DAILY SETTLEMENT RATES OF THE ZEBRA MUSSEL, DREISSENA-POLYMORPHA, ON AN ARTIFICIAL SUBSTRATE CORRELATE WITH VELIGER ABUNDANCE

The relationship between daily settlement rates and local concentratio ns of veligers of the zebra mussel, Dreissena polymorpha, was investig ated using plankton sampling and scouring pad collectors. A total of 1 02 plankton and 136 collector samples were taken from a nearshore site near Wheatley, Ontario, in west-central Lake Erie, over 17 consecutiv e d in August 1992. Results demonstrate a strong correlation between d aily settlement rates and daily concentrations of late-stage (competen t) veligers in the water column (determined at shell lengths greater-t han-or-equal-to 170 mum; r = 0.93-0.98; p < 0.001; log10-transformed d ata). Variations in settlement rates of 1-3 orders of magnitude occurr ed within 24-96 h. Results also suggest that wind-induced hydrodynamic s can affect settlement rates of zebra mussel larvae; the period used to monitor settlement (24 h) was much shorter than that employed (appr oximately 1-2+ wk) in previous studies. Daily monitoring of concentrat ions of late-stage veligers in the water column as well as settlers (f ibrous collectors) may help to identify biological and physical factor s affecting short-term variability in settlement; it may also prove ad vantageous for industries where early detection of colonization by the zebra mussel is critical for cost-effective control of this invasive mollusc.