Thermal constraints on the respiration and excretion rates of krill, Euphausia hanseni and Nematoscelis megalops, in the northern Benguela upwelling system off Namibia

Abstract

Rates of respiration and ammonia excretion of Euphausia hanseni and Nematoscelis megalops were determined experimentally at four temperatures representative of conditions encountered by these euphausiid species in the northern Benguela upwelling environment. The respiration rate increased from 7.7 μmol O 2 h -1 g ww -1 at 5 °C to 18.1 μmol O 2 h -1 g ww -1 at 20 °C in E. hanseni and from 7.0 μmol O 2 h -1 g ww -1 (5 °C) to 23.4 μmol O 2 h -1 g ww -1 (20 °C) in N. megalops. The impact of temperature on oxygen uptake of the two species differed significantly. Nematoscelis megalops showed thermal adaptations to temperatures between 5 °C and 10 °C (Q 10 = 1.9) and metabolic constraint was evident at higher temperatures (Q 10 = 2.6). In contrast, E. hanseni showed adaptations to temperatures of 10-20 °C (Q 10 = 1.5) and experienced metabolic depression below 10 °C (Q 10 = 2.6). Proteins were predominantly metabolised by E. hanseni in contrast to lipids by N. megalops. Carbon demand of N. megalops between 5 and 15 °C was lower than in E. hanseni versus equal food requirements at 20 °C. It is concluded that the two species display different physiological adaptations, based on their respective temperature adaptations, which are mirrored in their differential vertical positioning in the water column.

Diel vertical migration behaviour in Euphausiids of the northern Benguela current: seasonal adaptations to food availability and strong gradients of temperature and oxygen

“…However, an intermediate conversion factor of F ¼ 70 was used for diatoms which dominated between Walvis Bay and Kunene River (N. Wasmund, IOW Warnemünde, personal communication). Temperature-dependent oxygen consumption rates of E. hanseni and N. megalops given by Werner et al (Werner et al, 2012) were used to calculate the oxygen consumption at a depth-specific temperature. It was assumed that during migration, euphausiids had a 2.7 times higher respiration rate than at rest (non-migrating) (Torres and Childress, 1983).…”

“…We developed a conceptual model to investigate the effect of temperature and food availability on the migration behaviour of E. hanseni and N. megalops, accordingly. Temperature has a strong impact on metabolic rates and thus influences the DVM behaviour of krill species (Lampert, 1989), due to different thermal adaptations of species, different energy expenditures (Werner et al, 2012), e.g. swimming costs, and a variety of other physiological processes, e.g.…”

“…Stratified net catches were conducted during three different cruises in summer 2004, autumn 2008 and winter 2010 at three locations over a period of 36 h. The data were related to the concurrent temperature profiles and the oxygen content of the water column. Furthermore, metabolic rates at different temperatures measured during shipboard experiments (Werner et al, 2012) were used to assess the energy demand of krill and the trophic environment was observed to investigate possible food-induced changes in the DVM behaviour of these species. These parameters were implemented in a conceptual model developed to estimate the carbon demand of different DVM behaviours and to allow comparison between cruises/seasons.…”

Responses of the arcto-boreal krill species Thysanoessa inermis to variations in water temperature: coupling Hsp70 isoform expressions with metabolism

“…After acclimation, the specimens were individually incubated in closed tubular respiration chambers (Perspex; 20 ml) specially designed for measuring routine rates in krill (Huenerlage and Buchholz 2013;Werner et al 2012). The chambers were filled with filtered seawater at the experimental temperature and stored in a water bath in a temperaturecontrolled refrigerator.…”

Life in the sea of plenty: Seasonal and regional comparison of physiological performance of Euphausia hanseni in the northern Benguela upwelling system

“…Specially designed small tube-shaped chambers (volume 20 mL) were used as respiration chambers optimized for krill (cf. Werner et al, 2012). As E. hanseni is a strong diel vertical migrator (Barange, 1990;Werner and Buchholz, 2013) respiration measurements were conducted in a temperature-controlled water bath at three different temperatures (5, 10 and 15°C) reflecting the water temperatures around Walvis Bay (23°S) between 50, 300 and deep water layers and around 700 m respectively.…”