Respiration rate and ammonium excretion data for the squat lobster Pleuroncodes monodon measured during METEOR cruise M93

Sampling was conducted during RV Meteor cruise M93 in austral summer 2013 in an area from 11ºS to 14ºS and approximately 120 km offshore to within 10 km of the Peruvian coast. Specimens were collected using a Hydrobios Multinet Maxi (0.5 m2 mouth opening, 330 µm mesh size, 9 nets) and a WP-2 net (Hydrobios, 0.26 m2 mouth opening, 200 µm mesh size). P. monodon were identified according to http://researchdata.museum.vic.gov.au/squatlobster/delta/deltakey.html. Specimens were transferred into filtered, well-oxygenated seawater immediately after the catch and maintained for 4 to 16 hours prior to physiological experiments. Maintenance and physiological experiments were conducted at 13°C as the temperature observed at 100 to 200 m depth in the OMZ ranged from 13.7 to 12.7°C.

Increased feeding and nutrient excretion of adult antarctic krill, Euphausia superba, exposed to enhanced carbon dioxide (CO2)

Ocean acidification has a wide-ranging potential for impacting the physiology and metabolism of zooplankton. Sufficiently elevated CO2 concentrations can alter internal acid-base balance, compromising homeostatic regulation and disrupting internal systems ranging from oxygen transport to ion balance. We assessed feeding and nutrient excretion rates in natural populations of the keystone species Euphausia superba (Antarctic krill) by conducting a CO2 perturbation experiment at ambient and elevated atmospheric CO2 levels in January 2011 along the West Antarctic Peninsula (WAP). Under elevated CO2 conditions (~672 ppm), ingestion rates of krill averaged 78 µg C/individual/d and were 3.5 times higher than krill ingestion rates at ambient, present day CO2 concentrations. Additionally, rates of ammonium, phosphate, and dissolved organic carbon (DOC) excretion by krill were 1.5, 1.5, and 3.0 times higher, respectively, in the high CO2 treatment than at ambient CO2 concentrations. Excretion of urea, however, was ~17% lower in the high CO2 treatment, suggesting differences in catabolic processes of krill between treatments. Activities of key metabolic enzymes, malate dehydrogenase (MDH) and lactate dehydrogenase (LDH), were consistently higher in the high CO2 treatment. The observed shifts in metabolism are consistent with increased physiological costs associated with regulating internal acid-base equilibria. This represents an additional stress that may hamper growth and reproduction, which would negatively impact an already declining krill population along the WAP.

Ammonium excretion and respiration rate of tropical copepods and euphausiids measured during METEOR cruise M93, M97 and Maria S. Merian cruise MSM22

Respiration and ammonium excretion rates at different oxygen partial pressure were measured for calanoid copepods and euphausiids from the Eastern Tropical South Pacific and the Eastern Tropical North Atlantic. All specimens used for experiments were caught in the upper 400 m of the water column and only animals appearing unharmed and fit were used for experiments. Specimens were sorted, identified and transferred into aquaria with filtered, well-oxygenated seawater immediately after the catch and maintained for 1 to 13 hours prior to physiological experiments at the respective experimental temperature. Maintenance and physiological experiments were conducted in darkness in temperature-controlled incubators at 11, 13 or 23 degree C (±1). Before and during experiments, animals were not fed. Respiration and ammonium excretion rate measurements (both in µmol h-1 gDW-1) at varying oxygen concentrations were conducted in 12 to 60 mL gas-tight glass bottles. These were equipped with oxygen microsensors (ø 3 mm, PreSens Precision Sensing GmbH, Regensburg, Germany) attached to the inner wall of the bottles to monitor oxygen concentrations non-invasively. Read-out of oxygen concentrations was conducted using multi-channel fiber optic oxygen transmitters (Oxy-4 and Oxy-10 mini, PreSens Precision Sensing GmbH, Regensburg, Germany) that were connected via optical fibers to the outside of the bottles directly above the oxygen microsensor spots. Measurements were started at pre-adjusted oxygen and carbon dioxide levels. For this, seawater stocks with adjusted pO2 and pCO2 were prepared by equilibrating 3 to 4 L of filtered (0.2 µm filter Whatman GFF filter) and UV - sterilized (Aqua Cristal UV C 5 Watt, JBL GmbH & Co. KG, Neuhofen, Germany) water with premixed gases (certified gas mixtures from Air Liquide) for 4 hours at the respective experimental temperature. pCO2 levels were chosen to mimic the environmental pCO2 in the ETSP OMZ or the ETNA OMZ. Experimental runs were conducted with 11 to 15 trial incubations (1 or 2 animals per incubation bottle and three different treatment levels) and three animal-free control incubations (one per experimental treatment). During each run, experimental treatments comprised 100% air saturation as well as one reduced air saturation level with and without CO2. Oxygen concentrations in the incubation bottles were recorded every 5 min using the fiber-optic microsensor system and data recording for respiration rate determination was started immediately after all animals were transferred. Respiration rates were calculated from the slope of oxygen decrease over selected time intervals. Chosen time intervals were 20 to 105 min long. No respiration rate was calculated for the first 20 to 60 min after animal transfer to avoid the impact of enhanced activity of the animal or changes in the bottle water temperature during initial handling on the respiration rates and oxygen readings. Respiration rates were obtained over a maximum of 16 hours incubation time and slopes were linear at normoxia to mild hypoxia. Respiration rates in animal-free control bottles were used to correct for microbial activity. These rates were < 2% of animal respiration rates at normoxia. Samples for the measurement of ammonium concentrations were taken after 2 to 10 hours incubation time. Ammonium concentration was determined fluorimetrically (Holmes et al., 1999). Ammonium excretion was calculated as the concentration difference between incubation and animal-free control bottles. Some specimens died during the respiration and excretion rate measurements, as indicated by a cessation of respiration. No excretion rate measurements were conducted in this case, but the oxygen level at which the animal died was noted.

