Human-induced changes in ocean salinity threaten biodiversity and marine ecosystems

In the ceaseless blue expanses of the world’s oceans and the unfathomed expanse of our coastal ecosystems and estuaries, an overlooked agent is shaping the lives of countless organisms – 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 – the salt content of the water – in a rapidly shifting oceanic and coastal environment is both critically important and dramatically understudied.

The study is titled “Human-induced salinity changes impact marine organisms and ecosystems” and was published in the globally recognized journal, Global Change Biology.

At the helm of this influential research is biologist Till Röthig from the Fraunhofer Institute for Molecular Biology and Applied Ecology in Giessen. Alongside him is co-author Christian Voolstra, a professor specializing in the genetics of adaptation in aquatic systems at the University of Konstanz.

How changes in ocean salinity impact important ecosystems

The focus of their research? The potentially devastating impacts of changes in ocean salinity on vital ecosystems and the repercussions for coastal communities.

According to Röthig, “Our work shows that salinity is the elephant in the room. While we know comparably well how changing temperatures, acidification, and nutrients affect ocean and coastal ecosystems, the effects of human-induced changes in salt content, or salinity, are severely understudied.”

It turns out, salt exposure levels are indispensable for a variety of organisms. Ranging from microscopic life forms to plants and larger animals, salt is an incredibly vital element.

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

Voolstra explains the importance of salinity, “Salinity is a central factor for many metabolic processes – marine organisms are built to live in salty environments. Salinity is also interacting with other physical and chemical properties, such as temperature and oxygen levels, and thereby shapes the physical environment of the ocean.”

How climate change impacts salinity

However, the changing climate brings with it variations in rainfall. This leads to extreme flood and drought events that impact freshwater availability, thus disturbing these sensitive ecosystems. Local human activities like land-use changes, urbanization, river regulation, and terrestrial runoff further amplify these challenges.

Salinity changes, unfortunately, aren’t just another isolated problem. The researchers warn that they are expected to increase along with ocean warming, deoxygenation, nutrient enrichment, and increased sediment loads brought on by climate change and human activity.

The team argues that the expansion caused by warming, freshwater addition, and salinity changes contribute to sea-level rise. This rise leads to more saltwater flowing into coastal and low-lying areas, shaking up the ecosystem structures and functions.

Ocean salinity can no longer be taken for granted

The study’s authors underscore the urgency of addressing these salinity-related challenges to protect marine and coastal ecosystems and their biodiversity. They draw particular attention to the vulnerability of specific habitats and their crucial members. These include microorganisms, plankton, coral, mangroves, tidal marshes, macroalgae, and seagrass.

Professor Voolstra warns about the gravity of the situation, “Our data show that projected salinity changes alone can lead to ecosystem collapse. Unfortunately, salinity change will not happen in a bubble, and these sensitive ecosystems will also have to cope with changes in temperature, oxygen, acidification, and pollution.”

The study serves as a wake-up call. It sheds light on the threats posed by human-induced salinity changes to marine and coastal ecosystems. It also sketches out potential consequences for the health and economy of local communities in these often densely populated regions, underlining the interconnectedness of humanity’s fate and the health of our oceans and coasts.

More about ocean salinity

Ocean salinity refers to the concentration of dissolved salts in seawater, primarily made up of sodium and chloride ions. Salinity is vital for marine life as it influences the physical and biological properties of the oceans.

However, it’s not only about the organisms living in the seas. Salinity also affects the global climate and has wide-ranging implications for human life. Let’s delve into why salinity is so important and how it’s affected by climate change.

Biological Importance of Ocean Salinity

Ocean salinity is critical for marine organisms. Different species have adapted to live in different salinity levels. For instance, most marine species can’t survive in freshwater and vice versa due to the differences in salt concentrations.

Salinity affects the metabolism, growth, reproduction, and distribution of marine species. It can influence where organisms are found, and drastic changes can lead to mass die-offs or shifts in species distribution. Some organisms, like mangroves and estuarine species, have specialized adaptations to cope with changes in salinity.

Physical Properties and Global Climate

Ocean salinity plays a significant role in the global climate. The ocean’s density is influenced 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 global ocean circulation system, known as the “global conveyor belt,” distributing heat around the world and influencing climate patterns.

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

Impact of Climate Change on Ocean Salinity

Climate change is altering the salinity of the world’s oceans in several ways.

Changes in Rainfall and Evaporation

Changes in global weather patterns can lead to increased rainfall in some areas and increased evaporation in others. More rainfall dilutes the salt concentration in seawater, decreasing salinity. Conversely, higher evaporation rates increase salinity as the 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 the salt concentration, reducing the overall salinity in certain regions, particularly near the poles.

Sea Level Rise

Rising sea levels, caused by melting ice and thermal expansion of warming ocean water, can change salinity by causing more saltwater intrusion into freshwater systems like estuaries and aquifers.

Changes in Ocean Circulation

Changes in salinity can affect ocean currents because they’re driven in part by differences in water density, which is determined by salinity and temperature. Altering these currents can impact global climate patterns and disrupt marine ecosystems.

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

It’s a complex, interconnected system where shifts in one aspect can have far-reaching impacts, affecting biodiversity, food security, and the livelihoods of communities that rely on the ocean.

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