Phytoplankton Community Dynamics Research Articles

Phytoplankton community dynamics during Alexandrium blooms in 2019 off the Qinhuangdao coast, Bohai Sea, China

Phytoplankton community dynamics during Alexandrium blooms in 2019 off the Qinhuangdao coast, Bohai Sea, China

Stochastic and Deterministic Processes Regulate Phytoplankton Assemblages in a Temperate Coastal Ecosystem.

Assessing the relative contributions of the interacting deterministic and stochastic ecological processes for phytoplankton community assembly is crucial in understanding and predicting community organization and succession at different temporal and spatial scales. In this study, we hypothesized that deterministic and stochastic ecological processes regulating phytoplankton, present seasonal and repeating patterns. This hypothesis was explored during a 5-year survey (287 samples) conducted at a small spatial scale (~15km) in a temperate coastal ecosystem (eastern English Channel). Microscopy and flow cytometry quantified phytoplankton abundance and biomass, while metabarcoding data allowed an extended evaluation of diversity and the exploration of the ecological processes regulating phytoplankton using null model analysis. Alpha diversity of phytoplankton was governed by the effect of environmental conditions (environmental filtering). Temporal community turnover (beta diversity) evidenced a consistent interannual pattern that determined the phytoplankton seasonal structure. In winter and early spring (from January to March), determinism (homogeneous selection) was the major process in the phytoplankton community assembly. The overall mean in the year was 38%. Stochastic processes (ecological drift) prevailed during the rest of the year from April to December, where the overall mean for the year was 55%. The maximum values were recorded in late spring and summer, which often presented recurrent and transient monospecific phytoplankton peaks. Overall, the prevalence of stochastic processes rendered less predictable seasonal dynamics of phytoplankton communities to future environmental change. IMPORTANCE While ecological deterministic processes are conducive to modeling, stochastic ones are far less predictable. Understanding the overall assembly processes of phytoplankton is critical in tracking and predicting future changes. The novelty of this study was that it addressed a long-posed question, on a pluriannual scale. Was seasonal phytoplankton succession influenced by deterministic processes (e.g., abiotic environment) or by stochastic ones (e.g., dispersal, or ecological drift)? Our results provided strong support for a seasonal and repeating pattern with stochastic processes (drift) prevailing during most of the year and periods with monospecific phytoplankton peaks.

Spatio-temporal dynamics of phytoplankton community in a well-mixed temperate estuary (Sado Estuary, Portugal)

Estuaries are highly productive ecosystems, which are strongly affected by several anthropogenic pressures. Phytoplankton is a key element for assessing the ecological quality status in these transitional waters. Moreover, understanding physico-chemical and biological drivers is crucial to disentangle their effect on the structure of phytoplankton community. The present work aims to study the effect of the main physico-chemical drivers on the phytoplankton community structure and dynamics in a temperate well-mixed estuary (Sado Estuary). Four sampling stations were analyzed monthly in three regions of the estuary, from 2018 to 2019. Surface water samples were collected to analyze the phytoplankton community and several concomitant physico-chemical parameters. Temperature, turbidity, salinity, and nutrients availability were the drivers that best explained the spatio-temporal patterns observed in the phytoplankton community. The upper estuary was characterized by higher phytoplankton cell abundances and biomass. Three phytoplankton groups stood out in the characterization of the estuarine assemblages: diatoms, cryptophytes, and dinoflagellates. Diatoms were the dominant group most of the year, being dominated by small cell species (single and chain-forming) upstream, and by larger chain-forming species downstream. Cryptophytes had a high contribution to the community in the inner regions of the estuary, while dinoflagellates contributed more for the community composition downstream, where high abundances of harmful algal species were sporadically found. Previous studies on the phytoplankton community dynamics in this estuary are limited to the 1990s. Thus, the present study provides insight into changes in the dominant phytoplankton groups of the Sado Estuary in the last 25 years, namely an increase in cryptophytes over diatoms in the inner estuarine regions, and an increase in dinoflagellates near the estuary mouth.

