agriculture and industry.

The Earth’s oceans are polluted by an innumerable amount of substances that not only affect the areas bordering human settlements but the entire planet due to atmospheric and oceanic transport processes.

In this sense, in recent years the use of many substances has been prohibited or limited due to their toxic effects. However, they remain a problem for environmental health.

The ocean is an essential but finite resource, and we are only beginning to understand the impacts of pollution on this ecosystem.

Effects of pollution on the oceans

Water pollution causes harmful substances to enter marine food chains and places the organisms that make them up in a critical position of exposure to these substances.

Many of the water contaminants have the capacity to generate reproductive, immune, nervous and behavioral alterations in living beings and can induce cancer. Above all, when living beings are chronically exposed to pollutants. They can even be so throughout life.

This is a complex issue due to the large number of synthetic chemicals introduced into the environment. In addition, the severity of the effects produced by pollutants can vary according to the time of exposure, the species, the age, the sex of the animals and the general condition of the individual. Also due to the combined presence of other contaminants.

The toxic effects described above, and others that also occur, are closely related to human disease, and occur even at extremely low concentrations.

What is the situation of marine mammals?

According to the International Union for Conservation of Nature, 25% of marine mammal species are in danger of extinction. Water contamination could be considered one of the main reasons for this situation.

Thus, for example, in the Mediterranean Sea, the monk seal (monachus monachus) and the common dolphin (delphinus delphis) are endangered and the bottlenose dolphin (Tursiops truncatus) is considered vulnerable. Although there is still little information, it seems likely that it is due in part to the accumulation of toxins due to water pollution.

Despite the special protection these animals receive, experts consider that there is still great uncertainty about the specific effects of pollutants on marine mammals, to what extent they can produce these effects in their natural environment and what impact they have on their population dynamics .

sentinel species

Sentinel species are organisms that can give early warning signals of potential risks to humans, so that preventive measures can be taken in time to avoid serious health consequences. Many of the animals provide information that is often underestimated or misunderstood.

The use of animals as sentinels for biomedical research is not new. Thus, in forensic medicine, animal corpses are analyzed and canaries are used to warn of the risk of gas release in mines.

The use of wild species living in their natural environment as indicators of risks to human and environmental health offers several advantages. It is considered the best form of warning of risk situations for the human species.

Back in 1996, the European Environment Agency published a report on endocrine-disrupting chemicals. The conclusions included, already then, the important connection between man and fauna and the importance of determining which species could act as valid sentinels.

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striped dolphin (Stenella coeruleoalba).
Paloma Carrasco, @palodelmar, Author provided

Marine mammals have a series of physiological peculiarities that favor the accumulation of pollutants:

  • They are animals that have a large layer of hypodermic fat that covers the entire body and effectively stores pollutants. They also have a limited capacity to metabolize and excrete this type of substance.

  • They are usually very long-lived species, so they can be exposed throughout their lives to high concentrations of pollutants. Exposure to these chemicals can occur during conception in the mother’s womb, during lactation (some contaminants can be eliminated through breast milk), and during adolescence and adulthood through the food chain marine, especially in superpredator species.

These characteristics mean that marine mammals are considered good indicators of change in the marine environment and sentinels for public health and the health of our oceans.

In addition, they are charismatic species that tend to favor a positive response in human behavior. Therefore, it is more likely that through them and their study more attention will be paid to the health problems of the oceans.

Indicators of risks to human health

Many of the diseases that these animals can suffer have been shown to have direct implications for public health. Others may be indicative of environmental stress.

Beluga whales in the St. Lawrence Estuary, located on the Atlantic coast of North America and polluted by persistent organic compounds, have developed a wide variety of neoplasms, many of them similar to those seen in humans. This also occurs in the development of neoplasms produced by metals such as chromium in whales. Chromium is used as an anticorrosive and as a colorant in many paints and is a potent human carcinogen.

Another example is the use of marine mammals to assess the risk of exposure to persistent organic compounds in people living in the Arctic who depend on marine resources. These species take similar prey and many are in turn eaten by indigenous peoples. In addition to neoplasms, these compounds can cause endocrine disturbances, immune suppression, and decreased bone density.

In addition, zoonotic diseases have been described in this group of animals – diseases that can be transmitted from animals to humans and vice versa – of bacterial, viral and fungal origin. In one study, three human patients were infected with marine mammal brucellosis. They had not had direct contact with them, but they had all consumed raw shellfish.

Neurotoxic effects of pollutants

Most of these species are highly intelligent, with complex behaviors and social structures, and highly developed cerebral cortex.

There are contaminants that can produce effects at the level of the central nervous system even in extremely low concentrations. The central nervous system is one of the most sensitive parts of the body. Damage at this level can trigger other types of consequences that, together with alterations in other essential systems, can lead to population declines. A particularly alarming situation for the most vulnerable marine mammals.

The neurotoxic effects of environmental contaminants on these species remain unknown to date. However, many international studies suggest that the concentrations of some of these substances, such as certain metals, may be related to neurological problems in humans, such as autism, attention deficit disorder and Alzheimer’s.

Understanding how pollutants harm wildlife, humans, and ecosystems is critical to understanding their true impact on the global health of the planet.

The Conversation

Emma Martínez López does not receive a salary, does not consult, does not own shares, or receive funding from any company or organization that may benefit from this article, and has declared that she has no relevant links beyond the academic position cited.

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