Contribution of marine macrophytes to pCO2 and DOC variations in human-impacted coastal waters

Abstract

Carbon cycles in coastal waters are highly sensitive to human activities and play important roles in global carbon budgets. CO2 sink–source behavior is regulated by spatiotemporal variations in net biological productivity, but the contribution of macrophyte habitats including macroalgae aquaculture to atmospheric CO2 removal has not been well quantified. We investigated the variations in the carbonate system and dissolved organic carbon (DOC) in human-impacted macrophyte habitats and analyzed the biogeochemical drivers for the variations of these processes. Cultivated macroalgal metabolism (photosynthesis, respiration, calcification, and DOC release) was quantified by in situ field-bag experiments. Cultivated macroalgae took up dissolved inorganic carbon (DIC) (16.2–439 mmol-C m−2 day−1) and released DOC (1.2–146 mmol-C m−2 day−1). We estimated that seagrass beds and macroalgae farming contributed 0.8 and 0.4 mmol-C m−2 day−1 of the in situ total CO2 removal (5.7 and 6.7 mmol-C m−2 day−1, respectively) during their growing period in a semi-enclosed embayment but efficient water exchange (i.e., short residence time) in an open coastal area precluded detection of the contribution of macrophyte habitats to the CO2 removal. Although hydrological processes, biological metabolism, and organic carbon storage processes would contribute to the net CO2 sink–source behavior, our analyses distinguished the contribution of macrophytes from other factors. Our findings imply that macroalgae farming, in addition to restoring and creating macrophyte habitats, has potential for atmospheric CO2 removal.

Genome-wide markers reveal geographical isolation by distance and barriers as well as local heterogeneity in the genetic structure of a seagrass

“…The intra-site variability was an exceptional feature of that site compared to the SIS and Akkeshi sites. Intra-site variability may not be caused by environmental selection, because there is less of a gradient in water quality within the subsites around the YSP (Watanabe et al 2024). The heterogeneity of the eelgrass population in the YSP has been impacted the most by transplantation during the ten years since the construction of the shallow at (https://www.spf.org/opri/newsletter/120_3.html).…”

“…There has been an eelgrass bed at the Futtsu site since before urbanization (Yamakita and Nakaoka 2009;Yamakita et al 2011). The Yokohama Seaside Park (YSP) is an arti cial, shallow at that lies within 1 km of another seagrass bed that is distributed on the at (Watanabe et al 2024). Eelgrass seed was arti cially dispersed at the YSP as part of restoration programs (https://www.spf.org/opri/newsletter/120_3.html).…”