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Article

Spatio-Temporal Dynamics of Larval Fish Assemblage in the Nakdong River Estuary, South Korea

by
Hee-Chan Choi
1,
Seok-Hyun Youn
2,
Sangil Kim
2 and
Joo Myun Park
3,*
1
Marine Environment Impact Assessment Center, National Institute of Fisheries Science, Busan 46083, Republic of Korea
2
Oceanic Climate & Ecology Research Division, National Institute of Fisheries Science, Busan 46083, Republic of Korea
3
Dokdo Research Center, East Sea Research Institute, Korean Institute of Ocean Science & Technology, Uljin 36315, Republic of Korea
*
Author to whom correspondence should be addressed.
Diversity 2024, 16(6), 315; https://doi.org/10.3390/d16060315
Submission received: 3 April 2024 / Revised: 11 May 2024 / Accepted: 22 May 2024 / Published: 24 May 2024
(This article belongs to the Special Issue Dynamics of Marine Communities)
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Abstract

:
Estuaries are crucial fish nursery habitats owing to their high productivity and the presence of various microhabitats for the early development of aquatic organisms. This study investigated the temporal and spatial patterns of the species composition and abundance of larval fish assemblages in the Nakdong River estuary, South Korea, through bi-monthly sampling in the inner and outer estuaries. Fifty-five larval taxa were collected, and the larval fish assemblages were dominated by a few species. Engraulis japonicus (28.8%) was the most abundant, followed by Gobiidae sp.1 (22.6%), Clupea pallasii (13.9%), and Omobranchus sp. (6.1%). The species richness, abundance, and diversity tended to be higher during the warm season in the inner estuary. Multivariate analyses revealed that the structures of larval fish assemblages were significantly influenced by the season and site. Spatial and seasonal changes in larval fish assemblages resulted from the different occurrence patterns of common fish larvae in relation to water temperature and salinity. Among the predominant fish larvae, E. japonicus was captured more frequently in more saline outer estuaries during the warm season, whereas Gobiidae sp.1 and C. pallasii were more abundant in less saline inner estuaries during the warm and cold seasons, respectively. The results of this study improve our understanding of larval biodiversity in estuarine habitats in relation to environmental modification and contribute to the evaluation of nursery functions in the Nakdong River estuary.

1. Introduction

Estuaries are often referred to as areas of high biological productivity primarily because they receive a significant influx of nutrients from upstream sources, which nourishes their diverse ecosystems [1]. The influx of river water has significant physical, chemical, and biological effects on estuarine environments and their surrounding waters, which, in turn, affect the distribution and abundance of biological communities inhabiting these areas [2,3]. For example, the spatiotemporal dynamics of larval fish assemblages are largely influenced by volatile physical and biological processes, such as temperature, salinity, freshwater flows, and primary productivity, in estuarine ecosystems [4,5]. Different ecological guilds of fish species exhibit variations in their responses to environmental changes, indicating complex spatial and temporal dynamics [6,7]. In addition, regulating river flow from estuary barrages negatively impacts the connectivity of estuaries with adjacent coastal areas [8].
The Nakdong River estuary is an essential spawning and breeding ground for commercial fish and shellfish because of its high fishery productivity and abundance of young individuals [9,10]. However, the construction of estuary barrages has been identified as the primary factor causing sudden changes in estuarine ecosystems, including changes in the oceanographic environments [11], the biota of mollusks and crustaceans [12], macrobenthos communities [13]], and fish assemblages [14]. Estuarine barrages were initially constructed in the eastern main channel of the lower Nakdong River in 1987, and eight additional barrages were added to the western channel as part of river-dredging activities in 2013. These newly constructed barrages reduced fluid velocity [15,16], which has been linked to a decrease in total freshwater discharge since 2013 (K-water, http://www.kwater.or.kr/). A reduction in the total discharge can significantly impact marine organisms, including fish inhabiting estuaries and surrounding sea areas [17].
Fish eggs and larvae are extremely vulnerable and often experience high early mortality due to mismatches between early life history characteristics and environmental conditions [18]. As stated, the construction of estuarine barrages can negatively impact not only adult fish [19,20], but also their larvae and juveniles [21]. For example, the construction of estuarine barrages led to decreased stream flow and often adversely affected numerous native fish species that depend on the estuary as a refuge, breeding, nursery, and feeding ground by reducing suitable habitats, particularly during drought periods [22]. In addition, the modernization of estuary barrages reduced fish larvae transport, altering larval distribution patterns [23]. However, only a few studies have investigated the distribution of ichthyoplankton in estuarine environments in Korean waters, and the understanding of how the structures of larval fish assemblages change in response to environmental changes in estuarine habitats in Korea is limited [24,25,26,27].
As stated above, the construction of artificial structures in river estuaries has a significant impact on the estuarine ecosystem. Therefore, the objective of this study was to examine the species composition of larval fish assemblages in the Nakdong River estuary from 2013 to 2015 (post-construction period of estuary barrages) and their spatio-temporal variations according to the year (three consecutive years), season (cold–dry and warm–rainy seasons, based on Park et al. [7]), and site (inner and outer estuaries). In addition, this study identified potential environmental factors that could influence spatial and seasonal variations in ichthyoplankton populations. The results of this study emphasize the significance of estuaries as nursery grounds in the Nakdong River estuary and provide crucial data for assessing the impact of artificial structures on estuarine ecosystems.

