China has one of the longest coastlines in the world, stretching over 14 500 km from the border with North Korea in the north to Vietnam in the south (Liu 2013). Estuaries with mixed waters constitute a complex of different habitat types with sudden changes in temperature, salinity and depth, and are regarded as feeding grounds and nursery areas for both migrant and resident species (Blaber 1997; Elliott et al. 2007; Kerr et al. 2010; Potter et al. 2015), thus supporting high levels of fisheries (McLusky & Elliott 2007). Meanwhile, estuaries are also excellent sites for people to live and access to rivers and oceans helps to develop trade and communication. As anthropogenic impact continues to spread, it is crucial to improve the management of resources to protect and preserve habitats and maintain ecosystem functions (Banks-Leite et al. 2014; Lundquist et al. 2017).
In response to oceanographic dynamics and variation in solar irradiation, rainfall and wind conditions, estuaries show very strong environmental gradients, limiting some fish species to a particular section, which contributes to complex spatio-temporal patterns in fish communities (Nicolas et al. 2010; de Moura et al. 2012; Basset et al. 2013). Furthermore, the sequential immigration and emigration of fish species for spawning, nursing and wintering result in pronounced cyclical seasonal changes in the fish fauna composition (Hoeksema & Potter 2006; Eick & Thiel 2014). Such complexity makes it difficult to manage and control sustainable fisheries and it is therefore necessary to understand the processes and mechanisms of dynamic fisheries through detailed quantitative analysis of fish communities (Elliott & Hemingway 2002; Franco et al. 2008). Some measures, such as species composition, diversity, abundance and biomass provide information on the structure of fish assemblages and corresponding environmental conditions, thus offering complementary insights into fish assemblages for both theoretical and field studies (Magurran 2004; Eick & Thiel 2014). In addition to the classic index, i.e. species richness and, to a lesser extent, species evenness, which continue to play a dominant role as substitutes for diversity measures in many studies, the use of a multi-component diversity index should be encouraged to properly describe and monitor the main components of species diversity, e.g. Margalef’s species richness, the Shannon– Wiener index, Pielou’s index, Heip’s evenness index, the Simpson concentration index, the taxonomic distinctness index, etc., in order to take full account of the ecosystem functions at different management scales (Gaertner et al. 2010; Loiseau et al. 2016).
Species of a given assemblage constituting the largest biomass in an ecosystem is considered a dominant species that can affect the distribution of other organisms and define that ecosystem and its characteristics. A dominant species may be more effective in obtaining resources, resisting disturbance or deterring competitors compared to other species (Miller et al. 2015). In addition, information on spatial niche overlap and segregation among species is essential for further understanding the population structure and dynamics (Cohen 1977; Navarro et al. 2013). Species with similar habitat preferences tend to engage in biological interactions and co-occur together ( Mahon et al. 1998; Tews et al. 2003). Spatial patterns of fish movement can be determined by a number of factors, including the size of individuals and modes of reproduction (Dunlop et al. 2009; Enberg et al. 2010; Heino et al. 2015), interspecific and intraspecific competition for resources (Shulman 1985; Marshall & Elliott 1997; Svanbäck et al. 2008), habitat composition ( Kamrani et al. 2016; Maree et al. 2016; Polansky et al. 2018), and abiotic factors ( Bacheler et al, 2009; Payne et al. 2013; da Silva Jr et al. 2016). However, knowledge of niche partitioning among sympatric fish species in estuaries has remained scarce.
The Min estuary, located in the southeastern part of China, is a typical subtropical estuary. The complexity and variability of hydrodynamic characteristics of the Min estuary attract many types of fish and make the Min estuary an important fishery resource. The Min estuary is currently an important economic area with increasing industrialization, urbanization, population growth and rapidly developing agricultural practices (Yue et al. 2015; Gao et al. 2017), which pose a major challenge to the ecological health of the estuarine ecosystem. However, there is still a substantial lack of detailed information regarding the quantitative composition and seasonal variation of the fish fauna in the Min estuary, as well as the internal mechanism as to how the structure is maintained. The main objectives of the present work were: 1) to describe the composition and species diversity of the fish community; 2) to identify dominant species based on their abundance, biomass and seasonal turnover; 3) to explain the seasonal variation of the fish community through interspecific relationships and ecological niche overlap among dominant species.
