Seawater carbonate chemistry and seasonal mesocosm community experiments with warming and acidification treatments in Kiel Outdoor Benthocosms

• Main Authors: Wahl, Martin, Werner, Franziska Julie, Buchholz, Björn, Raddatz, Stefanie, Graiff, Angelika, Matthiessen, Birte, Karsten, Ulf, Hiebenthal, Claas, Hamer, Jorin, Ito, Maysa, Gülzow, Elisa, Rilov, Gil, Guy-Haim, Tamar, Yang, Yan
• Format: Dataset
• Language: English
• Published: PANGAEA 2023
• Subjects: Abundance change; Alkalinity; total; Aragonite saturation state; Asterias rubens; survival; Balanus improvisus; plate; growth rate; Benthos; Bicarbonate ion; Calcite saturation state; Calculated using seacarb after Nisumaa et al. (2010); Carbon; inorganic; dissolved; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Coast and continental shelf; Community composition and diversity; Entire community; Experiment; Fucus vesiculosus; length; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); Growth/Morphology; Laboratory experiment; Mesocosm or benthocosm; Mortality/Survival; Mytilus edulis; shell length; North Atlantic; OA-ICC; Ocean Acidification International Coordination Centre; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); pH; Replicate; Rocky-shore community; Salinity; Season; Temperate; Temperature; Ocean acidification
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.959649; https://doi.org/10.1594/PANGAEA.959649

The plea for using more “realistic,” community‐level, investigations to assess the ecological impacts of global change has recently intensified. Such experiments are typically more complex, longer, more expensive, and harder to interpret than simple organism‐level benchtop experiments. Are they worth the extra effort? Using outdoor mesocosms, we investigated the effects of ocean warming (OW) and acidification (OA), their combination (OAW), and their natural fluctuations on coastal communities of the western Baltic Sea during all four seasons. These communities are dominated by the perennial and canopy‐forming macrophyte Fucus vesiculosus—an important ecosystem engineer Baltic‐wide. We, additionally, assessed the direct response of organisms to temperature and pH in benchtop experiments, and examined how well organism‐level responses can predict community‐level responses to the dominant driver, OW. OW affected the mesocosm communities substantially stronger than acidification. OW provoked structural and functional shifts in the community that differed in strength and direction among seasons. The organism‐level response to OW matched well the community‐level response of a given species only under warm and cold thermal stress, that is, in summer and winter. In other seasons, shifts in biotic interactions masked the direct OW effects. The combination of direct OW effects and OW‐driven shifts of biotic interactions is likely to jeopardize the future of the habitat‐forming macroalga F. vesiculosus in the Baltic Sea. Furthermore, we conclude that seasonal mesocosm experiments are essential for our understanding of global change impact because they take into account the important fluctuations of abiotic and biotic pressures.