The origin and population genetic structure of the ‘golden tide’ seaweeds, Sargassum horneri, in Korean waters

Abstract

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.

Climate-Driven Range Shifts of Brown Seaweed Sargassum horneri in the Northwest Pacific

“…Of the latter, H5 (JF461023) in lineage III was found in samples from China (=haplotype 3, in Hu et al, 2011) and South-Pacific-Japan (=haplotype D, in Watanabe et al, 2019; Figure 1B, Supplementary Table S1). A haplotype in the center of a star-like topology is often regarded as being an ancient haplotype, and H29 (AB430550) in lineage III fit this description and predominated among the samples from South-Pacific-Japan (=haplotype A, in Watanabe et al, 2019), Korea (=haplotype 1, in Byeon et al, 2019), China and Sea of Japan (=haplotype 7, in Hu et al, 2011; Figure 1B). We found the H50 (AB430580) in lineage II among samples from North-Pacific-Japan (=haplotype 39, in Hu et al, 2011), South-Pacific-Japan (=haplotype 2, in Byeon et al, 2019), and Korea (=haplotype O, in Watanabe et al, 2019; Figure 1B, Supplementary Table S1).…”

“…Previous studies have amplified the cox3 sequences for S. horneri populations ranging from Hokkaido, Japan (43 • 12 N) to Zhanjiang, China (20 • 53 N), including 54 sites in Japan (Uwai et al, 2009;Watanabe et al, 2019), 14 sites in Korea (Byeon et al, 2019), and 8 sites in China (Hu et al, 2011). In total, the mtDNA cox3 of 996 individuals yielded 62 haplotypes, which were downloaded from NCBI 1 ( Supplementary Table S1).…”

Population Dynamics of the ‘Golden Tides’ Seaweed, Sargassum horneri, on the Southwestern Coast of Korea: The Extent and Formation of Golden Tides

“…Large mats of drifing S. horneri were introduced to the Korean coasts by the Kuroshio Current and Taiwan Warm Current in the late January-February and April-early May periods of 2015-2019. These rafts accumulated along the southern coast of Korea, including Jeju Island [14,54]. High mortality rates and/or densities likely also occurred among the islands off Zhejiang Province during the December-January period and March.…”

“…They have aggressively spread along the length of the southwestern coast of Korea (including Jeju Island) and the western coast of Japan [11,[49][50][51]. Floating S. horneri rafts originated from attached thalli in the subtidal zones of islands off Zhejiang Province, China, and were transported northeastwards with oceanic currents and wind [5,11,13,14]. The floating S. horneri biomass therefore depends on the biomass of the attached source populations.…”

The complete chloroplast genome of Sargassum horneri and its phylogenetic analysis

“…There are cultivation and application research in China. However, the phenomenon of S. horneri explosive growth and accumulating at coastal waters is called 'golden tides' (Smetacek and Zingone 2013), which causes detrimental effects on aquaculture, fisheries and the coastal ecosystems (Byeon et al 2019). In this study, we obtained the complete chloroplast genome of S. horneri.…”