One of the many challenges that currently threaten our marine environment is the increase of poisonous substances in aquatic ecosystems. Not only these substances can be harmful or even lethal to the species that populate these habitats, they can also create severe health issues to humans due to the spread of these compounds in fish or other sea living food sources.
One of the compounds that can be found in these ecosystems that also is listed in “the top ten chemicals of public health concern” by WHO, is mercury, or more precise methylmercury. A study conducted by a Swedish team now reveals a previously unknown phenomenon which links together global climate change with a dramatic increase of mercury in large regions of the northern hemisphere.
This can all be explained by a change in the marine food web. What this study has concluded is that global warming tends to increase the input of organic matter and humic substances from land to water environments due to more frequent precipitation. This in turn will prevent sunlight to reach deeper into lakes and seas, which favor the growth of bacteria on account of the production of phytoplankton. In other words a trophic shift is expected towards a heterotrophic food web which tends to have a more complex food web structure with an increased number of levels of organisms. As a result the food chain, from the bacteria to the top predators, contains more steps in which the mercury can be concentrated. The study concludes that a 15-20 percent increase of organic matter can cause a structural shift that is expected to lead to methylmercury increasing two to sevenfold in the higher levels of the food web, like in fish.
This study and article shows in a good way the complexity of how climate change can affect the marine environment and emphasis the grave importance of not neglecting how this in the long run can cause severe health risks even to land living organisms.