The herbivorous habits of Mysis relicta in Lake Michigan 1

Abstract

IIerbivorous feeding by Mysis relicta on three size fractions of natural phytoplankton from Lake Michigan was measured from the change in concentration of chlorophyll a. Mysis fed primarily on the largest size fraction. When offered only the largest size fraction, Mysis fragmented the material and the fragments were observed as increases in the smallest size fraction Diuptomus ashlandi, which could feed only on the smallest size fraction, is a possible recipient of such fragmented cells or chains. A simple compartmental model indicated that filtering rates of Mysis were significantly greater on the largest than on the smallest fraction, and that during feeding 56% of the largest size fraction was broken up into the smallest size fraction. Mysis may feed on large phytoplankton by migrating at night into a chlorophyll a maximum in the thermocline containing mostly the largest size fraction. Moonlight inhibited the ascent of Mysis at night and may indirectly affect phytoplankton mortality due to mysid grazing.

The possibility of predator avoidance by Lake Michigan zooplankton

“…2c) . These observations are similar to those of Beeton (1960), Bowers & Grossnickle (1978), and Bowers & Vanderploeg (1982) . Furthermore, sonar recorded an aggregation of small fish from the surface to 12 m between 2100 h August 29 and 0500 h August 30 (Fig .…”

“…Studies of the vertical community structure in Lake Michigan have shown that maximum concentrations of planktivorous fish, omnivorous mysids, and chlorophyll a often coincide during summer stratification (Brooks & Torke, 1977;Bowers & Grossnickle, 1978 ;Janssen & Brandt, 1980). Relationships between distributions of all these taxa and the microcrustaceans in the lake have not, however, been reported previously.…”

Feeding of Mesopodopsis slabberi (Crustacea, Mysidacea) on naturally occurring phytoplankton

“…Bowers & Grossnickle (1978) felt that differential grazing pressure through selectivity might be a mechanism influencing phytoplankton community composition. In this light, possible interactions between Mesopodopsis slabberi and the large diatoms Asterioneila glaciahs and Aulacodiscus luttonii require further investigation as both species are potentially capable of generating accumulations in the surf zone.…”

“…Clutter (1966) suggested that the accumulation of a large amount of detrital food outside the breaker zone could be the major factor influencing the distribution of nearshore mysids such as Metamysidopsis elongata. Bowers & Grossnickle (1978) and Grossnickle (1979) have shown that Mysis relicta in Lake Michigan feeds on phytoplankton at night by migrating to the subsurface layer containing maximum chlorophyll a concentrations. A similar feeding strategy, involving shoreward migration at night to behind the breaker line where rip currents deposit Anaulus birostratus and detrital food material, may be practised by Mesopodopsis slabberi.…”

“…Mysis relicta is considered to be a major grazer of phytoplankton in Lake Michigan (Bowers & Grossnickle 1978) and in Lake Vattern, Sweden (Stalberg 1933), but most mysid feeding experiments to date have dealt with predation on zooplankton (Parker 1979, Cooper & Goldman 1980, Murtaugh 1981, Fulton 1982, Folt et al 1982, Johnston & Lasenby 1982 and there are currently insufficient data to allow a clear understanding of the dynamics of phytoplankton grazing by these animals. This study was designed to investigate some aspects of the feeding behaviour of Mesopodopsis slabberi on the most common accummulation-forming diatom species occuring in Algoa Bay.…”