The study was carried out in the brackish area (25°50’00”–26°20’00”N; 119°30’00”–120°00’00”E) of the Min estuary (Fig. 1). The climate of the area is characterized by a typical subtropical monsoon with seasonal variations. The mean annual temperature is 19.85°C with a range of 9.8–32.2°C (Hu et al. 2017). The mean annual discharge of the Min River is 1760 m3 s−1, with a seasonally uneven distribution as a maximum value occurs in April–July (average 3200 m3 s−1) and a minimum in October–March (average 620 m3 s−1; Yang et al. 2007; Hu et al. 2014). The mean depth of the river is 3 m upstream and the maximum depth is 30 m downstream (Zhang et al. 2015). The tide is irregular and semi-diurnal, and salinity significantly increases when the runoff drastically decreases (Fang et al. 2017).
Sketch map of the study area (the Min estuary, southeastern China) with the sampling sites as solid circles
Fish surveys were performed seasonally (May in spring, August in summer, November in autumn and February in winter) at 11 sampling locations in 2015 (Table 1). Bottom trawling was used (horizontal aperture 7.5 m, vertical opening height 3 m, deploy distance 45 m, and mesh size 63 mm at the net opening and 25 mm at the cod end). The net was operated for half an hour at each sampling site at a towing speed of approximately 3.3–4.3 knots (corresponding to 6.02–7.85 km h−1) to collect fish. Samples from each site were put into an ice container by site groupings for preservation and sent to the laboratory for further analysis. Species were taxonomically identified according to the monographs “Fishes of the Fujian Province” (Part I, II; Fishes of the Fujian Province Editorial Subcommittee, 1984; 1985), and scientific names were checked against
Geological and environmental information on sampling locations in different seasons in the Min estuary
Location | Latitude | Longitude | Water temperature | Salinity | Water depth | |||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Spring | Summer | Autumn | Winter | Spring | Summer | Autumn | Winter | Spring | Summer | Autumn | Winter | |||
1 | 26.189 | 119.652 | 20.8 | 26.2 | 21.9 | 14.9 | 28.0 | 29.5 | 29.1 | 27.5 | 11.2 | 10.5 | 10.7 | 10.9 |
2 | 26.240 | 119.741 | 21.0 | 27.1 | 21.9 | 14.7 | 30.3 | 32.5 | 29.4 | 31.3 | 10.2 | 13.6 | 13.2 | 11.7 |
3 | 26.288 | 119.842 | 20.4 | 26.2 | 21.5 | 15.3 | 32.2 | 33.0 | 28.2 | 33.1 | 20.8 | 18.2 | 19.9 | 19.6 |
4 | 26.111 | 119.669 | 21.7 | 26.5 | 22.6 | 15.5 | 25.8 | 29.6 | 25.6 | 27.0 | 10.6 | 11.6 | 8.2 | 9.1 |
5 | 26.121 | 119.770 | 20.9 | 27.4 | 21.8 | 16.2 | 30.3 | 31.6 | 28.9 | 32.2 | 12.7 | 11.5 | 10.0 | 13.1 |
6 | 26.131 | 119.867 | 20.9 | 25.6 | 22.7 | 15.6 | 23.8 | 32.5 | 29.0 | 34.0 | 19.7 | 23.4 | 22.3 | 22.6 |
7 | 26.040 | 119.697 | 21.1 | 27.0 | 22.6 | 14.8 | 23.7 | 25.9 | 19.8 | 27.1 | 7.3 | 7.1 | 8.2 | 9.1 |
8 | 26.018 | 119.780 | 21.2 | 27.0 | 22.7 | 14.7 | 28.5 | 31.1 | 16.1 | 32.3 | 13.1 | 12.7 | 14.8 | 15.1 |
9 | 25.987 | 119.863 | 22.2 | 26.6 | 22.5 | 13.3 | 20.7 | 31.5 | 30.0 | 36.2 | 18.3 | 22.0 | 19.0 | 17.8 |
10 | 25.931 | 119.770 | 22.1 | 27.7 | 22.5 | 13.3 | 25.5 | 31.3 | 23.7 | 31.0 | 15.7 | 16.6 | 13.7 | 14.3 |
