Seasonal Photophysiological Performance of Adult Western Baltic Fucus vesiculosus (Phaeophyceae) Under Ocean Warming and Acidification

Angelika Graiff,Karin Glaser,Inka Bartsch,Ulf Karsten

doi:10.3389/fmars.2021.666493

Abstract

Shallow coastal marine ecosystems are exposed to intensive warming events in the last decade, threatening keystone macroalgal species such as the bladder wrack (Fucus vesiculosus, Phaeophyceae) in the Baltic Sea. Herein, we experimentally tested in four consecutive benthic mesocosm experiments, if the single and combined impact of elevated seawater temperature (Δ + 5°C) and pCO2 (1100 ppm) under natural irradiance conditions seasonally affected the photophysiological performance (i.e., oxygen production, in vivo chlorophyll a fluorescence, energy dissipation pathways and chlorophyll concentration) of Baltic Sea Fucus. Photosynthesis was highest in spring/early summer when water temperature and solar irradiance increases naturally, and was lowest in winter (December to January/February). Temperature had a stronger effect than pCO2 on photosynthetic performance of Fucus in all seasons. In contrast to the expectation that warmer winter conditions might be beneficial, elevated temperature conditions and sub-optimal low winter light conditions decreased photophysiological performance of Fucus. In summer, western Baltic Sea Fucus already lives close to its upper thermal tolerance limit and future warming of the Baltic Sea during summer may probably become deleterious for this species. However, our results indicate that over most of the year a combination of future ocean warming and increased pCO2 will have slightly positive effects for Fucus photophysiological performance.

Highlights

Recent hot weather conditions in Central Europe, such as the weeks of record-breaking air temperatures during the summer of 2003 and 2018 (Schär et al, 2004; Imbery et al, 2018), pose a significant threat to macrophyte keystone species and their associated organisms, especially in shallow waters (Roth et al, 2010; Winters et al, 2011; Gouvêa et al, 2017)
The photosynthetic performance measured as in vivo chlorophyll a fluorescence, oxygen production and chlorophyll concentrations of F. vesiculosus vegetative apical tissue varied over the four seasons and the experimental treatment
Seasonal variations in the light utilization coefficient (α), relative maximal electron transport rates, and saturation irradiance for photosynthesis (Ik) were evident for Fucus grown in its native habitat (Table 1 and Supplementary Table 3)

Summary

Introduction

Recent hot weather conditions in Central Europe, such as the weeks of record-breaking air temperatures during the summer of 2003 and 2018 (Schär et al, 2004; Imbery et al, 2018), pose a significant threat to macrophyte keystone species and their associated organisms, especially in shallow waters (Roth et al, 2010; Winters et al, 2011; Gouvêa et al, 2017). (hereafter Fucus) is the most common canopy-forming and biomass dominating brown macroalga (Kautsky et al, 1992; Torn et al, 2006; Rönnbäck et al, 2007). Shallow subtidal habitats of the temperate regions like in the Baltic Sea are a highly variable environment where organisms are regularly exposed to strong fluctuations in temperature, pH, irradiance, salinity and nutrient availability. The Baltic Fucus tolerates highly variable environmental conditions, especially annual and seasonal fluctuations in pH (7.4–8.5) and temperature (

Methods

Results

Discussion

Conclusion