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Marine Ecotoxicology: The "Medical Exam" of the Sea

By Carolina Maciel

A drawing of an erlenmeyer flask composed of silhouettes of marine animals, such as fish, birds, mammals, sea stars and plankton

Illustration by Joana Ho

When we become ill or are exposed to things that could make us sick, we go (or we should go) to the doctor, a professional trained to help us solve our health problems. It is not much different in the marine environment. The "health" of all ecosystems (defined as the integration of all living beings in an environment and their relationships to each other and the physical and chemical properties of the environment) can be diagnosed through testing, in the science we call ecotoxicology.

Within ecotoxicology, animal tests may be performed similar to medical laboratory exams, giving results as to how the organisms are reacting to a "sick" environment. The animals used in the tests can range from (my beloved) plankton, fish, bats, and birds to large marine mammals such as whales. We also must not forget the algae and other plant life that can also be used for testing. In the case of organisms that have a vertebral column (vertebrates), the tests must be carried out with the approval of an ethics council, often regulated at a country-wide level.

Example of organisms that are commonly used in ecotoxicological tests in seawater and freshwater. (Top left: Vibrio fischeri, CC BY-NC 2.0; Top right: Lytechinus variegatus, by Hans Hillewaert CC BY AS 4.0; Bottom left: Ceriodaphnia sp., by Andrei Savitsky CC BY AS 4.0; Bottom right: Danio rerio, by Tohru Murakami CC BY-NC 2.0) .

Just as doctors give patients diagnoses of diseases, ecotoxicology's main objective is to detect what the problem is in order to heal the weakened environment, always aiming to preserve the species that live there. In this way, the tests indicate how "sick" an ecosystem is and how serious this "disease" is, and in many cases, assist in the treatment.

Photograph of a bird covered in oil on an equally oiled beach after an environmental disaster

Oiled bird after the Black Sea Oil Spill on November 12, 2006

But the test results do not come out magically, and it takes a lot of work to test the organisms and then to interpret the results in relation to the environment. The organisms examined must be acquired directly from nature, or possibly grown in laboratory cultures, before testing can be performed.

Although the title of the text refers to the marine environment, ecotoxicology is important in many environments. The pollutants that end up in the sea generally originate in freshwater, so ecotoxicologists often also do tests with freshwater organisms. Environmental quality testing can be done after natural disasters and major disruptions to the environment, and also for routine environmental "check ups" (or what we call environmental monitoring).

A recent example of how important ecotoxicology is to assist the diagnosis of a "sick" environment impacted by human action is the Samarco's dam rupture in November last year in Mariana (MG). The event dumped large quantities of harmful substances into the environment that could potentially cause drastic effects to animals and plants living in nearby rivers. The mud even reached the marine environment. The collapse of this dam caused an environmental disaster, and took the environment out of its natural balance, effectively making it "sick" with mud contaminated with mining tailings. This is where (fortunately) ecotoxicology comes in.

 Photograph of the landscape showing the Doce River with muddy waters after the Samarco dam broke

Mud from the Samarco dam that broke in the city of Mariana on 5 November 2015 reached the Doce River and flowed into the ocean

Another very familiar example (and one that has already been published here on the blog) was a doctoral study conducted by a student that aimed to quantify the levels of heavy metals (arsenic, selenium, lead, chromium, etc.) in the muscle tissue of flatfish. Besides being very important ecologically, an interesting point about this study is that a nuclear physics technique was employed to diagnose the level of these metals in the tissues! In this situation, a vertebrate was used to diagnose the degree of metal contamination in an environment (in the Bay of Santos, on the coast of São Paulo). The importance of studying levels of contamination in organisms is to reveal to society the damage that heavy metals are doing to living things and to try to prevent further degradation of the environment.

The damage caused by the pollution of rivers and seas can be estimated through animal testing (that I explained a little bit above), where the effects of that toxic load on the mortality, growth and/or reproduction of those organisms present in the polluted environment are analyzed.

One of the most important aspects of ecotoxicology is that by knowing the degree of environmental toxicity (how toxic substances can be to living organisms), it is possible to act to save the species that live in the polluted environment. Ecotoxicology studies can also provide evidence to the relevant authorities in order to assign appropriate punishment to those responsible for the pollution of a natural system.

However, ecotoxicology also acts in happy cases, such as monitoring areas that are constantly receiving a load of potentially harmful substances without causing harm to the organisms that live in that environment. In this sense, the ecotoxicological "test" can be used to confirm that the environment is healthy.

But why use living organisms to test the "health" of an environment? Well, this is easy! Precisely because they are in direct contact with the environment and are adapted to live in very specific ecological situations. Any small change in their ecosystem can be detected through the damage that organisms suffer from these changes. And now you ask yourself: what damage? Damage may appear as a decrease or complete stop of reproduction, immobility, mortality, or many other physical issues. Because of the nature of some testing, ecotoxicology is often seen as "cruel" by some, but it is extremely necessary to ensure a balanced life for many!


About Carolina Maciel:

A “caiçara” (native coastal resident of southern Brazil) and sea lover, I graduated from Universidade Santa Cecília (Santos, SP) with a degree in biology. Among all of the amazing sea creatures, I chose to work with zooplankton. I have experience identifying the main animal groups of the plankton and their distribution in the Santos estuary. Besides the sea, education is another of my passions: I have taught biology classes in a community “cursinho” (preparatory school) for underprivileged youth and for elementary school children in public schools. In 2016, I started my master's degree at the Oceanographic Institute of São Paulo (IOUSP), and I am studying the swimming behavior of plankton in Ubatuba (SP), trying to understand how these tiny organisms behave in this huge and complex ocean.

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1 Comment

lais neves
lais neves
Aug 18, 2021

Amei o artigo, muito bem explicado 😍

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