Yangtze River Estuary Research Articles

Effect of typhoon on suspended sediment concentration, bed erosion and sediment transport in the Yangtze Estuary

Annually 5–6 typhoons strike the Yangtze Estuary (YE) as extreme events. However, their high energy and importance for sediment transportation and geomorphic changes are still not fully understood. In this study, high-resolution observations of wind, wave, flow velocity, and suspended sediment concentration (SSC) at two in-situ stations were carried out during the 2022 Hinnamnor typhoon. Additionally, we simulated the change in SSC, estuarine bed erosion/deposition, and flow and sediment transport with and without a typhoon in the YE using MIKE3 numerical model. The findings revealed that the Hinnamnor typhoon-induced waves increased the SSC of the turbidity maximum zone (TMZ) by a factor of 5.6 times (maximum is 2.8 kg/m3). The TMZ area also extended by 2.68 times (maximum is 7880km2, 70.4% of YE) in the YE. Moreover, the typhoon caused a dramatic change in sediment transport and bed erosion/deposition in the YE. First, in the delta front area where the mean water depth is >5 m, the typhoon significantly increased the southward flux of residual flow and sediment, causing sediment transport into Hangzhou Bay to abruptly increase 26.3 times (increase of 52 million tons, accounting for 1/3 of the present annual flux of the Yangtze River (150 million tons)) during a single spring-neap period. The net erosional area and volume extended to 6770km2 (60.4% of YE) and 91.18 × 106 m3. Second, in the delta shoals (where the mean water depth is <5 m, including east Chongming Shoal, Hengsha Shoal, Jiuduansha Shoal, and east-south Nanhui Shoal), residual flow and sediment flux decreased northward from the typhoon and resulted in the erosion of the shoal. Third, in channels with trumpet-shaped mouths (North Branch (NB), North Channel (NC) and South Passage (SP), except for North Passage (NP)), the upward flux of residual flow and sediment increased due to the typhoon, resulting in bed deposition in these channels (NB, NC and SP). This study highlights the important influence of typhoons on flow and sediment transport and bed erosion in estuarine areas.

Towards a comprehensive assessment of ichthyofaunal diversity in the Yangtze River estuary: Leveraging environmental DNA technology and bottom trawl surveys

The fishery resources in the Yangtze River Estuary (YRE) have declined drastically because of overfishing and environmental changes, leading to ecosystem degradation of the YRE, and bringing numerous rare fish species to the brink of extinction. As a new technology with great prospects for popularization and application, environmental DNA (eDNA) technology has been utilized and proven by many studies to have high potential in revealing the various species' biodiversity. In this study, we analyzed the species composition and diversity of the Yangtze River Estuary using a combination of eDNA technology and bottom trawling approaches, and later, the comparison of both methods. The results showed that combining eDNA technology and bottom trawling, 30 fish species from 7 orders and 11 families were identified. Among the 30 fish species, a total of six species of fish could be observed in catches from both methods. Perciformes were the most abundant and Coilia mystus was the dominant species. According to diversity indices, the eDNA technology reveals significant differences in fish community richness and diversity in the Yangtze River Estuary compared to the bottom trawl. In summary, the eDNA technology is feasible for monitoring fishery resources in the waters of the Yangtze River Estuary, thereby serving as a valuable supplementary tool for conducting comprehensive surveys in this region. Moreover, it holds significant implications and promising prospects for conserving the diverse ecosystem of the YRE in future conservation efforts.

Redescription of two Euplotes species (Ciliophora, Euplotida) from Yangtze River Estuary, China, with a note on the distributions of this genus in China

Ciliates are important unicellular organisms in the studies of biomolecules, genetics, and evolution. Euplotids are a highly diversified and widely distributed group. The morphology of two euplotids, Euplotes dominicanus and E. parkei, isolated from the Yangtze River Estuary, China, were investigated based on live observation, protargol-, and Chatton-Lwoff staining methods. The Chinese population of E. dominicanus resembles the original abyssal population except for having two caudal cirri and seven dorsolateral kineties. The Chinese population of E. parkei corresponds well with the original description in size, having eight frontoventral cirri, two marginal cirri, and a double-eurystomus dorsal silverline system. The diagnoses were improved by incorporating newly obtained data, detailed illustrations, and photomicrographs were supplemented. Euplotes parkei sensu needs to be reinvestigated. Phylogenetic analyses based on SSU rRNA gene sequence data confirmed the branching position of the two taxa within the genus Euplotes. The geographical distribution of the genus Euplotes in China was also briefly reviewed, and further exploration is needed in the brackish habitat, particularly focusing on the estuary zone.

