Effects of progressive hypoxia on oxygen uptake in juveniles of the Peruvian scallop, Argopecten purpuratus (Lamarck, 1819)

International audienceA field survey performed in Paracas Bay (Peru), a major scallop culture area, showed that the Peruvian scallop, Argopecten purpu-ratus, periodically faces severe hypoxic events. Oxygen uptake rate (VO2) of A. purpuratus juveniles facing progressive decrease of environmental oxygen saturation (from 100% to 5%) was measured at two contrasting temperatures ("normal condition" = 16°C and "warm condition" = 25°C). In normoxia, (oxygen saturation >70%) average VO2 was significantly (p < 0.001) higher in warm condition (0.20 ±0.004 mgO 2 ind −1 h −1) than in normal condition (0.12 ±0.007 mgO 2 ind −1 h −1). The shape of the VO2 response curve during increasing hypoxic conditions was evaluated using a segmented linear regression. The break points between linear segments allowed estimating the oxygen critical points (PcO2 , oxygen saturation units), while the slopes of the various segments was used to assess the VO2 regulatory capacity. In both temperature conditions at oxygen saturation lower than PcO2 , VO2 was a fourth of the values recorded in normoxic condition. This trend was more pronounced in the warm condition. Paradoxically, the estimated PcO2 was lower in warm condition (21.4% ±0.7) compared to the normal condition (24.4% ±1.9). However, the study of the slopes at oxygen saturations higher than PcO2 revealed that A. purpuratus can regulate its respiratory rate similarly and efficiently at both 16 and 25°C. Moreover, for VO2 above PcO2 , the estimated Q10 between normal and warm conditions was 1.78 (Arrhenius temperature = 4983 K), highlighting a moderate effect of temperature on VO2. These results reflect the adaptive capacity of this species to the changing environment along the Peruvian-Chilean coasts influenced by upwelling system and ENSO events. However, results from this study indicate that, at least during some periods, A. purpuratus spend more than 70% of its time exposed to hypoxic conditions below the estimated PcO2. Such conditions could have negative consequences on the species metabolism and harm the performance of A. purpuratus culture