ALBERT

Description: Recent evolution experiments have revealed that marine phytoplankton may adapt to global change, for example to ocean warming or acidification. Long-term adaptation to novel environments is a dynamic process and phenotypic change can take place thousands of generations after exposure to novel conditions. Using the longest evolution experiment performed in any marine species to date (4 yrs, = 2100 generations), we show that in the coccolithophore Emiliania huxleyi, long-term adaptation to ocean acidification is complex and initial phenotypic responses may revert for important traits. While fitness increased continuously, calcification was restored within the first 500 generations but later reduced in response to selection, enhancing physiological declines of calcification in response to ocean acidification. Interestingly, calcification was not constitutively reduced but revealed rates similar to control treatments when transferred back to present-day CO2 conditions. Growth rate increased with time in controls and adaptation treatments, although the effect size of adaptation assessed through reciprocal assay experiments varied. Several trait changes were associated with selection for higher cell division rates under laboratory conditions, such as reduced cell size and lower particulate organic carbon content per cell. Our results show that phytoplankton may evolve phenotypic plasticity that can affect biogeochemically important traits, such as calcification, in an unforeseen way under future ocean conditions.

Description: Although oceanwarming and acidification are recognized as two major anthropogenic perturbations of today's oceanswe know very little about how marine phytoplankton may respond via evolutionary change.We tested for adaptation to ocean warming in combination with ocean acidification in the globally important phytoplankton species Emiliania huxleyi. Temperature adaptation occurred independently of ocean acidifcation levels. Exponential growth rates were were up to 16% higher in populations adapted for one year to warming when assayed at their upper thermal tolerance limit. Particulate inorganic (PIC) and organic (POC) carbon production was restored to values under present-day ocean conditions, owing to adaptive evolution, and were 101% and 55% higher under combined warming and acidification, respectively, than in non-adapted controls. Cells also evolved to a smaller size while they recovered their initial PIC:POC ratio even under elevated CO2. The observed changes in coccolithophore growth, calcite and biomass production, cell size and elemental composition demonstrate the importance of evolutionary processes for phytoplankton performance in a future ocean. At the end of a 1-yr temperature selection phase, we conducted a reciprocal assay experiment in which temperature-adapted asexual populations were compared to the respective non-adapted control populations under high temperature, and vice versa (1. Assay Data, Dataset #835336). Mean exponential growth rates m in treatments subjected to high temperature increased rapidly under all high temperature-CO2 treatment combinations during the temperature selection phase (2. time series, Dataset #835339).

Description: Quantifying effects of Ocean Acidification (OA) on marine primary and secondary producers is of acute interest, as they could translate up to higher trophic levels and ultimately may alter ecosystem services including fishery yields. A mesocosm approach was used to investigate the effects of OA on a natural plankton community in coastal waters off Norway by manipulating CO2 partial pressure (pCO2). Eight enclosures were deployed in the Raunefjord near Bergen. Treatment levels were ambient and elevated pCO2 of ~ 2000 µatm each in four replicate enclosures. The experiment lasted for 53 days in early summer of 2015. To assess impacts of OA on the plankton community, we measured phytoplankton and protozooplankton biomass and total seston fatty acid (FA) content. In both the control and the elevated pCO2 treatment, the plankton community was dominated by the dinoflagellate Ceratium longipes. In the elevated pCO2 treatment, however, this species as well as other dinoflagellates were strongly negatively impacted: At the end of the experiment, total dinoflagellate biomass was fourfold higher in the control group than under elevated pCO2 treatment. In a size comparison of C. longipes, individuals in the high pCO2 treatment were significantly larger. Fatty acid analysis revealed a decreased ratio of polyunsaturated fatty acids (PUFA) to saturated fatty acids (SFA) at elevated pCO2. Further, docosahexaenoic acid (DHA, C 22:6n3c), essential for development and reproduction of copepods and higher trophic levels, was lower in the high pCO2 treatment. Both in quality and quantity of their food, higher trophic levels thus experienced worse conditions in a community exposed to elevated pCO2, with potentially severe consequences for higher trophic levels.