A novel regional ship collision risk assessment framework for multi-ship encounters in complex waters

To address the issue of precisely quantifying ship collision risk and identifying collision hotspots in complex waters, this study proposed a regional ship collision risk assessment framework that includes a multi-ship encounter recognition model, a multi-ship comprehensive collision risk assessment model, and a collision hotspot recognition model. Firstly, the directed distance density-based spatial clustering of applications with noise (DBSCAN) algorithm was proposed. Based on this algorithm, a multi-ship encounter recognition model was established to cluster ship positions and obtain ship encounter clusters. Subsequently, the multi-ship comprehensive collision risk assessment model was constructed for multi-ship encounter situations based on the hierarchical classification method, enabling the determination of each ship's Comprehensive Collision Risk Value (CCRV). Finally, the collision hotspot recognition model was built using the grid analysis method, which can identify areas with a higher risk of ship collision. The automatic identification system (AIS) data of the Yangtze River estuary were used to validate the effectiveness of our framework. The results show that our framework can accurately measure ship collisions risks and identify areas with high collision risks, offering valuable insights to maritime authorities, providing actionable insights for real-time ship collision risk monitoring.

Autonomous navigation decision-making for ships in complex estuarine waters: Methodology and validation

This study focused on key scientific issues in the autonomous navigation for ships, including constraints on environmental and navigation rules, limitations on ship maneuverability, and collision avoidance mechanisms, to address the challenges of autonomous navigation decision-making for ships in complex estuarine waters and validate the feasibility and accuracy of the proposed methodology. A novel autonomous navigation decision-making method that can dynamically adapt to residual errors in a system and the random movements of target ships was proposed. The predictive model used to calculate decision plans and the simulation model used to execute and validate decision plans were separated. Environmental constituent elements were classified and modeled to digitize the environment. A navigation scenario was constructed based on the fusion of virtual and real information. The control and process prediction methods were proposed based on the nonlinear ship maneuvering characteristics. Navigation rules were summarized, analyzed, and integrated into the decision-making and execution process. The collision avoidance mechanism and calculation method for feasible course and speed range were studied. Simulation experiments were conducted using the North Channel of the Yangtze River Estuary as an example. The results demonstrated that the proposed method can accurately make autonomous navigation decisions, safely avoid collisions, and timely track routes in nearly realistic scenarios.

Spatio-Temporal Variation in Suspended Sediment during Typhoon Ampil under Wave–Current Interactions in the Yangtze River Estuary

Suspended sediment plays a major role in estuary morphological change and shoal erosion and deposition. The impact of storm waves on sediment transport and resuspension in the Yangtze River Estuary (YRE) was investigated using a 3D coupling hydrodynamic-wave model with a sediment transport model during Typhoon Ampil. This model has been validated in field observations of water level, current, wave, and sediment concentration. The model was run for tide only, tide + wind, tide + wind and wave forcing conditions. It was found that: (1) typhoons can increase the suspended sediment concentration (SSC) by enhancing bed shear stress (BSS), especially in the offshore area of the YRE, and there is hysteresis between SSC and BSS variation; (2) exponential and vertical-line types are the main vertical profile of the SSC in the YRE and typhoons can strengthen vertical mixing and reconstruct the vertical distribution; and (3) waves are the dominating forcing factor for the SSC in the majority of the YRE through wave-induced BSS which releases sediment from the seabed. This study comprehensively investigates the spatio-temporal variation in SSC induced by Typhoon Ampil in the main branch of the YRE, which provides insights into sediment transport and resuspension during severe storms for estuaries around the world.