Dynamics of phytoplankton community in relation to seasonal variation and Laminaria japonica culturing in coastal area

Seaweed aquaculture is an important industry with great social and eco-environmental values. This study assessed the water quality and phytoplankton community during the four seasons around the Taohua Island where seaweed aquaculture has been practiced for near 70 years. Sampling was conducted in Laminaria japonica culturing area. Significant seasonal effects were observed among measured environmental factors and phytoplankton community. The species number and density of phytoplankton were positively correlated with temperature (T), Secchi depth (SD) and total nitrogen (TN) but were negatively correlated with dissolve oxygen (DO). In spring (the late culturing period), the seaweed culture increased pH, DO and salinity, while slightly reduced total phosphorous (TP). The phytoplankton abundance was lower in the culturing area than in control area, whereas the Shannon-Wiener diversity were found to be higher. Our study demonstrated that seasonal environment changes (especially T, SD, TN and DO) had strong influence on the functional characteristics of the phytoplankton community and L. japonica cultivation can absorb the nutrients and enhance phytoplankton diversity, thus alleviating eutrophication and reducing the risk of algal blooms. This is of significance to remediate the coastal eutrophicated and to restore the ecosystem.

Seasonal shifts in assembly dynamics of phytoplankton communities in a humans-affected river in NE China

Seasonal shifts in assembly dynamics of phytoplankton communities in a humans-affected river in NE China

Effects of large-scale Sargassum fusiforme culture on phytoplankton community structure and water quality

The large-scale cultivation of S. fusiforme was hypothesized to effectively improve water quality and environmental characteristics. Specifically, such cultivation could promote habitat restoration effects by increasing DO and pH levels in addition to decreasing nitrogen and phosphorus levels within cultivation area waters. Phytoplankton diversity could also reflect the quality and health of waters. This study explored the effects of large-scale cultivation of Sargassum fusiforme on the biodiversity and the ecosystem of a phytoplankton community in the coastal waters of Dongtou island, China. S. fusiforme cultivation increased DO and pH values within the area but decreased N contents of the cultivation area waters. A total of 75 phytoplankton species were identified based on morphological identification, while a parallel survey of phytoplankton communities using high-throughput cultivation-independent sequencing identified 601 phytoplankton OTUs. Large scale cultivation of S. fusiforme was associated with increased phytoplankton diversity as reflected by multiple alpha and beta diversity metrics. These data suggested that S. fusiforme cultivation could affect phytoplankton community structure when the S. fusiforme biomass reached maximum levels. Redundancy analysis (RDA) indicated that S. fusiforme played an important role in controlling the dynamics of phytoplankton communities in coastal ecosystems. Thus, the results suggested that S. fusiforme cultivation could enhance phytoplankton community biodiversity. Overall, this study demonstrated that large-scale cultivation of S. fusiforme in coastal regions was an effective approach for mitigating environmental problems in marine ecosystems.

Multi-annual comparisons of summer and under-ice phytoplankton communities of a mountain lake

Little is known on the dynamics of under-ice phytoplankton communities. We investigated phytoplankton communities in the upper (0–20 m) and lower (30–35 m) layer of oligotrophic Lake Tovel, Brenta Dolomites (Italy) over 6 years during summer and under ice. Winter conditions were different from one year to another with respect to ice thickness and snow cover. Proxies for light transmission (Secchi disc transparency, light attenuation) were similar between seasons, even though the incident solar radiation was lower in winter. Algal richness and chlorophyll-a were not different between seasons while biomass was higher during summer. In four of the 6 years, Bacillariophyta dominated during summer and Miozoa (class Dinophyceae) under ice while in 2 years Bacillariophyta also dominated under ice. Generally, a shift to larger size classes from summer to under ice was observed for Bacillariophyta, Chlorophyta, and Ochrophyta (class Chrysophyceae) while Dinophyceae showed the opposite pattern. No strong links between phytoplankton community composition and abiotic factors (under-ice convective mixing, snow on ice, under-ice light) were found. We suggest that inter-species relationships and more precise indicators of under-ice light should be considered to better understand under-ice processes.

