MEPS 263:217-234 (2003)  -  doi:10.3354/meps263217

ABSTRACT: Predator-prey dynamics between the sand shrimp Crangon septemspinosa and juvenile winter flounder Pseudopleuronectes americanus were examined in laboratory experiments to assess the joint effects of varying prey density and temperature on shrimp foraging behavior and flounder mortality. The functional response of shrimp to 6 densities of flounder was determined at 2 temperatures (10 and 16°C). The behavioral mechanisms underlying the shrimp¹s functional response were quantified with visual observations and compared to the foraging parameters predicted by continuous-time functional response models. Shrimp consumption rates increased significantly with increasing flounder density, irrespective of water temperature. At low flounder densities, however, significantly more flounder were consumed at 16°C than at 10°C. Analysis of proportional mortality of flounder across prey density and general functional response models revealed a sigmoidal, Type III functional response at 10°C, and a hyperbolic, Type II functional response at 16°C. Model parameter estimates and visual observations of shrimp foraging behavior suggest that the variable functional responses at different temperatures are the result of cold temperatures decreasing predator activity at low flounder densities, and conversely, shrimp maintaining high attack rates at low flounder densities when exposed to warm temperatures. These findings indicate that shrimp are capable of driving flounder populations to local extinction during warm water conditions. The recent warming trend experienced in northwest Atlantic estuaries, and its impact on trophic dynamics, may therefore explain the failure of the winter flounder stocks to recover in these areas.

KEY WORDS: Crangon septemspinosa · Pseudopleuronectes americanus · Sand shrimp · Winter flounder · Functional response · Foraging behavior · Predation