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Clarke, M. and R. F. McMahon, 1996. The Effects of Hypoxia and Low-frequency Agitation on Byssal Attachment and Byssal Thread Production in Zebra Mussels (Dreissena polymorpha), The University of Texas at Arlington Abstract from The Sixth International Zebra Mussel and Other Aquatic Nuisance Species Conference, Dearborn, Michigan, March 1996 The Effects of Hypoxia and Low-frequency Agitation on Byssal Attachment and Byssal Thread Production in Zebra Mussels (Dreissena polymorpha)The effects of hypoxia and low-frequency agitation on byssal thread formation were studied in zebra mussels. Adult specimens were collected from the Niagara River at Black Rock Navigation Lock, Buffalo, New York, and shipped overnight emersed on moist paper toweling in a cooled, insulated container to Arlington, Texas, where they were held at a constant temperature of 5°C until experimentally utilized. Prior to experimentation, mussels were acclimated to 25°C > 14 days. Their byssal threads were then removed by cutting at the byssal gape. For agitation experiments, debyssated mussels were allowed too byssally reattach to 7x7x0.2 mm clear plexiglass plates overnight. In hypoxia experiments, debyssated mussels reattached to 14x14x0.2 mm plexiglass plates. In agitation experiments, mussels attached to plexiglass plates were immersed in a fixed position within a tank holding 15 l of continuously aerated water held at 25°C. The tank was agitated on the stage of a shaker bath allowing water to be cycled back and forth across the mussels at rates of 0, 10, 15, 30 or 40 cycles per minute (cpm). For testing hypoxia effects, plates with attached mussels were immersed in 5 l plastic tanks holding 4 l of water. The tanks were fitted with plastic covers providing a 1 l gas-head space. Tank media was held at 25°C and bubbled with mixtures of O2 and N2 gas to maintain O2 concentrations of 0.41 ppm O2 (Po2 = 8.0 Torr), 0.81 ppm O2 (15.9 Torr), 1.24 ppm O2 (23.9 Torr), 1.65 ppm O2 (31.8 Torr), and 8.26 ppm O2 (159.1 Torr). In both experiments, media was changed every two days. During the 21 day exposure periods of both experiments, plates were removed daily and the number of newly produced byssal attachment plaques for each individual counted. Sample size for all treatments was 20 individuals except that at 40 cpm in which only 10 individuals remained attached over the 21-day experimental period. A multifactor analysis of variance (MFANOVA) with days of exposure as a repeated measure indicated that O2 concentration significantly affected byssal thread production rate (P < 0.05). A least squares difference test (LSD) indicated that, by 7 days exposure, byssal thread production was not different in the 23.9, 31.8 and 159.1 Torr treatments, but was significantly reduced at Po2’s of 15.9 Torr (reduced by ~ 62%) and 8.0 Torr (reduced by ~ 73%). The apparent critical Po2 of 15.9 Torr for inhibition of byssal production coincides with that for zebra mussel survival of hypoxia at 25°C and is further evidence of the low hypoxia tolerance of D. polymorpha relative to most native N.A. freshwater bivalves. MFANOVA with days as a repeated measure indicated that agitation rate significantly affected zebra mussel byssal thread production, byssal thread production being generally inhibited with increasing agitation. LSD testing indicated that, after 21 days, byssal thread production was similar among the 0, 10 and 15 cpm treatments and the 30 and 40 cpm treatments. However, at 40 cpm, it was significantly inhibited relative to the rates achieved at 0, 10 and 15 cpm and at 30 cpm it was significantly reduced relative to that achieved at 0 ppm and 15 cpm. Suppression of byssus production by low-frequency agitation may prevent successful establishment of adult zebra mussels in wave-swept shallow waters (< 1 m depth), inhibit their attachment to the hulls of small, shallow-draft vessels and could be utilized to control mussel fouling in raw water systems.
Keywords: Zebra_mussel, Byssal_attachment, Colonization |