Comparative analysis of biological variables in situ and at the onset of experiments.

Upper panel: Physical and biological parameters at 5 m depth, from the three sampling sites (in situ) where water was collected for experiments. Mean and standard deviation values (of 2–3 replicates, in parenthesis) of ammonium (NH4+), dissolved organic carbon (DOC), iron (Fe), chlorophyll a (Chl a), bacterial abundance (BA) and bacterial production from Leucine uptake (BP-Leu). Lower panel: Mean and standard deviation values (of 2–3 replicates, in parenthesis) of NH4+, DOC, BA and BP at the onset (T0) of the three experiments in the two treatments (ammonium, A; krill excretion products, K) and controls (C). Fe = Iron concentrations in the pre-filtered water used for experiments, before adding any treatment.