temporal and spatial variation of fish assemblages in dianshan lake, shanghai, china

Chinese Journal of Oceanology and LimnologyVol. 32 No. 4, P. 799-809, 2014http://dx.doi.org/10.1007/s00343-014-3193-4

Temporal and spatial variation of fi sh assemblages in Dianshan Lake, Shanghai, China*

HU Zhongjun (胡忠军) 1 , WANG Siqing (王思卿) 1 , WU Hao (吴昊) 1 , CHEN Qingjiang (陈庆江) 2 , RUAN Renliang (阮仁良) 2 , CHEN Liqiao (陈立侨) 3 , LIU Qigen (刘其根) 1 , ** 1 Key Laboratory of Freshwater Fishery Germplasm Resources , Ministry of Aqriculture of China , Shanghai Ocean University ,

Shanghai 201306 , China 2 Shanghai Water Authority , Shanghai 200040 , China 3 School of Life Science , East Normal University , Shanghai 200062 , China

Received Jul. 22, 2013; accepted in principle Sep. 16, 2013; accepted for publication Jan. 9, 2014 © Chinese Society for Oceanology and Limnology, Science Press, and Springer-Verlag Berlin Heidelberg 2014

Abstract Using multi-mesh gillnets and trawls, the fi sh communities in Dianshan Lake at 6 stations from Oct. 2009 to Jul. 2010 were investigated seasonally to reveal the biodiversity and its spatial and temporal distribution patterns. The long-term changes in their structural characteristics were then analyzed to identify the main infl uencing factors and several measures for lake restoration were put forward. Thirty six species, belonging to 9 family and 30 genera, were collected, amongst which, the order Cypriniformes accounted for 61.1% of the total species number. In terms of importance value, Cypriniformes was the predominant group, Coilia nasus the dominant species, while Cyprinus carpio and Rhinogobius giurinus were the sub-dominant taxa. The community types did not differ among stations, but between seasons. There were no signifi cant differences between seasons and among stations in species diversity, but richness differed both spatially and seasonally. Along with the process of eutrophication and the drastic reduction of the area colonized by macrophytes from 1959 to 2009–2010, the fi sh diversity declined markedly, and species numbers of herbivores and piscivores declined proportionately more than those of invertivores, omnivores, and planktivores. The decline of potamophilus and river-lake migratory fi sh was more marked than those of sedentary, river-sea migratory, and estuarine fi shes. Eutrophication concomitant with sharp reduction of macrophyte area and overfi shing may be the main reasons for the decline in fi sh diversity in Dianshan Lake.

Keyword : fi sh community; biodiversity; spatiotemporal change; feeding functional group; ecological group

1 INTRODUCTION

Fish are a key component of lake ecosystems, playing an important role in primary production regulation, nutrient regeneration and cycling, and energy fl ow (Sarvala et al., 1998). They can also refl ect long-term changes in the trophic state of water bodies (Jeppesen et al., 2000), and are frequently used as biological indictors of aquatic ecosystem health (Ibarra et al., 2003).

Dianshan Lake, one of the important drinking water sources of Shanghai Municipality, is the largest natural freshwater lake in the city. Its water quality bears on the health of local people and on the development of agriculture and industry. Water quality has deteriorated from grade 2 to grade 4–5 of

the Chinese surface water quality standard (Ha et al., 2009), cyanobacterial blooms have occurred every year since 1985 (Ruan and Wang, 1993), and presently macrophytes, which covered the whole lake in 1959, have almost disappeared (Shi et al., 2011), so the function as a drinking water source for the city have deteriorated. Recently, a series of management measures has been adopted to guarantee drinking-

* Supported by the Science and Technology Commission of Shanghai Municipality (Nos. 08DZ1203101, 08DZ1203102), the Shanghai University Knowledge Service Platform, Shanghai Ocean University Aquatic Animal Breeding Center (No. ZF1206), and the Open Project of Key Laboratory of Freshwater Biodiversity Conservation and Utilization, Certifi cated by Ministry of Agriculture of China ** Corresponding author: [email protected]

800 CHIN. J. OCEANOL. LIMNOL., 32(4), 2014 Vol.32

water safety, such as banning of cage culture and controlling polluting discharges. Meanwhile, many projects to control blue-green algae blooms, and for ecological restoration have been launched, while investigations on water chemistry, hydrobiological ecology and energy fl ows of the ecosystem have started in large numbers (Sun et al., 2007; Cheng and Li, 2008; Lu et al., 2010; Feng et al., 2011; Shi et al., 2011; Wang et al., 2011).