Temporal Dynamics in Energy Fluxes and Trophic Structure of a Portunus trituberculatus Polyculture Ecosystem During Different Culture Periods

Swimming crab (Portunus trituberculatus) are an important aquaculture species in eastern coastal areas of China. To improve the understanding of P. trituberculatus culture ecosystem functioning, the dynamics of energy flow and trophic structure of a P. trituberculatus polyculture system (co-culture with white shrimp Litopenaeus vannamei and short-necked clam Ruditapes philippinarum) were investigated in this study. Three Ecopath models representing the early, middle, and late culture periods of a P. trituberculatus polyculture ecosystem, respectively, were constructed to compare ecosystem traits at different culture periods. The results demonstrated that detritus was the main energy source in this polyculture ecosystem, and most of the total system throughput occurred at trophic levels I and II. Artificial food input and consumption by the culture organisms increased from early to middle and late periods, which produced marked impacts on biomass structure and primary production. R. philippinarum was considered to have a dominant influence on phytoplankton community dynamics which changed from nano- to pico-phytoplankton predominance, from the middle to the late period. Considering the low utilization efficiency of pico-phytoplankton production, large amounts of detritus accumulated in the sediment in the late period, which may constitute a potential risk for the ecosystem. Ecological network analyses indicated that the total energy flow and level of system organization increased from the early to the middle and late periods, whereas food web complexity and system resilience decreased from early to middle and late periods, which may indicate a trend of decreasing ecosystem stability. The system may be further optimized by increased stocking density of R. philippinarum and by introducing macro-algae at a suitable biomass to increase ecosystem stability, energy utilization efficiency, and aquaculture production.

The influence of trophic status and seasonal environmental variability on morpho-functional traits in tropical man-made shallow lakes

In the tropics, seasons are delimitated by the extent of rainfall resulting in seasonal differences in water parameters shaping phytoplankton community dynamics. Dry periods can intensify eutrophication and often result in seasonal or even perennial cyanobacterial dominance. This study was developed to evaluate phytoplankton response to trophic state and seasonal differences of environmental filters (dry and rainy periods) using the morphology-based functional groups (MBFG) approach. We also aimed at identifying environmental thresholds of each MBFG dominance in six man-made lakes located in the tropical semiarid region of Brazil. Our results showed clear MBFG association with lakes’ trophic states. The dominant groups in mesotrophic conditions were members of MBFGs V (unicellular flagellates) and VI (non-flagellated with a siliceous exoskeleton), and in meso-eutrophic MBFG IV (medium size without specialized traits) dominated. Conversely, MBFG VII (with mucilage and aerotopes) and VIII (nitrogen-fixing cyanobacteria) dominated mostly under eutrophic conditions, though linked to shallower euphotic zones. Light and phosphorous were the most important environmental thresholds associated with MBFG’s dominance. Overall, most of the lakes displayed seasonal differences in environmental filters. In contrast to what was expected, the rainy season was associated with higher nutrients, suspended solids, and reduced euphotic depth compared to the dry season. Our results, overall, show that the effects of seasonality varied across lakes and highlight eutrophication as the main environmental factor for MBFG selection suggesting reduced seasonality effects during dry years in the tropics.

Phytoplankton community dynamics in response to seawater intrusion in a tropical macrotidal river-estuary continuum

Phytoplankton community dynamics in response to seawater intrusion in a tropical macrotidal river-estuary continuum

Composition and spatial-temporal dynamics of phytoplankton community shaped by environmental selection and interactions in the Jiaozhou Bay

The Jiaozhou Bay as a model marine ecosystem in China has been intensively investigated over the last 90 years. However, detailed phytoplankton community composition, spatial-temporal dynamics, and its assembly mechanism were still unclear. To address these, we systematically examined the composition and spatial-temporal dynamics of phytoplankton in the Jiaozhou Bay through high-throughput sequencing of 18S rDNA V4. Analysis of 468 samples from 12 sampling sites over one full year revealed much higher phytoplankton diversity than previous reports, and strong seasonal succession patterns. Some phytoplankton also showed spatial variations, although the phytoplankton community didn't show significant distance-decay pattern. Environmental factors (especially temperature), species-species interrelationships and unique resting stages were uncovered to be the main contributors instead of stochastic process in shaping the phytoplankton community assembly. The overwhelming positive correlations between phytoplankton and other protists suggested that coevolution might be critical in this marine ecosystem. Complementary distributions of different amplicon sequence variants (ASVs) of same genera, such as Skeletonema marinoi (ASV_2) and Skeletonema tropicum (ASV_263) of the genus Skeletonema, suggested that phytoplankton have evolved differentially to exploit a wide range of ecological niches. This study laid a solid foundation for asertaining phytoplankton composition and spatial-temporal dynamics in temperate seawaters and mechanisms underlying phytoplankton community assembly, allowing in-depth studies of marine ecology.

