How freshwater mussels are threatened by sea-level rise

Freshwater mussels, known for their sensitivity to water quality changes, may be at heightened risk due to the impacts of increasing sea levels on coastal rivers. 

A recent investigation has shed light on the potential dangers that these species, along with other salt-sensitive organisms, face in the wake of climate-induced sea level changes.

Focus of the study 

The goal of the research, published in Environmental Toxicology and Chemistry, was to understand the threshold of sea salt concentration that could jeopardize the survival of juvenile mussels. 

This information is crucial in understanding the implications of rising sea levels on these species and the ecosystems they inhabit.

Increased salinity levels 

“Sea levels across the planet are rising, particularly along the eastern coast of the United States. Climate-induced sea level rise can result in the inundation and intrusion of seawater into freshwater drainages. This would alter salinity regimes and lead to the salinization of coastal freshwater ecosystems,” wrote the study authors. 

“Increased salinity levels in freshwater can negatively affect freshwater-dependent species, including native mussels belonging to the order Unionida, which are highly sensitive to changes in water quality.” 

“Sea salt is largely made up of sodium and chloride ions, forming sodium chloride, a known toxicant to freshwater mussels. However, sea salt is a mixture that also contains other major ions, including potassium, sulfate, calcium, strontium, and magnesium, among others.”

“Freshwater mussels exposed to sea salt would be exposed to each of the sea salt ions at the same time, resulting in a mixture toxicity effect. The mixture toxicity of these ions on early life stages of freshwater mussels is largely unknown because most research to date has evaluated individual salt ions in relative isolation.” 

How the research was conducted

To investigate, the researchers conducted acute toxicity tests on early life stages (glochidia and juvenile) of three freshwater mussel species. 

The southeastern coast of the US became the focal point of the study, given that this region has observed a consistent sea-level rise, ranging from 2 to 6mm annually. 

What the researchers learned 

The study revealed that salt water is toxic to both glochidia and juvenile life stages of freshwater mussels, with glochidia being the most sensitive life stage.

This is consistent with previous research that has shown glochidia to be the most sensitive life stage and that glochidia are more sensitive to sodium chloride than juveniles, noted the researchers.

By identifying the toxic levels of salt water for mussels at different stages of their life cycle, the study offers a roadmap for conservation initiatives. Such insights could pave the way for developing better strategies that factor in the challenges of sea level rise and the subsequent saltwater intrusion.

Study significance 

Study co-author Joseph McIver from North Carolina State University emphasized the global significance of the issue. 

“Climate change represents a serious threat to our aquatic ecosystems worldwide and the organisms that live there,” said McIver. 

“Protecting and conserving our already highly imperiled freshwater mussels is of paramount importance and our research on the effects of salinity and sea level rise will hopefully contribute valuable information toward these goals.”

Study implications 

The potential ramifications of sea level rise stretch beyond mussels and could reshape the balance of entire ecosystems. 

As freshwater sources face the threat of increased salinity, a ripple effect may be felt throughout the food chain, impacting not only salt-sensitive species but also the larger web of life they support.

Protecting vulnerable species like freshwater mussels may be a small piece of a much larger puzzle, but it is a critical step towards preserving the delicate balance of our planet’s ecosystems.

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