Biomanipulation based on top-down effects by fi sh is widely applied to control eutrophication and blue-green algae blooms (Zhong et al., 2001). The water quality of shallow lakes improves when fi sh community structure is reasonably reestablished (Meijer et al., 1994), such as by stocking phytoplanktivorous fi sh or piscivorous fi sh to successfully control phytoplankton and rehabilitate lake system. It is thus important to determine the composition of the fi sh assemblage in Dianshan Lake for water quality management and ecosystem rehabilitation. In this study, we investigated the fi sh community of the lake at 6 sites in 4 seasons. The objective of our study is to reveal the current biodiversity and its spatial and temporal distribution patterns for the fi sh community in Dianshan Lake, which could not only serve as a good indicator of the variation of lake ecosystem over the recent decades, but also provide a fundamental database and sound theoretical support for the protection of fi sh diversity

and future management of the fi sheries and water quality of this lake.

2 MATERIAL AND METHOD

2.1 Study area

Dianshan Lake (31°04′–31°12′N, 120°54′–121°01′E), a tidal fresh-water lake, is located at the boundaries of Zhejiang and Jiangsu Provinces, and Shanghai City. It is co-administered by Kunshan City of Jiangsu and Qingpu District of Shanghai. It is situated in the lower reaches of Taihu Lake watershed, with an area of 63 km 2 and a mean water depth of 2.1 m (maximum water depth 3.6 m), while it is connected with the Changjiang (Yangtze) River Estuary through Huangpu River (length 113 km). Jishui Port and Dazhushe are the two main water inlets, contributing about 35% and 33% of the total infl ows, respectively. Lanlu Port is the main drainage outlet, accounting for about 71% of the total outfl ow. Dianshan Lake has a subtropical, monsoon climate, with an annual mean air temperature of 15.5°C and precipitation of 1 037.7 mm (You, 1994; Cheng and Li, 2008).

2.2 Fish sampling

A combination of trawling and multi-mesh gillnetting was used to sample fi sh communities seasonally (Jan., Apr., Jul., and Oct.) from Oct. 2009 to Jul. 2010 at 6 stations (S1: Wangyang basin, S2: Transect of provinces; S3: West-northern playground; S4: Jishui Port; S5: Lanlu Port; S6: Southern basin) (Fig.1) in Dianshan Lake. At each station, the benthic gillnets (about 25 m long panels of 6 mesh-sizes (2, 4, 6, 8, 10, and 12 cm) and height of 1–1.5 m) were set on the bottom. The nets were set at 03:30–05:30, and raised after 2 h. A bottom trawl, with mesh size of 1.8 cm, net width of 3.6 m, and net height of 1.4 m, was towed just after set-down of the gillnets, and the length of the trawled transects ranged from 750–850 m at each station. Gillnet setting and trawling were both conducted once at each location. Based on the fi nding of Zhou et al. (2010), Coilia brachygnathus was considered the senior synonym of Coilia nasus . All other fi sh caught were identifi ed according to East China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences and Shanghai Fisheries Research Institute (1990) and Ni and Zhu (2005); they were measured for body length (BL, cm±0.1) and total weight (W, g±0.1).

31°1

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Wusong RiverChangjiang River estuaryDianshan Lake

Huangpu River

31°1

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″31

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Lanlu Port

Jishui Port

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Dianshan Lake

E

S5

S6

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Sampling site

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Fig.1 The fi shing stations in Dianshan Lake

801No.4 HU et al.: Temporal and spatial variation of fi sh assemblages of Dianshan Lake

2.3 Calculation of importance value and clustering analysis

Dominant species were determined by importance value (IV) of each species, calculated using all the data. The spatial and temporal variation of dominant species and community types was determined from IV based on stations and seasons, respectively. IVs were calculated by averaging the relative number (RN), the relative weight (RW), and the relative frequency (RF) (Brower and Zar, 1977; Velázquez-Velázquez et al., 2008). Based on data from IV, fi sh communities were clustered seasonally and spatially, respectively, using un-weighted pair group method with arithmetic averaging (UPGMA) (Velázquez-Velázquez et al., 2008). All data used in cluster analysis were SUM-standardized, and d (1–Pearson correlation coeffi cient) was selected as a measure of similarity in cluster analysis (Hu et al., 2009).