11 | 25.850 | 119.833 | 21.1 | 26.8 | 22.6 | 13.0 | 30.8 | 34.3 | 25.3 | 33.0 | 25.6 | 24.7 | 24.3 | 24.7 |
Non-metric multi-dimensional scaling (nMDS) was performed on species biomass across sampling locations in the Min estuary. The resulting ordinations were examined for seasonal groupings that indicate potential structuring within the fish community. The non-parametric analysis ANOSIM was used to test the statistically significant (
To identify different aspects of the species diversity, the demersal fish community was analyzed employing four types of indices representing the main components of the diversity (Table 2): 1) species richness, using two indices as the number of species
Species diversity components and descriptors. xi (i = 1, 2, ..., S ) denotes the abundance of the
Component | Descriptor name | Formula | Expected properties | Reference |
---|---|---|---|---|
Richness | Species density | Standardize species richness per unit area | ||
Margelef | Adjusted species richness by |
Margelef (1958) | ||
Evenness | Pielou index | Evenness based on the Shannon-Wiener index |
Pielou (1966) | |
Heip | Sensitive to rare species | Heip (1974) | ||
Heterogeneity | Shannon-Wiener | Sensitive to rare species | Shannon and Weaver (1949) | |
Simpson diversity | Sensitive to dominant species | Simpson (1949) | ||
Taxonomy | Average taxonomic distinctness | natural extensions taxonomic of Simpson relatedness diversity including | Clarke and Warwick (1998) | |
Variation in taxonomic distinctness | Evenness of the taxonomic level distribution in the taxonomic tree | Clarke and Warwick (1998) |
Dominant species were identified with the index of relative importance
The ecological niche index, describing the n-dimensional space associated with survival and reproduction of living organisms, has been frequently used to analyze the shift of dominant species through interspecific relationship, and can be calculated as follows:
where
(Pianka 1973), where
Table 3 shows taxonomic characteristics of fish species, their abundance and biomass in different seasons. A total of 127 species belonging to 91 genera, 49 families and 14 orders were sampled. In total, 57 species were from Perciformes, accounting for about 45% of the total number of species, followed by about 10% from Clupeiformes and 9% from Pleuronectiformes. At the family level, both Sciaenidae and Gobiidae ranked first, each accounting for 8% of the total number of species, followed by Engraulidae (7%) and Tetraodontidae (7%).
List of fish with their taxonomic status, seasonal abundance and biomass in the Min estuary (-- denotes no samples)
Order | Family | Genus | Species | Spring | Summer | Autumn | Winter | ||||
---|---|---|---|---|---|---|---|---|---|---|---|
abundance (ind.) | biomass (g) | abundance (ind.) | biomass (g) | abundance (ind.) | biomass (g) | abundance (ind.) | biomass (g) | ||||
Carcharhiniformes | Carcharhinidae | -- | -- | 7 | 409.6 | -- | -- | -- | -- | ||
Rajiformes | Rhinobatidae | -- | -- | -- | -- | -- | -- | 2 | 886.2 | ||
-- | -- | -- | -- | 2 | 693.3 | -- | -- | ||||
1 | 300.0 | 3 | 455.8 | -- | -- | 1 | 351.7 | ||||
Myliobatiformes | Dasyatidae | -- | -- | -- | -- | -- | -- | 1 | 210.5 | ||
