Microzooplankton grazing and phytoplankton growth in marine mesocosms with increased CO<sub>2</sub> levels

Abstract

Abstract. Microzooplankton grazing and algae growth responses to increasing pCO 2 levels (350, 700 and 1050 µatm) were investigated in nitrate and phosphate fertilized mesocosms during the PeECE III experiment 2005. Grazing and growth rates were estimated by the dilution technique combined with taxon specific HPLC pigment analysis. Microzooplankton composition was determined by light microscopy. Despite a range of up to 3 times the present CO 2 levels, there were no clear differences in any measured parameter between the different CO 2 treatments. During days 3-9 of the experiment the algae community standing stock, measured as chlorophyll a (Chl-a), showed the highest instantaneous grow rates (k=0.37-0.99 d −1 ) and increased from ca. 2-3 to 6-12 µg l −1 , in all mesocosms. Afterwards the phytoplankton standing stock decreased in all mesocosms until the end of the experiment. The microzooplankton standing stock, that was mainly constituted by dinoflagellates and ciliates, varied between 23 and 130 µg C l −1 (corresponding to 1.9 and 10.8 µmol C l −1 ), peaking on day 13-15, apparently responding to the phytoplankton development. Instantaneous Chl-a growth rates were generally higher than the grazing rates, indicating only a limited overall effect of microzooplankton grazing on the most dominant phytoplankton. Diatoms and prymnesiophytes were significantly grazed (12-43% of the standing stock d −1 ) only in the prebloom phase when they were in low numbers, and in the post-bloom phase when they were already affected by low Correspondence to: K. Suffrian

Dynamics of dimethylsulphoniopropionate and dimethylsulphide under different CO<sub>2</sub> concentrations during a mesocosm experiment

“…The ecosystem composition, bacterial and phytoplankton abundances and productivity, grazing rates and total grazer abundance and reproduction were not significantly affected by CO 2 induced effects Riebesell et al, 2008;Egge et al, 2007;Paulino et al, 2007;Larsen et al, 2007;Suffrian et al, 2008;Carotenuto et al, 2007). This finding suggests that the system under study was surprisingly resilient to abrupt and large pH changes.…”

Rapid shifts in picoeukaryote community structure in response to ocean acidification

“…Acidification has been shown to reduce viral production in mixed blooms dominated by diatoms and E. huxleyi (Larsen et al, 2008), for example, although little effect was found on microzooplankton standing stock or grazing activity (Suffrian et al, 2008). M. pusilla populations can collapse rapidly due to viral lysis and microzooplankton grazing (Evans et al, 2003), and it is possible that the shifts in picoeukaryote community composition we observed in the present study may have been due to reduced predation of Micromonas in the acidified enclosures.…”

High tolerance of microzooplankton to ocean acidification in an Arctic coastal plankton community

“…in food availability, phytoplankton community structure, size classes and stoichiometry (Suffrian et al, 2008;Feng et al, 2009;Rossoll et al, 2012). On the other hand MZP are known for a direct pH sensitivity (Hinga, 2002;, and a drop in seawater pH as a result of increasing pCO 2 could directly affect the physiology of both autotrophic and heterotrophic protists by changing, e.g.…”

“…Only some small, chloroplast-bearing dinoflagellates were considered as predominantly autotrophic and included into the phytoplankton. MZP were identified to the lowest possible taxonomic level (species or genus level) according to Kahl (1932), Foissner et al (1995), Strüder-Kypke et al (2002), Tomas (1996) and Scott (2005). For biovolume calculations geometric proxies were used according to Hillebrand et al (1999), and carbon biomass was calculated using the conversion factors given in Putt and Stoecker (1989).…”

“…In this study we focussed on heterotrophic dinoflagellates and ciliates since these were numerically the most important MZP components and they are considered as major phytoplankton consumers worldwide Sherr and Sherr, 2007). Bacterivorous protozoa (e.g.…”