2.4 Biodiversity

Margalef species richness ( r ), Shannon-Wiener species diversity ( H ' ), Simpson’ measure of evenness ( E a ), and Simpson’ dominance index ( λ ) were calculated for each station in each month to explore the seasonal and spatial variation of these indices. The equations used to calculate these four indices are as follows (Ma et al., 1995; Smith and Wilson, 1996;

Zhang, 2004): r =( S –1)/ln N , H' =Σ( n i / N )ln( n i / N ), E 1/D =

(1/ λ )/ S , ( 1)( 1)

i in nN N

, where S , n i , and N denote

species number, abundance of each species, and total abundance of all species at each station in each month, respectively. The differences of each index among stations and between seasons were tested by one-way ANOVA followed by Duncan’s multiple range tests ( P <0.05). All fi sh data were combined to calculate the four indices mentioned above in order to compare them with historical data.

2.5 Functional feeding groups (FFGs) and ecological groups (EGs)

The classifi cations of species into functional feeding groups and ecological groups mainly followed three publications reporting fi sh communities in Shanghai (Chen et al., 2008; Xia et al., 2009; Yue et al., 2010), with modifi cations for Sarcocheilichthys nigripinnis , Hyporhamphus intermedius , Pseudorasbora parva , Toxabramis swinhonis , Rhinogobius giurinus , Squalidus sihuensis , Acheilognathus chankaensis

(Zhang, 2005), for C . nasus (Liu et al., 2007; Ye et al., 2007), for Pelteobagrus fulvidraco and Pelteobagrus nitidus (Yuan, 2010) because the respective investigations had been designed for particular diets of the fi shes concerned. Moreover, our unpublished data about fi sh diet supported the above revisions for C . nasus , P . nitidus , and R . giurinus .

3 RESULT

3.1 Fish composition

A total of 4 771 fi sh specimens weighing about 80 kg were collected, belonging to 36 species, representing 30 genera, 14 families, and 9 orders (Tables 1 and 2). Of these, Cypriniformes showed the largest number of species, 22 (61.1% of the total). The Perciformes followed with 6 species (16.7%) and the Siluriformes with 2 species (5.6%). The remaining 6 orders had only one species each (2.8%) (Table 1). The Cypriniformes dominated in terms of IV, representing 51.74% of the total IV, followed by Clupeiformes (27.52%), Perciformes (11.87%) and Siluriformes (6.11%). The IV proportion contributed by each of the other orders was lower than 1.07% (Table 1).

Coilia nasus was the most abundant species (54.5%), followed by R . giurinus (19.1%), and the relative abundance of each of the other 34 species was lower than 7.4%. Cyprinus carpio , C . nasus , and Hypophthalmichthys molitrix contributed with amounts as large as 33.7%, 18.1%, and 16.5% of the total biomass, respectively, while the catch weight proportion of each of the other 33 species was lower than 7.8% (Table 2). In terms of IV, C . nasus was the dominant species, accounting for 27.52% of the total IV, while C . carpio (12.21%) and R . giurinus (10.29%) were subdominant. The common species included Acheilognathus taenianalis , Cultrichthys erythropterus , Carassius auratus , Pseudobrama simoni , Hypophthalmichthys molitrix , and P. nitidus , the IVs of which ranged from 3.1 to 7.2. The other 27 species including Neosalanx taihuensis , Anguilla japonica , Abbottina rivularis , Hemiculter leucisculus , Culter alburnus , Liza haematocheila , Siniperca chuatsi , and Callionymus olidus were rare species, the IVs of which were all lower than 2.0 (Table 1).

3.2 Spatial and temporal variation of the fi sh community

Cluster analysis of seasons pooled for the whole


Table 1 Species list of fi sh and seasonal changes of their importance values in Dianshan Lake from Aug. 2009 to Jul. 2010

