Highlights
- Seaweeds significantly increased the growth rates of oysters by 20–70%, of clams by 60–70%, and of scallops by 130–140%.
- Seaweeds caused significant increases in pH, DO, and the saturation state of calcium carbonate (Ω).
- Seaweeds caused a significant increase in the concentrations of suspended chlorophyll a.
- Co-culture of seaweeds with bivalves accelerates the growth rate of bivalves by increasing pH, DO, Ω, and food availability.
Abstract
While bivalve populations are threatened by climate change stressors including ocean acidification and hypoxia, the photosynthetic activity of seaweeds can raise the pH and dissolved oxygen (DO) of seawater, combatting these stressors. Here, three commercially important North Atlantic bivalves (Eastern oysters, Crassostrea virginica; hard clams, Mercenaria mercenaria; bay scallops, Argopecten irradians) were grown in the presence and absence of two common seaweeds (Ulva sp. and Gracilaria sp.) in replicated 300 L outdoor aquaculture tables with flow-through seawater. Environmental conditions including pH, DO, and chlorophyll a were continuously monitored and levels of dissolved inorganic carbon and the complete carbonate chemistry of seawater were quantified. The presence of seaweeds significantly increased shell- and tissue-based growth rates of oysters by 20–70%, of clams by 60–70%, and of scallops by 130–140% (p < 0.05) with both seaweeds being similarly effective. Both seaweed species caused significant increases in pH, DO, and the saturation state of calcium carbonate (Ω) during the day (p < 0.05) whereas differences at night were muted with night-time Ωaragonite levels being at or below saturation in all treatments. In some experiments, the presence of seaweeds caused a significant increase in the concentrations of suspended chlorophyll a, suggesting that seaweeds increased the total amount and diversity of food available to bivalves. Collectively, this study demonstrates that the co-culture of seaweeds with bivalves in a land-based aquaculture setting can significantly accelerate the growth rate of bivalves by increasing pH, DO, Ω, and food availability.
Gobler C. J., Young C. S., Sylvers L. H., Banik U., Seo D. & Doall M. H., 2026. Seaweeds (Ulva, Gracilaria) significantly increase the growth rates of North Atlantic oysters, scallops, and clams grown in an aquaculture setting. Aquaculture 617: 743745. doi: 10.1016/j.aquaculture.2026.743745. Article.
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