Physiological performance of Gammarus chevreuxi under normoxia and moderate hypoxia. (a) Rates of mass-specific O2 uptake, (b) heart rate, (c) ventilation rate, (d) expression levels (variance stabilised counts) of ten transcripts putatively identified as haemocyanin. ID represents the most significant annotation, (e) haemocyanin (λ = 335 nm) to protein (λ = 280 nm) ratios and (f) contribution to the total gill area of gills from each pereon segment. Gill form outlines from a representative adult male are given above the bars. Numbers identify pereopod of origin. Amphipods were exposed to either normoxic (100% air saturation) or hypoxic (40% air saturation) conditions for one week. Mechanisms investigated are those typically associated with responses to short-term (hours to days), (b–c) and prolonged (weeks to months), (d–f) exposure to hypoxia in crustaceans. Values are expressed as mean ± s.e.m. Letters above bars indicate significant differences between groups (P < 0.05).