Laboratory-derived temperature preference and effect on the feeding rate and survival of juvenile Hemimysis anomala

Hemimysis anomala is a warm-water mysid that invaded the Great Lakes region in 2006 and has since rapidly spread throughout the basin. We conducted three laboratory experiments to better define the temperature preference, tolerance limits, and temperature effects on feeding rates of juvenile Hemimysis, using individuals acclimated to mid (16°C) and upper (22°C) preferred temperature values previously reported for the species. For temperature preference, we fit a two-parameter Gaussian (μ, σ) function to the experimental data, and found that the peak values (μ, interpreted as the preference temperature) were 22.0°C (SE 0.25) when acclimated to 16 and 21.9°C (SE 0.38) when acclimated to 22°C, with the σ-values of the curves at 2.6 and 2.5°C, respectively. No mysids were observed in temperatures below 10 or above 28°C in these preference experiments. In short-term tolerance experiments for temperatures between 4 and 32°C, all mysids died within 8h at 30.2°C for 16°C acclimated mysids, and at 31.8°C for 22°C acclimated mysids. No lower lethal limit was found. Feeding rates increased with temperature from an average of 4 Bosmina eaten per hour at 5°C to 19 Bosmina eaten per hour at 27°C. The results of our experiments indicate an optimal temperature for Hemimysis between 21 and 27°C, which corresponds with temperatures during periods of high population growth in the field. These results contribute a better understanding of this species' biological response to temperature that will help guide field studies and inform bioenergetics modeling.