The spatial pattern of the small fish community in the Biandantang Lake - a small shallow lake along the middle reach of the Yangtze River, China

The spatial pattern of the small fish community was studied seasonally in 1996 in the Biandantang Lake. Based on plant cover, the lake was divided into five habitats, arranged in the order by plant structure complexity from complex to simple: Vallisneria spiralis habitat (V habitat), Vallisneria spiralis-Myriophyllum spicatum habitat (V-M habitat), Myriophyllum spicatum habitat (M habitat), Nelunbo nucefera habitat (N habitat), and no vegetation habitat (NV habitat). A modified popnet was used for quantitative sampling of small fishes. A total of 16 fish species were collected; Hypseleotris swinhonis, Ctenogobius giurinus, Pseudorasbora parva, Carassius auratus and Paracheilognathus imberis were the five numerically dominant species. In both summer and autumn, the total density of small fishes was about 10 ind m(-2). Generally, Ctenogobius giurinus, a sedatory, benthic fish, was distributed more or less evenly among the five habitats, while the other four species had lower densities in the N habitat and NV habitat, which had the simplest structures. The distribution of the small fish species showed seasonal variations. In winter, most species concentrated in the V habitat, which had the most complex structure. In spring, the fish had low densities in the N and NV habitat, and were more or less evenly distributed in the other habitats. In summer, the fish had a low density in the NV habitat, and were evenly distributed in the other habitats. In autumn, the fish had higher densities in the V-M and M habitats than in the others. Generally, spatial overlaps between the dominant species were higher in winter than in the other seasons. It was suggested that the variations in the importance of predation risk and resource competition in habitat choice determined the seasonal changes of spatial patterns in the small fishes in the Biandantang Lake.

Diet overlap between the endemic fish Anablariflus grahami(Cyprinidae) and the exotic noodlefish Neosalanx taihuensis (Salangidae) in lake Fuxian, China

We studied diet composition and overlap of the exotic noodlefish (Neosalanx taihuensis) and the endemic fish Anaborilius grahami in a deep, oligotrophic lake in the Yunnan Plateau. A. grahami dominated the fish community in Lake Fuxian before the invasion of N. taihuensis in 1982, but it is now in the process of extinction, corresponding with an explosive increase in N. taihuensis population. Schoener's index (alpha=0.773) indicate that N. taihuensis and A. grahami have significant diet overlap, with both fish feeding mainly on zooplankton. An increased proportion of littoral prey, such as Procladius spp., Coleoptera, and epiphytes, in the diet of A. grahami indicated that this endemic fish shifted its main habitat from the off-shore zone in the late 1980s to the littoral zone at the present. A difference in reproduction between the two fishes, along with the overfishing, may have exacerbated the occupation of A. grahami's pelagic niche by N. taihuensis. The endemic species has shown large competitive disadvantage for food and space in the presence of N. taihuensis.

Community structure of small fishes in a shallow macrophytic lake (Niushan Lake) along the middle reach of the Yangtze River, China

This study describes the current status of the small fish community in Niushan Lake in China, and examines the spatial and seasonal variations of the community in relation to key environmental factors. Based on macrophyte cover conditions, the lake was divided into three major habitat types: (1) Potamogeton maackianus habitat, (2) Potamogeton maackianus and Myriophyllum spicatum habitat, and (3) uncovered or less-covered habitat. Fish were sampled quantitatively in the three habitat types by block nets seasonally from September 2002 to August 2003. A total of 10 469 individuals from 27 fish species were caught, among which 20 species were considered as small fishes. Rhodeus ocellatus, Paracheilognathus imberbis, Pseudorasbora parva, Micropercops swinhonis and Cultrichthys erythropterus were recognized as dominant small fishes according to their abundance and occurrence. It was noted that (1) small fishes predominated the total number of fish species in the lake, which reflected to some degree the size diminution phenomenon of fish resources; (2) many small fishes had plant detritus as their food item, which was consistent with the abundance of macrophyte detritus in the lake and implied the importance of detritus in supporting small fish secondary production. Canonical correspondence analysis suggested that the spatial distributions of most small fishes were associated with complex macrophyte cover conditions. Macrophyte biomass was positively correlated with species richness, diversity index and the catch per unit of effort (CPUE) of the fish community. Water depth had no significant effects on species diversity and distribution of the small fishes. Correspondence analysis revealed a higher occurrence of the small fishes and higher abundance of individuals in summer and autumn. Seasonal length-frequency distributions of several species indicated that more larval and juvenile individuals appeared in spring and summer. This study provides some baseline information which will be essential to long-term monitoring of small fish communities in the Yangtze lakes.

