Description: The acidification of the oceans could potentially alter marine plankton communities with consequences for ecosystem functioning. While several studies have investigated effects of ocean acidification on communities using traditional methods, few have used genetic analyses. Here, we use community barcoding to assess the impact of ocean acidification on the composition of a coastal plankton community in a large scale, in situ, long-term mesocosm experiment. High-throughput sequencing resulted in the identification of a wide range of planktonic taxa (Alveolata, Cryptophyta, Haptophyceae, Fungi, Metazoa, Hydrozoa, Rhizaria, Straminipila, Chlorophyta). Analyses based on predicted operational taxonomical units as well as taxonomical compositions revealed no differences between communities in high CO2 mesocosms (~ 760 μatm) and those exposed to present-day CO2 conditions. Observed shifts in the planktonic community composition were mainly related to seasonal changes in temperature and nutrients. Furthermore, based on our investigations, the elevated CO2 did not affect the intraspecific diversity of the most common mesozooplankter, the calanoid copepod Pseudocalanus acuspes. Nevertheless, accompanying studies found temporary effects attributed to a raise in CO2. Differences in taxa composition between the CO2 treatments could, however, only be observed in a specific period of the experiment. Based on our genetic investigations, no compositional long-term shifts of the plankton communities exposed to elevated CO2 conditions were observed. Thus, we conclude that the compositions of planktonic communities, especially those in coastal areas, remain rather unaffected by increased CO2.

Description: Hydrothermal vent deposits form on the seafloor as a result of cooling and mixing of hot hydrothermal fluids with cold seawater. Amongst the major sulfide and sulfate minerals that are preserved at vent sites, barite (BaSO4) is unique because it requires the direct mixing of Ba-rich hydrothermal fluid with sulfate-rich seawater in order for precipitation to occur. Because of its extremely low solubility, barite crystals preserve geochemical fingerprints associated with conditions of formation. Here, we present data from petrographic and geochemical analyses of hydrothermal barite from the Endeavour Segment of the Juan de Fuca Ridge, northeast Pacific Ocean, in order to determine the physical and chemical conditions under which barite precipitates within seafloor hydrothermal vent systems. Petrographic analyses of 22 barite-rich samples show a range of barite crystal morphologies: dendritic and acicular barite forms near the exterior vent walls, whereas larger bladed and tabular crystals occur within the interior of chimneys. A two component mixing model based on Sr concentrations and 87Sr/86Sr of both seawater and hydrothermal fluid, combined with 87Sr/86Sr data from whole rock and laser-ablation ICP-MS analyses of barite crystals indicate that barite precipitates from mixtures containing as low as 17% and as high as 88% hydrothermal fluid component, relative to seawater. Geochemical modelling of the relationship between aqueous species concentrations and degree of fluid mixing indicates that Ba2+ availability is the dominant control on mineral saturation. Observations combined with model results support that dendritic barite forms from fluids of less than 40% hydrothermal component and with a saturation index greater than ∼0.6, whereas more euhedral crystals form at lower levels of supersaturation associated with greater contributions of hydrothermal fluid. Fluid inclusions within barite indicate formation temperatures of between ∼120 °C and 240 °C during barite crystallization. The comparison of fluid inclusion formation temperatures to modelled mixing temperatures indicates that conductive cooling of the vent fluid accounts for 60–120 °C reduction in fluid temperature. Strontium zonation within individual barite crystals records fluctuations in the amount of conductive cooling within chimney walls that may result from cyclical oscillations in hydrothermal fluid flux. Barite chemistry and morphology can be used as a reliable indicator for past conditions of mineralization within both extinct seafloor hydrothermal deposits and ancient land-based volcanogenic massive sulfide deposits.

Description: Ocean acidification may affect zooplankton directly by decreasing in pH, as well as indirectly via trophic pathways, where changes in carbon availability or pH effects on primary producers may cascade up the food web thereby altering ecosystem functioning and community composition. Here, we present results from a mesocosm experiment carried out during 113 days in the Gullmar Fjord, Skagerrak coast of Sweden, studying plankton responses to predicted end-of-century pCO2 levels. We did not observe any pCO2 effect on the diversity of the mesozooplankton community, but a positive pCO2 effect on the total mesozooplankton abundance. Furthermore, we observed species-specific sensitivities to pCO2 in the two major groups in this experiment, copepods and hydromedusae. Also stage-specific pCO2 sensitivities were detected in copepods, with copepodites being the most responsive stage. Focusing on the most abundant species, Pseudocalanus acuspes, we observed that copepodites were significantly more abundant in the high-pCO2 treatment during most of the experiment, probably fuelled by phytoplankton community responses to high-pCO2 conditions. Physiological and reproductive output was analysed on P. acuspes females through two additional laboratory experiments, showing no pCO2 effect on females’ condition nor on egg hatching. Overall, our results suggest that the Gullmar Fjord mesozooplankton community structure is not expected to change much under realistic end-of-century OA scenarios as used here. However, the positive pCO2 effect detected on mesozooplankton abundance could potentially affect biomass transfer to higher trophic levels in the future.

