Copepods in a changing sea : Ocean acidification, long-term changes and short-term variability

Anna-Karin Almén conducted field and lab work for this thesis at Tvärminne Zoological Station

Effect of ocean acidification on the structure and fatty acid composition of a natural plankton community in the Baltic Sea

Increasing atmospheric carbon dioxide (CO2) is changing seawater chemistry towards reduced pH, which affects various properties of marine organisms. Coastal and brackish water communities are expected to be less affected by ocean acidification (OA) as these communities are typically adapted to high fluctuations in CO2 and pH. Here we investigate the response of a coastal brackish water plankton community to increasing CO2 levels as projected for the coming decades and the end of this century in terms of community and biochemical fatty acid (FA) composition. A Baltic Sea plankton community was enclosed in a set of offshore mesocosms and subjected to a CO2 gradient ranging from natural concentrations (similar to 347 mu atm fCO(2)) up to values projected for the year 2100 (similar to 1333 mu atm fCO(2)). We show that the phytoplankton community composition was resilient to CO2 and did not diverge between the treatments. Seston FA composition was influenced by community composition, which in turn was driven by silicate and phosphate limitation in the mesocosms and showed no difference between the CO2 treatments. These results suggest that CO2 effects are dampened in coastal communities that already experience high natural fluctuations in pCO(2). Although this coastal plankton community was tolerant of high pCO(2) levels, hypoxia and CO2 uptake by the sea can aggravate acidification and may lead to pH changes outside the currently experienced range for coastal organisms.Peer reviewe

Ocean acidification challenges copepod phenotypic plasticity

Ocean acidification is challenging phenotypic plasticity of individuals and populations. Calanoid copepods (zooplankton) are shown to be fairly plastic against altered pH conditions, and laboratory studies indicate that transgenerational effects are one mechanism behind this plasticity. We studied phenotypic plasticity of the copepod Acartia sp. in the course of a pelagic, large-volume mesocosm study that was conducted to investigate ecosystem and biogeochemical responses to ocean acidification. We measured copepod egg production rate, egg-hatching success, adult female size and adult female antioxidant capacity (ORAC) as a function of acidification (fCO(2) similar to 365-1231 mu atm) and as a function of quantity and quality of their diet. We used an egg transplant experiment to reveal whether transgenerational effects can alleviate the possible negative effects of ocean acidification on offspring development. We found significant negative effects of ocean acidification on adult female size. In addition, we found signs of a possible threshold at high fCO(2), above which adaptive maternal effects cannot alleviate the negative effects of acidification on egg-hatching and nauplii development. We did not find support for the hypothesis that insufficient food quantity (total particulate carbonPeer reviewe

Negligible effects of ocean acidification on Eurytemora affinis (Copepoda) offspring production

Ocean acidification is caused by increasing amounts of carbon dioxide dissolving in the oceans leading to lower seawater pH. We studied the effects of lowered pH on the calanoid copepod Eurytemora affinis during a mesocosm experiment conducted in a coastal area of the Baltic Sea. We measured copepod reproductive success as a function of pH, chlorophyll a concentration, diatom and dinoflagellate biomass, carbon to nitrogen (C : N) ratio of suspended particulate organic matter, as well as copepod fatty acid composition. The laboratory-based experiment was repeated four times during 4 consecutive weeks, with water and copepods sampled from pelagic mesocosms enriched with different CO2 concentrations. In addition, oxygen radical absorbance capacity (ORAC) of animals from the mesocosms was measured weekly to test whether the copepod's defence against oxidative stress was affected by pH. We found no effect of pH on offspring production. Phytoplankton biomass, as indicated by chlorophyll a concentration and dinoflagellate biomass, had a positive effect. The concentration of polyunsaturated fatty acids in the females was reflected in the eggs and had a positive effect on offspring production, whereas monounsaturated fatty acids of the females were reflected in their eggs but had no significant effect. ORAC was not affected by pH. From these experiments we conclude that E. affinis seems robust against direct exposure to ocean acidification on a physiological level, for the variables covered in the study. E. affinis may not have faced acute pH stress in the treatments as the species naturally face large pH fluctuations.Peer reviewe

Feeding, survival, and reproduction of two populations of Eurytemora (Copepoda) exposed to local toxic cyanobacteria

Studying the responses of crustacean zooplankton to harmful algal blooms is important for understanding changes in lower food webs following eutrophication in the Laurentian Great Lakes and other regions around the world. Here we examine responses to toxic cyanobacteria by crustacean copepods of the genus Eurytemora from eutrophic coastal regions of Lake Michigan (Green Bay) and the Baltic Sea (Gulf of Finland). We measured grazing, survivorship, reproduction, and juvenile (nauplius) size in short-term laboratory experiments. Females were incubated with representative non-toxic food and mixtures of non-toxic food with either cyanobacteria or cyanobacteria filtrate. Eurytemora from both locations were affected negatively by cyanobacteria filtrates, even with non-toxic food available. Eurytemora carolleeae from Green Bay exhibited reduced grazing rates when exposed to filtrates, but this effect was not observed when animals were fed the cyanobacteria and filtrate along with non-toxic food. Eurytemora sp. from the Baltic Sea given filtrates and non-toxic food also exhibited decreased grazing rates, as well as decreased adult survival and nauplius size. Similarly, when cyanobacterial cells were included along with filtrate and non-toxic food these effects were not observed. Our results also demonstrated a significant trade-off between offspring quantity and quality for both groups of animals, being more pronounced when food quality was manipulated by the presence of cyanobacterial cells. These findings further our knowledge of how a widely distributed group like Eurytemora may respond in the face of changing local selection pressures from natural and anthropogenic stressors. (C) 2017 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.Peer reviewe

Influence of Ocean Acidification on a Natural Winter-to-Summer Plankton Succession : First Insights from a Long-Term Mesocosm Study Draw Attention to Periods of Low Nutrient Concentrations

Every year, the oceans absorb about 30% of anthropogenic carbon dioxide (CO2) leading to a re-equilibration of the marine carbonate system and decreasing seawater pH. Today, there is increasing awareness that these changes-summarized by the term ocean acidification (OA)-could differentially affect the competitive ability of marine organisms, thereby provoking a restructuring of marine ecosystems and biogeochemical element cycles. In winter 2013, we deployed ten pelagic mesocosms in the Gullmar Fjord at the Swedish west coast in order to study the effect of OA on plankton ecology and biogeochemistry under close to natural conditions. Five of the ten mesocosms were left unperturbed and served as controls (similar to 380 mu atm pCO(2)), whereas the others were enriched with CO2-saturated water to simulate realistic end-of-the-century carbonate chemistry conditions (mu 760 mu atm pCO(2)). We ran the experiment for 113 days which allowed us to study the influence of high CO2 on an entire winter-to-summer plankton succession and to investigate the potential of some plankton organisms for evolutionary adaptation to OA in their natural environment. This paper is the first in a PLOS collection and provides a detailed overview on the experimental design, important events, and the key complexities of such a "long-term mesocosm" approach. Furthermore, we analyzed whether simulated end-of-the-century carbonate chemistry conditions could lead to a significant restructuring of the plankton community in the course of the succession. At the level of detail analyzed in this overview paper we found that CO2-induced differences in plankton community composition were non-detectable during most of the succession except for a period where a phytoplankton bloom was fueled by remineralized nutrients. These results indicate: (1) Long-term studies with pelagic ecosystems are necessary to uncover OA-sensitive stages of succession. (2) Plankton communities fueled by regenerated nutrients may be more responsive to changing carbonate chemistry than those having access to high inorganic nutrient concentrations and may deserve particular attention in future studies.Peer reviewe