鄱阳湖物理生境特征及其对鱼类群落结构的影响

湖泊鱼类群落结构与物理生境特征密切相关。为了探究鱼类群落结构与物理生境特征之间的关系,在鄱阳湖设立17个采样点,通过采集鱼类样本研究其群落结构,并利用遥感技术分析样点物理生境特征（包括岸线分形维数、距离指数和高程值）及其空间区域差异。结果表明,依据17个采样位点的物理生境特征,鄱阳湖丰水期物理生境空间上可以划分为3个区域,分别为北方区、南方区和主湖区,但枯水期鄱阳湖生境没有显著的区域划分规律。丰水期鄱阳湖鱼类可以分为北方群、南方群和主湖区群3个类群,而枯水期鱼类组成没有明显规律。从功能类群上看,鄱阳湖鱼类以杂食性、湖泊定居性和偏好于底层以及中下层栖息的中小型鱼类为主。不同区域的鱼类功能群之间存在时间和空间上的变化,北方区和南方区鱼类功能群组成相似,主湖区与北方区和南方区存在差异。总体上,鱼类群落结构的时空变化和差异与物理生境特征具有良好的一致性;未来鄱阳湖鱼类的保护工作需要关注湖泊物理生境特征,不同区域应制定不同的保护措施。     

The role of environmental filtering in the functional structure of fish communities in tropical wetlands

Understanding the mechanisms that structure communities has been a major challenge in ecological theory. In wetlands with a clear seasonal hydroperiod (wet and dry seasons), such as Sian Ka'an Biosphere Reserve (SKBR), Mexico, fish communities experience successive habitat contraction/expansion, with a high mortality rate during the dry season. In this study, we tested the role of environmental filtering in structuring fish communities along an environmental gradient in permanent pools, during three consecutive stages of the dry season. We analysed fish communities using a functional dispersion index weighted by the relative abundance compared against a null model. While the concentration of dissolved oxygen remained low throughout the season, depth and temperature showed a gradient as the season progressed. Independently of their starting composition, at the end of the dry season the communities were dominated by a combination of the same three species. For the key function of locomotion, the functional dispersion was significantly lower at the end of the season in three of the five pools. For food acquisition, no significant differences were found. When the overall functional variation was considered, at the beginning of the dry season no single community differed significantly compared to the random models. However, as the season progressed, significant differences were recorded in four of the five pools. Our study supports the hypothesis that environmental filters have a major role in community structure in severe environmental conditions. Furthermore, our results show that the role of environmental filters gain importance as the dry season progresses.     

Damming and seasonality as modulators of fish community structure in a small tributary

River damming alters the physical–chemical variables of water and often causes compartmentalisation of aquatic habitats. Seasonality can add complexity to the longitudinal compartmentalisation. The spatial and temporal effects of these two phenomena on the structure of ichthyofauna from a tributary under the influence of damming were evaluated, based on the following hypotheses: (1) transition habitats have the greatest species richness; (2) community similarity decreases with increasing distance between sites; (3) conservation of free‐flowing areas upstream reservoir contributes to the maintenance of migratory species. To evaluate the effects of these two phenomena, twelve monthly fish samples (September/12 to August/13) were performed with gillnets in three sample areas distributed longitudinally in the tributary. Limnological variables were measured in the same sample areas to confirm compartmentalisation. We observed three distinct limnological compartments (lotic, transition and lentic), with increase differentiation during the rainy season. This compartmentalisation influenced fish fauna where localised communities exhibited different compositions among the three sampled habitats. During the rainy season, these differences become pronounced, with transition habitat showing greater species richness than the others. More pronounced differences in species composition and structure in extremes sampling sites were also observed. Migratory fish presented higher proportion of fish composition in lotic habitat. In conclusion, damming and seasonality acted concomitantly as modulators of fish fauna in a tributary influenced by damming. However, compartmentalisation of habitats was the primary driver of ichthyofauna community structure with the rainy season increasing differences in community composition.     