1 | 293.0 | 1 | 1468.0 | -- | -- | -- | -- | ||||
1 | 641.0 | 4 | 1478.5 | 7 | 1987.5 | -- | -- | ||||
1 | 10018.0 | -- | -- | 2 | 4339.3 | -- | -- | ||||
1 | 299.9 | -- | -- | -- | -- | -- | -- | ||||
Anguilliformes | Muraenesocidae | 26 | 1120.4 | 52 | 2951.4 | 2 | 245.7 | 7 | 226.5 | ||
Muraenidae | -- | -- | 2 | 124.6 | -- | -- | -- | -- | |||
Congridae | -- | -- | -- | -- | -- | -- | 1 | 30.0 | |||
Ophichthidae | 9 | 211.8 | 4 | 151.2 | 11 | 214.3 | -- | -- | |||
-- | -- | 6 | 131.4 | -- | -- | -- | -- | ||||
-- | -- | 31 | 707.5 | -- | -- | -- | -- | ||||
-- | -- | 2 | 61.0 | -- | -- | -- | -- | ||||
Lophiiformes | Antennariidae | -- | -- | 2 | 51.2 | -- | -- | -- | -- | ||
Gonorynchiformes | Gonorynchidae | -- | -- | 5 | 140.5 | -- | -- | -- | -- | ||
Siluriformes | Bagridae | 2 | 238.8 | -- | -- | 5 | 109.3 | 3 | 59.01 | ||
Clupeiformes | Clupeidae | 49 | 1050.6 | -- | -- | 1 | 88.3 | 6 | 158.9 | ||
20 | 312.8 | 1 | 4.5 | -- | -- | -- | -- | ||||
Pristigasteridae | 7 | 160.5 | 1 | 13.4 | 77 | 1913.2 | 4 | 150.7 | |||
Engraulidae | 110 | 1944.8 | 182 | 2829.6 | 90 | 866.2 | 1 | 3.3 | |||
211 | 2422.7 | 19 | 231.5 | 546 | 5261.7 | 1250 | 9977.8 | ||||
330 | 1020.0 | 13 | 30.5 | 255 | 2002.1 | 20 | 44.3 | ||||
7 | 72.7 | 5 | 13.5 | 15 | 147.2 | -- | -- | ||||
2 | 20.1 | -- | -- | -- | -- | 24 | 170.7 | ||||
-- | -- | -- | -- | 3 | 22.2 | -- | -- | ||||
99 | 102.4 | 8 | 21.1 | 8 | 7.3 | -- | -- | ||||
30 | 52.2 | -- | -- | -- | -- | -- | -- | ||||
Aulopiformes | Synodontidae | 1 | 3.9 | -- | -- | -- | -- | -- | -- | ||
-- | -- | 5 | 6.5 | -- | -- | -- | -- | ||||
63 | 1505.8 | 1144 | 34623.2 | 2284 | 29280.9 | 279 | 9622.1 | ||||
5 | 38.9 | -- | -- | -- | -- | -- | -- | ||||
4 | 258.2 | 56 | 2738.0 | 1 | 32.4 | 28 | 1612.3 | ||||
Scorpaeniformes | Scorpaenidae | -- | -- | 1 | 1.7 | -- | -- | -- | -- | ||
-- | -- | -- | -- | -- | -- | 10 | 157.2 | ||||
Sebastidae | 2 | 1.8 | 4 | 30.2 | 2 | 152 | -- | -- | |||
Synanceiidae | -- | -- | -- | -- | 1 | 1.0 | -- | -- | |||
Platycephalidae | -- | -- | 7 | 61.4 | -- | -- | -- | -- | |||
5 | 208.4 | 2 | 108.2 | 4 | 42.8 | 1 | 13.1 | ||||
2 | 169.9 | 4 | 52.1 | 1 | 85.2 | -- | -- | ||||
Triglidae | 328 | 2254.7 | 3 | 82.25 | -- | -- | 3 | 258.7 | |||
Mugiliformes | Mugilidae | 1 | 28.3 | -- | -- | 2 | 67.4 | -- | -- | ||
-- | -- | -- | -- | -- | -- | 2 | 35.0 | ||||
1 | 26.9 | 3 | 80.1 | -- | -- | -- | -- | ||||
Syngnathiformes | Syngnathidae | -- | -- | 1 | 0.9 | -- | -- | -- | -- | ||
Fistulariidae | -- | -- | 5 | 13.5 | -- | -- | -- | -- | |||
Perciformes | Lateolabracidae | -- | -- | -- | -- | 8 | 4273.0 | 5 | 1063.0 | ||
Leiognathidae | -- | -- | -- | -- | -- | -- | 1 | 7.04 | |||
-- | -- | 3 | 1.3 | -- | -- | -- | -- | ||||
-- | -- | -- | -- | 1 | 9.9 | -- | -- | ||||
6 | 79.37 | -- | -- | -- | -- | 3 | 22.15 | ||||
982 | 5120.7 | 1654 | 10399.9 | 299 | 1545.3 | 107 | 282.69 | ||||
Terapontidae | -- | -- | 1 | 11.1 | 2 | 30.4 | -- | -- | |||
Siganidae | -- | -- | 4 | 35.35 | -- | -- | -- | -- | |||
-- | -- | 168 | 1824.5 | -- | -- | -- | -- | ||||
Carangidae | -- | -- | 10 | 340.8 | -- | -- | -- | -- | |||
-- | -- | 141 | 2661.9 | -- | -- | -- | -- | ||||
2647 | 6918.6 | -- | -- | -- | -- | -- | -- | ||||
