In recent years, drifting and inundating brown seaweed ( Sargassum horneri ) biomass, called ‘golden tides’, has frequently drifted and accumulated along the southern coastlines of Korea, causing devastating impacts on the local economy and coastal ecosystems. In this study, based on combined analyses of mitochondrial DNA cox3 gene and seven microsatellites, we investigated the genetic makeup of the floating S . horneri populations ( N = 14) in comparison to Korean benthic populations ( N = 5), and tracked their genetic sources. Given a shared mtDNA haplotype and oceanic circulation systems, the floating populations may have been originated from the southeastern coast of China (e.g. Zhoushan, Zhejiang province). Population structure analyses with microsatellites revealed two distinct genetic clusters, each comprising floating and benthic populations. High levels of inter-population differentiation were detected within Korean benthic samples. The floating populations from the same periods during a 2015–2018 year were genetically more different from one another than those from different periods. These results suggest that the floating populations might be of multiple genetic sources within geographic origin(s). This study will inform management efforts including the development of “ S . horneri blooming forecasting system”, which will assist in mitigating ecological and economic damages on the Korean coastal ecosystems in the future.
Photoacclimatory responses of the seagrass Zostera marina in the intertidal and subtidal zones were investigated by measuring chlorophyll a fluorescence parameters, photosynthetic pigments, leaf δ13C values, and shoot morphology in two bay systems. Intertidal plants had higher carotenoid concentrations than subtidal plants to avoid photodamage under excess light conditions during the day. The maximum relative electron transport rate (rETRmax) and minimum saturation irradiance (Ek) of the intertidal plants were higher than those of the subtidal plants, whereas photosynthetic efficiency (α) and maximum quantum yield (Fv/Fm) were higher in subtidal plants. The intertidal plants also had significantly greater Stern–Volmer non-photochemical quenching (NPQ) than that of the subtidal plants. These results suggest that the subtidal plants photoacclimated to use limited light more efficiently, and the intertidal plants exhibited photosynthetic responses to minimize photodamage at excess irradiance. The δ13C values of leaf tissues were more negative in the intertidal plants than those in the subtidal plants, suggesting that the intertidal plants used atmospheric or dissolved CO2 for photosynthesis during emersion. Effective quantum yield (ΔF/Fm´) in the intertidal plants decreased more slowly after emersion than that in the subtidal plants, indicating higher desiccation tolerance of the intertidal plants. The intertidal plants also recovered more rapidly from desiccation damage than the subtidal plants, suggesting photosynthetic adaptation to desiccation stress. The photosynthetic plasticity of Z. marina in response to variable environmental conditions most likely allows this species to occur in the intertidal and subtidal zones.
Species diversity in the genus Ulva remains understudied worldwide. Using molecular analyses we investigated the species composition, diversity, distribution, and relative frequencies of the genus Ulva along the entire coast of Jeju Island, off the southern tip of Korea. Species identification was performed for 215 samples collected from 23 sites, based on comprehensive phylogenetic and model-based species delimitation analyses using the sequences of two molecular markers, chloroplast elongation factor Tu ( tuf A) and nuclear rDNA internal transcribed spacer (ITS). We identified 193 specimens as nine Ulva species, 14 specimens as Blidingia spp., and eight samples undetermined, based on the combined analysis of tuf A and ITS phylogenies. Two model-based approaches generally supported nine groups of Ulva species. Previously documented species complex, such as U . ohnoi−U . spinulosa and U . procera−U . linza showed discordant relationships between the two phylogenies. The occurrence of U . torta on Jeju Island was first observed, despite its existence on the mainland previously reported. Ulva australis [16 of 23 sites; 34.4% (relative frequency)], U . ohnoi (16; 21.9%), and U . procera (11; 14%) were found to be the predominant species. Our study highlights that molecular analysis is critical for species delimitation in the genus Ulva and provides fundamental information for an understanding of green-tide assemblages on the “biological hotspot” coastal ecosystem, Jeju Island in Korea. This study will also help to monitor and manage local green tides at the areas that are currently encountering rapid climate changes.
We investigated the growth and bioremediation potential of five local seaweed species (Codium fragile, Ulva pertusa, Ecklonia stolonifera, Saccharina japonica and Gracilariopsis chorda), using an integrated fish-seaweed culture system as a biofilter for effluents from black rockfish (Sebastes schlegelii) tanks. The specific growth rate, biomass and net yield values of green algae were higher than those of brown algae. The tissue N and P levels of all species increased at the end of the experiment, but N:P ratios varied among seaweed species. The uptake rate and efficiency of total ammonia nitrogen uptake were the highest in U. pertusa and lowest in S. japonica. The phosphate uptake efficiency among all species ranged from 43% for S. japonica to 30% for G. chorda. These results suggest that all species can efficiently remove enriched nitrogen and phosphorus from fish tank effluents and are suitable for integrated aquaculture and bioremediation. However, inter-specific differences were observed among seaweeds with regard to the biofiltration performance for different forms of nitrogen. The highest total oxidized nitrogen (ToxN) uptake efficiency was observed in E. stolonifera and S. japonica, while the lowest was observed in U. pertusa. ToxN uptake rates of E. stolonifera and S. japonica was 1.8 times higher than that of U. pertusa. Thus, a seaweed polyculture that included species with varying nitrogen source-specific biofiltration activities might allow us to remove nutrients from effluents more effectively. These results provide valuable information regarding the selection of optimal seaweed species in fish-seaweed integrated systems.
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