Description: The ongoing acidification process of the oceans is likely to have consequences for many marine biota. Although evolutionary responses are expected during persisting environmental change, little is known about the adaptability of copepods. Therefore, we set up a 3 ½ years long selection experiment, culturing Acartia tonsa populations in water treated with 200 and 800 µatm pCO2, feeding them with algae grown in f/2 medium under 200 µatm pCO2 and in f/2 N P medium under 800 µatm pCO2. After three reciprocal transplant experiments we measured copepods' developmental rates, carbon to nutrient ratios, egg production and hatching rates. Under high CO2 conditions, stoichiometric discrepancies between the requirements of A. tonsa and its food resulted in a significantly decreased developmental rate independent from the selective history. After one year, these discrepancies appeared alleviated by an optimised homeostasis regulation of the copepods, indicating a high body stoichiometry regulation plasticity. Egg production and hatching success were unaffected by the experimental conditions, however, results indicated a premature hatching of eggs from females with a high CO2 selective history. Over the experimental period we did not detect any beneficial adaptations of the copepods cultured under high CO2 conditions of elevated seawater pCO2 and associated food quality reduction. Towards the end of the experiment, copepods cultured under elevated pCO2 and fed with high CO2 algae, showed an increased body mass and decreased prosome length. Such physiological changes could have profound long term consequences for marine copepods, food web interactions, and ultimately ecosystem structures and functions.

Description: Ocean acidification (OA) is one of the major symptoms of the current increase in atmospheric CO2. Here, we present results from a mesocosm experiment carried out during 113 days in the Gullmar Fjord, Skagerrak coast of Sweden, studying plankton responses to predicted end-of-century pCO2 levels. Abundances of both copepods (Pseudocalanus acuspes, Temora longicornis, and Oithona similis) and hydromedusae (Hybocodon prolifer and Aglantha digitale) responded to pCO2. Furthermore, stage-specific pCO2 sensitivities were detected in copepods, copepodites being the most sensitive stage.

Description: Ocean acidification impacts many marine biota. Although evolutionary responses should occur during persisting environmental change, little is known about the adaptability of copepods. Therefore, we set up a 3½ yr long selection experiment, maintaining Acartia tonsa populations in seawater treated with 200 and 800 μatm CO2, and feeding them with algae cultured under corresponding CO2 conditions. In 3 reciprocal transplant experiments, roughly 1 yr apart, we measured developmental rates, C:N and C:P ratios, egg production and hatching rates of the different lines. In the transplant experiments, we observed significantly lower developmental rates in the high CO2 treatment independent of the selective history. Egg production and hatching success were unaffected by the experimental conditions, but we observed an earlier hatching of eggs from females with a high CO2 selective history. Over the experimental period, beneficial adaptations of the copepods cultured under high CO2 conditions of elevated seawater pCO2 and associated food quality were not detected. However, towards the end of the experiment, copepods cultured under elevated pCO2 and fed with high CO2 algae showed increased body mass and decreased prosome length.

Description: The acidification of the oceans could potentially alter marine plankton communities with consequences for ecosystem functioning. While several studies have investigated effects of ocean acidifications on communities using traditional methods, few have used genetic analyses. Here, we use community barcoding to assess the impact of ocean acidification on the composition of a coastal plankton community in a large scale, in situ, long-term mesocosm experiment. High-throughput sequencing resulted in the identification of a wide range of planktonic taxa (Alveolata, Cryptophyta, Haptophyceae, Fungi, Metazoa, Hydrozoa, Rhizaria, Straminipila, Chlorophyta). Analyses based on predicted operational taxonomical units as well as taxonomical compositions revealed no differences between communities in high CO2 mesocosms (~760 µatm) and those exposed to present day CO2 conditions. Observed shifts in the planktonic community composition were mainly related to seasonal changes in temperature and nutrients.