Insights on the Sargassum horneri golden tides in the Yellow Sea inferred from morphological and molecular data

Abstract

Large‐scale drifting Sargassum biomass, known as golden tides, has caused considerable damage to the local environment and economy associated with the Yellow Sea of China. To understand the reoccurrence of Sargassum horneri golden tides in the Yellow Sea, large‐scale spatio‐temporal sampling was performed across nine cruises and five coastal surveys. Morphological data indicated that the floating S. horneri thalli with differing reproductive timing coexisted in the Yellow Sea. A total of 196 S. horneri samples had identical sequences of partial cox3 and rbcL‐S spacer region, revealing very low genetic diversity in the floating biomass. A total of 19 haplotypes for partial cox3 previously found in the Yellow Sea were not detected in our large‐scale sampling. Based on four novel mtDNA markers, the 196 samples could be further distinguished into two forms, which varied in proportions at various locations, but coexisted in each of the spatio‐temporal sampling. These results indicated that the floating Sargassum biomass in the Yellow Sea came from only two dominating haplotypes. The novel findings uncovered by this work will provide further insight into the underlying mechanisms of reoccurring golden tides in the Yellow Sea, and lead to the improved management of the Sargassum biomass.

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

“…Although mtDNA cox3 gene has frequently been used as a molecular marker to examine intraspecific polymorphism for S . horneri 17,22 , variation in the cox3 is not sufficiently enough to discriminate between benthic and floating populations in our study. Hence, further studies using more polymorphic markers with additional samples from “benthic” populations on the east coast of China, particularly from the Zhoushan region will be required to determine the origins of floating S .…”

“…Information on geographic or genetic origins (sources) of the floating S . horneri biomass provides an important insight into advancing our understanding of the recurrent golden tides 21,22 . Often a drifting seaweed biomass is hardly predictable to gauge their movement direction, as they are not usually distributed in an equal amount for every year and also ocean currents sometimes dramatically change their dispersal direction, owing to environmental factors such as wind direction 38 .…”

“…A more recent study investigated the genetic composition of only floating samples of S . horneri exclusively from China’s east coast 22 . Hence, the phylogeographic/population structure and genetic diversity of drifting populations of S .…”

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

“…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.…”

First Draft Genome Assembly of the Seaweed Sargassum fusiforme

“…Many of these species are essential in the ecosystem and are economically important marine crops. For example, Sargassum horneri is the dominant golden-tide seaweed in the ocean (Liu et al, 2018). Despite its wide distribution, there are no available complete or draft genomes for any of the Sargassum genus microalgae to date.…”