Leaching potentials of microplastic fibers and UV stabilizers from coastal-littered face masks

Synthetic fibrous textiles are ubiquitous plastic commodities in everyday existence. Nevertheless, there exists a dearth of understanding regarding their environmental occurrence and the releasing capacities of associated additives. In this study, ten additives were determined in twenty-eight kinds of daily used plastic products including face masks, synthetic clothing, and food containers. Our results revealed that a typical kind of fibrous plastic, face masks, contained a greater variety of additives with UV stabilizers in particular, when compared to other plastic commodities. The above phenomena triggered our field investigation for the occurrence and release potentials of face mask fibers and the co-existing UV stabilizers into the environment. We further collected 114 disposed masks from coastal areas and analyzed their UV stabilizer concentrations. Results showed that the abundance of littered face masks ranged from 40–1846 items/km2 along the Yangtze Estuary, China; and UV stabilizers were of 0.3 ± 0.7 ng/g and 0.7 ± 1.7 ng/g in main bodies and ear ropes, respectively. The UV stabilizer concentrations in the field collected masks were only ∼7 % of their new counterparts, implying their potential leaching after disposal. By simulating the weathering scenario, we predict that a substantial amount of microplastics, with 1.1 × 1010 polypropylene fibers and 3.7 × 1010 polyester fibers, are probably be released daily into the coastal environment after face masks disposal; whereas the accompanied leaching amount of UV stabilizers was relatively modest under the current scenario.

Spatiotemporal variation in size and abundance of juvenile Chinese mitten crab (Eriocheir sinensis) in Yangtze Estuary

IntroductionIntertidal habitat preferences and spatiotemporal variation in the abundance of juvenile Chinese mitten crab Eriocheir sinensis in Yangtze Estuary are reported.MethodsThe size and abundance of this crab are reported for mud flat, gravel, root belt, and marsh habitats in this estuary’s lower, middle, and upper reaches from June 2021 (spring) to February 2022 (winter) using quadrat method.ResultsJuvenile E. sinensis of carapace length (CL) 5.5 ± 2.1 mm (mean ± standard deviation) were collected; no juveniles were found in February 2022. Crab abundance in root belt and gravel habitats usually exceeded that of marsh habitat; no juveniles were found in mud flat habitat. The greatest abundances and smallest individuals were found when megalopa recruited in early spring (June); juvenile abundance decreased sharply afterwards, and crabs were absent from the intertidal during winter. Size and relative growth rate of juvenile crabs were greater in root belt and gravel habitat than in marsh habitat from June to August. Recruitment primarily drove changes in crab abundance and size during June and July, and temperature best correlated with changes in the winter. Many stage I juveniles (CL &amp;lt; 3.1 mm) occurred in the lower estuarine reaches, while stage III and IV juveniles (CL 3.9–6.5 mm) primarily occurred in the middle and upper estuarine reaches.DiscussionAlthough intertidal wetland habitat in Yangtze Estuary is severely degraded and reduced in area, it remains important for recruitment and maintenance of mitten crab populations. An understanding of the habitat requirements of this species will benefit management of this crab resource and the prioritized restoration of intertidal habitat.

Compound- and element-specific accumulation characteristics of persistent toxic substances and metals in sediments of the Yellow Sea

This study investigated the large-scale distributions of persistent toxic substances (PTSs) and heavy metals in sediments of the Yellow Sea, collected from six transects between latitudes 32 and 37 degrees north (n = 35). Elevated concentrations of polychlorinated biphenyls (PCBs) were detected near the mainland, with a predominance of low-chlorinated congeners (di to tetra, ∼60%), indicative of atmospheric deposition. Analysis of traditional and emerging polycyclic aromatic hydrocarbons (t-PAHs and e-PAHs) revealed notable enrichment in the Central Yellow Sea Mud Zone (CYSM), attributing fossil fuel combustion as the significant source. Styrene oligomers and alkylphenols exhibited notable accumulation near the Han River Estuary in South Korea and the Yangtze River Estuary in China, respectively. The accumulation of heavy metals was predominantly observed in the CYSM, with element-specific distribution patterns. Cluster analysis revealed distinct distribution patterns for PTSs and metals, highlighting their source-dependent and grain size-dependent behaviors. In addition, the distribution and accumulation of PTSs tended to depend on their partitioning coefficients, such as the octanol-air partition coefficient (log KOA) and octanol-water partition coefficient (log KOW). This study offers valuable insights into the sources, transport, and fate of hazardous substances in the Yellow Sea, emphasizing the necessity for targeted environmental management strategies.

