Cryptic species diversity in Korean benthic populations of golden tide seaweed, Sargassum horneri, based on phylogeographic and population genetic analyses

Abstract

The sea basins of the Northwest Pacific (NWP) were geologically separated from the land during the Pleistocene, which largely influenced the current geographic distributions of many marine species that were able to survive in the glacial refugia in those regions. The NWP coastal ecosystem harbors a high regional biodiversity with abundant seaweed populations, which is perhaps attributed to complex and dynamic oceanic current system. In recent years, individuals of some Sargassum species detached from the substrate drift on the sea surface and form enormous patches, sometimes causing severe damage to coastal ecosystems globally. In particular, Sargassum horneri often brings about ‘golden tide’ blooming in the NWP open ocean. However, S. horneri is commonly distributed along the NWP coast and its benthic populations play an important role in the marine ecosystem by forming marine forests. In this study, we determined the phylogeographic distributions and current population genetic structure of benthic S. horneri on the entire coasts of South Korea including Jeju Island, the East Sea, South Sea, and West Sea using mitochondrial (mt) DNA and seven microsatellite markers. Comparisons of the four sea areas revealed that populations from Jeju Island, the West Sea, and the East Sea were divided into two distinct clades, while the South Sea represent admixture of two clades. The analyses of FST statistics showed limited genetic connectivity among populations in general. Based on the results of network analysis, we identified two unique lineages showing potential as cryptic species complex evolved in S. horneri. This study is the first to evaluate the population genetic features of Korean benthic S. horneri and provide the genetic information on two well-separated lineages with a rather deep evolutionary divergence. This study will further help to manage non-indigenous and floating S. horneri effectively in Korean waters.