Order Family Species name Importance value

FFG EG Total Spring Summer Autumn Winter

Clupeiformes Engraulidae Coilia nasus 27.52 17.60 40.64 29.28 34.53 PL ES

Salmoniformes Salangidae Neosalanx taihuensis 1.06 0.56 0.59 0 3.58 PL SE

Anguilliformes Anguillidae Anguilla japonica 0.57 1.29 0 0.74 0 PI RS

Cypriniformes Cyprinidae 51.74 60.81 43.36 54.14 36.98

Acheilognathus taenianalis 6.10 9.26 8.69 5.48 2.62 PL SE

Abbottina rivularis 0.16 0 0 0 0.80 OM SE

Hemiculter leucisculus 0.32 0 0 1.12 0 OM SE

Pseudolaubuca engraulis 0.83 0 2.71 1.24 0 OM SE

Sarcocheilichthys nigripinnis 0.59 1.49 0 0.73 0 OM SE

Cultrichthys erythropterus 3.38 1.17 6.01 4.64 3.90 PI SE

Hemibarbus maculatus 1.89 3.80 3.44 0.88 0 IN SE

Sarcocheilichthys sinensis 0.68 1.41 1.19 0 0 IN SE

Carassius auratus 5.23 3.06 7.23 7.04 5.75 OM SE

Cyprinus carpio 12.21 21.10 0.88 3.67 7.92 OM SE

Hypophthalmichthys molitrix 7.19 5.81 4.76 13.93 2.64 PL RL

Pseudorasbora parva 0.29 0 0.6 0 0.74 PL SE

Culter mongolicus mongolicus 0.15 0 0 0 0.76 PI SE

Culter alburnus 0.75 0.57 0 1.22 1.22 PI SE

Culter dabryi dabryi 1.99 2.20 0 1.78 4.12 PI SE

Pseudobrama simoni 3.11 2.92 0.72 6.01 2.23 OM RL

Toxabramis swinhonis 1.12 0 0.75 2.25 1.59 OM SE

Squalidus sihuensis 0.90 1.16 0 0.62 1.93 IN SE

Acheilognathus chankaensis 0.77 0 2.49 0.57 0.00 OM SE

Aristichthys nobilis 1.56 3.98 0 0 0 PL RL

Hemiculter bleekeri 1.29 0.59 3.10 1.37 0.76 OM SE

Cobitidae Misgurnus anguillicaudatus 1.23 2.29 0.79 1.59 0.00 OM SE

Siluriformes Bagridae 6.11 8.2 5.75 5.77 5.25

Pelteobagrus nitidus 5.55 6.81 5.75 5.22 5.25 IN SE

Pelteobagrus fulvidraco 0.56 1.39 0 0.55 0 IN SE

Beloniformes Hemiramphidae Hyporhamphus intermedius 0.84 0 0.68 0.51 2.59 IN ES

Mugiliformes Mugilidae Liza haematocheila 0.16 0 0 0.54 0 OM ES

Perciformes 11.87 10.97 9.00 9.01 17.05

Taenioididae Taenioides cirratus 0.48 0 2.09 0 0 IN ES

Serranidae Siniperca chuatsi 0.46 0 0.69 1.04 0 PI SE

Lateolabrax japonicus 0.17 0 0.79 0 0 PI ES

Eleotridae Odontobutis obscura 0.15 0 0 0.51 0 PI SE

Gobiidae Rhinogobius giurinus 10.29 10.97 5.43 6.35 17.05 IN SE

Callionymidae Callionymus olidus 0.32 0 0 1.11 0 IN ES

Pleuronectiformes Cynoglossidae Cynoglossus gracilis 0.15 0.57 0 0 0 OM ES

FFG: feeding functional group (HE: herbivores; OM: omnivores; PL: planktivores; IN: invertivores; PI: piscivores); EG: ecological group (SE: sedentary; PO: potamophilus; ES: estuarine; RS: river-sea migratory; RL: river-lake migratory).


year produced two distinct groups. The fi rst group consisted of summer, autumn, and winter samples (Fig.2), named as the C . nasus community. The second part consisted of the spring sample, named as the C . carpio + C . nasus community. However, a cluster analysis of stations pooled for the whole year yielded no distinct groupings (Fig.3), which all fell in the C . nasus community.

3.3 Analysis of functional feeding groups and ecological groups

This study has shown that there are now (2009–2010) 4 functional feeding groups in Dianshan Lake, consisting of 13 invertivorous, 10 omnivorous, 8 piscivorous, and 5 planktivorous species, accounting for 36.1%, 27.8%, 22.2%, and 13.9% of the total species number, respectively (Table 1 and Fig.4a). There is no longer a herbivorous group. Classed according to ecological group, there are 1, 3, 7, and 25 species of river-sea migratory, river-lake migratory, estuarine, and sedentary fi sh, accounting for 2.8%, 8.3%, 19.4%, and 69.4% of the total species number, respectively (Table 1 and Fig.4b).

From 1959 to 2009–2010 the species diversity decreased for all the functional feeding groups. The largest decrease was in the herbivores (3 species in 1959 to zero at present, 100% of decreasing proportion), then piscivores (18 to 8 species, 55.6%), planktivores (7 to 5 species, 28.6%), insectivores (17 to 13 species, 23.5%) and omnivores (12 to 10 species, 16.7%) (Fig.4a). The number of species of sea-lake migratory and estuarine fi sh remained stable, and the other three ecological groups all declined: the three potamophilus fi shes occurring in

1959 have all disappeared and the number of species of river-lake migratory and sedentary fi sh has decreased by 66.7% (9 species in 1959 to 3 species at present) and 32.4% (37 to 25 species), respectively (Fig.4b).

