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.
Highlights
Drifting biomass of Sargassum spp., called “golden tides”[2] accumulates nearshore coastal waters usually during spring to summer, which causes detrimental effects on aquaculture and fisheries and the whole coastal ecosystems in many parts of the world including the Gulf of Mexico, Caribbean, West Africa, eastern Pacific coast, China coast and the southwestern coast of Korea[5,6,7,8,9]
Despite its detrimental effects as the golden tide seaweed, S. horneri and other Sargassum spp. in a natural state form kelp forests (Fig. 1F) and play an important role in ecosystem functioning such as serving as spawning and nursery grounds for various marine species in coastal ecosystems[14]
A recent genetic survey of floating and benthic populations of S. horneri primarily focused on the east coast of China and sample sizes of Korean samples used for their study are limited (N = 1 for each of the five samples)[21]
Summary
Drifting biomass of Sargassum spp., called “golden tides”[2] accumulates nearshore coastal waters usually during spring to summer, which causes detrimental effects on aquaculture and fisheries and the whole coastal ecosystems in many parts of the world including the Gulf of Mexico, Caribbean, West Africa, eastern Pacific coast, China coast and the southwestern coast of Korea[5,6,7,8,9] This phenomenon of the golden tides has been intensified dramatically in frequency, range, and magnitude over recent years perhaps due to growing anthropogenic pressure, such as climate change, nutrient loadings (e.g. coastal eutrophication) and inadvertent algal species transport by ship movements[10,11]. The genetic structure of benthic populations of S. horneri on the Korean coast has not yet been studied
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