Respiration and ingestion rates of calanoid copepod in the northern Benguela Current System measured ex situ during the RSS Discovery D356 cruise in 2010

Respiration rates of 16 calanoid copepod species from the northern Benguela upwelling system were measured on board RRS Discovery in September/October 2010 to determine their energy requirements and assess their significance in the carbon cycle. Copepod species were sampled by different net types. Immediately after the hauls, samples were sorted to species and stages (16 species; females, males and C5 copepodids) according to Bradford-Grieve et al. (1999). Specimens were kept in temperature-controlled refrigerators for at least 12 h before they were used in experiments. Respiration rates of different copepod species were measured onboard by optode respirometry (for details see Köster et al., 2008) with a 10-channel optode respirometer (PreSens Precision Sensing Oxy-10 Mini, Regensburg, Germany) under simulated in situ conditions in temperature-controlled refrigerators. Experiments were run in gas-tight glass bottles (12-13 ml). For each set of experiments, two controls without animals were measured under exactly the same conditions to compensate for potential bias. The number of animals per bottle depended on the copepods size, stage and metabolic activity. Animals were not fed during the experiments but they showed natural species-specific movements. Immediately after the experiments, all specimens were deep-frozen at - 80 °C for later dry mass determination (after lyophilisation for 48 h) in the home lab. The carbon content (% of dry mass) of each species was measured by mass-spectrometry in association with stable isotope analysis and body dry mass was converted to units of carbon. For species without available carbon data, the mean value of all copepod species (44% dry mass) was applied. For the estimation of carbon requirements of copepod species, individual oxygen consumption rates were converted to carbon units, assuming that the expiration of 1 ml oxygen mobilises 0.44 mg of organic carbon by using a respiratory quotient (RQ) of 0.82 for a mixed diet consisting of proteins (RQ = 0.8-1.0), lipids (RQ = 0.7) and carbohydrates (RQ = 1.0) (Auel and Werner, 2003). The carbon ingestion rates were calculated using the energy budget and the potential maximum ingestion rate approach. To allow for physiological comparisons of respiration rates of deep- and shallow-living copepod species without the effects of ambient temperature and different individual body mass, individual respiration rates were temperature- (15°C, Q10=2) and size-adjusted. The scaling coefficient of 0.76 (R2=0.556) is used for the standardisation of body dry mass to 0.3 mg (mean dry mass of all analysed copepods), applying the allometric equation R= (R15°C/M0.76)×0.30.76, where R is respiration and M is individual dry mass in mg.

Seasonal fatty acid and fatty alcohol composition of Pseudocalanus minutus and Oithona similis in Kongsfjorden (Svalbard)

Seasonal lipid dynamics of various developmental stages were investigated in Pseudocalanus minutus and Oithona similis. For P. minutus, the dominance of 16:1(n?7), 16:4(n?3) and 20:5(n?3) fatty acids indicated a diatom-based nutrition in spring, whereas 22:6(n?3), 16:0, 18:2(n?6) and 18:1(n?9) pointed to a flagellate-based diet during the rest of the year as well as omnivorous/carnivorous low-level feeding during winter. The shorter-chain fatty alcohols 14:0 and 16:0 prevailed, also reflecting biosynthetic processes typical of omnivores or carnivores. Altogether, the lipid signatures characterized P. minutus as an opportunistic feeder. In contrast, O. similis had consistently high amounts of the 18:1(n?9) fatty acid in all stages and during all seasons pointing to a generally omnivorous/carnivorous/detritivorous diet. Furthermore, the fatty alcohol 20:1(n?9) reached high percentages especially in adult females and males, and feeding on Calanus faecal pellets is suggested. Fatty alcohols, as wax ester moieties, revealed significant seasonal variations in O. similis and a seasonal trend towards wax ester accumulation in autumn in P. minutus. P. minutus utilized its lipid deposits for development in the copepodite stages III and IV and for gonad maturation in CV and females during the dark season. However, CVs and females depended on the spring phytoplankton bloom for final maturation processes and reproduction. O. similis fueled gonad maturation and egg production for reproduction in June by wax esters, whereas reproduction in August/September co-occurred with the accumulation of new depot lipids. Both species revealed significantly higher wax ester levels in deeper (>50 m) as compared to surface (0-50 m) dwelling individuals related to a descent prior to overwintering.