Winter0.05

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ance 0.25

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Autumn Summer Spring

Fig.2 Dendrogram of seasonal fi sh communities in Dianshan Lake from Aug. 2009 to Jul. 2010

0.04S1 S3 S4 S6 S2 S5

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0.14

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Fig.3 Dendrogram of spatial fi sh communities in Dianshan Lake from Aug. 2009 to Jul. 2010

0

10

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40

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60

1959 2009–2010

Spec

ies n

umbe

r

HE OM PL IN PI

0

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20

30

40

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1959 2009–2010

Spec

ies n

umbe

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SE PO ES RS RLb

a

Fig.4 Composition of feeding functional groups (a) and ecological groups (b) in the fi sh community in Dianshan Lake from Aug. 2009 to Jul. 2010 SE: sedentary; PO: potamophilus; ES: estuarine; RS: river-sea migratory; RL: river-lake migratory; HE: herbivores; OM: omnivores; PL: planktivores; IN: invertivores; PI: piscivores. The data in 1959 are compiled in terms of reference (Shanghai Fisheries College, 1960).


3.4 Temporal and spatial variations in biodiversity

One-way ANOVA showed that there are signifi cant differences in species richness between seasons, which is conspicuously higher in spring, summer and autumn than in winter ( P <0.05). The other diversity indices did not differ among seasons (Table 3).

Species diversity, evenness and dominance index as well as water depth displayed no spatial difference, however the number of species and species richness did (One-way ANOVA). Multiple comparison showed that number of species at S3 and S6 is signifi cantly higher than at the other 4 stations ( P <0.05), whereas species richness at S6 is conspicuously larger than at S1, S2 and S4 ( P <0.05), and there are no differences between the other two stations ( P >0.05) (Table 4).

3.5 Long-term changes in the diversity of fi sh assemblage and species composition

From 1959 to 2006, 6 fi sh investigations showed that both genera and species number exhibited decreasing trends. The genera and species numbers in 2006 were equal to or less than one-third of those in 1959, which in 2009–2010 increased by 66.7% and 56.5%, respectively, compared with those in 2006 (Table 5). Diversity (Shannon-Weaver) and evenness (Pielou) both declined from 1959 to 2006 until 2009–2010. Species richness (Magalef) decreased signifi cantly from 1959 to 2006, but increased by 42.6% from 2006 to 2009–2010 (Table 6).

The proportion of the total catch decreased in Dianshanhu Lake for piscivores [mandarinfi sh

Table 2 Capture details of the main fi shes in Dianshan Lake from Aug. 2009 to Jul. 2010

Species Number (ind.) Number proportion (%) Weight (g) Weight proportion (%)

Acheilognathus taenianalis 350 7.3 2 469.9 3.1

Coilia nasus 2 602 54.5 14 445.7 18.1

Pseudolaubuca engraulis 16 0.3 411.8 0.5

Pelteobagrus nitidus 248 5.2 2 207.1 2.8

Cultrichthys erythropterus 40 0.8 2 480.1 3.1

Hemibarbus maculatus 57 1.2 1 254.4 1.6

Carassius auratus 85 1.8 6 136.6 7.7

Cyprinus carpio 19 0.4 26 898.6 33.7

Hypophthalmichthys molitrix 25 0.5 13 165.5 16.5

Culter alburnus 17 0.4 511.9 0.6

Culter dabryi dabryi 71 1.5 1 598.5 2.0

Pseudobrama simoni 129 2.7 1 660.9 2.1

Toxabramis swinhonis 12 0.3 174.2 0.2

Rhinogobius giurinus 912 19.1 1 474.8 1.9

Other fi shes 188 3.9 4 836 6.1

Total 4 771 100 79 726 100

Table 3 Seasonal changes in biodiversity of fi sh assemblages in Dianshan Lake

Season S r H ′ E a λ

Winter 7.8±1.7 1.206±0.241 b 0.959±0.123 0.310±0.058 0.524±0.065

Spring 10.5±1.5 1.901±0.229 a 1.530±0.140 0.386±0.085 0.319±0.054

Summer 10.3±0.9 2.196±0.259 a 1.491±0.237 0.380±0.086 0.357±0.100

Autumn 11.7±1.2 2.013±0.207 a 1.161±0.212 0.211±0.038 0.507±0.099

Mean 10.1±0.7 1.829±0.135 1.285±0.100 0.322±0.036 0.427±0.043

F -value 1.413 3.400 * 2.121 1.365 1.598

Different subscripts in the second (Table 4) and third (this Table and Table 4) column denote signifi cant differences at the level of P <0.05. *: signifi cant differences at the level of P <0.05. The same as in Table 4.


