Effects of current velocity on byssal-thread production in the zebra mussel (Dreissena polymorpha)

Abstract

The effect of current velocity on byssal-thread production by adult zebra mussels (Dreissena polymorpha) was investigated. The number of threads produced by 20 individuals at currents of 0.10, 0.15, 0.20, 0.27 m/s was recorded daily over 21 consecutive days, after which individual shell length and dry tissue masses were measured and the byssal complex was removed. Increasing the current velocity from 0.10 to 0.20 m/s significantly elevated rates of byssal-thread production, but the rate was reduced at 0.27 m/s. Current-induced suppression of byssal-thread production may be due to mechanical disturbance of attached mussels, interfering with their ability to press the tip of the foot against the substratum as the thread cures. The mean thread number in a newly formed byssal complex after 21 days was 52.5, 63.8, 73.3 and 60.4 at currents of 0.10, 0.15, 0.20 and 0.27 m/s, respectively. Current velocity had no effect on thread width. The mean number of threads found in the byssal complex of individuals from the wild taken from the same population from which experimental subjects were drawn was 148.3/mussel. There was no correlation between thread number and shell length in the wild population. Results indicate that there are both similarities and differences in the response of byssal-thread production to variable current velocity in freshwater dreissenids and marine mytilids.