Description: Although coccolithophore physiological responses to CO2-induced changes in seawater carbonate chemistry have been widely studied in the past, there is limited knowledge on the variability of physiological responses between populations from different areas. In the present study, we investigated the specific responses of growth, particulate organic (POC) and inorganic carbon (PIC) production rates of three populations of the coccolithophore Emiliania huxleyi from three regions in the North Atlantic Ocean (Azores: six strains, Canary Islands: five strains, and Norwegian coast near Bergen: six strains) to a CO2 partial pressure (pCO2) range from 120 to 2630µatm. Physiological rates of each population and individual strain increased with rising pCO2 levels, reached a maximum and declined thereafter. Optimal pCO2 for growth, POC production rates, and tolerance to low pH (i.e., high proton concentration) was significantly higher in an E. huxleyi population isolated from the Norwegian coast than in those isolated near the Azores and Canary Islands. This may be due to the large environmental variability including large pCO2 and pH fluctuations in coastal waters off Bergen compared to the rather stable oceanic conditions at the other two sites. Maximum growth and POC production rates of the Azores and Bergen populations were similar and significantly higher than that of the Canary Islands population. This pattern could be driven by temperature–CO2 interactions where the chosen incubation temperature (16°C) was slightly below what strains isolated near the Canary Islands normally experience. Our results indicate adaptation of E. huxleyi to their local environmental conditions and the existence of distinct E. huxleyi populations. Within each population, different growth, POC, and PIC production rates at different pCO2 levels indicated strain-specific phenotypic plasticity. Accounting for this variability is important to understand how or whether E. huxleyi might adapt to rising CO2 levels.

Description: This dataset is from an experiment with large-volume in situ mesocosms (~55-60 m3 and 21 m depth) in Raunefjord (Bergen), Norway in 2015. In this pelagic in situ mesocosm experiment, we assessed how ocean acidification (particularly episodic extreme events) affect natural plankton communities. A particular focus was the response of the appendicularian Oikopleura dioica, and its influence on vertical carbon fluxes. Therefore, we sampled ecological and biogeochemical key parameters for 49 days in regular intervals.

Description: Thermal reaction norms for growth rates of six Emiliania huxleyi isolates originating from the central Atlantic (Azores, Portugal) and five isolates from the coastal North Atlantic (Bergen, Norway) were assessed. We used the template mode of variation model to decompose variations in growth rates into modes of biological interest: vertical shift, horizontal shift, and generalist-specialist variation. In line with the actual habitat conditions, isolates from Bergen (Bergen population) grew well at lower temperatures, and isolates from the Azores (Azores population) performed better at higher temperatures. The optimum growth temperature of the Azores population was significantly higher than that of the Bergen population. Neutral genetic differentiation was found between populations by microsatellite analysis. These findings indicate that E. huxleyi populations are adapted to local temperature regimes. Next to between-population variation, we also found variation within populations. Genotype-by-environment interactions resulted in the most pronounced phenotypic differences when isolates were exposed to temperatures outside the range they naturally encounter. Variation in thermal reaction norms between and within populations emphasizes the importance of using more than one isolate when studying the consequences of global change on marine phytoplankton. Phenotypic plasticity and standing genetic variation will be important in determining the potential of natural E. huxleyi populations to cope with global climate change.

Description: Ocean acidification, the drop in seawater pH associated with the ongoing enrichment of marine waters with carbon dioxide from fossil fuel burning, may seriously impair marine calcifying organisms. Our present understanding of the sensitivity of marine life to ocean acidification is based primarily on short-term experiments, in which organisms are exposed to increased concentrations of CO2. However, phytoplankton species with short generation times, in particular, may be able to respond to environmental alterations through adaptive evolution. Here, we examine the ability of the world's single most important calcifying organism, the coccolithophore Emiliania huxleyi, to evolve in response to ocean acidification in two 500-generation selection experiments. Specifically, we exposed E. huxleyi populations founded by single or multiple clones to increased concentrations of CO2. Around 500 asexual generations later we assessed their fitness. Compared with populations kept at ambient CO2 partial pressure, those selected at increased partial pressure exhibited higher growth rates, in both the single- and multiclone experiment, when tested under ocean acidification conditions. Calcification was partly restored: rates were lower under increased CO2 conditions in all cultures, but were up to 50% higher in adapted compared with non-adapted cultures. We suggest that contemporary evolution could help to maintain the functionality of microbial processes at the base of marine food webs in the face of global change.