IN-SITU ESTIMATION OF ZEBRA MUSSEL METABOLIC RATES USING THE ELECTRON-TRANSPORT SYSTEM (ETS) ASSAY

We used the electron transport system (ETS) assay to estimate in situ respiration rates of zebra mussels. Laboratory studies revealed a line ar relationship (r(2) = 0.93) between respiration rates and ETS enzyme activity across all sizes of mussels tested (10-30 mm shell length; 0 .03-0.55 g tissue wet mass); ETS activity and respiration rates (mg 0, mussel(-1) h(-1)) were both strongly and similarly related to soft-ti ssue wet mass (r(2) > 0.92). Zebra mussels used only 6-7% of their ETS for respiration (R); this average R/ETS ratio of 0.06-0.07 did not va ry with mussel sizes. Independent statistical tests revealed that the ETS-respiration rate relationship provided accurate estimates of respi ration rates in zebra mussel individuals and populations. After calibr ation of the ETS-respiration rare ratio, we used the relationship to e stimate in situ oxygen demand by zebra mussel populations in the Upper Mississippi River. There was a strong relationship between oxygen dem and (mg O-2 m(-2) h(-1)) and zebra mussel density per square meter(r(2 ) = 0.93. p < 0.0001). A zebra mussel population of approximately 23,0 00 individuals/m(2) is estimated to have an oxygen demand of 9.41 g O- 2 m(-2) d(-1), twice as high as that of highly enriched organic deposi ts. Dense populations of zebra mussels are expected to exert strong de mands on the oxygen resources of large rivers.