Assessment of germling ability of the introduced marine brown alga, Sargassum horneri, in Northern Taiwan

Abstract

Sargassum horneri is a large marine brown alga, originally described from the Strait of Korea, that typically grows up to 1 to 5 m in length. In recent years, floating populations of S. horneri have drifted to Northern Taiwan via the southward flowing cold current along the Chinese coast. Nevertheless, no populations of this alien alga have been established in Northern Taiwan. In this study, we designed a series of culture conditions in order to understand the life cycle of this introduced alga. Several thalli bearing developed receptacles were collected from the field in the spring of 2015 and 2016, and fertilized eggs were obtained by conducting artificial fertilization in the lab. Two experiments were performed to determine whether or not the rafts of floating Sargassum that arrive in Northern Taiwan are capable of producing viable offspring under temperature conditions analogous to those of their native home, as well as in an environment where the seawater surface temperature (SST) is above 22 °C (the average SST in spring of Northern Taiwan). This study on the life cycle of the floating S. horneri in Northern Taiwan showed that these embryos could grow well and develop into viable new generations with reproductive capacity. However, incubation experiments under different temperatures suggest that the embryos derived from these floating S. horneri can only survive well at a SST of 20 °C or below in the natural seawater obtained from Northern Taiwan. We suggest that the sea surface temperature in the spring is a limiting factor for determining the distribution range of the floating S. horneri in Taiwan. However, further outdoor cultivation experiments are needed, specifically in combination with various natural nutrient and irradiance regimes under natural conditions, for testing the sensitivity of germlings to water temperature.