2. Materials and Methods

2.1. Sampling and Laboratory Procedures

From April 2013 to December 2015, bi-monthly field sampling was conducted at 10 stations in the Nakdong River estuary, including three stations in the inner estuary (A1–A3) and seven stations in the outer estuary (B1–B7) (Figure 1). Hydrological parameters, including sea surface temperature (SST), bottom water temperature (BWT), sea surface salinity (SSS), and bottom water salinity (BWS) were also measured at each sampling event using a conductivity temperature depth profiler (SBE-19 Plus/Sea Bird). The values of four hydrological parameters in all stations were averaged separately within each inner and outer site and presented with a time-series line chart from February 2013 to December 2015.
Larval fish were collected using an RN80 net, with an inlet diameter of 80 cm and a mesh size of 300 μm, equipped with a flowmeter (General Oceanics, Miami, FL, USA). During each sampling event, the net was towed at a water depth of 1–2 m, traveling at 2.5 knots for 5 min. Immediately after capture, the samples were fixed with 95% ethanol onboard and transported to the laboratory. In the laboratory, fish larvae were selected from the samples and subsequently identified to the lowest taxonomic level under a dissecting microscope (Olympus SZ40) utilizing various taxonomic sources [28,29,30]. Taxonomic classifications and scientific names were based on those in FishBase [31]. Species that could not be identified based on body morphometry were classified as unidentified species. With the exception of Acanthogobius flavimanus, most Gobiidae species were classified as unidentified and labeled Gobiidae sp.1, Gobiidae sp.2, etc., up to Gobiidae sp.8, owing to the lack of available information on their morphological characteristics for taxonomic classification to the species level in the literature. The abundance of fish larvae of each species was converted to the amount per 1000 m3 volume filtered.