( Siniperca chuatsi ) and culters (fi shes from genus of Culter and Cultrichthys )] and herbivores ( Megalobrama skolkovii ) displayed decreasing tendency. The contribution of the four Chinese carps to fi sh catch increased markedly from 1958 to 1982 and decreased from 1982 to 2009–2010, which of common carp ( Cyprinus carpio ) and golden carp ( Carassius auratus ) decreased obviously from 1958 to 1982 and increased from 1982 to 2009–2010 (Table 7).

4 DISCUSSION

Fish communities are generally closely related to habitat heterogeneity (Keast, 1978). Fish species composition and density differ in different habitats (Gaudreau and Boisclair, 1998; Xie et al., 2001; Ye et al., 2006; Li et al., 2010). Vegetation cover and water depth are two of the most important factors infl uencing spatial distribution of fi sh, such as species composition, richness and diversity (Keast, 1978; Holland and Huston, 1984; Hosn and Downing, 1994; Laffaille et al., 2001; Petry et al., 2003; Castillo-Rivera et al., 2005; Cheng et al., 2012). In Dianshan Lake, the mean water depth at each station did not differ signifi cantly and macrophytes were rare at all stations.

Similarly, there was no signifi cant difference in Carlson’s trophic state index among stations, fl uctuating from 70.7 to 73.7 (Wang, 2008). Each of our six stations are close to one of Wang’s (2008) in longitude and latitude. Therefore, we can infer that our stations probably also did not differ signifi cantly in trophic state. The fact that the species composition, Shannon-Wiener species diversity, Simpson’ measure of evenness and Simpson’ dominance index of fi sh communities did not display spatial variations likely refl ects the uniformity of physiochemical factors. However, species richness such as Margalef richness index and species number differed signifi cantly among stations in Dianshan Lake. The disagreement of spatial variation of species diversity and richness may be explained by the following reasons. On one hand, the spatial and seasonal changes of species richness of fi sh community are not always consistent with those of species diversity (Balik et al., 2011). On the other hand, species diversity and richness are related with different ecological factors. For example, Cheng et al. (2012) reported that fi sh species diversity is primarily associated with density of rotifer while its species richness is mainly affected by water depth. Therefore, further research is needed to understand the relationship between species diversity and richness and environmental factors in Dianshan Lake.

Coilia nasus and C . brachygnathus have long been regarded as two species: the former is a sea-lake migratory fi sh and the later is a land-locked species. However, Zhou et al. (2010) found that they are the

Table 4 Spatial variations in biodiversity of fi sh assemblages in Dianshan Lake

Station Water depth S r H ′ E a λ

S1 2.6±0.2 8.3±1.1 b 1.359±0.143 b 0.907±0.243 0.326±0.130 0.559±0.147

S2 2.3±0.2 8.3±1.9 b 1.454±0.373 b 1.179±0.166 0.318±0.064 0.448±0.052

S3 2.6±0.5 13.0±0.4 a 2.218±0.185 ab 1.365±0.215 0.210±0.060 0.438±0.086

S4 2.3±0.1 8.5±1.3 b 1.535±0.266 b 1.146±0.293 0.299±0.038 0.475±0.134

S5 3.0±0.5 8.5±1.3 b 1.795±0.356 ab 1.382±0.317 0.437±0.099 0.373±0.120

S6 2.3±0.2 14.0±1.5 a 2.614±0.188 a 1.732±0.122 0.341±0.118 0.266±0.056

F -value 0.806 4.083 * 3.418 * 1.395 0.643 0.879

The letters in the fi rst row denote different biodiversity indices.

Table 5 Long-term change of species and genus number in fi sh community in Dianshan Lake

Year Number of genera Species number Sources

1959 60 75 Zeng et al. (2002)

1974 47 61 Zeng et al. (2002)

1981–1982 42 62 Zeng et al. (2002)

1982–1985 44 55 Zeng et al. (2002)

1987–1988 34 45 Zeng et al. (2002)

2006 18 23 Sun et al. (2007)

2009–2010 30 36 Present study

Table 6 Long-term change of fi sh biodiversity in Dianshan Lake

Year r H ′ J λ Sources

1959 10.720 3.755 0.894 0.035 Sun et al. (2007)

2006 2.898 1.900 0.606 0.226 Sun et al. (2007)

2009–2010 4.132 1.652 0.461 0.344 Present study


same species. This species dominates the fi sh assemblages in many Changjiang River connected lakes, such as Taihu, Poyang, and Dongting Lake (Li, 1999; Ru et al., 2008; Hu et al., 2011).

