Differing effects of suspended sediments on the performance of native and exotic Daphnia

Freshwater Biology
Soeken-Gittinger, ;Stoeckel, James;Havel,
Pub ID:
1. Although large cladocerans are usually uncommon in large rivers, Daphnia lumholtzi (an
exotic species in North America) is widespread and occasionally abundant. We
collected zooplankton on the Illinois River (Illinois, U.S.A.) in 1995 and 1996 and found
that the peak density of D. lumholtzi (25 L)1) typically exceeded that of all native species
combined. Maximum density occurred during warm periods (up to 27 C) when
concentrations of inorganic suspended sediments were high (>50 mg L)1).
2. Using a life table experiment, we examined the effects of variation in suspended
sediment (0 and 80 mg L)1) and food (104 and 105 Ankistrodesmus cells mL)1) on fitness of
D. lumholtzi and the native Daphnia parvula. Daphnia lumholtzi had greater survivorship
than D. parvula in most treatments and higher life-time fertility than D. parvula in all
treatments. Both species achieved their fastest intrinsic rates of growth in treatments
with high food, but their responses to suspended solids differed. The growth rate of
D. lumholtzi in high food was slightly increased by higher turbidity, whereas that of
D. parvula was depressed.
3. Results suggest that the ability of D. lumholtzi to tolerate suspended solids is an
important factor contributing to its success in invading North American rivers.
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