2.2. Data Analysis

The community variables of species richness (number of species), abundance (number of individuals), and diversity index at all stations were averaged separately within each inner and outer site across each season and presented with a bar chart including standard deviations. Because the Shannon–Wiener index [32] assumes that individuals are randomly sampled from an infinite population and that all taxa are represented in the sample, the Shannon diversity index was used to analyze spatial and temporal variations in larval fish composition. Differences in the species richness, abundance, and diversity of larval fish assemblages with respect to the year, site, and season (month) were analyzed using a three-way analysis of variance (ANOVA), with all factors as fixed effects. Prior to the ANOVA, the homogeneity of variance was tested using Levene’s test [33]. The relative diameter of the circle was used to present spatial trends in the abundance of the four most abundant species of fish larvae at each sampling month.
Multivariate statistical analyses were performed using PRIMER v7 with the PERMANOVA + module [34,35]. Abundance data were log-transformed ([log10(x + 1)]), and the Bray–Curtis similarity index was constructed to calculate the similarity of the assemblages. The Bray–Curtis technique is suitable for use in assemblage datasets where maintaining relative abundance and species composition is crucial [36]. The homogeneity of multivariate dispersions within the groups was tested using PERMDISP [37]. As the PERMSISP results revealed that the average within-group dispersion was not equivalent among the groups, a one-way analysis of similarity (ANOSIM) was conducted to examine spatial and temporal variations in the species composition of larval fishes. The “R” value in the ANOSIM indicated similarity between the two groups, ranging from −1 to +1. If the value was closer to either −1 or +1, the disparity between the two groups increased. A similarity percentage (SIMPER) analysis was conducted to identify the species that contributed the most to the spatio-temporal variation in species composition.
A distance-based linear model (DistLM) was used to investigate the relationship between the structure of larval fish assemblages and environmental variables. The resulting DistLM and associated distance-based redundancy analysis (dbRDA) plots can determine the extent to which variability can be explained by the remaining predictor variables [34]. The dbRDA method enables the partitioning of variability in the data based on a complex design or model and is based on a multivariate distance measure suitable for ecological datasets [38]. The BEST selection procedure examines the value of the selection criterion for all possible combinations using normalized predictor variables [39]. The optimal model for selecting the most efficient combination of variables influencing the assemblage composition was determined using the Akaike Information Criterion (AIC) [34,40]. In addition, the principal coordinate (PCO) analysis was conducted to examine trends in the relative abundance of larval fish assemblages in relation to the year, site, and season [34]. Correlation coefficients between the factors and the PCO axis were examined as evidence of contributions from larval fish species. Pearson correlations of individual species higher than 0.6 and greater than 1% of the total abundance were graphically plotted on the PCO 1 and 2 axes.

3. Results

3.1. Environmental Parameters

According to the average SST during the study period, the lowest SST (5.7 °C) was recorded at the inner stations in February 2013, while the highest SST (28.3 °C) was recorded at the inner stations in August 2013 (Figure 2A). Despite interannual differences in the SST throughout the survey period, the highest SSTs were consistently recorded in August, while the lowest SSTs were typically observed in February or December. The BWT exhibited a similar pattern to that of the SSTs; however, in 2013 and 2014, at the outer stations, the highest BWTs were observed in October, deviating from the typical SST pattern (Figure 2B).
According to the average SSS, the lowest SSS was 8.1 psu at the inner stations in February 2013, while the highest SSS (33.3 psu) was recorded at the outer stations in June 2015 (Figure 2C). The BWS reached its lowest value at the inner stations in February 2013 (11.8 psu) and peaked at the outer stations in February 2015 (34.1 psu) (Figure 2D). The average salinity tended to be lower at the inner stations and during the warmer season (i.e., June and August); however, a slight seasonal trend was observed at the outer stations.

3.2. Composition of Larval Fish Assemblages

In total, 25 families and 55 taxa of larval fishes were collected from the Nakdong River estuary between April 2013 and December 2015 (Table S1). The most abundant larval species was Engraulis japonicus, accounting for 28.8% of the total catch. The second most abundant fish larva was Gobiidae sp.1 (22.6%), followed by Clupea pallasii (13.9%) and Omobranchus sp. (6.1%). In addition to these species, Amblychaeturichthys sp. and Callionymidae sp. accounted for 3.7% and 3.4% of the total abundance, respectively. These six most abundant taxa accounted for 78.5% of the total catch.

3.3. Variations in Species Richness, Abundance, and Diversity of Larval Fish Assemblages

Throughout the year-round survey conducted over three years at both the inner and outer sites of the Nakdong River estuary, the species richness, abundance, and diversity index of the larval fish assemblages showed distinct temporal and spatial patterns (Figure 3). The mean species richness was highest at the outer stations during the cold season of 2014, while it was lowest at the inner stations during the cold seasons of both 2014 and 2015. The maximum mean abundance of fish larvae was recorded at the inner stations during the warm season of 2015, while the lowest value was observed at the outer stations during the cold season of 2014. The mean diversity tended to be higher during the warm season than during the cold season. A three-way ANOVA indicated no significant differences in the species richness, abundance, or diversity of larval fish assemblages among the three years or between the inner and outer sites; however, abundance and diversity were found to be significantly different between the cold and warm seasons, consistently showing higher values during the warm season (Table 1). No significant two- or three-way interactions were found for any of the dependent variables, except for the two-way interaction between site and season for diversity (Table 1).

