Conserving original in situ diversity in microzooplankton grazing set-ups

Abstract

Grazing experiments targeting the determination of in situ grazing rates are standard. In two separate experiments the effect of the frequently used siphon filling technique on the abundance of microzooplankton during the set-up of grazing experiments was investigated and compared to results from an alternative filling method. Hereby, water containing natural communities from Helgoland Roads, Germany (54811.3 ′ N 7854.0 ′ E), was transferred into incubation bottles using a funnel system (funnel-transfer technique (FTT)). The impact of pre-screening with a 200 mm net for excluding larger mesozooplankton grazers from the incubations was evaluated. Results show that the ciliate community was strongly affected by siphoning and pre-screening, leading to significant differences in abundance and Margalef diversity. The most affected ciliates were Lohmanniella oviformis and Myrionecta rubra, both important species in the North Sea. Dinoflagellates did not show any significant response to either siphoning or pre-screening with the exception of one athecate species. Such artificial bias in ciliate assemblages is very problematic for biodiversity consideration and grazing investigations. Simply changing the method of filling during the experimental set-up can ensure the measurement of accurate grazing rates of field abundances of microzooplankton. We thus recommend using conservative filling approaches like the FTT in experiments, especially when sensitive species are present, in order to avoid shifts in the overall microzooplankton community. Furthermore, we recommend introducing a control to evaluate the degree of changes in the target community due to the experimental set-up.

Winners and Losers of Atlantification: The Degree of Ocean Warming Affects the Structure of Arctic Microbial Communities

“…The remaining water was used to sample parameters of the starting community (t0) in triplicate. We took care not to introduce any bubbles during the filling procedure to prevent more fragile organisms, such as ciliates, from dying [ 33 ].…”

Dietary and seasonal variability in trophic relations at the base of the North Sea pelagic food web revealed by stable isotope and fatty acid analysis

“…Phytoplankton carbon concentrations were obtained from the Helgoland Roads long-term monitoring program (Wiltshire et al, 2008). Samples of surface water for the determination of microzooplankton were preserved with acid Lugol's solution (2% final concentration), and the organisms identified to species level as described by Löder et al (2010). Many of the dinoflagellates in the plankton are considered to be mixotrophs and able to take up particles via phagotrophy, even if they contain chloroplasts.…”

“…Many of the dinoflagellates in the plankton are considered to be mixotrophs and able to take up particles via phagotrophy, even if they contain chloroplasts. Hence, for our division of heterotrophic versus autotrophic components in the plankton they were assigned to the microzooplankton (Löder et al, 2010). Biovolume of microzooplankton was calculated from the measurement of cell dimensions using geometrical formula according to Hillebrand et al (1999) and subsequent conversion to carbon content was done after Putt and Stoecker (1989) and Menden-Deuer and Lessard (2000).…”

Ocean acidification effects on haploid and diploid Emiliania huxleyi strains: Why changes in cell size matter

“…Many marine protists, including E. huxleyi, are acutely sensitive to mechanical stress, and react poorly when subjected to it (Gifford, 1993;Löder et al, 2010;Wolfe et al, 2002). Because of this, a CO 2 delivery system was designed to minimize mechanical stress (e.g.…”