Mysis relicta: Assessment of Metalimnetic Feeding and Implications for Competition with Fish in Lakes Ontario and Michigan

Abstract

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.

Acoustic characterization of Mysis relicta

“…m Ϫ3 . Mysids reach such densities or higher (Moen and Langeland 1989;Lehman et al 1990;Johannsson 1995). If this acoustic backscattering is assumed to be fish, fish abundances might be severely overestimated.…”

“…Mysids collected in the Lake Ontario and Cayuga Lake samples were later enumerated, sexed, and measured (tip of the rostrum to base of telson) to the closest millimeter. Lengths and densities were converted to dry weights (DWs) based on the relationship ln(weight) ϭ Ϫ12.27 ϩ 2.72 ϫ ln(length) (Johannsson 1995), where lengths were in millimeters and DWs in grams.…”

“…k is the wave number (ϭ2/), a is the radius of the cylinder cross-section, and s L is the standard deviation of the length. The cylindrical cross-section, a, was deter- mined assuming a DW to WW ratio of 0.15 (Johannsson et al 1994); volume was defined as V ϭ WW ϫ 10 Ϫ6 , and a ϭ (V/L) 0.5 , where weights are in grams and lengths in meters (Demer and Martin 1995). Pϭ2 was defined as Ϫ(/ 2)ka/(ka ϩ 0.4).…”

Assessing the impact of a recent predatory invader: The population dynamics, vertical distribution, and potential prey of Cercopagis pengoi in Lake Ontario

“…Furthermore, apparent year-class strength of alewife cannot explain why the greatest impacts on smallbodied zooplankton occurred in 2000. Finally, Mysis relicta is an important planktivore in Lake Ontario, but mysid planktivory is restricted to water depths below the thermocline due to their avoidance of temperature and light during the summer (Johannsson et al 1994). …”

Behavioral response of Lake Michigan Daphnia mendotae to Mysis relicta

“…Invertebrate predators are recognized as playing a critical role in the structure of aquatic food webs, including those of the Great Lakes food webs (Bowers and Vanderploeg 1982, Branstrator and Lehman 1991, Johannsson et al 1994, Schulz and Yurista 1998. To fully understand the effects of invertebrate predators it may be important to determine if they affect zooplankton prey phenotype such as vertical position.…”