东海北部鱼类群落多样性和结构特征变化研究

在海洋渔业资源不断衰退的今天，渔业资源管理正经历着由单种和多种资源管理向生态系统水平管理的转变。开展在各种干扰因素影响下鱼类群落演替方向的研究是引入基于生态系统渔业管理策略的必要环节，本文以东海北部海域鱼类群落为研究对象，对其近十几年来结构和功能的变化趋势进行分析，以期今后为渔业资源的科学管理提供理论基础。 捕捞是引起鱼类群落结构变化的最为重要的因素，本研究首先就捕捞对鱼类群落影响的国内外研究方法进行了综述与归纳。在研究捕捞对鱼类群落的影响时，所选用的群落参数指标应符合预期性、可测性、敏感性和排他性标准，业已利用的研究方法大致可为生物多样性、聚合特征指标、群落功能性指标、多元分析以及生态系统模型五大类。各研究方法单独使用均无法全面反映群落的结构变化状况，建议在实际研究过程中同时使用多种研究方法进行鱼类群落结构的变化分析，以期全面掌握捕捞活动影响下鱼类群落结构的变动状况，更好地为渔业资源的科学管理提供理论支撑。 根据1991年1月和2004～2006年1月东海北部水域渔业资源底拖网调查资料，从物种和同功能种团两个层面分析了东海北部鱼类群落多样性及其结构组成特征的变化。同功能种团是生态系统中起着相似生态作用、并占据相近或相似生态位的若干物种集合体，本文结合各鱼种的摄食习性和活动能力差异，将该水域内的鱼类划分为8个同功能种团，分别为浮游动物食性种团、浮游/底栖动物食性种团、底栖动物食性种团、底栖/游泳动物食性种团、杂食性种团、活动能力强的游泳动物食性种团、软骨鱼类种团、活动能力弱的游泳动物食性种团。研究结果显示：东海北部冬季鱼类群落的物种多样性和同功能种团多样性呈显著线性正相关。经过十余年后，尽管该群落的物种多样性和同功能种团多样性均未发生显著变化，但各同功能种团内的物种数发生了明显变化，物种多样性与同功能种团多样性之间的关系曲线斜率由0.547增加到0.627，群落的生态冗余性有所降低。相似性分析检验表明，两时段群落间的物种和同功能种团结构组成均发生了显著变化，带鱼、龙头鱼、小黄鱼、黄鲫、灰鲳等物种和软骨鱼类种团、浮游/底栖动物食性种团相对量的变化是造成鱼类群落结构变化的主要因素。鱼类群落结构已显现出向以浮游动物食性和活动能力强的游泳动物食性鱼种为主体的方向发展的趋势。 最后本研究对实施伏季休渔以后近十年来东海北部鱼类群落的动态进行了分析。研究表明：实施伏休以后部分物种得到一定程度的恢复，而另些物种在伏休结束后强大的捕捞压力下仍然不断衰退，群落的物种生物量组成正朝一定的方向进行变化，但是这种变化并没有给鱼类群落带来稳定性和功能性方面的好转，群落仍处于中度干扰状态，物种多样性没有得到显著提高；群落的生产力水平以及营养传递效率没有恢复的迹象。每年伏休结束后强大的捕捞压力使伏季休渔没有达到预期的效果。为更有效的保护渔业资源、恢复东海北部生态系统，建议继续加大管理力度，进一步降低该海域的捕捞强度。

The environment effect on fish assemblage structure in waters adjacent to the Changjiang (Yangtze) River estuary (1998-2001)

