Man-made changes in ocean salinity threaten marine biodiversity and ecosystems

In the endless blue of the world’s oceans and the endless expanse of our coastal and estuarine ecosystems, an overlooked agent is shaping the lives of countless creatures – salt. and ocean salinity.

This is the powerful message of an eye-opening study led by an international team of researchers. They argue that the role of ocean salinity – salt content in water – in a rapidly changing coastal and oceanic environment is critically important and understudied.

The study is titled «Human-Induced Salinity Changes Impact on Marine Organisms and Ecosystems» and has been published in the globally recognized journal, Global Change Biology.

Leading this influential study is biologist Till Röthig from the Fraunhofer Institute for Molecular Biology and Applied Ecology in Giessen. With him is co-author Christian Voolstra, professor specializing in adaptive genetics in aquatic systems at the University of Konstanz.

How changes in ocean salinity affect important ecosystems

Their research focus? The potentially devastating effects of changes in ocean salinity on critical ecosystems and the consequences on coastal communities.

According to Röthig, “Our work shows that salinity is the elephant in the room. Although we know relatively well how changes in temperature, acidification and nutrients affect ocean and coastal ecosystems, the impact of anthropogenic changes on with salt content or salinity have not been well studied.”

As it turns out, a degree of salt exposure is integral to many types of organisms. Ranging from microscopic life forms to larger plants and animals, salt is an extremely important element.

Particularly vulnerable to the effects of changes in ocean salinity are coastal and estuarine ecosystems. They are famous for their high productivity.

Voolstra explains the importance of salinity, “Salinity is central to many metabolic processes – marine organisms are designed to live in saline environments. Salinity also interacts with other physical and chemical properties, such as temperature and oxygen concentration, and thus shapes the physical environment of the ocean.”

How does climate change affect salinity?

However, climate change brings with it a change in rainfall. This leads to extreme floods and droughts that affect freshwater availability, thereby disturbing these sensitive ecosystems. Local human activities such as land-use change, urbanization, river regulation and terrestrial runoff further exacerbate these challenges.

Unfortunately, changing salinity isn’t just another isolated problem. They are expected to increase with ocean warming, deoxygenation, nutrient enrichment and increased sediment loads caused by climate change and human activity, the researchers warn. .

The team argues that warming expansion, freshwater addition and changes in salinity contribute to sea level rise. This increase leads to more saline water flowing into coastal areas and low-lying areas, changing the structure and function of ecosystems.

Ocean salinity is no longer taken for granted

The study’s authors emphasize the urgency of addressing these salinity-related challenges to protect marine and coastal ecosystems and their biodiversity. They pay particular attention to the vulnerability of specific habitats and their important members. These include microorganisms, plankton, corals, mangroves, tidal marshes, macroalgae, and seagrasses.

Prof Voolstra warned of the severity of the situation, “Our data show that the expected salinity change alone can lead to ecosystem collapse. Unfortunately, salinity changes won’t happen in the bubble, and these sensitive ecosystems will also have to deal with changes in temperature, oxygen, acidification and pollution.»

Research serves as a wake-up call. It sheds light on the threats posed by anthropogenic changes in salinity to marine and coastal ecosystems. It also outlines the potential consequences for the health and economies of local communities in these often densely populated areas, emphasizing the interlinkages between the fate of humanity and the health of the world. our oceans and shores.

Learn more about ocean salinity

Ocean salinity refers to the concentration of dissolved salts in seawater, which is mainly made up of sodium and chloride ions. Salinity is important to marine life because it affects the physical and biological properties of the ocean.

However, it is not only about creatures that live in the sea. Salinity also affects the global climate and has many impacts on human life. Learn why salinity is so important and how it is affected by climate change.

The biological importance of ocean salinity

The salinity of the ocean is very important for marine life. Different species have adapted to live in different salinities. For example, most marine species cannot survive in fresh water and vice versa due to differences in salt concentrations.

Salinity affects the metabolism, growth, reproduction and distribution of marine species. It can affect where organisms are found, and drastic changes can lead to mass deaths or change the distribution of species. Some organisms, such as mangroves and estuarine species, have specialized adaptations to cope with changes in salinity.

Physical properties and global climate

Ocean salinity plays an important role in global climate. The density of the ocean is affected by its temperature and salinity.

Cold, salty water is denser and tends to sink, while warmer, less salty water tends to rise. This difference creates a system of global ocean circulation, known as the «global conveyor», which distributes heat around the world and influences climate patterns.

Furthermore, salinity plays an important role in the ocean’s ability to store carbon, which has implications for climate change. The ocean acts as a carbon sink, absorbing a significant amount of the carbon dioxide that humans release into the atmosphere. This absorption capacity is affected by the temperature and salinity of the ocean.

Impact of climate change on ocean salinity

Climate change is changing the salinity of the world’s oceans in many ways.

Changes in precipitation and evaporation

Changes in global weather patterns could lead to increased precipitation in some areas and increased evaporation in others. More rainfall dilutes the salt concentration in seawater, reducing salinity. Conversely, a higher rate of evaporation increases salinity as water vapor leaves behind its dissolved salts.

Melting glaciers and ice sheets

Climate change is causing rapid melting of ice caps and glaciers. This influx of freshwater into the ocean dilutes salt concentrations, reducing overall salinity in certain regions, especially near the poles.

Sea level rise

Rising sea levels, due to melting ice and the thermal expansion of warming seawater, can alter salinity by causing more saline intrusion into freshwater systems such as estuaries and aquifers. .

Changes in ocean circulation

Changes in salinity can affect ocean currents because they are driven in part by differences in water densities, which are determined by salinity and temperature. Changing these ocean currents could impact global climate patterns and disrupt marine ecosystems.

Increased salinity can be harmful to marine life, especially those that are not adapted to changes in salinity. Furthermore, changes in ocean circulation could disrupt the ocean’s ability to store carbon, exacerbating climate change.

It is a complex, interconnected system in which changes in one aspect can have far-reaching effects, affecting biodiversity, food security and the livelihoods of communities living there. based on the ocean.

Therefore, understanding the role of salinity in the ocean and the impact of climate change on it is crucial for predicting future climate scenarios and managing marine resources effectively.

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