EFFECTS OF TEMPERATURE ON BYSSAL THREAD PRODUCTION BY THE FRESH-WATERMUSSEL, DREISSENA-POLYMORPHA (PALLAS)

Byssal thread production by specimens of Dreissena polymorpha (papas, 1771) was monitored at water temperatures of 5 degrees, 10 degrees, 15 degrees, 25 degrees and 30 degrees C following re-attachment. Increme ntal increases in byssal thread number were recorded and the mean numb er of byssal threads produced by 20 mussels at each temperature calcul ated over a 21 day period. Rate of byssal thread production increased proportionally with increasing temperature, the slowest rate being at 5 degrees C, the highest rate at 30 degrees C, just 1 degrees C below the reported upper lethal temperature for this species. A significantl y greater number of byssal threads were formed by mussels exposed to h igh test temperatures (15 degrees, 25 degrees and 30 degrees C) than t hose exposed to low temperatures (5 degrees and 10 degrees C). At 30 d egrees C, byssus reformation appeared to consist of two phases, an ini tial phase of rapid thread production (1-7 days), followed by a phase in which production rate slowed (8-21 days). At low temperatures, ther e was no evidence of a two phase re-formation of the byssal mass withi n the experimental time period, the rate of thread production being co nstant throughout. This suggests that the length of the initial phase of rapid byssal thread production is temperature dependent. Mussels ma intained at lower temperatures could have remained in the initial phas e of byssal mass re-formation throughout the 21 day experimental perio d. Alternatively, mussels held at low temperatures could produce a mat ure byssus containing significantly fewer byssal threads than those ex posed to higher environmental temperatures.