Sciaenidae | 1 | 32.1 | 6182 | 20174.7 | 52 | 1345.5 | -- | -- | |||
-- | -- | -- | -- | -- | -- | 7 | 31.34 | ||||
-- | -- | 3 | 71.2 | -- | -- | -- | -- | ||||
6 | 465.3 | -- | -- | 21 | 643.9 | 5 | 405.2 | ||||
17 | 1168.3 | 353 | 8112.0 | 3 | 250.8 | -- | -- | ||||
1 | 100.7 | -- | -- | -- | -- | -- | -- | ||||
1 | 51.9 | 2 | 199.2 | -- | -- | -- | -- | ||||
6 | 149.3 | 81 | 4839.3 | 54 | 1116.6 | -- | -- | ||||
130 | 3563.6 | 38 | 334.0 | 228 | 4161.3 | 544 | 12549.7 | ||||
1 | 71.6 | -- | -- | -- | -- | -- | -- | ||||
Sparidae | -- | -- | -- | -- | -- | -- | 1 | 428.5 | |||
357 | 1268.6 | 122 | 1601.0 | -- | -- | -- | -- | ||||
1 | 218.9 | -- | -- | -- | -- | -- | -- | ||||
-- | -- | 6 | 401.8 | -- | -- | -- | -- | ||||
Priacanthidae | -- | -- | 156 | 2488.4 | -- | -- | -- | -- | |||
Apogonidae | -- | -- | -- | -- | 4 | 7.3 | -- | -- | |||
1 | 15.0 | -- | -- | 4 | 8.2 | -- | -- | ||||
Hapalogenyidae | -- | -- | 1 | 3.8 | -- | -- | -- | -- | |||
1 | 11.0 | -- | -- | -- | -- | -- | -- | ||||
Callionymidae | -- | -- | 17 | 148.0 | -- | -- | -- | -- | |||
-- | -- | 3 | 21.5 | -- | -- | -- | -- | ||||
Uranoscopidae | -- | -- | 3 | 105.5 | -- | -- | -- | -- | |||
-- | -- | -- | -- | 1 | 47.9 | -- | -- | ||||
Mullidae | -- | -- | 1524 | 15023.7 | -- | -- | 1 | 17.3 | |||
Sphyraenidae | -- | -- | 6 | 203.4 | -- | -- | -- | -- | |||
Sillaginidae | 2 | 116.1 | 31 | 175.7 | 4 | 149.2 | 26 | 854.8 | |||
Stromateidae | -- | -- | 4 | 190.0 | -- | -- | -- | -- | |||
-- | -- | 10 | 500.6 | -- | -- | -- | -- | ||||
303 | 2227.8 | 24 | 2412.7 | 15 | 2391.2 | 3 | 45.5 | ||||
-- | -- | 25 | 1108.1 | -- | -- | -- | -- | ||||
Centrolophidae | 59 | 405.1 | 124 | 4162.3 | -- | -- | -- | -- | |||
Trichiuridae | -- | -- | 8 | 468.5 | 2 | 21.5 | -- | -- | |||
1 | 31.6 | 151 | 7776.8 | 20 | 488.2 | 9 | 356.3 | ||||
Polynemidae | -- | -- | 13485 | 30886.6 | 1929 | 13965.1 | -- | -- | |||
-- | -- | -- | -- | 3 | 234.5 | -- | -- | ||||
Scombridae | -- | -- | -- | -- | 3 | 2056.1 | 6 | 3987.0 | |||
16 | 106.3 | -- | -- | -- | -- | -- | -- | ||||
Gobiidae | 3 | 33.6 | -- | -- | -- | -- | -- | -- | |||
448 | 2452.1 | 70 | 149.7 | 436 | 1899.4 | 160 | 1169.6 | ||||
2 | 25.8 | -- | -- | -- | -- | 2 | 29.7 | ||||
9 | 108.4 | 60 | 593.9 | 8 | 80.2 | 81 | 840.3 | ||||
67 | 1081.7 | 12 | 40.8 | 5 | 26.8 | 1 | 4.5 | ||||
3 | 13.4 | -- | -- | -- | -- | -- | -- | ||||
2 | 13.0 | -- | -- | -- | -- | -- | -- | ||||
-- | -- | -- | -- | -- | -- | 2 | 29.7 | ||||
Pleuronectiformes | Paralichthyidae | -- | -- | 15 | 661.3 | -- | -- | -- | -- | ||
1 | 144.9 | -- | -- | -- | -- | -- | -- | ||||
1 | 15.7 | -- | -- | -- | -- | -- | -- | ||||
Pleuronectidae | 1 | 4.2 | -- | -- | -- | -- | -- | -- | |||
Cynoglossidae | -- | -- | 7 | 71.5 | -- | -- | -- | -- | |||
233 | 8567.4 | 352 | 4290.4 | 145 | 2820.1 | 276 | 6396.6 | ||||
-- | -- | -- | -- | -- | -- | 1 | 23.3 | ||||
2 | 29.0 | -- | -- | -- | -- | 10 | 227.7 | ||||
1 | 9.9 | -- | -- | -- | -- | 1 | 4.3 | ||||
8 | 450.3 | 35 | 1899.2 | 6 | 500.5 | 9 | 631.03 | ||||
Soleidae | -- | -- | 19 | 191.1 | -- | -- | -- | -- | |||
Monacanthidae | -- | -- | 78.6 | 328.3 | -- | -- | -- | -- | |||
-- | -- | 5 | 33.5 | -- | -- | -- | -- | ||||
