Physiology, growth and development of larval krill Euphausia superba in autumn and winter in the Lazarev Sea, Antarctica

The physiological condition of larval Antarctic krill was investigated during austral autumn 2004 and winter 2006 in the Lazarev Sea, to provide better understanding of a critical period of their life cycle. The condition of larvae was quantified in both seasons by determining their body length (BL), dry mass (DM), elemental- and biochemical composition, as well as stomach content analysis, and rates of metabolism and growth. Overall the larvae in autumn were in better condition under the ice than in open water, and for those under the ice there was a decrease in condition from autumn to winter. Thus growth rates of furcilia larvae in open water in autumn were similar to winter values under the ice (mean 0.008 mm/d), whereas autumn, under ice values were higher: 0.015 mm/d. Equivalent larval stages had up to 30% lower BL and 70% lower DM in winter compared to autumn, with mean oxygen consumption 44% lower (0.54 µl O2 DM/h). However, their ammonium excretion rates doubled (from 0.03-0.06 µg NH4 DM/h) so their mean O:N ratio was 46 in autumn and 15 in winter. Thus differing metabolic substrates were used between autumn and winter, suggesting a flexible overwintering strategy, as suggested for adults. The larvae were eating small copepods (Oithona spp.) and/or protozoans as well as autotrophic food under the ice. However, pelagic Chlorophyll a (Chl a) was a good predictor for growth in both seasons. The physics (current speed/ice topography) probably has a critical part to play in whether larval krill can exploit the food that may be associated with sea ice or be advected away from such suitable feeding habitat

Calibrated chlorophyll concentrations based on fluorescence sensor and reference sample data for ship CTD profiles during RV POLARSTERN cruise PS124

This dataset contains calibrated chlorophyll concentrations for CTD profile data collected with the ship based CTD rosette during the cruise PS124 - COSMUS (Continental Shelf Multidisciplinary Flux Study) in the southern Weddell Sea between January and March 2021. Factory calibrated chlorophyll fluorescence sensor data was field calibrated using chlorophyll reference samples measured against chlorophyll a standard (see chlorophyll dataset for CTD bottles). Note the intense noise in fluorescence signals and resulting chlorophyll concentrations at station PS124_5-2 which was caused by optical interference. This effect might require noise reduction (convolving) methods in order to allow a reliable interpretation. Quality flags were given based on paragraph 6 Quality flags from SeaDataNet (2010)

Calibrated chlorophyll concentration based on fluorescence sensor and reference sample data for water bottle samplings during RV POLARSTERN cruise PS124

This dataset contains calibrated chlorophyll concentrations for CTD bottle data collected with the ship based CTD rosette during the cruise PS124 - COSMUS (Continental Shelf Multidisciplinary Flux Study) in the southern Weddell Sea between January and March 2021. Factory calibrated chlorophyll fluorescence sensor data was field calibrated using chlorophyll reference samples measured against chlorophyll a standard. Pigment extraction from 1L water samples filtered onto GFF filters was performed with 90 % acetone including cell disruption with glass beads. Linear regression between sample chlorophyll concentration (n=62) and chlorophyll fluorescence sensor data from CTD bottle measurements was accomplished with a Robust Linear Model and Andrew's Wave weight function using the python package statsmodels v0.14.0. Coefficient of determination (R²) of the resulting regression was 0.95 while excluding 3 outliers. The resulting coefficient was 0.4118 and the constant 0.004. Note the intense noise in fluorescence signals and resulting chlorophyll concentrations at station PS124_5-2 which was caused by optical interference. This effect might require noise reduction (convolving) methods in order to allow a reliable interpretation. Quality flags were given based on paragraph 6 Quality flags from SeaDataNet (2010)

Seasonal variation in body composition, metabolic activity, feeding, and growth of adult krill Euphausia superba in the Lazarev Sea

We investigated physiological parameters (elemental and biochemical composition, metabolic rates, feeding activity and growth) of adult Antarctic krill in the Lazarev Sea in late spring (December), mid autumn (April) and mid winter (July and August) to evaluate proposed hypotheses of overwintering mechanisms. Our major observations are: (1) respiration rates were reduced by 30 to 50% in autumn and winter, compared to values in late spring; (2) feeding activity was reduced by 80 to 86% in autumn and winter, compared to late spring, at similar food concentrations; (3) feeding was omnivorous during winter; (4) with each moult, krill grew by 0.5 to 3.8% in length; (5) body lipids and, to a small extent, body proteins were consumed during winter. Adult Euphausia superba thus adopt metabolic slowdown and omnivorous feeding activity at low rates to survive the winter season in the Lazarev Sea. By mid autumn, metabolic activity is reduced, most likely being influenced by the Antarctic light regime, which is accompanied by a reduction in feeding activity and growth. Although at a low level, the feeding activity during winter seems to provide an important energy input