Seasonal Zooplankton Abundance and Size Fluctuations across Spatial Scales in Lake Pend Oreille, ldaho

Abstract

We studied seasonal zooplankton community dynamics along spatial scales in Lake Pend Oreille, Idaho in 1997-1998 to determine if zooplankton community changes brought about by establishment of Mysis relicta in the 1970's persist today, and to relate zooplankton length and abundance fluctuations to zooplanktivory. Long-term trends in zooplankton species composition and relative abundance, as well as seasonal patterns of species succession are apparently unchanged since M. relicta establishment. Cladoceran zooplankters became abundant earlier in the spring and remained abundant later into autumn in 1998 than in 1997. Fluctuations in zooplankton lengths and abundance were more pronounced along horizontal gradients extending from littoral to pelagic zones than along vertical gradients extending downward from the surface, and these fluctuations were more pronounced in 1998 than in 1997. Zooplankton length variability along spatial scales occurred most often in late springlearly summer, and in autumn. The trends we observed are consistent with prior speculation that zooplanktivory by M. relicta structures the Lake Pend Oreille zooplankton community, although abiotic factors may also explain our results.

Distribution, abundance, and vertical migrations ofLeptodora kindtiiin a mainstem Missouri River reservoir, Montana, USA

“…Abundances never reached those of the first sample period, however. The great temporal variation in Leptodora abundance during the study was consistent with numerous studies indicating that zooplankton populations fluctuate widely over the course of a growing season (Watson 1976;Wiedenheft 1984;Koapaha 1989;Clarke & Bennett 2003). When the suspended sediments begin to settle, the influx of nutrients associated with the inflow causes an increase in primary production which typically rapidly regenerates the abundance of consumers (Wetzel 2001).…”

Autumn‐to‐Spring Energetic and Diet Changes among Kokanee from North Idaho Lakes with and without Mysis relicta

“…Cladoceran densities declined in autumn, but still exceeded 1.0 individual/L in November. Presently, cladocerans are often absent from samples collected before July or after October (Rieman and Falter 1981;Clarke and Bennett 2003). However, stratification of the lake in midsummer reduces foraging of M. relicta in the epilimnion (Chipps and Bennett 2000), and midsummer zooplankton densities are similar to those measured historically.…”

Behavioral response of Lake Michigan Daphnia mendotae to Mysis relicta

“…This is because, at night, Mysis migrate up from the hypolimnion and lower metalimnion, into the upper metalimnion and lower epilimnion. D. mendotae have been shown to simultaneously migrate away from the regions inhabited by Mysis to higher regions in the epilimnion (Bowers and Vanderploeg 1982 (Clarke and Bennet 2003) and Flathead Lake, Montana (Spencer et al 1999).…”

“…It has been hypothesized that this vulnerability to Mysis contributes to a vertical diel migration by Daphnia spp. that minimizes spatial overlap, and therefore vulnerability (Bowers and Vanderploeg 1982, Spencer et al 1999, Clarke and Bennet 2003. Based on these patterns, we hypothesized that Mysis induce a change in Daphnia mendotae behavior, in particular vertical migration patterns, and we tested this hypothesis with laboratory experiments.…”