3.4. Spatial Trends in the Abundance of Dominant Fish Larvae

The major fish larvae collected during the study period showed different trends of spatial distribution and seasonal occurrence in the Nakdong River estuary. The abundances of the four most dominant species (E. japonicus, Gobiidae sp.1, C. pallasii, and Omobranchus sp.; dominance rates of more than 5% of the total individuals) varied temporally and spatially (Figure 4). Engraulis japonicus primarily occurred during the warm season and was more abundant in 2013 and 2015 than in 2014. In terms of spatial patterns, this species was primarily distributed at the outer stations; however, during the warm seasons of 2014 and 2015, its distribution extended toward the upstream region when salinity levels were not as low as in 2013 (Figure 3). Gobiidae sp.1 typically appeared during the warm season, particularly during August, and was more abundant at the inner stations. Conversely, C. pallasii was the dominant species during the cold season, with the highest abundance recorded in February 2014 at the innermost station of the estuary. Larval Omobranchus sp. occurred only during the warm season and was most abundant in August 2013 and 2015 at the inner stations of the estuary.

3.5. Assemblage Structure of Larval Fish

The results of the ANOSIM showed that the species composition of larval fish differed significantly among the three years (global R = 0.038, p < 0.05), between the two seasons (global R = 0.058, p < 0.05), and between the two study sites (global R = 0.421, p < 0.05). The SIMPER analysis revealed that E. japonicus was the most significant contributor in all three years, and Callionymidae sp., Gobiidae sp.1, and C. pallasii were the second-largest contributors in the 2013, 2014, and 2015 groups, respectively. The predominant larval fishes in the inner estuary were C. pallasii and Gobiidae sp.1, whereas those in the outer estuary were E. japonicus and Callionymidae sp. The most observed larval fishes contributing to the cold- and warm-season assemblages were C. pallasii and E. japonicus, respectively.
The DistLM identified SST as the most significant variable influencing assemblage composition, with two combinations of variables (SST and SSS) having the most significant influence. Marginal tests from the DistLM showed that SST and BWT exhibited p-values < 0.05, and the total contribution of all variables was 68.1%. According to the BEST solution model, the most efficient explanation for environmental influences was associated with SST and SSS, contributing to 54.3% of the proportional variation in the assemblage.
The dbRDA of the larval fish assemblage showed that dbRDA1 described 82.4% of the fitted variation and 44.7% of the total variation, and dbRDA2 described 17.6% of the fitted variation and 9.6% of the total variation (Figure 5A). Distinct correlations were evident in the dbRDA ordination, with data points distributed primarily in response to water temperature (both surface and bottom) along dbRDA1 and secondarily to salinity (both surface and bottom) along dbRDA2 (Figure 5A). Data points within the ordination were generally distributed into two groups, with water temperature sequentially correlated along the x-axis, resulting in the separation of warm and cold seasons on both sides. The two sites (inner and outer estuaries) were distributed separately along the y-axis (Figure 5A).
The PCO ordination of species abundance was strongly structured according to season and study site. The PCO1 axis delineated seasonal variations, separating warm-season assemblages from those in the cold seasons (Figure 5B). Data points from the outer site were distributed in the upper region of the plot, while those from the inner site were positioned in the bottom region, along the secondary axis (PCO2 axis) (Figure 5B). Pearson correlations indicated that higher abundances of E. japonicus, Parablennius yatabei, Callionymidae sp., Omobranchus sp., Gobiidae sp.1, Gobiidae sp.2, and Konosirus punctatus were strongly associated with warm-season assemblages, while a higher abundance of C. pallasii contributed to the separation of cold-season assemblages from the warm season. The abundances of E. japonicus and Scomber japonicus contributed to the outer-site assemblages, whereas six (P. yatabei, Callionymidae sp., Omobranchus sp., Gobiidae sp.1, Gobiidae sp.2, and K. punctatus) and one (C. pallasii) species were associated with the inner-site assemblages in the warm and cold seasons, respectively (Figure 5B).