Metabolism of mesozooplankton in the North-Eastern Aegean Sea during SES_GR2 in October 2008

The dataset is based on samples taken during October 2008 in the North-Eastern Aegean Sea. NH4 excretion rate: Mesozooplankton is collected by vertical tows within the Black sea water body mass layer in the NE Aegean, using a WP-2 200 µm net equipped with a large non-filtering cod-end (10 l). Macrozooplankton organisms are removed using a 2000 µm net. A few unsorted animals (approximately 100) are placed inside 8 bottles of 350 or 650 ml filled with GF/F or 0.2 µm Nucleopore filtered seawater and then on a wheell at dim light and maintaining the in situ temperature. 4 bottles without animals are used as control. After 24hours bottles are opened and water samples taken for NH4 chemical analysis. Then the bottle content is filtered on pre-combusted preweighted CF/F filters, which are then dried at 60 C and weighted. Calculations are made as described by Ikeda et al. (2000). Samples for the NH4 determination were collected in pre-cleaned 50 ml Duran bottles and analysed onboard immediately after collection. Ammonium concentration was measured on a Perkin Elmer Lambda 25 UV/VIS Spectrometer according to the method of Koroleff (1970). PO4 excretion rate: Mesozooplankton is collected by vertical tows within the Black sea water body mass layer in the NE Aegean, using a WP-2 200 µm net equipped with a large non-filtering cod-end (10 l). Macrozooplankton organisms are removed using a 2000 µm net. A few unsorted animals (approximately 100) are placed inside 8 bottles of 350 or 650 ml filled with GF/F or 0.2 µm Nucleopore filtered seawater and then on a wheell at dim light and maintaining the in situ temperature. 4 bottles without animals are used as control. After 24hours bottles are opened and water samples taken for PO4 chemical analysis. Then the bottle content is filtered on pre-combusted preweighted CF/F filters, which are then dried at 60 C and weighted. Calculations are made as described by Ikeda et al. (2000). Samples for the determination of PO4 were collected in pre-cleaned 50 ml polyethylene volumetric tubes and analysed on board immediately after collection. PO4 concentration was measured on a Perkin Elmer Lambda 25 UV/VIS Spectrometer following the protocol of Murphy and Riley (1962). O2 consumption rate: Mesozooplankton is collected by vertical tows within the Black sea water body mass layer in the NE Aegean, using a WP-2 200 µm net equipped with a large non-filtering cod-end (10 l). Macrozooplankton organisms are removed using a 2000 µm net. A few unsorted animals (approximately 100) are placed inside 8 bottles of 350 or 650 ml filled with GF/F or 0.2 µm Nucleopore filtered seawater and then on a wheell at dim light and maintaining the in situ temperature. 4 bottles without animals are used as control. After 24hours bottles are opened and water samples taken for O2 chemical analysis. Then the bottle content is filtered on pre-combusted preweighted CF/F filters, which are then dried at 60 C and weighted. Calculations are made as described by Ikeda et al. (2000). For the dissolved O2 determination, the samples were fixed immediately after collection and analysed with the Winkler method as modified by Carpenter (1965a and 1965b). Carbon specific CO2 respiration rate: O2 consumption rate was converted to CO2 production using a RQ value of 0.87 (Mayzaud et al. 2005). Conversion of mesozooplankton dry weight to carbon was done using the % of carbon content measured in the same station from the SESAME dataset of zooplankton biomass. Carbon specific NH4 excretion rate: Conversion of mesozooplankton dry weight to carbon was done using the % of carbon content measured in the same station from the SESAME dataset of zooplankton biomass. Carbon specific PO4 excretion rate: Conversion of mesozooplankton dry weight to carbon was done using the % of carbon content measured in the same station from the SESAME dataset of zooplankton biomass.

