EFFECT OF SALINITY AND TEMPERATURE ON SURVIVAL AND DEVELOPMENT OF YOUNG ZEBRA (DREISSENA-POLYMORPHA) AND QUAGGA (DREISSENA-BUGENSIS) MUSSELS

We reared larval zebra mussels, Dreissena polymorpha, and quag ga muss els, D. bugensis, through and beyond metamorphosis (settlement) at sal inities of 0-8 parts per thousand. Juvenile zebra mussels gradually ac climated to 8 parts per thousand and 10 parts per thousand have been r eared at these salinities for over 8 mo. Tolerance to both higher temp eratures and higher salinities increases with larval age in both speci es (though zebra mussel embryos and larvae have a greater degree of sa linity tolerance than quagga mussel embryos and larvae). Thus, only 6% of 3-day-old zebra mussel veligers survived after exposure to 4 parts per thousand for 8 additional days, whereas there was 22% survival of veligers placed in 4 parts per thousand at day 13 and grown to settle ment 11 d later. Zebra mussel pediveligers, acclimated to increasing s alinity in 2 parts per thousand increments beginning at day 23, contin ued to survive and grow in 8 parts per thousand after 5-mo exposure, t hough the growth rates of these juveniles were significantly less than those of juveniles reared in lower salinities. Quagga mussels did not metamorphose and settle as quickly as zebra mussel pediveligers. No q uagga mussel pediveligers had settled before exposure to artificial fr esh water (AFW), 2 parts per thousand, 4 parts per thousand, 6 parts p er thousand, and 8 parts per thousand on day 30. Percent settlement of these quagga mussel juveniles (based on 100% survival at the start of experiments on day 30) was 90% in AFW, 67% at 2 parts per thousand, 6 9% at 4 parts per thousand, 46% at 6 parts per thousand, and 0.1% at 8 parts per thousand.