Isotopic evidence for the dietary difference between Rhizostomeae Nemopilema nomurai and Semaeostomeae Cyanea nozakii

Blooms of the Rhizostomeae Nemopilema nomurai and the Semaeostomeae Cyanea nozakii have become more prominent in the coastal waters of China since the end of the 20th century. However, the trophic ecology of these jellyfish species remain incompletely understood. In this study, the trophic characterizations of N. nomurai and C. nozakii populations were assessed using stable isotope analysis (SIA), with a focus on the important bloom area offshore of the Yangtze Estuary. Our results indicated obvious trophic differences between two scyphomedusae. The higher trophic position of the C. nozakii population in the coastal planktonic food web was reflected by its relatively large δ15N value compared to that of N. nomurai. The MixSIAR model indicated that small copepods (<1000 μm) and seston were important food sources for N. nomurai, and showed a stable dietary, irrespective of N. nomurai size. Conversely, C. nozakii exhibited a more diverse diet composition, and gelatinous organisms also were an important part of the diet of C. nozakii. Moreover, a pronounced ontogenetic shift in the diet of C. nozakii was observed, consisting of an increase in the proportion of zooplanktonic prey (excluding seston) in the C. nozakii diet with diameter. This study provides isotopic evidence of the substantial difference in trophic ecology between N. nomurai and C. nozakii, which resulted from the variations in SI values and diet compositions. Inconsistent size-based variation patterns were observed in trophic ontogenetic shifts within the N. nomurai and C. nozakii groups, highlighting a need for further investigation. These results will give insights into the characteristics of trophic ecology and functional roles of Rhizostomeae and Semaeostomeae, and indicate the need for a more careful consideration of the representations of Rhizostomeae and Semaeostomeae in coastal ecosystems, so as not to underestimate the knowledge of taxon-specific ecological effects on energy flow.

Unraveling the control factors of long-term morphological evolution in the Yangtze Estuary: A synthesis of natural processes and human interventions

Quantitative research regarding the effects and contribution rates of both natural processes and human interventions on the long-term evolution of the Yangtze Estuary is currently insufficient. To address this, we employ the Mann-Kendall (M-K) test to analyze hydrological changes and utilize bathymetric maps from 1958 to 2019 to quantify erosion and deposition patterns. Subsequently, combined with the empirical orthogonal function (EOF) to separately identify the top three control factors and elucidate spatiotemporal characteristics of the main factors controlling the Yangtze Estuary's morphological evolution. The results showed that sediment load and runoff consistently rank within the top three with respective mean contribution rates of 40.5% and 19.4%. Sediment load prevails as the first control factor across all regions except for the North Passage, which experienced a transition from natural dominance to human domination in 1998. Notably, extremely events like the 1998 flood occupied more eigenweighting in the short term and progressed in ranking due to the strong channel-forming capacity. Regarding escalating human interventions, estuarine engineering projects affect estuarine shoals following initial deposition and subsequent erosion patterns. However, their influence tends to wane post-completion, often surpassed by natural processes. Specifically, since 2010, continuous navigation channel dredging has governed the morphological evolution of the North Passage. Additionally, sand mining targeting the Ruifeng Shoal has driven the post-evolution dynamics of the South Channel as the second control factor. Overall, this study enhances our understanding of the coupling driving mechanisms involving both natural processes and human interventions, thereby enabling improved strategies for future sustainable management in estuarine environments.

Characterizing spatio-temporal variations of dimethyl sulfide in the Yellow and East China Sea based on BP neural network

Dimethyl sulfide (DMS), an organic volatile sulfide produced from Dimethylsulfoniopropionate (DMSP), exerts a significant impact on the global climate change. Utilizing published literature data spanning from 2005 to 2020, a BP neural network (BPNN) model of the surface seawater DMS in the Yellow and East China Sea (YECS) was developed to elucidate the influence of various marine factors on the DMS cycle. Results indicated that the six parameters inputted BPNN model, that include the time (month), latitude and longitude, sea-surface chlorophyll a (Chl-a), sea-surface temperature (SST), and sea-surface salinity (SSS), yielded the optimized simulation results (R2 = 0.71). The optimized estimation of surface seawater DMS in the YECS were proved to be closely aligned with the observed data across all seasons, which demonstrated the model’s robust applicability. DMS concentration in surface seawater were found to be affected by multiple factors such as Chl-a and SST. Comparative analysis of the three environmental parameters revealed that Chl-a exhibited the most significant correlation with surface seawater DMS concentration in the YECS (R2 = 0.20). This underscores the pivotal role of chlorophyll in phytoplankton photosynthesis and DMS production, emphasizing its importance as a non-negligible factor in the study of DMS and its sulfur derivatives. Furthermore, surface seawater DMS concentration in the YECS exhibited positive correlations with Chl-a and SST, while displaying a negative correlation with SSS. The DMS concentration in the YECS show substantial seasonal variations, with the maximum value (5.69 nmol/L) in summer followed in decreasing order by spring (3.96 nmol/L), autumn (3.18 nmol/L), and winter (1.60 nmol/L). In the YECS, there was a gradual decrease of DMS concentration from the nearshore to the offshore, especially with the highest DMS concentration concentrated in the Yangtze River Estuary Basin and the south-central coastal part off the Zhejiang Province. Apart from being largely composed by the release of large amounts of nutrients from anthropogenic activities and changes in ocean temperature, the spatial and temporal variability of DMS may be driven by additional physicochemical parameters.