We collected fish abundance data in the Changjiang (Yangtze River) estuary and adjacent waters in November 1998, May 1999, November 2000, and May 2001. Using the data, we evaluated the characteristics of the fish assemblages at each site and investigated the effect of several environmental factors. We used a multivariate analysis, including community ordination methods such as detrended correspondence analysis (DCA) and canonical correspondence analysis (CCA), and two-way indicator species analysis (TWINSPAN). We analyzed the biological community structure and environmental factors to determine their spatial distributions, temporal dynamics, and seasonal variations. Among the fish species, five exceeded 5% of the total abundance: Harpodon nehereus (42.82%), Benthosema pterotum (13.85%), Setipinna taty (11.64%), Thryssa kammalensis (9.17%) and Apogonichthys lineatus (6.49%). These were separated into four ecological assemblages: hypsithermal-saline, hypsithermal-brackish, hypothermal-brackish, and hypothermal-saline. We evaluated the degree of influence of environmental factors on the fish community. Our analyses suggested that environmental factors including water depth, salinity, turbidity, transparency, nutrient, and suspended matter formed a synthetic spatial gradient between the coastal and pelagic areas. Ecological and environmental factors changed temporally from 1998 to 2001, and drove the fish community succession. The environmental factors driving the fish community structure included bottom temperature, water depth, bottom and surface pH, surface total phosphorous, and bottom dissolved oxygen. This investigation was completed before completion of the Three Gorges Dam; therefore the results of this study provide an important foundation for evaluating the influence of the human activities.

Community structure of macrobenthos in coastal water off Rushan, southern Shandong Peninsula, and the relationships with environmental factors

To understand the present actuality of the marine ecosystem in the southern coastal water region of the Shandong Peninsula and the impact of the global change and the human activities to the marine ecosystem of the region, the macrobenthic community structure was researched based on data from 26 sampling stations carried out on four seasonal cruises from December 2006 to November 2007. The data was analyzed using PRIMER 6.0 and SPSS 15.0 software packages. The results showed that 236 macrobenthic species in total were collected from the research region by the field works. Most of the species belong to Polychaeta (76 species), Mollusca (75) and Crustacea (60). Of which, 33 species were common species by the four cruises. The dominant species were different among the four seasons, however, the polychaete species Nephtys oligobranchia and Sternaspis scutata were always dominant in the four seasons. The abundances and biomasses of the macrobenthos from the research region were variable in tire four seasons. The results of CLUSTER and MDS analysis showed that the similarities of macrobenthic structures among the stations were low, most of the similarities were at about 40% of similarity values, only that of two stations were up to 60%. In accordance with the similarity values of the macrobenthic structures, the 26 stations were clustered as six groups at arbitrary similarity level of 30%. The ABC curve indicated that the marcofauna communities in the research region had riot been disturbed distinctly. The results of BIOENV and BVSTEP (Spearman) analysis implied that the concentrations of organic matter in bottom water and heavy metal copper in sediment, water depth and temperature of bottom were the most significant environmental factors to affect the macrobentic community.

长江口及其邻近海域鱼类群落结构分析

根据长江口及其邻近海域鱼类群落的历史调查资料，综合运用主成分分析(PCA)、无偏对应分析(DCA)和典范对应分析(CCA)等群落排序方法，以及双向指示种分析(TWINSPAN)等数量分类方法，分析了1998-2004年长江口鱼类群落结构，以及其相关环境因子的变化特征。从群落和环境两方面，分别探讨了其空间分布、时间动态和季节变化的特征，并着重讨论了环境因子对群落特征的影响程度。结果表明： 在空间分布上，自近岸到外海的水深、盐度、浊度、透明度、营养盐和悬浮物这一综合梯度，与鱼类丰度关系最密切。近岸区以营养盐丰富、初级生产力高等特点，为近岸的广盐性和半咸水鱼类提供了充足的食物来源；以高浊度和高溶解氧浓度，提供了良好的庇护所。外海区鱼类种类丰富，但丰度较低。南北方向上大致以31°30′N为界，鱼类群聚在特定季节表现出明显的空间分化。 在时间动态上，1998-2004年长江口及邻近海域生态环境的改变，驱动了鱼类群落的演替，具体表现为：三峡水库蓄水前，群落主控因子为水深、底层水温和底层溶解氧，蓄水后主控因子为表底层pH值、表层温度和表层溶解氧；蓄水后冲淡水量的减少导致海域内盐度升高，悬浮物的减少改善了浮游植物生长的光照条件；与此相关，春季和秋季鱼类群聚均发生了显著变化，海洋性鱼类和浮游生物食性鱼类在群落中比重分别有所增加。 在季节变化上，冬季环境以低水温、高溶解氧为突出特点，夏季则反之；春季表层pH值显著高于其他季节，而表底层温度与秋季相比偏低；秋季环境条件接近中等水平。受此影响，鱼类群落发生明显的季节性演替，主要表现为鱼类丰度的波动、物种组成和优势种组成的更替，以及各功能群相对比例的此消彼长。