4. Discussion

4.1. Common Larval Fish Species

In this study, among 55 taxa of larval fishes collected, only a few species dominated the larval fish assemblages. The most dominant species was E. japonicus, which constituted more than one-third of the total abundance. This species has also been documented as a dominant species in other estuaries and their adjacent sea areas in the Northwest Pacific regions [25,26,41,42,43], including the southern coastal areas of Korea [44,45,46]. Adult E. japonicus is widely distributed throughout the coastal areas of Korea and constitutes a major commercial species, with a yearly catch exceeding 200,000 tons [47]. Although their numbers vary depending on the region, this species appears to be dominant in various sea areas during its spawning period from spring to autumn [48,49].
The second most dominant taxon was Gobiidae sp.1, constituting 22.6% of the total larval abundance. Eight different species of larval gobies were also identified during the sampling period, and they exhibited a high dominance rate during the warm season and inside the estuary region. Most larval gobies have been found in brackish and/or coastal waters, often constituting the dominant larval fish group in the estuarine waters of Korea [24,25,26], as well as other estuaries globally [50,51]. Board ichthyoplankton surveys throughout coastal and offshore waters in Korean seas have shown that larval gobies are only abundant near coastal areas, including estuaries, but exhibit rare abundances or are nearly absent in offshore waters, especially in the East Sea and Korea Strait [52,53,54]. Most Gobiidae species are amphidromous and estuarine resident [51], and their larvae belong to the brackish water ecological guild [5], whereas E. japonicus is a typical marine larval species.

4.2. Structure of Larval Fish Assemblage

In the present study, variations in the structure of larval fish assemblages were primarily influenced by season and site. Among the environmental variables, water temperature was the key determinant of the seasonal structure of larval fish assemblages, while salinity was the major indicator of their spatial patterns in the Nakdong River estuary. Generally, the occurrence of larval fish shows distinct seasonality, corresponding to the reproductive seasons of adult fish, because most fish species have a distinct seasonal spawning period that aligns with the seasonal patterns of gonadal maturation and water temperature [55]. In the coastal areas of southeastern Korea, the spawning seasons of coastal fish assemblages are primarily divided into warmer (late spring to summer) and colder (winter and early spring) seasons based on their gonadosomatic indices [56]. Among the dominant larval fishes in the Nakdong River estuary, spring–summer spawners, such as E. japonicua and K. punctatus, were more prevalent during the warm season, whereas winter spawners (e.g., C. pallasii and P. yokohamae) were abundant during the cold season [56]. Several previous studies have also shown that the seasonal variation in larval fish assemblages is influenced by the timing of the spawning activities of adult fish [57,58,59], and water temperature is regarded as a key environmental variable influencing such seasonal changes in larval fish communities [5].

4.3. Estuarine Distributions of Common Fish Larvae

In the Nakdong River estuary, common larval fish species showed distinct spatial distribution patterns between the inner and outer estuaries. In particular, E. japonicus larvae were more abundant at the outer site during the warm season, while C. pallasii larvae were distributed toward the inner site during the cold season. The larval stages of E. japonicus have limited distribution in estuaries depending on the salinity gradient [24,25,42]. In the Mangyeong–Dongjin and Yeongsan River estuaries (on the western coast of Korea), the eggs and larvae of E. japonicus are nearly absent or scarce near the mouth of the estuary [24,25]. Choi et al. [26] also reported that larval E. japonicus collected in the Nakdong River estuary appeared to be sensitive to low salinity, as their relative abundance was substantially higher in the high-salinity outside region of the estuary compared to that in the inside region. Similarly, we observed a relatively high abundance of larval E. japonicus in the outer site of the estuary. However, their spatial distribution reached more upstream regions (inner sites) during the warm seasons of 2014 and 2015 compared to that recorded in 2013. This could be attributed to the unusually high salinity levels in the inner region of the estuary in 2014 and 2015 (Figure 2). Generally, E. japonicus eggs and larvae are present when the water salinity is above 30 psu [60,61]; however, they are nearly absent when the water salinity is lower than 20 psu [42]. Therefore, a relatively high salinity (>20 psu) appears to have allowed for the upstream distribution of E. japonicus larvae during the warm seasons of 2014 and 2015.
The spawning behavior of C. pallasii is characterized by attaching eggs to seagrasses and/or seaweeds in densely vegetated inner estuaries or closer coastal habitats at depths shallower than 5 m [62,63]. The inside region of the Nakdong River estuary has a shallow water depth and nutrient-rich water mass, which favor the growth and residence of dense halophytes and macroalgae [64]. These environmental conditions can provide favorable habitat structures for attaching the eggs of C. pallasii onto the bottom stem parts of halophytes or seaweeds submerged in shallow water. In addition, fish larvae belonging to Gobiidea and Blenniinae were abundant in the inner areas of the estuary during the warm season (Table S1). These two groups of fishes are typical estuarine residents, and their distribution is generally limited to shallow euryhaline estuarine habitats and/or near coastal areas [65]. Several previous studies have also reported that the spatial distributions of these two groups of fish larvae are concentrated inside or near the mouths of estuaries [42,66]. Such seasonal and spatial distribution patterns of common fish larvae in relation to water temperature and salinity contribute to the distinct structure of larval fish assemblages in the Nakdong River estuary.