Abundance, Electron transport System (ETS) activity and respiration rates of pelagic decapods from the Benguela upwelling system during AFR258, D356 and MSM17/3

Decapods were sampled with a 1 m**2 MOCNESS (mainly upper 1000 m) in the northern Benguela Current during three cruises in December 2009, September/October 2010 and February 2011. Although pelagic decapods are abundant members of the micronekton community, information about their ecophysiology is very limited. Species-specific regional distribution limits were detected for various decapod species (e.g. Plesionika carinata, Sergestes arcticus, Pasiphaea semispinosa). Significant diel vertical migration patterns were determined for three caridean and three penaeiodean species. Biomass was variable and ranged from 23 to 2770 mg dry mass m**-2 with highest values for P. semispinosa. Fatty acid and stable isotope analyses revealed that the examined decapod species are omnivorous tocarnivorous except for the herbivorous to omnivorous species P. carinata. Calanid copepods such as Calanoides carinatus were identified as an important prey item especially for caridean species. Community consumption rates of pelagic decapods derived from respiration rates ranged from 7 mg C m**-2 d**-1 (231S) to 420 mg C m**-2 d**-1 (191S, 171S). A potential active respiratory carbon flux was calculated for migrating pelagic decapods with 4.4 mg C m**- d**-1 for the upper 200 m and with 2.6 mg C m**-2 d**-1 from the base of the euphotic zone to a depth of 600 m. Overall, pelagic decapods apparently play a more prominent role in the northern Benguela Current ecosystem than previously assumed and may exert a substantial predation impact on calanid copepods (up to 13% d**-1 of standing stock).

Fatty acid and stable isotope composition of calanoid copepods in the open eastern Atlantic Ocean during POLARSTERN cruise ANT-XXIX/1

The majority of global ocean production and total export production is attributed to oligotrophic oceanic regions due to their vast regional expanse. However, energy transfers, food-web structures and trophic relationships in these areas remain largely unknown. Regional and vertical inter- and intra-specific differences in trophic interactions and dietary preferences of calanoid copepods were investigated in four different regions in the open eastern Atlantic Ocean (38°N to 21°S) in October/November 2012 using a combination of fatty acid (FA) and stable isotope (SI) analyses. Mean carnivory indices (CI) based on FA trophic markers generally agreed with trophic positions (TP) derived from d15N analysis. Most copepods were classified as omnivorous (CI ~0.5, TP 1.8 to ~2.5) or carnivorous (CI >=0.7, TP >=2.9). Herbivorous copepods showed typical CIs of <=0.3. Geographical differences in d15N values of epi- (200-0 m) to mesopelagic (1000-200 m) copepods reflected corresponding spatial differences in baseline d15N of particulate organic matter from the upper 100 m. In contrast, species restricted to lower meso- and bathypelagic (2000-1000 m) layers did not show this regional trend. FA compositions were species-specific without distinct intra-specific vertical or spatial variations. Differences were only observed in the southernmost region influenced by the highly productive Benguela Current. Apparently, food availability and dietary composition were widely homogeneous throughout the oligotrophic oceanic regions of the tropical and subtropical Atlantic. Four major species clusters were identified by principal component analysis based on FA compositions. Vertically migrating species clustered with epi- to mesopelagic, non-migrating species, of which only Neocalanus gracilis was moderately enriched in lipids with 16% of dry mass (DM) and stored wax esters (WE) with 37% of total lipid (TL). All other species of this cluster had low lipid contents (< 10% DM) without WE. Of these, the tropical epipelagic Undinula vulgaris showed highest portions of bacterial markers. Rhincalanus cornutus, R. nasutus and Calanoides carinatus formed three separate clusters with species-specific lipid profiles, high lipid contents (>=41% DM), mainly accumulated as WE (>=79% TL). C. carinatus and R. nasutus were primarily herbivorous with almost no bacterial input. Despite deviating feeding strategies, R. nasutus clustered with deep-dwelling, carnivorous species, which had high amounts of lipids (>=37% DM) and WE (>=54% TL). Tropical and subtropical calanoid copepods exhibited a wide variety of life strategies, characterized by specialized feeding. This allows them, together with vertical habitat partitioning, to maintain high abundance and diversity in tropical oligotrophic open oceans, where they play an essential role in the energy flux and carbon cycling.