Seawater carbonate chemistry, calcification and respiration duirng experiments with a pteropod Creseis acicula, 2010

Among marine calcifiers, shelled pteropods are expected to be particularly sensitive to ocean acidification, generated by the uptake of anthropogenic CO2 by the ocean, and the associated decrease of the seawater saturation state with respect to aragonite (omega aragonite). The few available studies have mostly focused on polar species although pteropods are also important components of temperate and tropical ecosystems. It is also unknown which parameter of the carbonate system controls calcification. Specimens of the temperate Mediterranean species Creseis acicula were maintained under seven different conditions of the carbonate chemistry, obtained by manipulating pH and total alkalinity, with the goal to disentangle the effects of pH and omega aragonite. Respiration, excretion as well as rates of net and gross calcification were not directly affected by a decrease in pH but decreased significantly with a decrease of omega aragonite. The decrease of gross calcification rates is consistent with that reported for polar species. Although the organisms were apparently able to maintain gross calcification rates under slightly undersaturated aragonite conditions, the clear net dissolution signal observed below saturation suggests that they are not able to build a shell in seawater corrosive to aragonite. The decrease in respiration and excretion, and the low O:N molar ratio, could be due to the short time that the organisms were allowed to acclimatize to their new environment.

Haemolymph inorganic ion composition, physiology and behaviour dependent on temperature and ambient magnesium concentration in early life history stages of Paralomis granulosa (Decapoda, Anomura, Lithodidae)

Marine brachyuran and anomuran crustaceans are completely absent from the extremely cold (-1.8 °C) Antarctic continental shelf, but caridean shrimps are abundant. This has at least partly been attributed to low capacities for magnesium excretion in brachyuran and anomuran lithodid crabs ([Mg2+]HL = 20-50 mmol/L) compared to caridean shrimp species ([Mg2+]HL = 5-12 mmol/L). Magnesium has an anaesthetizing effect and reduces cold tolerance and activity of adult brachyuran crabs. We investigated whether the capacity for magnesium regulation is a factor that influences temperature-dependent activity of early ontogenetic stages of the Sub-Antarctic lithodid crab Paralomis granulosa. Ion composition (Na+, Mg2+, Ca2+, Cl-, [SO4]2-) was measured in haemolymph withdrawn from larval stages, the first and second juvenile instars (crabs I and II) and adult males and females. Magnesium excretion improved during ontogeny, but haemolymph sulphate concentration was lowest in the zoeal stages. Neither haemolymph magnesium concentrations nor Ca2+:Mg2+ ratios paralleled activity levels of the life stages. Long-term (3 week) cold exposure of crab I to 1 °C caused a significant rise of haemolymph sulphate concentration and a decrease in magnesium and calcium concentrations compared to control temperature (9 °C). Spontaneous swimming activity of the zoeal stages was determined at 1, 4 and 9 °C in natural sea water (NSW, [Mg2+] = 51 mmol/L) and in sea water enriched with magnesium (NSW + Mg2+, [Mg2+] = 97 mmol/L). It declined significantly with temperature but only insignificantly with increased magnesium concentration. Spontaneous velocities were low, reflecting the demersal life style of the zoeae. Heart rate, scaphognathite beat rate and forced swimming activity (maxilliped beat rate, zoea I) or antennule beat rate (crab I) were investigated in response to acute temperature change (9, 6, 3, 1, -1 °C) in NSW or NSW + Mg2+. High magnesium concentration reduced heart rates in both stages. The temperature-frequency curve of the maxilliped beat (maximum: 9.6 beats/s at 6.6 °C in NSW) of zoea I was depressed and shifted towards warmer temperatures by 2 °C in NSW + Mg2+, but antennule beat rate of crab I was not affected. Magnesium may therefore influence cold tolerance of highly active larvae, but it remains questionable whether the slow-moving lithodid crabs with demersal larvae would benefit from an enhanced magnesium excretion in nature.

