Food availability outweighs ocean acidification effects in juvenile Mytilus edulis:Laboratory and field experiments

• Published in: Global Change Biology
• Main Authors: Thomsen, Jörn, Casties, Isabel, Pansch, Christian, Körtzinger, Arne, Melzner, Frank
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2013
• Subjects: Adaptation; Amphibalanus improvisus; Calcification; CO enriched ecosystem; Community response; Energy availability; Eutrophication; Field study; Mytilus edulis; Ocean acidification
• Online Access: https://research.abo.fi/en/publications/a7bd768c-d669-4086-8cb2-6c658b5ba928; https://doi.org/10.1111/gcb.12109; http://www.scopus.com/inward/record.url?scp=84874772100&partnerID=8YFLogxK

Ocean acidification is expected to decrease calcification rates of bivalves. Nevertheless, in many coastal areas high pCO 2 variability is encountered already today. Kiel Fjord (Western Baltic Sea) is a brackish (12-20 g kg -1 ) and CO 2 enriched habitat, but the blue mussel Mytilus edulis dominates the benthic community. In a coupled field and laboratory study we examined the annual pCO 2 variability in this habitat and the combined effects of elevated pCO 2 and food availability on juvenile M. edulis growth and calcification. In the laboratory experiment, mussel growth and calcification were found to chiefly depend on food supply, with only minor impacts of pCO 2 up to 3350 μatm. Kiel Fjord was characterized by strong seasonal pCO 2 variability. During summer, maximal pCO 2 values of 2500 μatm were observed at the surface and >3000 μatm at the bottom. However, the field growth experiment revealed seven times higher growth and calcification rates of M. edulis at a high pCO 2 inner fjord field station (mean pCO 2 ca. 1000 μatm) in comparison to a low pCO 2 outer fjord station (ca. 600 μatm). In addition, mussels were able to out-compete the barnacle Amphibalanus improvisus at the high pCO 2 site. High mussel productivity at the inner fjord site was enabled by higher particulate organic carbon concentrations. Kiel Fjord is highly impacted by eutrophication, which causes bottom water hypoxia and consequently high seawater pCO 2 . At the same time, elevated nutrient concentrations increase the energy availability for filter feeding organisms such as mussels. Thus, M. edulis can dominate over a seemingly more acidification resistant species such as A. improvisus. We conclude that benthic stages of M. edulis tolerate high ambient pCO 2 when food supply is abundant and that important habitat characteristics such as species interactions and energy availability need to be considered to predict species vulnerability to ocean acidification.