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 linear relationship (r² = 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 O₂ mussel^-1 h^-1) were both strongly and similarly related to soft-tissue wet mass (r² > 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 vary with mussel sizes. Independent statistical tests revealed that the ETS-respiration rate relationship provided accurate estimates of respiration rates in zebra mussel individuals and populations. After calibration of the ETS-respiration rate ratio, we used the relationship to estimate in situ oxygen demand by zebra mussel populations in the Upper Mississippi River. There was a strong relationship between oxygen demand (mg O₂ m^-2 h^-1) and zebra mussel density per square meter (r² = 0.93, p < 0.0001). A zebra mussel population of approximately 23,000 individuals/m² is estimated to have an oxygen demand of 9.41 g O₂ m^-2 d^-1, twice as high as that of highly enriched organic deposits. Dense populations of zebra mussels are expected to exert strong demands on the oxygen resources of large rivers.