S. Burkhardt, SEASONAL SIZE VARIATION IN THE PREDATORY CLADOCERAN BYTHOTREPHES CEDERSTROEMII IN LAKE-MICHIGAN, Freshwater Biology, 31(1), 1994, pp. 97-108
1. Dry weight, body length and spine length were measured for the exot
ic cladoceran Byrhotrephes cederstroemii collected from offshore and i
nshore stations in southeastern Lake Michigan. Average dry weight of e
ach developmental stage exhibited seasonal variation by a factor of mo
re than 5. 2. Mean dry weight of Bythotrephes was closely correlated w
ith water temperature. Contrary to the inverse relationship between wa
ter temperature and body size frequently observed for other invertebra
tes, the dry weight of Bythotrephes increased at higher ambient temper
atures. 3. No significant correlation was observed between abundances
of major zooplankton taxa and the dry weight of Bythotrephes. An indir
ect effect of temperature on prey consumption may cause seasonal varia
tion in dry weight of Bythotrephes in Lake Michigan. 4. Distances betw
een adjacent pairs of barbs, added to the caudal spine with each moult
; are significantly shorter in Bythotrephes which produce resting eggs
. Less material investment in the exoskeleton of sexually reproducing
females was observed in favour of growth and reproduction.