Effects of high CO2 and warming on a Baltic Sea microzooplankton community

Abstract

Global warming and ocean acidification are among the most important stressors for aquatic ecosystems in the future. To investigate their direct and indirect effects on a near-natural plankton community, a multiple-stressor approach is needed. Hence, we set up mesocosms in a full-factorial design to study the effects of both warming and high CO2 on a Baltic Sea autumn plankton community, concentrating on the impacts on microzooplankton (MZP). MZP abundance, biomass, and species composition were analysed over the course of the experiment. We observed that warming led to a reduced time-lag between the phytoplankton bloom and an MZP biomass maximum. MZP showed a significantly higher growth rate and an earlier biomass peak in the warm treatments while the biomass maximum was not affected. Increased pCO2 did not result in any significant effects on MZP biomass, growth rate, or species composition irrespective of the temperature, nor did we observe any significant interactions between CO2 and temperature. We attribute this to the high tolerance of this estuarine plankton community to fluctuations in pCO2, often resulting in CO2 concentrations higher than the predicted end-of-century concentration for open oceans. In contrast, warming can be expected to directly affect MZP and strengthen its coupling with phytoplankton by enhancing its grazing pressure.

Community barcoding reveals little effect of ocean acidification on the composition of coastal plankton communities: Evidence from a long-term mesocosm study in the Gullmar Fjord, Skagerrak

“…The resilience of coastal plankton communities (bacteria, phytoplankton, micro- and mesozooplankton) towards future OA conditions was also demonstrated in earlier large scale mesocosm field and indoor studies [9–13, 57, 58]. In agreement with those results, we assume that low sensitivities for high CO 2 conditions are common for coastal plankton communities which are exposed to pronounced natural fluctuations in seawater pH.…”

Short-term responses to ocean acidification: effects on relative abundance of eukaryotic plankton from the tropical Timor Sea

“…The eCA concentration dropped more slowly in the ISCO treatment ( Supplementary Fig.2 Despite constant pumping of fresh ocean water into the sampling pool, heating of incubating bottles during the day because of the tropical climate (Supplementary Figure S1) was a clear limitation of our experiment. Previous studies did not detect a synergetic effect of OA and warming on plankton communities (Paul et al 2015, Horn et al 2016). But to exclude additional effects by warming, e.g., the decrease of heterotrophic flagellate biomass (Moustaka-Gouni et al 2016), we decided to compare effects of OA treatment only within but not between t0 and t2.…”

The Diatom/Dinoflagellate Index as an Indicator of Ecosystem Changes in the Baltic Sea 1. Principle and Handling Instruction

“…In their study of sediments from the Bornholm Basin, Dutz et al (2004) found high hatching rates of nauplii already in March and April, with strong increases in those rates as the incubation temperature increased. In mesocosm experiments, warming led to a reduced time-lag between the phytoplankton bloom and the microzooplankton biomass maximum (Horn et al, 2015). Therefore, early diatoms can be controlled by grazing, which implies lower and later algal peaks at higher temperatures (Gaedke et al, 2010).…”