Ecological risk assessment of dissolved heavy metals in the Yangtze River Estuary and Zhejiang coastal waters, China

The study applied a tiered ecological risk assessment method to evaluate the long-term status and trend of the ecological risks of dissolved heavy metals from 2011 to 2019 in the Yangtze River Estuary and Zhejiang coastal waters, China. The results for spring, summer, and autumn of 2019 indicated that Pb, Cd, and Zn posed no adverse ecological risk, Cu posed a potential ecological risk, and As posed an ecological risk. The annual results from 2011 to 2019 suggested that Pb, Cd, and Zn posed no adverse ecological risks, and As and Cu posed an ecological risk. The trend analysis in the nine years showed that the ecological risk of Cu is gradually decreasing, while that of As is still a concern. The overall trend is attributed to the environmental protection policies that reduced these contaminants' terrestrial sources and atmospheric sources.

Temporal-spatial change of China's coastal ecosystem resilience and driving factors analysis

Coastal regions, with both marine and terrestrial characteristics, play an important role in the global ecosystem and their ecological and environmental conditions are of global concern. A better understanding of regional differences in coastal resilience and its drivers facilitates ecosystem management and restoration. In this study, the level of ecological resilience of China's coastal regions from 2000 to 2020 was assessed using a three-pronged resilience assessment framework of resistance, adaptability and resilience, and the key drivers of ecological resilience were identified using geographic probes and geographically weighted regression analyses. The results of the study indicate that: (1) the ecological resilience of China's coastal region is spatially distributed as high resilience in the southern part of the study area and low resilience in the northern part of the study area; (2) the areas with higher rates of change are distributed in the Bohai Bay, Yangtze River estuary and Pearl River estuary; (3) in terms of drivers, economic development factors and environmental protection measures have a relatively large impact on changes in resilience and vary from region to region. The case study provides a systematic and quantitative framework for assessing the resilience of integrated coastal management and sustainable development.

Blood-Chemistry Parameters Comparison among Different Age Stages of Chinese Sturgeon Acipenser sinensis

The Chinese sturgeon (Acipenser sinensis), a critically endangered migratory fish native to the Yangtze River estuary, is experiencing alarming population declines. Understanding the physiological and biochemical profiles of this species is paramount for its conservation. However, due to limited sample availability, blood biochemical parameters have remained understudied. In this study, we examined blood chemistry in artificially cultured Chinese sturgeon ranging from 2 to 15 years of age. Our results revealed age-related trends: total protein (TP), albumin (ALB), globulin (GLO), total cholesterol (CHOL), high-density lipoprotein (HDL), low-density lipoprotein (LDL), estrogen (E2), testosterone (T), testosterone undecanoate (11-KT), and red blood cell count (RBC) increased with age, while glucose (GLU), uric acid (UA), and serum creatinine (CREA) decreased. Levels of C-reactive protein (CRP) declined from 3 to 7 years but rose from 8 to 15 years. Blood parameters showed stabilization with age, indicating enhanced resilience and immunity. Significant alterations in parameters at ages 2–3 and 14–15 suggest critical developmental stages. These findings are crucial for understanding sturgeon growth, development, migration, and reproduction, underscoring the necessity for targeted conservation efforts during pivotal life stages.

