Summer Distributional Characteristics of Surface Phytoplankton Related with Multiple Environmental Variables in the Korean Coastal Waters

Abstract

Multiple environmental variables related to ocean currents, freshwater runoff, and upwelling in a coastal area have complex effects on the phytoplankton community. To assess the influence of environmental variables on the phytoplankton community structure during the summer of 2019, we investigated the various abiotic and biotic factors in Korean coastal waters (KCWs), separated into five different zones. Summer environmental factors in KCWs were strongly influenced by Changjiang Diluted Water (CDW) in St. SO (Southern Offshore) 1 and 2, upwelling in St. SI (Southern Inshore) 2–4, and Nakdong River discharge in St. SI 12. In particular, low–salinity water masses (p < 0.05 for nearby locations) of CDW gradually expanded from the East China Sea to southwestern KCWs from June to July. In addition, there were high levels of nutrients following freshwater runoff from the Nakdong River in southeastern KCW, which led to the dominance of Cryptomonas spp. (81%), a freshwater and brackish water algae. On the other hand, upwelling areas in southwestern KCW were dominated by diatoms Skeletonema spp., and are characterized by high phosphate concentrations (p < 0.05) and low temperatures (p < 0.05) compared to nearby locations. Leptocylindrus danicus (20%) was dominant due to the effect of water temperature in the SE (Southeastern area) zone. Low nutrient concentrations were maintained in the East Sea (dissolved inorganic nitrogen (DIN) = 0.39 ± 0.40 μM; dissolved inorganic phosphate (DIP) = 0.09 ± 0.03 μM) and the Yellow Sea (DIN = 0.40 ± 0.07 μM; DIP = 0.04 ± 0.02 μM), which were characterized by low levels of chlorophyll a and dominated by unidentified small flagellates (35, 40%). Therefore, our results indicated that hydro–oceanographic events such as upwelling and freshwater run–off, but not ocean currents, provide nutrients to the euphotic layers of the coastal environment and play important roles in determining the phytoplankton community structure during summer in the KCWs.

Water mass structure determine the prokaryotic community and metabolic pattern in the Korea Strait during fall 2018 and 2019

“…Unlike in 2018, stations 1 and 2 in the UL of 2019 showed the different temperature (Figure 2E) and lower range of S (<32 PSU) than those observed at the same stations in 2018 (>33 PSU) (Figures 2B, F). This low-S water indicates FW influence from the Changjiang Diluted Water (CDW) from the East China Sea (ECS) (Figure S1) (Chang and Isobe, 2003;Gomes et al, 2018;Kim et al, 2022;Yoon et al, 2022). Similar to the S variation, the UL T in the fall of 2019 was higher (21.76-24.26°C) than that observed in the fall of 2018.…”

“…According to previous studies, 70% of CDW is transferred annually via KS to the East Sea (Chang and Isobe, 2003;Senjyu et al, 2006;Moon et al, 2019). As a result, CDW influence plays a significant role in the large biological effects on the ECS and Korean coastal environment (Son and Choi, 2022) and alters phytoplankton composition (Yoon et al, 2022). Within the past ten years, the CDW has had the largest FW discharge in 2019-2020 followed by 2016 and 2017, but there was no significant FW discharge in 2018 (Son and Choi, 2022).…”

“…although the T is a vital factor for Synechococcales, DIN has a greater influence on their composition because it tends to synthesize more sugar (Li et al, 2019) to create more proteins for phytoplankton adaption (Thangaraj and Sun, 2021) in the ocean environment (Zubkov et al, 2003). Shim and Yoon (2021) recently studied the long-term (20-year; 1999-2018) nitrate fluctuation in the East Sea and concluded that the TWW from the CDW, coupled with the input of other rivers (e.g., Changjiang, Nakdong, Taehwa, and Hyungsan), influences the nutrient concentration in the Kuroshio Current extension and Korean coastal environment (Asanuma et al, 2014;Yoon et al, 2022). Based on these earlier findings and our results, we hypothesized that although TSW influenced T more than photosynthetic properties in 2018 and 2019, DIN availability was a significant parameter from the surrounding rivers to determine the high photosynthetic potential in the UL of 2018.…”

“…The Changjiang River is known as a hotspot with a yearly T increase of approximately 3.5°C and an anticipated 30% increase in annual precipitation (Gu et al, 2015) due to climate change, which is expected to boost FW flow to ECS via CDW (Liu et al, 2021). Previous investigations found that approximately 70% of the ECS FW is transferred annually through KS (Senjyu et al, 2006;Moon et al, 2019;Yoon et al, 2022) which might change the environmental conditions of KS in the future. According to a recent study, the Kuroshio current extension is sensitive to global climate change and has the potential to warm significantly in the future (Lam et al, 2021), in addition to increasing warming TWW into the East Sea via the KS.…”

“…Previous research has revealed that KS is the most dynamic environment due to its topography, water mass, and river discharge (i.e., from Changjiang River) (Lee et al, 2010). The annual freshwater (FW) discharge from the Changjiang River to the KS has been estimated to be 9.25×10 11 m 3 yr -1 (Tian et al, 1993), which alters the hydrographic conditions (low S and high T) and modifies biological processes in the receiving region (Liu et al, 2003;Jiao et al, 2007;Onitsuka et al, 2007;Yoon et al, 2022). Yang et al (2000) demonstrated that the phytoplankton ecosystem changes along the KS because of the influence of T variation by TWW and excessive nutrient loading by FW.…”