Tetraodontidae | 4 | 118.6 | 4 | 23.9 | -- | -- | 5 | 132.6 | |||
-- | -- | -- | -- | 2 | 38.7 | -- | -- | ||||
7 | 195.4 | 352 | 3805.1 | 65 | 2333.0 | 11 | 252.1 | ||||
-- | -- | -- | -- | -- | -- | 2 | 280.7 | ||||
-- | -- | 1 | 9.9 | -- | -- | -- | -- | ||||
-- | -- | -- | -- | 5 | 1296.0 | -- | -- | ||||
-- | -- | 12 | 397.5 | -- | -- | -- | -- | ||||
-- | -- | -- | -- | -- | -- | 3 | 430.79 | ||||
-- | -- | 616 | 13003.2 | 22 | 1714.7 | -- | -- |
As far as the seasonal aspect is concerned, 64 species were sampled in spring and their number increased to 78 species in summer, then decreased to 49 species in autumn and 46 species in winter. In the non-metric multi-dimensional scaling analysis and the similarity test ANOSIM, the taxonomic composition of fish communities in different seasons could be effectively distinguished (
Non-metric multi-dimensional scaling ordination of the sampling locations in the Min estuary in 2015, ordered according to fish abundance (left) and biomass (right) recorded in each season
Table 4 shows eight diversity indices for different seasons. The two species-richness indices show a significant correlation at 0.823. They were not correlated with other indices, except for
Plots of correlations of different diversity indices
Seasonal variation in multi-component diversity indices of the fish community in the Min estuary
Spring | Summer | Autumn | Winter | ||
---|---|---|---|---|---|
Species richness | 64 | 78 | 49 | 46 | |
7.137 | 7.547 | 5.452 | 5.643 | ||
Evenness | 0.556 | 0.401 | 0.515 | 0.503 | |
0.144 | 0.061 | 0.134 | 0.123 | ||
Heterogeneity | 2.311 | 1.745 | 2.005 | 1.924 | |
1 − λ | 0.811 | 0.688 | 0.782 | 0.757 | |
Taxonomy | Δ+ | 78.556 | 58.159 | 74.553 | 73.279 |
˄+ | 96.900 | 84.564 | 95.342 | 96.832 |
The dominant species in the Min estuary showed seasonal variability. The species
Seasonal variation of dominant species in the fish community in the Min estuary
Table 5 shows all Pianka values of niche overlap among the dominant species in each season. In spring, there were four pairs showing a high niche overlap, including
Pianka values (%) of the overlapping ecological niche of dominant species in different seasons
Species | Season | ||||||||
---|---|---|---|---|---|---|---|---|---|
spring | 1.11 | 0.26 | 1.46 | 99.93 | 25.54 | 47.18 | |||
summer | 33.63 | 54.28 | 61.96 | 21.79 | 67.94 | 13.75 | 20.40 | ||
autumn | 2.01 | 2.39 | 59.23 | 15.82 | 5.85 | 1.95 | |||
winter | 33.46 | 34.99 | 21.90 | 24.35 | 23.56 | ||||
spring | 87.28 | 90.83 | 0.73 | 12.24 | 19.59 | ||||
summer | 13.26 | 41.35 | 94.70 | 17.54 | 4.63 | 5.07 | |||
autumn | 8.39 | 53.11 | 19.31 | 19.24 | 23.54 | ||||
winter | 37.48 | 80.08 | 3.39 | 2.12 | |||||
summer | 29.78 | 0.91 | 51.16 | 59.84 | 19.48 | ||||
autumn | 0.47 | 3.06 | 37.21 | 37.00 | |||||
spring | 93.40 | 0.00 | 2.65 | 14.49 | |||||
summer | 32.16 | 14.34 | 8.87 | 15.31 | |||||
autumn | 11.99 | 0.00 | 1.20 | ||||||
winter | 54.67 | 1.63 | 0.86 | ||||||
spring | 0.92 | 16.79 | 10.90 | ||||||
summer | 14.95 | 0.27 | 0.12 | ||||||
autumn | 6.39 | 7.22 | |||||||
winter | 0.88 | 0.00 | |||||||
spring | 24.14 | 45.23 | |||||||
summer | 19.86 | 0.12 | |||||||
autumn | 21.41 | ||||||||
spring | 28.13 | ||||||||