We found that C . nasus also dominated in Dianshan Lake. The seasonal shift in community types might be related to the timing of reproduction in the dominant species (Kattel et al., 2007). The peak time of reproduction of C . nasus is from late April to May, which can breed until December (East China Sea Fisheries Research Institute, Chinese Academy of Fishery Sciences and Shanghai Fisheries Research Institute, 1990). Therefore, C . nasus showed higher abundance in summer, autumn, and winter than in spring, which refl ects the continuous recruitment during the reproductive period lasting from late April to December.

Diversity and abundance are generally higher in aquatic plant habitats than non-macrophyte environments (Gilliam and Fraser, 1987; Xie et al., 2001; Ye et al., 2006). Since 1959, Dianshan Lake has experienced a marked decline in the area covered by submerged plants. Submerged plants were distributed over the whole lake in 1959, their coverage had decreased by 60% by early 1990s (You, 1994), and almost completely disappeared during 2009–2010, leaving an area of only 0.4% covered (Shi et al., 2011). Concomitantly, the biodiversity of the fi sh community in Dianshan Lake has decreased progressively. Species and genera numbers, Shannon-Wiener species diversity and Margalef species richness all have declined markedly from 1959 to 2009–2010 (Tables 5 and 6; Zeng et al., 2002; Sun et al., 2007). Two herbivorous fi shes have nearly disappeared: only one individual of Ctenopharyngodon idell a was caught and no M . skolkovii was found on any of three recent investigation trips (Sun et al., 2007; Tao et al., 2011; present study). The species composition has changed dramatically in association with the process of eutrophication and the

disappearance of aquatic plants. The general pattern of change in the fi sh community of lakes undergoing eutrophication has involved a shift from numerical dominance by Salmoniformes in unproductive lakes, to a dominance by Percids in medium productive lakes, then to a dominance by Cyprinids in highly productive lakes (Persson et al., 1991). The number of Percid species, based on catch data, has decreased in Dianshan Lake from 10 in 1959 (Shanghai Fisheries College, 1960) to 6 at present. The catch proportion of S . chuatsi (one of the main commercial fi shes) has decreased from 5% in 1958 to 2% in 1974 (Cao et al., 1988) and to only 0.02% in 2009–2010; the relative abundance and biomass of Percids are now less than 19.5% and 0.3%. Meanwhile, the relative abundance and biomass of piscivores are now lower than 3.0% and 6.3%. Historical data show that Cyprinids dominated the fi sh community, accounting for 61.4% of the total species number (Shanghai Fisheries College, 1960). The biomass of S . chuatsi caught, the most economically important percid fi sh, has become very low (Table 7). A dominance shift from Salmoniformes to Percids and then from Percids to Cyprinids would not occur in the process of eutrophication and macrophyte disappearance in Dianshan Lake. However, the changes in species number and composition of functional feeding group might refl ect the long-term change in the water quality of Dianshan Lake. Deterioration of aquatic environments can generally be characterized by decrease in the species number of fi sh, the proportion of piscivores, and an increase in the proportion of omnivores (Karr, 1981; Karr et al., 1986). In Dianshan Lake, species diversity had decreased signifi cantly, the proportion of piscivores dropped from 31.6% in 1959 to 22.2% in 2009–2010, and that of omnivores had risen from 21.1% to 27.8% (Fig.4).

Construction of hydraulic engineering and river-lake isolation often destroys migratory corridors of river-lake migratory and semi-migratory fi shes, and is

Table 7 Long-term changes in the composition of fi sh catch (% of biomass) in Dianshan Lake

Year CBC and CGC /CSC and CBC MS CC CA Culters SC NT PF/PN HM Trash fi sh Sources

1958 5 - 25 20 10 5 - - - 35 Cao et al. (1988)

1974–1975 5/16 8 8 13 10 2 3 - - 35 Cao et al. (1988)

1982 45 5 4 6 - 5 - - 35 Cao et al. (1988)