Highly-resolved interannual phytoplankton community dynamics of the coastal Northwest Atlantic

Microbial observatories can track phytoplankton at frequencies that resolve monthly, seasonal, and multiyear trends in environmental change from short-lived events. Using 4-years of weekly flow cytometry along with chloroplast and cyanobacterial 16S rRNA gene sequence data from a time-series station in the coastal Northwest Atlantic (Bedford Basin, Nova Scotia, Canada), we analyzed temporal observations for globally-relevant genera (e.g., Bolidomonas, Teleaulax, Minidiscus, Chaetoceros, Synechococcus, and Phaeocystis) in an oceanic region that has been recognized as a likely hotspot for phytoplankton diversity. Contemporaneous Scotian Shelf data also collected during our study established that the major phytoplankton within the Bedford Basin were important in the Scotian Shelf during spring and fall, therefore pointing to their broader significance within the coastal Northwest Atlantic (NWA). Temporal trends revealed a subset of indicator taxa along with their DNA signatures (e.g., Eutreptiella and Synechococcus), whose distribution patterns make them essential for timely detection of environmentally-driven shifts in the NWA. High-resolution sampling was key to identifying important community shifts towards smaller phytoplankton under anomalous environmental conditions, while further providing a detailed molecular view of community compositions underpinning general phytoplankton succession within the coastal NWA. Our study demonstrates the importance of accessible coastal time-series sites where high-frequency DNA sampling allows for the detection of shifting baselines in phytoplankton communities.

Dynamics of phytoplankton community in scallop farming waters of the Bohai Sea and North Yellow Sea in China

BackgroundAs the major suppliers of food for higher consumers, phytoplankton are closely related to the yield, nutritional ingredients and even toxin contents of mariculture animals, potentially influencing the human health when they are consumed. With the increase of shellfish culture density, phytoplankton in the coastal waters have been excessively consumed in recent years, and the nutrients they depend on are becoming more and more limited, which severely restrict the shellfish mariculture and threaten the coastal ecosystems.ResultsIn the present study, nutrient concentrations, phytoplankton assemblages and scallop growth status were investigated in the main bay scallop farming waters of the Bohai Sea (Qinhuangdao site) and North Yellow Sea (Zhuanghe site) in 2018. Both phosphate and silicate limitations were observed at the two sites, with the major determinant of phytoplankton assemblages being silicate in Qinhuangdao and phosphate in Zhuanghe, respectively. The phytoplankton assemblages at the two sites displayed different community structures and succession patterns. The phytoplankton community was dominated by dinoflagellates and diatoms in Qinhuangdao, while dinoflagellates were the most abundant group in Zhuanghe, which accounted for 41.9% of the total phytoplankton abundance. The dominant genera of diatoms in Qinhuangdao were Skeletonema, Thalassiosira and Leptocylindrus, while those in Zhuanghe were Thalassiosira and Cyclotella. Greater biomass and more appropriate structure of phytoplankton contributed to higher growth rate and glycogen content of cultured bay scallops.ConclusionsOur study characterized the relationship between nutrient concentration, phytoplankton community and scallop mariculture in the main bay scallop farming waters in northern China. The results suggest that, as nutrient limitation intensified, dinoflagellates are becoming the dominant phytoplankton species in the scallop farming waters of the Bohai Sea and the North Yellow Sea, which is harmful to the coastal mariculture.

Using null models and species traits to optimize phytoplankton monitoring: An application across oceans and ecosystems

Phytoplankton assemblages are privileged descriptors of the ecological status of marine ecosystems regularly included in routine monitoring programmes. The high spatial and temporal variability of phytoplankton and the intrinsic difficulties of species identifications, however, combine in making reiterate assessments of this component of marine biota particularly demanding. Coarse levels of taxonomic resolution (e.g., genus, family) or morpho-functional categories have been proposed to reduce identification efforts or to ease the analysis of phytoplankton assemblages for monitoring purposes, although with contrasting outcomes. A major issue is that, in the absence of control for the loss of information associated to these alternative approaches, their application may lead to poor representations of genuine spatial and/or temporal patterns of assemblages in relation to natural and anthropogenic sources of variation. We provided a new approach to reduce the efforts required to analyse phytoplankton assemblages that integrate morpho-functional classification of phytoplankton with the use of null models to estimate the consequent loss of information on species-level community patterns. Null models for information loss were built by randomly grouping the original species variables into a progressively decreasing number of groups, in order to identify the minimum number of aggregate variables needed to detect community patters as at species level. Aggregate variables were then defined as morpho-functional groups, by grouping species on the basis of a combination of morpho-functional traits, including general taxonomy, cell size, shape, elongation and complexity. We applied the approach to six case studies investigating the response of phytoplankton assemblages from marine and transitional water ecosystems under different environmental settings in areas spanning the world’s ocean, including coral atolls, mangroves, estuaries, coastal lagoons and inlets. The approach allowed obtaining parsimonious sets of morpho-functional groups, which were suitable to detect changes in phytoplankton assemblage structure as at species level in all case studies. Trait-based approaches to phytoplankton research and monitoring are crucial to shed light on processes underlying phytoplankton community assembly and dynamics in the face of global change. In this perspective, our framework incorporates cost-effectiveness, instances from traditional monitoring programmes aiming at the detection of community patterns, and the current need for a deeper understanding of functional responses of phytoplankton to environmental drivers.

