Range expansion and potential dispersal mechanisms of the exotic cladoceran Daphnia lumholtzi

. Recently the exotic cladoceran Daphnia lumholtzi has invaded freshwater systems throughout the southern and midwestern United States. We conducted regional surveys of eastern Kansas reservoirs to document the range expansion of D.lumholtzi. Daphnia lumholtzi was found in five of 35 reservoirs sampled in 1994, and 11 of the 35 reservoirs when re-sampled in 1997. In addition, we sampled 40 small ponds inaccessible to recreational boats, within the watershed of an invaded reservoir. We did not find D.lumholtzi in any of these ponds, suggesting that non-human dispersal mechanisms play an insignificant role in the range expansion of D.lumholtzi throughout the United States. Further experimentation, however, is needed to determine if the absence of D.lumholtzi from these small ponds is due to insufficient dispersal mechanisms or the inability of this invader to successfully colonize following arrival. Daphnia lumholtzi has broad limnological tolerances. However, invaded reservoirs tend to be larger in area, have higher Secchi disk depths, and lower total phosphorus, total nitrogen and chlorophyll a levels relative to non-invaded reservoirs. Analyses of pre-invasion zooplankton communities indicate that D.lumholtzi may be invading reservoirs in which native Daphnia species are rare. While the long-term effects of the invasion of D.lumholtzi are unknown, it has the potential to dominate late summer zooplankton communities in eastern Kansas reservoirs. Therefore, we need to continue to survey and monitor invaded reservoirs to document the range expansion of D.lumholtzi and determine the long-term implications of the introduction of this invader.