Turbo sazae, a commercially and ecologically significant marine gastropod traditionally found in Jeju Island and the southern coast of Korea, is experiencing a reported northward expansion into the East Sea, likely influenced by rising seawater temperatures. This study provides preliminary genetic insights into the genetic structure and connectivity of T. sazae populations between Jeju and the East Sea using mitochondrial COI sequences. Samples from 6 geographically distinct locations were analyzed, with three cloned replicates generated to enhance sequence reliability. Genetic diversity, haplotype distribution, and population differentiation were then assessed. Our analysis reveals potential genetic connectivity between Jeju and East Sea populations, possibly driven by larval dispersal via the Kuroshio and Tsushima Currents, highlighted by the predominance of shared haplotype EJ1 (60.0% in Jeju, 50.0% in East Sea). Bayesian phylogenetic analysis estimated the time to the most recent common ancestor (MRCA) between Jeju and East Sea populations at approximately 9.7 to 23.3 million years ago, indicating ancient divergence rather than very recent separation. Pairwise FST values and AMOVA results showed generally low levels of genetic differentiation. Given the small sample sizes and use of a single mitochondrial marker, these findings should be interpreted cautiously as preliminary evidence. Nevertheless, this study highlights the need for continued genetic monitoring of T. sazae populations under climate-driven range shifts and provides a foundation for future research incorporating broader genomic approaches.

We measured oxygen (O₂) fluxes in two major shallow subtidal benthic habitats (kelp bed (KB) and bare rock (BR) covered with crustose coralline algae) of Dokdo islet in the East Sea by applying noninvasive in-situ aquatic eddy covariance (AEC). The AEC device allows time series measurements (~24 h) of three-dimensional velocity (u, v, and w components) and high-resolution dissolved O₂. This allows estimation of O₂ exchange flux via benthic habitats. Local flow rates and irradiance levels were found to be major factors controlling O₂ exchange flux in the rocky habitats. Gross primary production rates tended to be significantly higher in KB (163 mmol O₂ m⁻² d⁻¹) than in BR (51 mmol O₂ m⁻² d⁻¹). The net ecosystem metabolisms were assessed as opposite types, with 8 mmol O₂ m⁻² d⁻¹ in KB (autotrophy) and –12 mmol O₂ m⁻² d⁻¹ in BR (heterotrophy). Our results indicate that kelp beds are important for organic carbon cycling in rocky coastal waters and that AEC application to macroalgae habitats is a useful assessment approach.

Fisheries and Aquatic Sciences

The coastal waters of Ulleungdo and Dokdo form a transition zone where cold and warm currents intersect, resulting in highly variable marine conditions and sensitive changes in macroalgal distribution. Improving the accuracy of remote-sensing-based macroalgae classification in such environments requires a region-specific dataset that systematically compiles taxon-level spectral reflectance. In this study, we designed a passive underwater observation system (type-1) and an active multi-purpose observation system (type-2), and acquired spectral reflectance using three observation methods applied to underwater and ground environments: T1U (type-1, underwater, natural sunlight), T2U (type-2, underwater, LED illumination with shading cover), and T2G (type-2, ground, natural sunlight). The objective of this study was to build spectral reflectance data for dominant macroalgae in the Ulleungdo–Dokdo coastal region and to quantitatively evaluate observation-condition–dependent spectral characteristics and their implications for classification. Based on reflectance spectra obtained from the three observation methods, taxon-specific spectral shapes of Phaeophyceae, Chlorophyta, and Rhodophyta reproduced characteristic features consistent with previous reports, including reflectance humps near to 575, 600, and 650 nm for Phaeophyceae, a relatively flat spectral shape for Chlorophyta, and an absorption feature within 400-550 nm with reflectance humps near to 600 and 650 nm for Rhodophyta. Cross-method comparisons using two species measured in all three methods (Eisenia bicyclis and Codium fragile) showed that species-specific spectral shapes were consistently reproduced in both reflectance and first-derivative reflectance, confirming interoperability among T1U, T2U, and T2G. In T2U, localized noise was observed in the 400-500 nm range due to insufficient LED radiance, indicating the need for signal correction in the blue band region. Cosine-similarity analysis based on first-derivative reflectance indicated generally high within-taxon similarity among species (approximately 0.90-0.99), whereas mean between-taxon similarity was lower (approximately 0.75-0.89), demonstrating that taxon-level spectral shapes are quantitatively distinguishable. The spectral reflectance dataset and observation protocols developed in this study provide hyperspectral reflectance reference information for dominant macroalgae and benthic substrates in the Ulleungdo-Dokdo coastal region, supporting remote-sensing–based classification and distribution monitoring, observation-method design, and future standardization of macroalgal spectral data.