Seasonal dynamics of phytoplankton community in the Anma Islands of Yeonggwang (AIY), West Sea, Korea

Seasonal dynamics of phytoplankton community in the Anma Islands of Yeonggwang (AIY), West Sea, Korea

Mucus from the Pulmonate Sea Slug Onchidium typhae: Biochemical composition and ecological implications for the intertidal community

AbstractMany marine organisms, especially molluscs, produce mucus, which can be used in several physiological processes, such as locomotion and defence. In addition to utilization for themselves, mollusc mucus may influence intertidal community dynamics. Therefore, the biochemical composition of Onchidium typhae Buchannan, 1800 mucus was investigated. The effects of mucus on the microphytobenthos growth rate, representing the ecological functions of the mucus, were also tested. The results showed that the mucus was mainly composed of water (82.5%), and a large proportion of the organic content in mucus consisted of proteins (40%), followed by carbohydrates (13.33%) and lipids (0.19%). The effects of mucus on microphytobenthos growth were conditional and genus‐specific. Growth of Navicular sp. and Nitzschia sp. significantly responded to different concentrations and incubation times of the slug mucus. Fresh and concentrated mucus inhibited the growth of both species; low mucus concentration and longer incubation time showed a significant increase in the growth rates of both species. However, no effect of mucus on the Thalassiosira sp. growth rate was observed. These effects of mucus on diatom growth are discussed. Moreover, our findings suggested that the intertidal slug O. typhae may act as an intertidal ecosystem engineer, which can facilitate and influence benthic phytoplankton community dynamics.

The interactive effects of temperature and nutrients on a spring phytoplankton community

AbstractA complex interplay of environmental variables impacts phytoplankton community composition and physiology. Temperature and nutrient availability are two principal factors driving phytoplankton growth and composition, but are often investigated independently and on individual species in the laboratory. To assess the individual and interactive effects of temperature and nutrient concentration on phytoplankton community composition and physiology, we altered both the thermal and nutrient conditions of a cold‐adapted spring phytoplankton community in Narragansett Bay, Rhode Island, when surface temperature was 2.6°C and chlorophyll > 9 μg L−1. Water was incubated in triplicate at −0.5°C, 2.6°C, and 6°C for 10 d. At each temperature, treatments included both nutrient amendments (N, P, Si addition) and controls (no macronutrients added). The interactive effects of temperature and resource availability altered phytoplankton growth and community structure. Nutrient amendments resulted in species sorting and communities dominated by larger species. Under replete nutrients, warming tripled phytoplankton growth rates, but under in situ nutrient conditions, increased temperature acted antagonistically, reducing growth rates by as much as 33%, suggesting communities became nutrient limited. The temperature–nutrient interplay shifted the relative proportions of each species within the phytoplankton community, resulting in more silica rich cells at decreasing temperatures, irrespective of nutrients, and C : N that varied based on resource availability, with nutrient limitation inducing a 47% increase in C : N at increasing temperatures. Our results illustrate how the temperature–nutrient interplay can alter phytoplankton community dynamics, with changes in temperature amplifying or exacerbating the nutrient effect with implications for higher trophic levels and carbon flux.