ATPase activity, proton gradients and proton secretion inhibition during experiments with Sepia officinalis and Sepioteuthis lessoniana

The constraints of an active life in a pelagic habitat led to numerous convergent morphological and physiological adaptations that enable cephalopod molluscs and teleost fishes to compete for similar resources. Here, we show for the first time that such convergent developments are also found in the ontogenetic progression of ion regulatory tissues; as in teleost fish, epidermal ionocytes scattered on skin and yolk sac of cephalopod embryos appear to be responsible for ionic and acid-base regulation before gill epithelia become functional. Ion and acid-base regulation is crucial in cephalopod embryos, as they are surrounded by a hypercapnic egg fluid with a Pco2 between 0.2 and 0.4 kPa. Epidermal ionocytes were characterized via immunohistochemistry, in situ hybridization, and vital dye-staining techniques. We found one group of cells that is recognized by concavalin A and MitoTracker, which also expresses Na+/H+ exchangers (NHE3) and Na+-K+-ATPase. Similar to findings obtained in teleosts, these NHE3-rich cells take up sodium in exchange for protons, illustrating the energetic superiority of NHE-based proton excretion in marine systems. In vivo electrophysiological techniques demonstrated that acid equivalents are secreted by the yolk and skin integument. Intriguingly, epidermal ionocytes of cephalopod embryos are ciliated as demonstrated by scanning electron microscopy, suggesting a dual function of epithelial cells in water convection and ion regulation. These findings add significant knowledge to our mechanistic understanding of hypercapnia tolerance in marine organisms, as it demonstrates that marine taxa, which were identified as powerful acid-base regulators during hypercapnic challenges, already exhibit strong acid-base regulatory abilities during embryogenesis.

Primary productivity and phytoplankton pigment measurements in the North Sea

During the culmination of the phytoplankton spring bloom in the Fladen Ground area in April-Mai 1976, gross primary production was between 1500 and 2000 mg particulate C m**-2 day**-1, at a crop density (mainly diatoms of the genus Chaetoceros) of about 1500-3500 mg C m**-2. Estimates of the C:chlorophyll a ratio in living cells were much lower than those reported in the literature, possibly because part of what is measured as "chlorophyll a" by the common fluorometric method is associated with particles that are not reported as cells. Most of the dark 14C fixation during the bloom's climax was due to abiotic processes. Excretion of 14C-labeled carbohydrates did not account for a significant fraction of the total photosynthetic rate. The low crop after the bloom period, in June, corresponded with nutrient depletion of the euphotic zone. The low photosynthetic efficiency in June may have been a gross underestimate. The presence of relatively high concentrations of chlorophyll derivatives signifies that the algal crop was consumed by heterotrophs, but at a lower rate in April/May than during the June cruise when particularly high molar ratios of phaeophorbide a and phaeophytin a relative to chlorophyll a were found. The high respiratory rate relative to autotrophic production in June manifested itself also in high dark 14C fixation values. The high concentration of phaeophorbide a in the upper 40 m and its scarcity below this depth during the spring bloom climax in April/May implies that copepod grazing at that time took place principally in the euphotic zone. The remarkably high concentration of chlorophyllide a in the surface layer during the bloom period indicates that the part of the crop that was destroyed by the grazers while eating was occasionally as high as the part that was actually ingested.

Abundance, biomass, ingestion rates and daily ratios of Salpa thompsoni individuals sampled during POLARSTERN cruise ANT-XVIII/5b to the Eastern Belingshausen Sea

Distribution, density, and feeding dynamics of the pelagic tunicate Salpa thompsoni have been investigated during the expedition ANTARKTIS XVIII/5b to the Eastern Bellingshausen Sea on board RV Polarstern in April 2001. This expedition was the German contribution to the field campaign of the Southern Ocean Global Ocean Ecosystems Dynamics Study (SO-GLOBEC). Salps were found at 31% of all RMT-8 and Bongo stations. Their densities in the RMT-8 samples were low and did not exceed 4.8 ind/m**2 and 7.4 mg C/m**2. However, maximum salp densities sampled with the Bongo net reached 56 ind/m**2 and 341 mg C/m**2. A bimodal salp length frequency distribution was recorded over the shelf, and suggested two recent budding events. This was also confirmed by the developmental stage composition of solitary forms. Ingestion rates of aggregate forms increased from 2.8 to 13.9 µg (pig)/ind/day or from 0.25 to 2.38 mg C/ind/day in salps from 10 to 40 mm oral-atrial length, accounting for 25-75% of body carbon per day. Faecal pellet production rates were on average 0.08 pellet/ind/h with a pronounced diel pattern. Daily individual egestion rates in 13 and 30 mm aggregates ranged from 0.6 to 4.8 µg (pig)/day or from 164 to 239 µg C/day. Assimilation efficiency ranged from 73 to 90% and from 65 to 76% in 13 and 30 mm aggregates, respectively. S. thompsoni exhibited similar ingestion and egestion rates previously estimated for low Antarctic (~50°S) habitats. It has been suggested that the salp population was able to develop in the Eastern Bellingshausen Sea due to an intrusion into the area of the warm Upper Circumpolar Deep Water