Description: Fatty acids were analyzed by gas chromatography using a DB-FFAP column of 30 m length and 0.25 mm inner diameter and a programmable temperature vaporizer injector. Following the trophic biomarker concept, the fatty acids 16:0, 20:5(n-3) and 22:6(n-3) were classified as typical components of biomembranes. High levels of 16:1(n−7) as well as 16:4(n−1) and 18:1(n−7) were used as diatom markers and 18:4(n−3) as fatty acid marker for dinoflagellates. The fatty acid 18:1(n-9) indicates carnivorous feeding. A carnivory index was applied based on the fatty acid ratio 18:1(n−9) / [16:1(n−7) + 16:4(n−1) + 18:1(n−7) + 18:4(n−3) + 18:1(n−9)] to reflect the proportion of carnivorous compared to herbivorous feeding in an organism. Fatty acid compositions of zooplankton and fish were taxon-specific and did not depend on sampling area or depth. Most species showed a dominance of typical membrane fatty acids, e.g., 16:0, 20:5(n-3) and 22:6(n-3). The dominant copepod Calanus chilensis had a low carnivory index and elevated amounts of diatom fatty acid markers which point to a predominantly herbivorous feeding. Among the krill species, Euphausia mucronata had the lowest carnivory index compared to the other euphausiids indicating a more herbivorous feeding. The squat lobster Pleuroncodes monodon had a significantly lower carnivory ratio compared to the deep-sea decapods Gennadas sp. and Acanthephyra sp. emphasizing its different trophic role compared to other decapods.

Description: Zooplankton metabolic processes play an important role in carbon budgets and fluxes of pelagic ecosystems. Respiration rates of several copepod species were determined to reveal their energy requirements and assess their significance in the carbon cycle. Respiration rates were measured by optode respirometry and allometrically based on body dry mass (DM). For the on-board measurements, a 10-channel optode respirometer (PreSens Precision Sensing Oxy-10 Mini) was used and experiments were run in gas-tight glass bottles (13-14 ml) filled with filtered seawater to reduce bias by microbial respiration. In addition, respiration rates for all dominant copepod species during MSM80 including copepodite stages C4 to C6 were determined based on individual DM and respective ambient temperatures after Bode et al. (2018). For that, individual DM, if not available from frozen specimens, was determined from formalin/Steedman-preserved samples by weighing the dried samples on a microbalance. Losses in body DM due to formalin/Steedman preservation were considered after Schukat et al. (2021). Respiration rates were calculated separately for the copepod family Eucalanidae (a) as they are rather sluggish while all other copepods exhibited normal activity (b). (a) lnRTF = -2.180 + 0.787 ln(DM) + 0.131T and (b) lnRAC = -0.890 + 0.646 ln(DM) + 0.094T, where R (μl O2 ind-1 h-1) is the individual respiration rate for eucalanid (RTF) and active (RAC) copepods, DM represents dry mass in mg and T the average temperature (°C) of the sampling interval. Respiration rates of the medium- to larger-sized copepods (female prosome length (PL) of 1.2-6.0 mm) were compared to those of "small copepods" (all copepods with female PL 〈1.1 mm and young stages). Medium- to larger-sized species ingested on average 13-212 mg C m-2 d-1 in coastal regions while "small copepods" on average consumed 118-328 mg C m-2 d-1. The potential egestion varied on average from 5-64 mg C m-2 d-1 for medium to larger-sized copepods and 35-98 mg C m-2 d-1 for "small copepods". Data of energy demands, consumption and egestion rates of copepod species differing in size are essential to improve carbon budgets and food-web models in the Humboldt Current System.