Northern shrimp (Pandalus borealis) oxygen consumption and metabolic enzyme activities are severely constrained by hypoxia in the Estuary and Gulf of St. Lawrence Aurélie Dupont-Prinet a, ⁎, Marion Pillet a , Denis Chabot b , Tanya Hansen b , Réjean Tremblay a , Céline Audet a a Institut des Sciences de la Mer — Université du Québec à Rimouski, 310, allée des Ursulines Rimouski, QC G5L 3A1, Canada b Institut Maurice-Lamontagne, Pêches et Océans Canada, 850 route de la Mer, C.P. 1000, Mont-Joli, QC G5H 3Z4, Canada abstract article info Article history: Received 4 April 2013 Received in revised form 26 July 2013 Accepted 30 July 2013 Available online xxxx Keywords: Antioxidant Biochemical pathways Critical oxygen threshold Crustacean Enzyme activities Metabolic rate Northern shrimp is an important commercial species in the Estuary and Gulf of St. Lawrence. It is usually found at depths N 150 m and thus frequently inhabits hypoxic areas (18–40% saturation) in this region. To evaluate the impact of hypoxia on adult shrimp, males and females were exposed to different levels of dissolved oxygen at two temperatures (5 and 8 °C). Standard and maximal metabolic rates as well as the critical oxygen threshold were measured. In addition, metabolic and antioxidant enzyme activities were measured at 5 °C. Females had a higher critical oxygen threshold than males at both temperatures (15.5 and 22.2 vs. 9.0 and 13.8 at 5 and 8 °C respectively), indicating that they were less tolerant of hypoxia. A decrease in glycolytic and fermentation enzyme activities confirmed this result: in females, severe hypoxia significantly decreased the specific activities of citrate synthase and of enzymes involved in anaerobic biochemical pathways (lactate dehydrogenase, pyruvate kinase, and phosphoenolpyruvate carboxykinase (PEPCK)); in males, only the PEPCK activity decreased significantly while glutathione peroxidase (antioxidant defense) activity increased significantly. In females, severe hypoxia (22% sat.) did not affect the standard metabolic rate but significantly reduced (by ~43%) the maximum metabolic rate compared to normoxia. Consequently, aerobic scope was reduced by ~58% at 22% sat. compared to normoxia. This suggests that the shrimp's flexibility to respond to metabolic demands, including such activities as vertical migration, foraging, and egg production, could be reduced in hypoxic conditions, especially in females. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Northern shrimp, Pandalus borealis (Krøyer, 1838), is a protandric hermaphrodite species that reproduces first as a male, then changes sex and reproduces as a female for the rest of its life (Bergström, 2000). It is an important commercial species in Canadian waters (Fig. 1), partic- ularly in the Estuary and Gulf of St. Lawrence (EGSL), where it is most abundant at 150–300 m (Chabot et al., 2007; Savard, 2012; Simard and Savard, 1990). In the EGSL, the deep layer (below the permanent cold intermediate layer, i.e., N 150 m) is of oceanic origin. A mixture of water from the Labrador Current and North Atlantic central water enters at the mouth of the Laurentian Channel and moves slowly to the head of the three main channels; thermal stratification prevents these waters from mixing with surface water (Bugden, 1991; Gilbert et al., 2005). Dissolved oxygen (DO) levels become progressively depleted as deep waters move upstream, and DO reaches ~ 30–50% sat. in the Gulf of St. Lawrence and ~18–25% sat. in the St. Lawrence Estuary and at the heads of Esquiman and Anticosti channels (D'Amours, 1993; Galbraith et al., 2012; Gilbert et al., 2005, 2007). Northern shrimp is located in areas with low DO levels (Fig. 1)(Chabot et al., 2007; Gilbert et al., 2007; Savard, 2012), suggesting that this species could be particularly tolerant to hypoxia. From the 1930s to the early 1980s, DO levels decreased by half in the deep waters of the lower estuary (Gilbert et al., 2005), but since the mid-1980s, DO concentration in the deep waters of the EGSL has been stable (Gilbert et al., 2007). However, both climate change and larger human popula- tions may accentuate hypoxia in the St. Lawrence system because of their potential impact on the entrance of warm hypoxic waters from the central North Atlantic and eutrophication. DO concentration is known to impose a limit on aerobic metabolic rate of aquatic animals and to compromise their survival (Brett, 1979; Fry, 1971). Many studies have shown that hypoxia modifies physiologi- cal performance (e.g., increased ventilation and heart rate, slowed diges- tion, decreased food consumption) and reduces growth in invertebrates (Cancer magister, Airriess and McMahon, 1994; Palaemonetes pugio, Cochran and Burnett, 1996; Palaemonetes vulgaris and Dyspanopeous sayi, Coiro et al., 2000; Callinectes sapidus, Mangum, 1997; crustaceans, Journal of Experimental Marine Biology and Ecology 448 (2013) 298–307 ⁎ Corresponding author. Tel.: +1 418 724 1650x1393. E-mail address: Aurelie.Dupont-Prinet@uqar.ca (A. Dupont-Prinet). 0022-0981/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jembe.2013.07.019 Contents lists available at ScienceDirect Journal of Experimental Marine Biology and Ecology journal homepage: www.elsevier.com/locate/jembe