Variation in Phytoplankton Community Due to an Autumn Typhoon and Winter Water Turbulence in Southern Korean Coastal Waters

Abstract

We evaluated changes in the phytoplankton community in Korean coastal waters during October 2016 and February 2017. Typhoon Chaba introduced a large amount of freshwater into the coastal areas during autumn 2016, and there was a significant negative relationship between salinity and nutrients in the Nakdong estuarine area, particularly in the northeastern area (Zone III; p < 0.001). The abundance of diatom species, mainly Chaetoceros spp., increased after this nutrient loading, whereas Cryptomonas spp. appeared as opportunists when there was relatively low diatom biomass. During winter, biotic and abiotic factors did not differ among the surface, middle, and lower layers (p > 0.01; ANOVA), implying that water mixing by winter windstorms and low surface temperature (due to the sinking of high-density water) physically accelerated mixing of the whole water column. Diatoms predominated under these conditions. Among diatoms, the centric diatom Eucampia zodiacus remained at high density at the inshore area and its abundance had a negative correlation with water temperature, implying that this species can grow at cold temperatures. On the other hand, the harmful freshwater diatom Stephanodiscus hantzschii mainly appeared in conditions with low salinity and high nutrients, implying that it can persist even in the saltwater conditions of the Nakdong Estuary. Our results indicate that hydro-oceanographic characteristics, such as river discharge after an autumn typhoon and winter water turbulence, have major effects on the composition of phytoplankton communities and can potentially affect the occurrence and characteristics of harmful algal blooms in southern Korean coastal waters.

Change in Paralytic Shellfish Toxins in the Mussel Mytilus galloprovincialis Depending on Dynamics of Harmful Alexandrium catenella (Group I) in the Geoje Coast (South Korea) during Bloom Season

“…Wind-driven surface currents have a major impact on the transport of phytoplankton blooms, and can be a key regulator of cell accumulation along coasts [ 20 , 21 , 22 ]. Based on our field observations and PST outbreak information from the NIFS, during April to May in 2017 and March to April in 2018, the population of A. catenella gradually expanded around Geoje Island, including Jinhae Bay.…”

Relationship of Spatial Phytoplankton Variability during Spring with Eutrophic Inshore and Oligotrophic Offshore Waters in the East Sea, Including Dokdo, Korea

“…Among them, the water layer up to 100 m was clearly mixed at Stn. 10, and this is a typical mixed water mass in the East Sea in winter [28]. In particular, a strong windstorm passed the Ulleung Basin on 28 February, and the southeast winds changed into strong northwest winds.…”

“…For the late spring survey (Figure 1c), samples were from 28 stations in three zones: the Uljin-Ulleungdo area from coast to open ocean (UU, Stns. [20][21][22][23][24][25][26][27][28][29][30][31][32]; the vicinity of Ulleungdo and Dokdo (UL, Stns. 33-39, 46, and 47) known to have an island effect; and the area between Ulleungdo and Dokdo which remains oligotrophic (UD, Stns.…”

“…During late spring, the nutrients had small spatial variations; they were highest at stations closest to the coast (Stns. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] and were lower in offshore regions (UU and UL zones; Figure 8). However, there were no significant differences among the zones (Table 1).…”

“…Another feature that maintains phytoplankton biomass in this region is the transport of eutrophic water from the southern coast to the Ulleung Basin by currents and the Ulleung Warm Eddy (UWE) [13,[25][26][27]. The waters of the southern coast of Korea are highly eutrophic due to the influx of nutrients from several rivers (Nakdong, Taehwa, Hyungsan), especially during the winter [28]. Moreover, Ahn et al [29] and Kim et al [30] reported a large-scale transport of algal blooms from the southern Korean coastal waters based on satellite imaging of chlorophyll a (Chl a).…”