Size-selective predation by roach (Rutilus rutilus) on zebra mussel (Dreissena polymorpha): field stuides

Area of Science:

• Ecology
• Ichthyology
• Invertebrate Zoology

Background:

• Roach (Rutilus rutilus) are known predators in freshwater ecosystems.
• Zebra mussels (Dreissena polymorpha) are an invasive species impacting aquatic environments.
• Predator-prey size dynamics are crucial for understanding food web interactions.

Purpose of the Study:

• To investigate the size-dependent predation of roach on zebra mussels.
• To determine the optimal foraging strategy for roach feeding on zebra mussels.
• To analyze the cost-benefit ratio of mussel consumption for different roach sizes.

Main Methods:

• Field observations of roach predation on zebra mussels in a eutrophic lake.
• Analysis of mussel size selection relative to abundance and accessibility.
• Application of an optimal foraging model incorporating prey size, predator mouth size, crushing resistance, and energy content.

Main Results:

• A distinct size threshold (∼160 mm standard length) was observed, above which roach began preying on zebra mussels.
• Roach exhibited size-selective predation on mussels, deviating from their availability.
• Ingested mussel size by larger roach (≥220 mm) aligned with a predator mouth size to prey size ratio of 0.59.
• Fish smaller than 160 mm had a high cost-benefit ratio for consuming small mussels.
• Optimal switch to significant Dreissena consumption was predicted for roach of 230-240 mm.

Conclusions:

• Roach exhibit a clear size-dependent feeding strategy for consuming zebra mussels.
• Optimal foraging theory explains the observed size selection based on energetic costs and benefits.
• Predator size and prey characteristics significantly influence predator-prey dynamics in this ecosystem.