2009–2010 0/19.9 0 33.7 7.7 5.8 0.02 0.07 3.1 1.6 28.1 Present study

CBC and CGC: Chinese black carp and grass carp; CSC and CBC: Chinese silver carp and bighead carp; MS: Megalobrama skolkovii ; CC: Cyprinus carpio ; CA: Carassius auratus ; Culters: fi shes from the genus of Culter and Erythroculter ; SC: Siniperca chuatsi ; NT: Neosalanx taihuensis ; PF: Pelteobagrus fulvidraco ; PN: Pelteobagrus nitidus ; HM: Hemibarbus maculatus . Symbol “-” denote that there is no data.


an important factor leading to decreases in biodiversity of fi sh assemblages (Wang et al., 2005; Ru et al., 2008). Historically, 12 river-lake migratory and potamophilus fi shes occurred in Dianshan Lake, including 4 major species of Chinese carps (black carp : Mylopharyngodon piceus , grass carp : C . idell a , silver carp : H . molitrix , and bighead carp: Aristichthys nobilis ), Myxocyprinus asiaticus , Elopichthys bambusa , Luciobrama macrocephalus , Opsariichthys bidens , Xenocypris argentea , Parabramis pekinensis , and P . simoni (Shanghai Fisheries College, 1960). However, now only 4 river-lake migratory fi shes occur in Dianshan Lake: the common species of silver carp, bighead carp, P . simoni , and a rare species ( C . idell a ), one individual caught in the recent three sampling trips (Sun et al., 2007; Tao et al., 2011; present study). However, the diversity of estuarine and river-sea migratory fi shes has not changed signifi cantly in Dianshan Lake. Dianshan Lake is a tidal lake, connected to Changjiang River Estuary via the Huangpu River, and therefore, there is no real isolation of the lake from the estuary and East Ocean. Eight river-sea migratory and estuarine fi shes were found in Dianshan Lake in 1959, including A . japonica , C . nasus , H . intermedius , L . japonicus , C . olidus , Trachidermus fasciatus , Cynoglossus gracilis , Takifugu obscurus (Shanghai Fisheries College, 1960). At present, there are still 8 sea-river migratory and estuarine fi shes (Table 1) in the Lake, plus 2 new species ( L . haematocheila and Taenioides cirratus ) found in our investigations, but 2 species ( T. fasciatus and T . obscurus ) caught in 1959 were not observed in the present study. Overfi shing is another serious threat to species biodiversity. Sun et al. (2007) reported that there are about 130 vessels licensed to fi sh and other commercial boats registered for fi shing for mollusks in Dianshan Lake. Yue et al. (2010) further put forward that illegal fi shing such as electric fi shing is also prevalent there. As a result, fi sh in this lake are confronted with high levels of overfi shing.

In summary, there were fi ve obvious changes in patterns of fi sh assemblage in Dianshan Lake from 1959 to 2009–2010, such as decreases in community diversity, species numbers of herbivores and piscivores, species number of potamophilus and river-lake migratory fi sh, and the contribution of piscivores and herbivores to fi sh catch. Environmental pollution, sharp reduction of macrophyte area and overfi shing are probably responsible for those decreasing patterns. Several measures should be taken to protect and restore fi sh diversity of the lake, such as strictly

controlling point and non-point source pollution, actively restoring aquatic plant, and effectively implementing fi sheries-management. The latter measure includes strictly cracking down on illegal fi shing, seriously implementing the closed fi shing seasons and areas, and reasonably carrying out stock enhancement based on scientifi c assessment of ecological carrying capacity.

The facts of the dominance of C . nasus as a zooplanktivores in the fi sh assemblage of 2009–2010 in term of importance value, relative abundance and biomass, and of the long-term decreases in contribution of piscivores to community richness and fi sh catch implicate that classic biomanipulation by restocking piscivores into Dianshan Lake may be an alternative tool of restoration of the lake ecosystem. Meanwhile, fi lter-feeding fi shes with ability of escape from being predated by piscivores, such as relatively large body-size Chinese silver carp and bighead carp, can be restocked into the lake to control large Cyanobacteria blue green algae.

The environmental factors cited from other reports can be used to explain the spatial distribution of fi sh composition but can’t always be applied to explain the spatial variations of different diversity indices, indicating that ecological variables should be measured during fi sh sampling to more accurately explain the relationships between structural characteristics of fi sh community and environmental variables.

5 ACKNOWLEDGEMENT

We would like to thank Professor WU Hanlin in Shanghai Ocean University for identifi cation of fi sh samples, and to thank master candidates ZHAO Liangjie and ZHANG Ying, and undergraduate LIN Zongyi, WEN Wenke, LI Xubo, and WANG Mengyang for their assistance in the fi eld sampling and laboratory dissection and measurement.

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temporal and spatial variation of fish assemblages in dianshan lake, shanghai, china

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