Antioxidative Properties of Baltic Sea Keystone Macroalgae (Fucus vesiculosus, Phaeophyceae) under Ocean Warming and Acidification in a Seasonally Varying Environment.

Angelika Graiff,Ulf Karsten

doi:10.3390/biology10121330

Abstract

Simple SummaryThe brown seaweed Fucus vesiculosus is the dominant and the most ecologically crucial primary producer and habitat founder in the Baltic Sea. In the shallow coastal zone, F. vesiculosus is particularly exposed to strongly and rapidly changing environmental conditions due to global change. This study examines how single and joint effects of elevated seawater temperature and pCO2 levels influence F. vesiculosus in all four seasons, using benthic mesocosms. The antioxidative properties and the sensitivity of F. vesiculosus photosynthetic performance to oxidative stress under different global change scenarios were assessed. F. vesiculosus tolerated strong hydrogen peroxide stress in all seasons, as reflected in high antioxidative enzyme activities and a low degree of membrane lipid peroxidation. Forecasted warming affected the antioxidative properties of F. vesiculosus stronger than acidification, causing significantly increased lipid peroxidation under elevated temperatures in all seasons. However, pCO2 levels modulated the oxidative stress of F. vesiculosus under warming. Overall, summer heatwaves reaching lethal temperatures in shallow waters will most likely determine the persistence of Baltic F. vesiculosus. The keystone macroalga Fucus vesiculosus (Phaeophyceae), dominating shallow hard bottom zones, encounters a strongly and rapidly changing environment due to anthropogenic change over the last decades in the Baltic Sea. Thus, in four successive benthic mesocosm experiments, the single and joint effects of increased temperature (Δ + 5 °C) and pCO2 (1100 ppm) under ambient irradiances were experimentally tested on the antioxidative properties of western Baltic F. vesiculosus in all seasons. The antioxidative properties (superoxide dismutase activity and lipid peroxidation) as well as the sensitivity of F. vesiculosus photosynthetic performance (i.e., effective quantum yield) to oxidative stress under these global change scenarios were seasonally examined. F. vesiculosus exhibited high and relatively constant photosynthetic performance under artificial hydrogen peroxide (H2O2) stress in all seasons. High activities of superoxide dismutase and a relatively low degree of the biomarker for lipid peroxidation (malondialdehyde concentration) were found in F. vesiculosus. Thus, Baltic F. vesiculosus is equipped with a high antioxidative potential to tolerate strong oxidative stress for at least short periods. Antioxidative properties of F. vesiculosus were more strongly affected by warming than by acidification, resulting in significantly increased malondialdehyde concentrations under elevated temperature levels in all seasons. Oxidative stress was enhanced in F. vesiculosus under warming but seem to be modulated by seasonally varying environmental conditions (e.g., high and low irradiances) and pCO2 levels. However, more frequent summer heatwaves reaching and surpassing lethal temperatures in shallow coastal waters may determine the F. vesiculosus population’s overall persistence in the Baltic Sea.

Highlights

Marine seaweeds that inhabit the shallow coastal area of temperate shorelines frequently experience an environment characterized by strong daily and seasonal variations in abiotic drivers, such as high and low irradiances, rapid temperature changes, and pH fluctuations
Perennial seaweeds in temperate latitudes can photosynthesize over broad temperature ranges, as they remain photosynthetically active throughout the year
It is assumed that F. vesiculosus is equipped with a high antioxidative potential to tolerate strong oxidative stress, for at least short periods

Summary

Introduction

Marine seaweeds that inhabit the shallow coastal area of temperate shorelines frequently experience an environment characterized by strong daily and seasonal variations in abiotic drivers, such as high and low irradiances, rapid temperature changes, and pH fluctuations. Due to anthropogenic global change, the continuing warming and its amplification of seasonal fluctuations generates stressful conditions in shallow waters, which seems to be a severe challenge for seaweeds [1,2,3]. Various metabolic processes in seaweeds induce ROS formation, photosynthesis. Plants and seaweeds accumulate ROS as a concomitant process of the electron transport systems during photosynthesis and respiration, even under normal metabolic conditions [7]. The main source of ROS in plant and seaweed tissues is the photosynthetic electron transport system that generates singlet oxygen (1 O2 ) and superoxide radicals (·O2 − ) [8,9]

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