4.4. Influences of Estuary Barrage on Fish Larvae

After the completion of the construction of barrages along the Nakdong River mainstream in 2013, there have been changes in environmental conditions that have potentially influenced biological assemblages in the Nakdong River estuary due to a reduction in water downflow from estuary barrages [67]. Reduced outflow can significantly affect biological communities, including larval and adult fish assemblages [8,14]. This reduction in freshwater discharge can affect the productivity of estuaries and their surrounding sea areas, thereby disrupting the food web, which can cause reductions in major commercial fish species [3,68]. Through comparison with a previous survey conducted during 1987–1988 in the Nakdong River estuary, the present study confirmed a new dominance of C. pallasii larvae, but observed a lower abundance of Coilia larvae, which previously constituted the major fish larvae [27]. The changes in dominant species between previous and present studies appear to have been a decrease in brackish fish larvae (i.e., Coilia larvae) and an increase in marine fish larvae (i.e., C. pallasii larvae) with reduced freshwater discharge [65]. Notably, Faria et al. [69] suggested that a reduced downflow of freshwater discharge could lead to the loss of unique features of an estuary and increase the possibility of unique habitat loss for species within the estuary. However, a sudden increase in outflow can threaten larval fish communities inhabiting estuarine systems [69]. During the study period, a significant amount of freshwater was discharged, particularly in August 2014. This might have led to the sudden collapse of the E. japonicus population in the Nakdong River estuary. Unfortunately, we could not obtain conclusive evidence regarding the influence of estuarine dam construction on historical changes in larval fish assemblages due to the absence of continuous annual surveys of larval fish communities. However, it is reasonable to assume that an increase in freshwater discharge to the estuarine regions would have affected the spawning of marine fishes in the estuarine habitats.

5. Conclusions

In conclusion, this study revealed that the larval fish assemblage in the Nakdong estuary is characterized by the dominance of a few species with high abundance. Furthermore, this assemblage is structured by season and estuarine region, with water temperature and salinity playing significant roles in shaping its composition. Seasonal differences in larval fish assemblages were dependent on the spawning season of adult fish, whereas the spatial distribution of larval fish was mostly influenced by variations in salinity. However, owing to the lack of information regarding the impact of environmental variables on biological communities in the Nakdong River estuary, further studies are needed to determine how fluctuations in freshwater discharge can affect the ecosystem of the Nakdong River estuary through continuous monitoring. The results of this study could potentially elucidate the biodiversity in estuarine habitats across Korea and contribute to the evaluation of nursery grounds in the Nakdong River estuary. In addition, a comparative analysis with the findings of other studies focusing on open-type river systems will provide scientific and systematic insights that will aid in the development of appropriate water management policies.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/d16060315/s1, Table S1: Family and taxa of larval fishes, as well as their mean abundances per 1000 m3 with respect to the year, estuarine site, and season in the Nakdong River estuary.

Author Contributions

H.-C.C.: conceptualization, data curation, formal analysis, investigation, methodology, visualization, writing—original draft; S.-H.Y.: funding acquisition, supervision, project administration; S.K.: data curation, supervision; J.M.P.: methodology, software, visualization, writing—original draft, writing—review and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by grants from the National Institute of Fisheries Sciences (grant number R2024013) and Korea Institute of Ocean Science and Technology project (grant number PEA0201).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

