Interactions Between Non-Native Western Mosquitofish and Native Bluegill Sunfish: Mesocosm Experiments

Area of Science:

• Ecology
• Invasive Species Biology
• Freshwater Ecology

Background:

• Invasive species negatively impact aquatic ecosystems.
• Biotic resistance by native species can mitigate invasive species impacts.
• Western Mosquitofish (Gambusia affinis) is a highly impactful invasive freshwater fish.

Purpose of the Study:

• To investigate the ecological interactions between native Bluegill Sunfish (Lepomis macrochirus) and invasive Western Mosquitofish (Gambusia affinis).
• To assess the potential for native species to exert biotic resistance against invasive fish.

Main Methods:

• Two mesocosm experiments were conducted in different years.
• Juvenile Bluegill Sunfish and adult Western Mosquitofish were used to examine interspecific and intraspecific interactions.
• Impacts on zooplankton communities were assessed.

Main Results:

• Interactions between Lepomis macrochirus and Gambusia affinis were observed but were asymmetric.
• Lepomis macrochirus were more affected by intraspecific interactions, while Gambusia affinis were more affected by interspecific interactions.
• Both species reduced large zooplankton abundance; invasive fish presence decreased total zooplankton.

Conclusions:

• Native Lepomis macrochirus can reduce the establishment and population maintenance of invasive Gambusia affinis through competition and intraguild predation.
• Consistent results across experiments support the role of native fish in biotic resistance.
• Controlling invasive Gambusia affinis benefits native fish and overall aquatic community health.