Impact of salinity variation and silicate distribution on phytoplankton community composition in Pearl River estuary, China

Monitoring the primary producer diversity is crucial in understanding ecosystems balance, as imbalanced nutrients richness and diversity may induce red tide situations. The present study deals with evaluating the impact of hydrological factors regulating the dynamics of phytoplankton communities and the influence of chemical parameters on phytoplankton growth in Pearl River Estuary (PRE). During wet season (April), around 50 different species of phytoplankton were identified at 14 different sampling sites including 24 diatoms, 9 dinoflagellates, 10 green algae and 6 cyanobacterial species respectively. The diatom Melosira granulate was the dominant species at most of the sampling sites. Phytoplankton surveys during the dry season (November) showed Bellerochea malleus and Skeletonema costatum species as dominant at most of the sampling locations. Silicate (SiO3) distribution was one of the reason for the abundance of diatoms in west shoal sites. The concentration of nutrients and hydrological factors like water depth and salinity strongly supported phytoplankton growth. In addition, PRE west and middle shoal sites showed evidence of rich phytoplankton diversity when compared to east shoal and channel sites. The Non-metric Multidimensional Scaling (NMDS) analysis and cluster grouping analysis demonstrated the uniqueness of plankton species diversity at PRE west and east shoal sites. The results of Canonical Correspondence Analysis (CCA) suggested that diversity of phytoplankton communities was significantly influenced by environmental factors such as salinity, depth and SiO3 concentration. From these results, one may conclude that salinity with SiO3 distribution plays a crucial role in PRE phytoplankton community composition assisting in maintaining healthy intertidal ecosystem.

Phytoplankton distribution related to different winter conditions in 2016 and 2017 in the open southern Adriatic Sea (eastern Mediterranean)

Phytoplankton community structure and dynamics were investigated in the open southern Adriatic Sea during two winter-spring seasons (2016 and 2017) under different oceanographic and meteorological conditions. The principal environmental factor was a pronounced inflow of the Levantine Intermediate Water into the Adriatic, favoured by the cyclonic circulation of the Northern Ionian Gyre. As a consequence, high salinity values of about 38.8–38.9, were registered. Fifteen research cruises were undertaken in the same sampling area situated in the northern part of the Southern Adriatic Pit (SAP) with a maximum depth of 1200 m. Two specific circumstances were encountered: (i) high abundances of phytoplankton in the deep layer associated with strong downward flow in 2016, and (ii) an intense surface phytoplankton bloom in March 2017. This particular event occurred following the strong vertical convective mixing, which increased nutrient availability in the euphotic layer. High in situ Chl-a concentrations (max. 1.65 mg m−3) and phytoplankton abundances higher than 105 cells L−1 are not common in the habitually oligotrophic open southern Adriatic Sea, and this study attempts to determine the driving force of that phenomenon. The phytoplankton community in SAP involved nanoflagellates and diatoms as the most abundant taxonomic groups during the March 2017 bloom. Presence of some coastal phytoplankton taxa suggests the influx of coastal water masses and transport of species either longitudinally, from the northern to the Southern Adriatic in concomitance of the Northern Adriatic Dense Water spreading, or transversal as a response to the strong mesoscale activity in the study region, comprising intense shelf - open sea interaction.

Phytoplankton Community Patterns in the Northeastern South China Sea: Implications of Intensified Kuroshio Intrusion During the 2015/16 El Niño

AbstractKuroshio intrusion into the South China Sea (SCS) varies seasonally and interannually under different climatic conditions. To characterize the intensity of the climate‐driven Kuroshio intrusion and its impact on the phytoplankton community in the northeastern South China Sea (NESCS), two cruises were conducted during the 2015/16 El Niño event. In situ observations and remote sensing data showed that the Kuroshio strongly intruded into the SCS in both summer and winter. The summer phytoplankton community was dominated by cyanobacteria (Trichodesmium erythraeum), associated with high surface temperature, shallower mixed layer depth, and low nutrient concentrations. The winter phytoplankton community was mainly dominated by cosmopolitan diatoms (Thalassiosira diporocyclus, Thalassionema nitzschioides, and Chaetoceros socialis), associated with low surface temperature, deeper mixed layers, and relatively higher nutrient concentrations. Meanwhile, the elevated abundance of T. erythraeum coupled well with the Kuroshio intrusion index during the El Niño summer. The phytoplankton network was unstable in summer but not in winter, induced by the Kuroshio intrusion. Our findings show that intensified Kuroshio intrusion during the El Niño event was a vital driving force for reshaping phytoplankton community dynamics of the NESCS through lateral advection and affecting temperature, mixed layer depth, and nutrient supply.