Functional connectivity in the Yangtze Estuary habitats for an “estuarine opportunist” fish: an otolith chemistry approach for small yellow croaker (Larimichthys polyactis)

Functional connectivity in the Yangtze Estuary habitats for an “estuarine opportunist” fish: an otolith chemistry approach for small yellow croaker (Larimichthys polyactis)

Inter-annual variations of dissolved oxygen and hypoxia off the northern Changjiang River (Yangtze River) Estuary in summer from 1997 to 2014

Inter-annual variations of dissolved oxygen and hypoxia off the northern Changjiang River (Yangtze River) Estuary in summer from 1997 to 2014

Development of environmental DNA metabarcoding primers for marine mollusks and comparison with published primers

Monitoring mollusk biodiversity is a great challenge due to their large diversity and broad distribution. Environmental DNA (eDNA) technology is increasingly applied for biodiversity monitoring, but relevant studies on marine mollusks are still limited. Although previous studies have developed several pairs of primers for mollusk eDNA analyses, most of them targeted only a small group of mollusks. In this study, seven primers were designed for the mollusk community and validated and compared with eight pairs of published primers to select the best candidates. After in silico test, MollCOI154 and MollCOI255 primers showed non-specific amplification, and same results were also obtained in published primers (COI204, Sepi, and veneroida). Moll12S100, Moll12S195 and Moll16S primers failed to amplify across all genomic DNA from selected mollusk. Except Moll16S, all developed and two published (unionoida and veneroida) primers were successfully amplified on four eDNA samples from Yangtze River estuary. After annotation of the amplified sequences, MollCOI253 showed higher annotation of the amplification results than the other primers. In conclusion, MollCOI253 had better performance in terms of amplification success and specificity, and can provide technical support for eDNA-based research, which will be beneficial for molluscan biodiversity investigation and conservation.

Chronosequence Changes of Soil Organic Carbon in Salt Marshes under Artificial Intervention: A Case Study of Hengsha Island in the Yangtze Estuary

Land formation seriously disturbs coastal salt marsh wetland ecosystems, while its influences on soil organic carbon (SOC) under chronosequences remain unclear. In this study, the impacts of the land formation time (from one to fourteen years) and soil properties on the chronosequences changes of SOC in the nascent wetland of Hengsha Island were investigated. The study results showed the following. (1) As the land-formation time extended, the SOC experienced a significant increase, tripling after a period of 14 years. The changes in SOC occurred mainly in the surface layer but not in the deep soil layer. Specifically, the surface layer’s average SOC reached 5.52 g·kg−1, markedly higher than 3.17 g·kg−1 in the deeper layer. (2) Spearman correlation analysis revealed that the ammonium nitrogen (NH4+-N), aboveground biomass (AGB), and soil water content (SWC) were positively correlated with the SOC. Methane emissions (CH4) and SOC exhibited a negative correlation. (3) The structural equation model (SEM) illustrated that the duration of soil deformation directly impacted the vegetation growth and affected the distribution characteristics of the SOC by modifying the soil environmental conditions. Changes in SOC following land formation influenced the rapid succession of soil properties and vegetation, with the modification of carbon sinks in the ecosystems.

Fronts affect fish community structure in the Yangtze River estuary and its adjacent area

Dispersal, a critical factor in the viability of marine organisms, is strongly influenced by the physical dynamics of the ocean. Fronts, as a common phenomenon in ocean dynamics, can theoretically impact the dispersal of organisms and ultimately cause spatial homogeneity or heterogeneity of marine communities. However, there is relatively limited understanding concerning whether frontal formation hinders the connectivity between communities and thus results in differences in community structure. To verify whether the formation of fronts caused differences between communities, 60 eDNA samples and their environmental parameters were collected from 32 sites in the Yangtze River estuary and its adjacent area, and four groups, the Yangtze River front-inner group (YRI), the Yangtze River front-outer group (YRO), the Zhejiang costa front-inner group (ZCI), and the Zhejiang coast front-outer group (ZCO), were compared to examine the differences in fish communities between the sides of the front. The results showed that there was a significant difference between YRI and YRO, suggesting that the front affected the community structure. There was no significant difference in fish communities between ZCI and ZCO, indicating that fronts could only hinder dispersal at high intensities. The difference between YRI and YRO possibly resulted from dramatic changes in temperature, salinity, and turbidity related to the front. Fronts also separated water masses with different environmental characteristics and thereby attracted fish to their optimal habitats. Overall, fronts appear to be ecologically significant for fish dispersal and community differentiation.