Southeast Asia is an important marine biodiversity hotspot. Revealing the spatial patterns and environmental drivers related to population genetic structure in this region is a prerequisite for conservation biogeography and genetics. In this study, we applied two chloroplast markers (tufA and rpl2-rpl16) to evaluate population genetic variation and phylogeographic structure of the green macroalga Halimeda macroloba (12 populations, 275 individuals) in Southeast Asia. Both markers showed extremely low genetic variation and haplotype diversity in H. macroloba, with no clear phylogeographic separation between both sides of the Thai-Malay Peninsula (TMP). A postglacial founder effect and predominant asexual reproduction by fragmentation in H. macroloba, together with monsoon-driven ocean currents driving stepping-stone dispersal, may account for the observed remarkable phylogeographic homogeneity around the TMP. However, the tufa and rpl2-rpl16 markers congruently detected a phylogeographic break between the TMP and the eastern South China Sea, despite no obvious observable barrier to gene flow. These results raise the importance to take in situ actions to conserve the indicator species Halimeda in an era of ocean acidification and warming.

The genus Monoraphidium is a green microalgae distributed globally in freshwater ecosystems, and it is difficult to classify morphologically. Molecular genetic markers have been used for their taxonomy, although they have not been thoroughly evaluated. Here, we investigated three nuclear rRNA molecules (18S, internal transcribed spacer [ITS] + 5.8S, and 28S) and four chloroplast genes (psbB, psbC, rbcL, and tufA) using 16 Monoraphidium strains consisting of 9 species. Upon comparisons of genetic diversity and marker performance evaluation, we found that ITS was the best marker for Monoraphidium to discriminate each species, followed by tufA. The taxonomic discrimination power of the ITS was supported by the neighbor-joining tree. In addition, a secondary structure of ITS2 combined with compensatory base changes showed the distinct differences among individual species of Monoraphidium. These suggest that ITS may be the best marker for species differentiation of the coccoid green algae Monoraphidium.

Bull kelp (Nereocystis luetkeana) possesses a heteromorphic lifecycle that alternates between two phases: a large, diploid sporophyte and a microscopic, haploid gametophyte. Recent research has suggested that bull kelp may be capable of bypassing the microscopic gametophytic stage via the direct release of structures identified in the literature as embryonic sporophytes. In order to verify the identity of these structures, we isolated and cultured multiple directly released structures over the course of three weeks in the lab and monitored their growth and development. We were able to track 67 directly released structures for more than one time interval, and found no evidence that the development of these structures followed that of embryonic sporophytes. We present the alternative hypothesis that these directly released structures are sporangia that have not yet released their spores. We conclude that even with the direct release of microscopic structures such as sporangia, there is currently no evidence that bull kelp are bypassing their established biphasic life history.

Hypoxia often causes the large-scale mortality of benthic organisms and alters the structure and function of pelagic and benthic communities. Protists are a major component of pelagic and benthic communities. Using a metabarcoding analysis, we explored the temporal changes in the structure of protist communities incubated for seven days under normoxic (7.0 mg L^-1) and hypoxic (1.5 mg L^-1) conditions. The incubated water was originally collected from Tongyeong Bay, Korea, where hypoxia frequently occurs. Among the phyla, the relative amplicon sequence variant (ASV) abundance of Cercozoa and Ochrophyta increased under hypoxia from day 0 to day 7, whereas that of other phyla declined or remained similar. Moreover, the relative ASV abundances in the phylum Dinoflagellata under both oxygen conditions were highest on days 0, 3, and 7. Among the dinoflagellate orders, the highest dinoflagellate ASV abundance under hypoxia on day 7 belonged to the order Peridiniales, whereas the highest relative read abundance belonged to Prorocentrales. The 35 dinoflagellate species that were detected under the hypoxic condition during incubation were autotrophic (two), phototrophic (autotrophic or mixotrophic) (15), mixotrophic (eight), kleptoplastidic (one), heterotrophic (eight), and parasitic (one), indicating that dinoflagellates with diverse trophic modes are present under hypoxia. Of these detected dinoflagellate species, 14 were present under the hypoxia on day 7. Furthermore, 19 dinoflagellate species were newly determined to be present under hypoxia, 6 of which were present on day 7. These findings highlight the ecological resilience and adaptability of protist communities under the hypoxic condition. The present study provides insights into the potential roles of protists in maintaining ecosystem functions in the oxygen-depleted environments.

Although Undaria pinnatifida sporophyll is rich in beneficial components such as polysaccharides, proteins, and phytochemicals, its inaccessible structure limits its usability. To overcome this limitation, we ultrasonically extracted U. pinnatifida sporophyll extract (UPE) under optimized conditions (20 kHz, 1,080 W, 30℃) for 8 h and used gradient ethanol precipitation to isolate the UPE fractions (UEF). The yield, composition, and molecular weight of the UEFs changed as fractionation progressed, and the galactose and fucose content increased. Interestingly, the sulfate polysaccharide contents were not related to the fractionation process: UEF3 showed the highest content among the fractions (33.89 ± 0.05%). UEFs had no cytotoxic effects on HaCaT, RAW 264.7, or BEAS-2B cells, and UEF3 prevented ultraviolet B (UVB)-induced cyclooxygenase-2 (COX-2) expression by regulating the ERK kinase pathway. The oral administration of UEF3 prevented epidermal thickening and COX-2 overexpression in UVB-exposed mice. UEF3 also alleviated oxidative stress by reducing reactive oxygen species levels via the activation of the HO-1 / NRF2 signaling pathway. This indicates that polysaccharide precipitation fractionation enhances efficacy by isolating the functional components. In conclusion, fractional processing using ultrasonic-assisted extracts can be an effective approach for developing nutraceutical materials for human health.