RANGE AND FECUNDITY OF DAPHNIA LUMHOLTZI IN THE ILLINOIS
RIVER

Kip E. Stevenson1, James A. Stoeckel1, K. Douglas Blodgett1 and Richard E.
Sparks2 

1 Illinois Natural History Survey, LTRMP La Grange Field Station, 704 N.
Schrader Ave., Havana, IL 62644
2 Illinois Natural History Survey, Forbes Biological Station, River Research Lab,
P.O. Box 590, Havana, IL 62644

     Daphnia lumholtzi, an exotic zooplankter, was first detected in the Illinois
River in 1995.  At this time, D. lumholtzi was found from the confluence of the
Illinois and Mississippi River to as far north as Illinois River Mile (IRM) 195.9. 
In 1996 we conducted several studies in the Illinois River to 1) monitor the
abundance of this species throughout the year, 2) monitor any northward range
expansion towards Lake Michigan, and 3) examine the effects of suspended
sediments, spine length and temperature on the fecundity of this species. 
Zooplankton samples were collected twice a week at IRM 121.1.  Head spine
length, tail spine length, body length and clutch size were determined for > 100
individuals/sample.  Water temperature, and suspended solids quantity and quality
were also monitored throughout the study.  
     In 1996, highest egg production occurred in July and late August with
clutch sizes ranging from 2 to 19 eggs/female.  Only those individuals with body
lengths > 800 m produced eggs.  Preliminary data indicates that clutch size was
not affected by suspended solids quantity or quality in the ranges observed in the
main channel and an associated backwater area.  Clutch size did not seem to be
affected by changes in spine length, indicating that any energetic costs associated
with spine production were not reflected in reduced egg production.  Temperature
seems to be the main factor regulating abundance and fecundity of this species in
the Illinois River. 
     Daphnia lumholtzi may have expanded its range northward in 1996.  In
1995 this species was found as far north as IRM 195.9 (130 river miles from Lake
Michigan). In 1996 D. lumholtzi was found in the Cal-Sag Channel approximately
30 river miles from Lake Michigan.  The invasion of Lake Michigan by this
species appears imminent although whether or not this species will be able to
successfully reproduce in the colder waters remains to be seen.

Keywords: Daphnia lumholtzi, fecundity, Illinois River, spines, suspended solids


Kip E. Stevenson
Illinois Natural History Survey, La Grange Field Station
704 N. Schrader Ave.
Havana, IL 62644
Phone: (309) 543-6000, Fax: (309) 543-2105
E-mail: kip_stevenson@nbs.gov

Preference: Platform presentation, will present poster