Comparative energetics and life cycle of the opossum shrimp (Mysis relicta) in native and non‐native environments

Summary 1. Life history, fecundity and energy ingestion were compared for non‐native Mysis relicta in Flathead Lake, Montana, and in Waterton Lake, Montana/Alberta, where the mysid is native. 2. Based on estimates from stomach contents, M. relicta in Flathead Lake consumed three to four times more energy per hour while foraging than M. relicta from Waterton Lake. The primary prey of M. relicta in Flathead Lake was Daphnia thorata . Diaptomus sicilis was the primary prey for M. relicta in Waterton Lake. 3. Mysis relicta in Flathead Lake had a 1‐year life history. It took 2 years for M. relicta in Waterton Lake to complete a generation. Mysis relicta from Flathead Lake produced significantly ( P < 0.05) more eggs per female (19.9 ± 4.7) compared to M. relicta in Waterton Lake (13.7 ± 3.6). The lipid content in eggs from M. relicta in Flathead Lake was also significantly ( P < 0.05) higher than eggs from M. relicta in Waterton Lake. 4. In Flathead Lake, M. relicta is able effectively to exploit Daphnia thorata , consuming greater biomass than M. relicta in Waterton Lake. Mysis relicta efficiently assimilates the greater biomass, which reduces generation time, increases fecundity, and increases lipid reserves of offspring. These results provide evidence of energetic mechanisms that enable M. relicta to colonize and affect foodwebs when introduced into lakes.