Seasonal Dynamic Response of Oxygen Flux in Ecklonia Cava Forests to Environmental Factors: An Aquatic Eddy Covariance Study

Artificial restoration and conservation of kelp forests are globally implemented as part of ‘blue carbon’ initiatives to achieve carbon neutrality in response to climate change. Ecklonia Cava, a kelp species distributed along the eastern and southern coasts of Korea, plays a significant role as a primary producer in coastal rocky shores. Quantitative analysis of its productivity is essential to evaluate the ecological importance of coastal rocky shores in global carbon sequestration.

We quantified the oxygen flux on daily to seasonal timescales in Ecklonia Cava forests located on the eastern coast of Jejudo Island using the aquatic eddy covariance method. Additional measurements were conducted within the forest using custom-made multiple oxygen optode sensors to investigate oxygen dynamics associated with kelp metabolism. The oxygen flux exhibited daily and seasonal variability, strongly influenced by light availability, tidal flow velocity, temperature, and biomass. Dependent relationships between oxygen flux and environmental parameters, based on a partial least squares regression model, indicate that Ecklonia cava was stressed by dynamic environmental conditions. While substantial gross primary production was observed across seasons, net autotrophic conditions were observed only in spring. Seasonal differences in ecological function were closely associated with increased respiration and biomass loss caused by elevated temperatures during summer and autumn. Additional measurements within the forest revealed diurnal variations in oxygen flux depending on distance above the seabed, reflecting active photosynthetic and respiratory processes of kelp and benthic communities. Moderately tall (50-60 cm) Ecklonia Cava significantly contributes to carbon sequestration and ecological services.