Assessing photosynthetic uptake of total inorganic carbon in an Ecklonia cava dominated seaweed artificial reef: Population- and community-level metabolisms

Abstract

With increasing climate crisis concerns, interest in primary production of marine ecosystems is also increasing. Recently, artificial transplantation of canopy-forming seaweed has been carried out to increase coastal productivity, but the contribution of this strategy to inorganic carbon uptake has not been evaluated. Here, we estimated photosynthetic uptake of total inorganic carbon (TIC) by measuring the population and community productivity of artificial reefs (ARs) implanted with seaweed (dominated by Ecklonia cava) to determine TIC uptake efficiency of the transplanted seaweed and ecosystem respiration. The community-level of TIC uptake rate in the ARs ecosystem was measured using a 24-h tent incubation method in July and October 2021 in the East Sea of Korea. From these experiments, GCP and NCP (gross and net community production, respectively) ranged from 0.81–4.84 g C m−2 day−1 and from -2.08–1.91 g C m−2 day−1, respectively. We also measured photosynthesis-irradiance curves of E. cava (population level) to estimate individual inorganic carbon uptake rate in October 2021. GPP and NPP (gross and net primary productivity) were 132.47 and 6.83 mg C ind.−1 day−1, respectively. Based on these results, we estimated TIC uptake rates via photosynthesis of ARs seaweed beds at a community level. About 95% of GCP was allocated for E. cava respiration, but seaweed-associated respiration at different trophic levels (i.e., microbial and meiofauna/macrofauna respiration) was allocated an additional 20%, creating a net heterotrophic environment. Together, productivity differences at the population and community levels are key in explaining seaweed contribution to TIC uptake and respiration at the community level.