e oxygen consumption by the faecal

pellet itself and the

e. oxygen consumption by the faecal

pellet itself and the increase in oxygen consumption by surrounding microbes because of the presence of the faecal pellet, which stimulated them by providing an alternative food source). Oxygen consumption rates were converted to carbon demand, assuming a respiration factor of 1 mol O2:1 mol CO2 ( Ploug et al. 2008). Faecal pellet carbon-specific degradation rates (FP-CSD) represents the carbon demand (μg d− 1) per faecal pellet carbon contents (μg FP− 1) and is expressed as percentage per day (% d− 1, Ploug et al. 2008). In order to determine the carbon contents of the faecal pellets, about 100 faecal pellets of each type (culture and in situ) were placed on 450°C ash-burned GFF filters for carbon analysis. Filters were fumed with HCl for 24 h and subsequently

analysed on a Leeman Lab CEC 440 CHN www.selleckchem.com/products/Thiazovivin.html analyser (Reigstad et al. 2008). Samples (250 ml) for counting phyto- and protozooplankton (i.e. heterotrophic ciliates and dinoflagellates) were fixed with acid Lugol (2% vol. final concentration). Subsamples (12.5 to 100 ml) were counted microscopically after settling in Utermöhl sedimentation chambers for 48 h. The entire chamber or parts of it were examined under an inverted microscope at a magnification of × 200 and × 400. Samples for bacterial abundance (BA) were fixed with fresh formaldehyde to a final concentration of 2%. BA was determined by direct counts of DAPI-stained filter samples (0.2 μm pore size membrane filters) using an epifluorescence microscope ( Porter & Feig 1980). A minimum of 10 frames and GSK2118436 research buy 500 cells were counted in each sample. In order to determine the effects of faecal pellet origin and water type on FP-CSD, these factors were tested using a two-way analysis of variance (ANOVA) followed by an LSD post-hoc test in the case of significant results. Differences in FP-CSD between treatments were tested by one-way ANOVA, followed by a LSD post-hoc test. Normality and homogeneity of

variance were subjected to the Bartlett test prior to the application of parametric tests Phospholipase D1 (Fisher Snedecor tests applied through ANOVA). For all the statistical results, a probability of p < 0.05 was considered significant. Statistical analyses were performed using Statgraphics Plus (Manugistics, Inc., Rockville, MD, USA). All the investigated plankton groups (i.e. bacteria, phyto- and protozooplankton) had higher abundances at the chl a max than at 90 m ( Figure 1). Phytoplankton at the chl a max was dominated by Phaeocystis pouchetii, which was absent at 90 m depth. Diatoms were less abundant but with 7100 cells l− 1 at the chl a max were about 3.6 times more abundant than at 90 m. Heterotrophic dinoflagellates were more abundant than ciliates at both depths. The carbon demand of the microbial community, used as a blank for measuring the FP-CSD, was 42.4 ± 6.0 SD μg C l− 1 d− 1 and 5.5 ± 0.

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