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 spring/early 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.