Differential population structuring and demographic history of two closely related fish species, Japanese sea bass (Lateolabrax japonicus) and spotted sea bass (Lateolabrax maculatus) in Northwestern Pacific

The Quaternary cold periods in the Northwestern Pacific are thought to have heavily influenced the amount and distribution of intraspecific genetic variation in marine fishes. To estimate the demographic history and genetic structure of Lateolabrax macula

Effects of fish stocking on the zooplankton community structure in a shallow lake in China

Changes in the zooplankton community structure in relation to fishery practices in Lake Donghu, Wuhan, China were examined. The number of Protozoa species increased slightly, whereas the number of rotifers and crustaceans decreased from the 1960s to the 1990s. The total annual average densities of zooplankton increased 15-20 times in the 1990s compared with the 1960s. This increase was largely attributed to Protozoa, which contributed 93.4% by number of the total zooplankton density in 1991. Cladoceran densities decreased markedly from 1987. Changes in densities of rotifers and copepods were not evident. Trends in zooplankton biomass were similar to density. Large changes in zooplankton community structure coincided with markedly changes in concentration of chlorophyll a and transparency in Lake Donghu in 1987. The year 1987 seems to be the threshold year when the zooplankton community structure changed considerably. These changes were related to continuously increasing fish stock biomass in the lake. It was suggested that fish stocking and fish biomass should be a better managed for improvement of the quality of the lake's environment.

Changes in the plankton community following introduction of filter-feeding planktivorous fish

1. We conducted enclosure experiments in a shallow eutrophic lake, in which a biomass gradient of the filter-feeding planktivore, silver carp, Hypophthalmichthys molitrix Valenciennes, was created, and subsequent community changes in both zooplankton and phytoplankton were examined. 2. During a summer experiment, a bloom of Anabaena flos-aquae developed (approximate to 8000 cells mL(-1)) solely in an enclosure without silver carp. Concurrent with, or slightly preceding the Anabaena bloom, the number of rotifer species and their abundance increased from seven to twelve species (1700-14 400 organisms L-1) after the bloom in this fish-free enclosure. Protozoans and bacteria were generally insensitive to the gradient of silver carp biomass. 3. During an autumn experiment, on the other hand, large herbivorous crustaceans were more efficient than silver carp in suppressing the algae, partly because the lower water temperature (approximate to 24 degrees C) inhibited active feeding of this warm-water fish and also formation of algal colonies. Heterotrophic nanoflagellate and bacterial densities were also influenced negatively by the crustaceans. 4. Correspondence analysis (CA) was applied to the weekly community data of zooplankton and phytoplankton. A major effect detected in the zooplankton community was the presence/absence of silver carp rather than the biomass of silver carp, whereas that in the phytoplankton community was the fish biomass before the Anabaena bloom, but shifted to the presence/absence of the fish after the bloom.

Onshore-offshore variations of copepod community in northern South China Sea

Copepod communities in onshore and offshore waters show a gradient from primarily near shore to primarily oceanic species. Understanding the transition between these communities is fundamental to determining the range of coastal influence. Copepod communities in the northern South China Sea (nSCS) were studied based on samples collected by vertically towing a net in 10 February-6 March (winter) and 26 August-6 September (summer) of 2004. Calanoida species richness, total copepod abundance, Shannon-Weaver diversity index, and onshore-offshore occurrence of dominant species showed obvious change from onshore to offshore waters. Although the offshore stations had lower abundance than the shelf stations, they had more species and larger diversity index. Abundance of some species (groups) with dominance index > 5% (Calanus sinicus, Euchaeta spp., Temora spp., Paracalanus parvus, and Subeucalanus subtenuis) declined from onshore to offshore waters. Warm water species (Pleuromamma abdominalis, P. gracilis, and P. robusta) occurred in offshore waters in both cruises. Station (q-type) cluster analysis in winter and summer separated copepod community into onshore and offshore communities at similar to 40% level of similarity. The two communities were divided at the position of similar to 100-m isobath. In summer, C. sinicus occurred in the upwelling area east of Hainan Island, indicating the presence of an oversummering stock of this species.