All data supporting the results of this study are provided in this manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Locations of the ten sampling stations in the Nakdong River estuary, divided into the inner (A1–A3) and outer (B1–B7) stations.
Figure 1. Locations of the ten sampling stations in the Nakdong River estuary, divided into the inner (A1–A3) and outer (B1–B7) stations.
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Figure 2. Temporal variation in surface (A,C) and bottom (B,D) water temperatures (A,B) and salinity (C,D) in the inner and outer stations of the Nakdong River estuary. SST = sea surface temperature, BWT = bottom water temperature, SSS = sea surface salinity (SSS), BWS = bottom water salinity.
Figure 2. Temporal variation in surface (A,C) and bottom (B,D) water temperatures (A,B) and salinity (C,D) in the inner and outer stations of the Nakdong River estuary. SST = sea surface temperature, BWT = bottom water temperature, SSS = sea surface salinity (SSS), BWS = bottom water salinity.
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Figure 3. Seasonal and interannual variations in the species richness, abundance, and diversity index of larval fish assemblages at the inner and outer stations of the Nakdong River estuary.
Figure 3. Seasonal and interannual variations in the species richness, abundance, and diversity index of larval fish assemblages at the inner and outer stations of the Nakdong River estuary.
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Figure 4. Spatial and seasonal distribution of the four dominant fish larvae (Engraulis japonicus, Gobiidae sp.1, Culpea pallasii, and Omobranchus sp.) in the Nakdong River estuary.
Figure 4. Spatial and seasonal distribution of the four dominant fish larvae (Engraulis japonicus, Gobiidae sp.1, Culpea pallasii, and Omobranchus sp.) in the Nakdong River estuary.
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Figure 5. Distance-based redundancy analysis (dbRDA) (A) and ordination plots for the principal coordinate analysis (B) of larval fish assemblages to assess the differences between cold and warm seasons and between inner and outer sites. Correlations of environmental variables and larval fish species with the dbRDA or PCO axes are presented as vectors with correlations > 0.6. Vectors represent Pearson correlations, and the circle indicates a correlation of one. SST = sea surface temperature, BWT = bottom water temperature, SSS = sea surface salinity (SSS), BWS = bottom water salinity.
Figure 5. Distance-based redundancy analysis (dbRDA) (A) and ordination plots for the principal coordinate analysis (B) of larval fish assemblages to assess the differences between cold and warm seasons and between inner and outer sites. Correlations of environmental variables and larval fish species with the dbRDA or PCO axes are presented as vectors with correlations > 0.6. Vectors represent Pearson correlations, and the circle indicates a correlation of one. SST = sea surface temperature, BWT = bottom water temperature, SSS = sea surface salinity (SSS), BWS = bottom water salinity.
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Table 1. Results of the three-way ANOVA on the species richness, the abundance, and the diversity of larval fish assemblages in the study areas. Bold letters indicate significant differences at p < 0.05.
Table 1. Results of the three-way ANOVA on the species richness, the abundance, and the diversity of larval fish assemblages in the study areas. Bold letters indicate significant differences at p < 0.05.
SourcedfSpecies RichnessAbundanceDiversity
FpFpFp
Year20.4940.6123.0270.0531.3960.253
Site10.3580.5512.2560.1360.0920.762
Season10.9770.3255.0120.0278.5660.004
Year × Site21.0060.3691.5160.2250.1730.841
Year × Season21.0200.3650.2490.7800.2270.797
Site × Season10.1610.6890.2160.6434.3670.039
Year × Site × Season21.9820.1430.8260.4412.3010.106
Residual24
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Choi, H.-C.; Youn, S.-H.; Kim, S.; Park, J.M. Spatio-Temporal Dynamics of Larval Fish Assemblage in the Nakdong River Estuary, South Korea. Diversity 2024, 16, 315. https://doi.org/10.3390/d16060315

AMA Style

Choi H-C, Youn S-H, Kim S, Park JM. Spatio-Temporal Dynamics of Larval Fish Assemblage in the Nakdong River Estuary, South Korea. Diversity. 2024; 16(6):315. https://doi.org/10.3390/d16060315

Chicago/Turabian Style

Choi, Hee-Chan, Seok-Hyun Youn, Sangil Kim, and Joo Myun Park. 2024. "Spatio-Temporal Dynamics of Larval Fish Assemblage in the Nakdong River Estuary, South Korea" Diversity 16, no. 6: 315. https://doi.org/10.3390/d16060315

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