Season affects strength and direction of the interactive impacts of ocean warming and biotic stress in a coastal seaweed ecosystem

Martin Wahl, Franziska Julie Werner, Björn Buchholz, Stefanie Raddatz, Angelika Graiff, Birte Matthiessen, Ulf Karsten, Claas Hiebenthal, Jorin Hamer, Maysa Ito, Elisa Gülzow, Gil Rilov, Tamar Guy-Haim

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish
Pages (from-to)807-827
Number of pages21
JournalLimnology and Oceanography
Issue number4
StatePublished - 1 Apr 2020

Bibliographical note

Publisher Copyright:
© 2019 The Authors. Limnology and Oceanography published by Wiley Periodicals, Inc. on behalf of Association for the Sciences of Limnology and Oceanography.

ASJC Scopus subject areas

  • Oceanography
  • Aquatic Science


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