Is salinity an obstacle for biological invasions?

Area of Science:

• Ecology
• Evolutionary Biology
• Invasive Species Research

Background:

• Marine and brackish species invasions into freshwater habitats are increasing, with many originating from the Ponto-Caspian region.
• Ponto-Caspian species have established in diverse regions, including the North and Baltic Seas and the Great Lakes-St. Lawrence River.
• Understanding salinity tolerance is crucial for predicting invasive species success.

Purpose of the Study:

• To investigate if Ponto-Caspian taxa acclimatize and colonize diverse salinity habitats more readily than taxa from other regions.
• To compare the salinity tolerance of Ponto-Caspian, Northern European, and Great Lakes-St. Lawrence River gammarid species.
• To explore the evolutionary relationships among these species and their populations.

Main Methods:

• Laboratory experiments were conducted on 22 populations of eight gammarid species across different salinity levels.
• A literature search was performed to determine the global salinity ranges of the studied species.
• Mitochondrial cytochrome c oxidase subunit I (COI) gene sequencing was used to analyze evolutionary relationships.

Main Results:

• All tested gammarid populations demonstrated tolerance to a wide range of salinities.
• Ponto-Caspian taxa exhibited lower mortality in freshwater conditions.
• Northern European taxa showed lower mortality in fully marine conditions, indicating regional adaptations.

Conclusions:

• Ponto-Caspian and Northern European species appear adapted to freshwater and marine environments, respectively.
• The perceived higher success of Ponto-Caspian invaders may be influenced by introductions into variable habitats like shipping ports.
• Environmental variability in introduction sites, including freshwater conditions, can limit the establishment of marine-origin species.