Food utilization of adult flatfishes co-occurring in the Bohai Sea of China

Stomach contents were examined of 4527 adult individuals of 12 flatfish species collected during the 1982 - 1983 Bohai Sea Fisheries Resources Investigation. Their food habits, diet diversity, similarity of prey taxa, trophic niche breadth and diet overlap were systematically analysed. Ninety-seven prey species belonging to the Coelenterata, Nemertinea, Polychaeta, Mollusca, Crustacea, Echinodermata, Hemichordata and fish were found and five of them were considered to be principal prey for flatfishes: Alpheus japonicus, Oratosquilla oratoria, Alpheus distinguendus, Loligo japonicus and Crangon affinis. Among the flatfishes, Paralichthys olivaceus was piscivorous, whereas Pseodopleuronectes yokohamae and Pseudopleuronectes herzensteini both had polychaetes and molluscs as their main prey groups. Pleuronichthys cornutus was classified as a polychaete-mollusc eater, with a strong preference for crustaceans. Verasper variegatus, Cynoglossus semilaevis, Eopsetta grigorjewi and Cleisthenes herzensteini ate crustaceans. Kareius bicoloratus was classified as a mollusc-crustacean eater: Cynoglossus abbreviatus, Cynoglossus joyneri and Zebrias zebra were grouped as crustacean-fish eaters. However, Z. zebra also took polychaetes and C. abbreviatus and C. joyneri preyed on some molluscs. Trophic relationships among the flatfishes were complicated, but they occupied distinctive microhabitats in different seasons and selected their specific prey items, which was favourable to the stability of the flatfish community in the Bohai Sea.

Zooplankton functional groups on the continental shelf of the yellow sea

Zooplankton plays a vital role in marine ecosystems. Variations in the zooplankton species composition, biomass, and secondary production will change the structure and function of the ecosystem. How to describe this process and make it easier to be modeled in the Yellow Sea ecosystem is the main purpose of this paper. The zooplankton functional groups approach, which is considered a good method of linking the structure of food webs and the energy flow in the ecosystems, is used to describe the main contributors of secondary produciton of the Yellow Sea ecosystem. The zooplankton can be classified into six functional groups: giant crustaceans, large copepods, small copepods, chaetognaths, medusae, and salps. The giant crustaceans, large copepods, and small copepods groups, which are the main food resources for fish, are defined depending on the size spectrum. Medusae and chaetognaths are the two gelatinous carnivorous groups, which compete with fish for food. The salps group, acting as passive filter-feeders, competes with other species feeding on phytoplankton, but their energy could not be efficiently transferred to higher trophic levels. From the viewpoint of biomass, which is the basis of the food web, and feeding activities, the contributions of each functional group to the ecosystem were evaluated; the seasonal variations, geographical distribution patterns, and species composition of each functional group were analyzed. The average zooplankton biomass was 2.1 g dry wt m(-2) in spring, to which the giant crustaceans, large copepods, and small copepods contributed 19, 44, and 26%, respectively. High biomasses of the large copepods and small copepods were distributed at the coastal waters, while the giant crustaceans were mainly located at offshore area. In summer, the mean biomass was 3.1 g dry wt m(-2), which was mostly contributed by the giant crustaceans (73%), and high biomasses of the giant crustaceans, large copepods, and small copepods were all distributed in the central part of the Yellow Sea. During autumn, the mean biomass was 1.8 g dry wt m(-2), which was similarly constituted by the giant crustaceans, large copepods, and small copepods (36, 33, and 23%, respectively), and high biomasses of the giant crustaceans and large copepods occurred in the central part of the Yellow Sea, while the small copepods were mainly located at offshore stations. The giant crustaceans and large copepods dominated the zooplankton biomass (2.9 g dry wt m(-2)) in winter, contributing respectively 57 and 27%, and they, as well as the small copepods, were all mainly located in the central part of the Yellow Sea. The chaetognaths group was mainly located in the northern part of the Yellow Sea during all seasons, but contributed less to the biomass compared with the other groups. The medusae and salps groups were distributed unevenly, with sporadic dynamics, mainly along the coastline and at the northern part of the Yellow Sea. No more than 10 species belonging to the respective functional groups dominated the zooplankton biomass and controlled the dynamics of the zooplankton community. The clear picture of the seasonal and spatial variations of each zooplankton functional group makes the complicated Yellow Sea ecosystem easier to be understood and modeled. (C) 2010 Elsevier Ltd. All rights reserved.