Mysis relicta: Assessment of Metalimnetic Feeding and Implications for Competition with Fish in Lakes Ontario and Michigan
Mysis relicta and planktivorous fish in Lakes Ontario and Michigan both feed on crustacean zooplankton in the metalimnion. Are these zooplankton sufficient to meet the energy requirements of mysids? Could mysids remove a significant proportion of zooplankton production? Are the energy requirements in the two lakes similar? Comparisons in Lake Ontario of zooplankton consumption based on clearance rates, with energy requirements based on bioenergetic modelling, revealed that individual mysids, particularly larger ones, required additional energy sources. The denser mysid populations beyond 100 m depth in Lake Ontario could exert high mortality rates on metalimnetic zooplankton, remove a significant proportion of daily zooplankton production, and consequently, potentially compete with planktivorous fish. At depths < 100 m, the mysid population was smaller and could remove only 6–19% of zooplankton production per day in summer when competition with planktivorous fish would be maximal. Generation time is shorter in Lake Michigan because winter growth rates remain high. Consequently, less energy is required to complete a generation in Lake Michigan than in Lake Ontario.