Seasonal changes in the respiratory electron transport system (ETS) and respiration of the zebra mussel, Dreissena polymorpha in Saginaw Bay, Lake Huron

Electron transport system activity (ETS) and respiration rates (R) of the z ebra mussel, Dreissena polymorpha, were determined monthly from April to No vember over 2 years at two sites in Saginaw Bay, Lake Huron. The sites were located in the inner and outer bay and contrasted in food quantity and qua lity. ETS ranged from 2 to 40 mug O-2 mg DW-1 h(-1) over the study period. Both ETS and respiration were strongly related to temperature, and maximum values were found between June and August. ETS also peaked in June/July whe n assays were conducted at a constant temperature (25 degreesC), indicating other factors besides temperature affected metabolic activity. R:ETS ratio s decreased with increased temperature at the inner bay site, but trends we re minimal at the outer bay site. In late summer, blooms of the cyanophyte Microcystis occurred in the inner bay, likely depressing filtration rates, and leading to lower respiration rates relative to ETS. ETS activity was co nsistently higher in the outer bay and was likely a result of higher food q uality. Despite these spatial differences, annual mean R:ETS ratios varied only from 0.04 to 0.09 at the two sites over the 2-year period. Based on th ese values, ETS may be useful as an indicator of long-term metabolic activi ty in annual energy budgets of D. polymorpha. However, food conditions diff erentially affect respiration relative to ETS, and variability in this rati o must be considered when interested in shorter time scales.