summer | 18.21 | ||||||||
winter | 99.99 |
The Min estuary is an important fishing area with a density of 997.36 kg km−2 of fish biomass, higher than that in coastal waters of the East China Sea (884.72 kg km−2) and the Bohai Sea (275.30 kg km−2), and lower than in the Yellow Sea (2323.57 kg km−2; Huang et al. 2010). The Min estuary also borders on the famous eastern Mindong Fishing Ground and the southern Minnan-Taiwan Bank Fishing Ground with higher productivity in China, providing an important place for migratory fish species, e.g.
In 2015, a total of 127 fish species were sampled in the Min estuary, which is more than 77 species sampled in the Yellow River estuary in 1959–2011 (Shan et al. 2013) and 62 species sampled in the Yangtze estuary in 2010–2011 (Shi et al. 2014). Unlike the temperate character of the Yangtze and Yellow River estuaries, the Min estuary is subtropical with a higher water temperature, which supports higher species richness. In terms of taxonomic composition, Engraulidae were the common dominant family in fish catches in the Yellow River estuary during all years of sampling (Shan et al. 2013), similar to the Min estuary. Furthermore, Sciaenidae comprising more subtropical species also dominated in the fish community from the Min estuary, e.g.
Biotic factors also play an important role in the estuarine fish community. Large seasonal environmental differences in a subtropical estuary lead to changes in seasonal composition. The content of nitrogen and phosphorus in the Min estuary was high, adjusted by diluted water of the Min River. As a phosphorus-limited eutrophicated estuary, phosphorus showed a relatively higher value in autumn and winter than spring and summer (Zheng 2010). Chlorophyll
Species diversity is a multi-component concept to expound thoroughly the biological and ecological characters of fish communities (Purvis & Hector 2000). Our results show not only that a single diversity descriptor cannot provide a complete description of species diversity, but also that in some cases it cannot even encapsulate a complete description of a specific diversity component. In addition, some of the descriptors considered complementary according to theoretical works proved to be redundant.
Estimates of the number of species (
In the Min estuary,
The taxonomic diversity is expected to allow for taxonomic relationships between individuals and thus to provide additional information to classical species diversity indices. The loss of taxonomic diversity of fish can lead to a loss of ecological responsiveness to environmental fluctuations and a loss of ecological functions providing goods and services to ecosystems ( Miranda et al. 2005; Ramos-Miranda et al. 2005). To simply show the meaning of taxonomy and the evolution of fish in a sampling area, presence/absence data would be better to avoid any disturbance resulting from abundance and biomass. In our study, in addition to the negative correlation between the two taxonomic indices at −0.6708, they were independent of other indices and should be used in biodiversity conservation.
The
In summer, after finishing their persistent migration,
In autumn, half of the
In winter,