The ability of macroalgae to mitigate the negative effects of ocean acidification on four species of North Atlantic bivalve

• Published in: Biogeosciences
• Main Authors: C. S. Young, C. J. Gobler
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2018
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; North Atlantic; Ocean acidification
• Online Access: https://doi.org/10.5194/bg-15-6167-2018; https://doaj.org/article/72ec83595a4f4378915638bf60ca034e

Coastal ecosystems can experience acidification via upwelling, eutrophication, riverine discharge, and climate change. While the resulting increases in p CO 2 can have deleterious effects on calcifying animals, this change in carbonate chemistry may benefit some marine autotrophs. Here, we report on experiments performed with North Atlantic populations of hard clams ( Mercenaria mercenaria ), eastern oysters ( Crassostrea virginica ), bay scallops ( Argopecten irradians ), and blue mussels ( Mytilus edulis ) grown with and without North Atlantic populations of the green macroalgae, Ulva . In six of seven experiments, exposure to elevated p CO 2 levels ( ∼ 1700 µatm) resulted in depressed shell- and/or tissue-based growth rates of bivalves compared to control conditions, whereas rates were significantly higher in the presence of Ulva in all experiments. In many cases, the co-exposure to elevated p CO 2 levels and Ulva had an antagonistic effect on bivalve growth rates whereby the presence of Ulva under elevated p CO 2 levels significantly improved their performance compared to the acidification-only treatment. Saturation states for calcium carbonate (Ω) were significantly higher in the presence of Ulva under both ambient and elevated CO 2 delivery rates, and growth rates of bivalves were significantly correlated with Ω in six of seven experiments. Collectively, the results suggest that photosynthesis and/or nitrate assimilation by Ulva increased alkalinity, fostering a carbonate chemistry regime more suitable for optimal growth of calcifying bivalves. This suggests that large natural and/or aquacultured collections of macroalgae in acidified environments could serve as a refuge for calcifying animals that may otherwise be negatively impacted by elevated p CO 2 levels and depressed Ω.