Thorsten Werner

First observation of krill spawning in the high Arctic Kongsfjorden, west Spitsbergen

In the past, two euphausiid species prevailed in the high Arctic Kongsfjorden, the arcto-boreal Thysanoessa inermis (Kroeyer, 1846) and Thysanoessa raschii (Sars. 1964). Both were considered expatriates from the Barents Sea or Norwegian Sea and non-reproductive due to low temperatures. The macro-zooplankton of the fjord has been studied as a component in an ecosystem context since 2006, including baseline investigation of distribution and functional performance of key species. In recent years, three additional krill species were regularly detected in the fjord and are the focus of an intensive long-term study. Of these species, Thysanoessa longicaudata (Kroeyer, 1846) and Meganyctiphanes norvegica (Sars, 1857) are typical for the boreal Atlantic whereas Nematoscelis megalops (Sars, 1883) has a broad distribution in temperate to subtropical provinces. Their occurrence in the Kongsfjorden clearly indicates increasing Atlantic influence. During the 2011 campaign, T. raschii was observed spawning in the field for the first time and showed development up to the naupliar stage in the laboratory. Should more evidence of reproduction be encountered in any of the five krill species in the Kongsfjorden in the future, it will be taken as an indication of a changing environment concerning temperature and food web composition.

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

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 O2 h−1 gww −1 at 5 °C to 18.1 µmol O2 h−1 gww −1 at 20 °C in E. hanseni and from 7.0 µmol O2 h−1 gww −1 (5 °C) to 23.4 µmol O2 h−1 gww −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 (Q10 = 1.9) and metabolic constraint was evident at higher temperatures (Q10 = 2.6). In contrast, E. hanseni showed adaptations to temperatures of 10–20 °C (Q10 = 1.5) and experienced metabolic depression below 10 °C (Q10 = 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.