Abstract
We examined the dynamics of dinoflagellate cyst and phytoplankton assemblages in eutrophic coastal waters of Korea, adjacent to fish and shellfish farms. Water temperature showed seasonality, whereas salinity and pH remained relatively consistent. Dissolved inorganic nutrient levels were higher in September and at the inner stations, where aquaculture fish farms are located than those in May and at the outer stations. Canonical correspondence analysis and artificial neural network analysis revealed multiple environmental factors that affect the distribution of phytoplankton and dinoflagellate cysts. Diatoms dominated in the phytoplankton assemblages, while the protoperidinioid group dominated in the dinoflagellate cyst assemblages. Cyst abundance was higher at the outer stations than at the inner stations due to transport by fast currents, and phytoplankton abundance was positively correlated with cyst abundance. An increase in diatom abundance led to an increase in heterotrophic/mixotrophic cyst abundance, indicating that excessive uneaten food and urinary waste from the fish farms caused eutrophication in the study region and fast growth of diatoms, thereby contributing to the growth of heterotrophic/mixotrophic dinoflagellates and consequently, high abundance of heterotrophic/mixotrophic dinoflagellate cysts.
Highlights
In this study, we examined the spatial and temporal distribution of dinoflagellate cyst assemblages in surface sediments and phytoplankton assemblages in the water column, using the paleontological method and the microscopy method, respectively, focusing on how eutrophic water quality and sediment environments influence phytoplankton and dinoflagellate cyst distribution
Tongyeong is located in Sanyang-eup in the Kyungsang-namdo province which is the central region of the southern coast of the Korean peninsula (39◦ 490 N, 128◦ 210 E; Figure 1), and its coastal waters surround the archipelago off the southern region of Korea
While there are no major rivers or streams that can contribute to the elevation of terrestrial nutrients, Tongyeong is representative of marine fish cages in the aquaculture industry and pollution driven from the marine fish cages has been aggravated [32]
Summary
Dinoflagellates are eukaryotic algae that produce resting cysts via sexual reproduction and/or temporary cysts in response to changes in environmental conditions such as temperature, salinity, and light [1]. The resting stage is a part of their life cycle, and the accumulated cysts can often resist harsh environmental conditions in sediments [2,3,4]; resting cysts play a pivotal role as seed populations, affecting phytoplankton communities during phytoplankton blooms [2,5,6,7]. Monitoring dinoflagellate cysts enables the temporal and spatial prediction of bloom initiation [2,8], tracking of historical records of harmful algal blooms [9], and analogy of historic environments in the water column and sediments [10]
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