Fish assemblages of the northern Argentine coastal system: spatial patterns and their temporal variations

The springtime spatial pattern of demersal fish assemblages in the northern Argentine coastal ecosystem (34°–41°S) and their relationships with environmental variables were investigated over 6 years (1981, 1983, 1994, 1995, 1998 and 1999). For each fish assemblage area for each year, we identified the most common species and those species that had the highest ability to discriminate it from adjacent assemblage areas. Within each area, species were considered as resident (common in all years) or facultative (contributing to less than 90% of similarity within any year). The analysis (detrended canonical correspondence analysis), conducted using species abundances (t nm^?2) and environmental data, indicated that six fish assemblage areas are consistently distinguishable. The fish assemblage areas correspond to inner, central and middle regions of the Río de la Plata estuary, and inner, central and middle regions of the coastal shelf. Spatial differences in the composition among areas were primarily due to changes in species composition rather than changes in relative abundance, and were primarily related to water mass characteristics. Salinity in the estuary and temperature on the shelf were more relevant to the spatial structuring of the fish community in each environment. The assemblage areas showed a remarkable degree of temporal persistence in species composition and geographical location. The facultative species contributed more to the species composition temporal dynamics than resident species. El Niño (La Niña) condition, associated with increase (decrease) of the Río de la Plata freshwater discharge, produced a movement of the estuarine assemblage areas to the coastal shelf (upriver). Under normal freshwater discharge conditions, the boundaries of the fish assemblages were relatively more stable.     

Temporary pools provide stability to fish assemblages in Amazon headwater streams

Temporal variations in the environment may function as disturbances that affect population processes and change the structure and composition trajectories of communities. The presence of refuges may buffer such variations and also support the recovery of communities after disturbances. In this study, we tested the effect of temporary pools as seasonal refuges for the ichthyofauna in upland forest streams in the Brazilian Amazon. We sampled environmental characteristics and fish in five occasions over one seasonal cycle in eight stream stretches and their adjacent temporary pools in Reserva Ducke, Manaus. We recorded 27 fish species, 13 of which occurred in both habitats and represented 81% of the total fish abundance in the stream–pool system (3695 records of fish, 54% made in pools). During rainy periods, fish abundance in pools was higher than in the channels. Total number of records varied inversely among habitats over time with a reduction in the pools and an increase in the channels as the pools gradually desiccated. The number of species exhibited a similar pattern. When data from pools and channels were pooled, representing the entire flood zone, fluctuations in all the measured variables along the time were smoothed. The variability in fish assemblage composition was associated with variability in the volume of water in the entire system. These results indicate that temporary pools are an important habitat component of upland forest streams, providing resources and spatial refuges for the fish during rainy periods, and regulating the stability of these communities.     

丰、枯水期里下河腹地典型水体浮游动物群落结构与水质评价

为了探究丰枯水期里下河腹地典型水体中浮游动物的群落结构特征,通过布设20个采样站点,于2014年丰水期(7月29日)和枯水期(12月24日)对里下河腹地典型水体进行了2次全面调查,并对水质状况进行了评价。结果表明,里下河腹地典型水体共鉴定出浮游动物21种(包括变种和变型),无节幼体1类;其中轮虫最多,共14种,占浮游动物总种数的66.6%;枝角类次之,共6种,占28.6%;桡足类最少,仅1种,占4.8%;各站点浮游动物种类组成和密度均以轮虫和枝角类为主,数量在5~15种,密度变化在9.8~102.2个/L。浮游动物相似性指数在0.18~0.55,平均为0.36,偏向于轻度相似,表明丰水期与枯水期的生境差异较大。优势种的优势度不高,在0.023~0.297;多样性指数在1.73~3.56,均匀度指数在0.67~0.95,表明丰、枯水期里下河腹地典型水体的浮游动物群落信息含量较大、群落结构处于较稳定状态。浮游动物多样性和水质监测结果均表明,枯水期水质优于丰水期,枯水期水质基本处于清洁状态,丰水期水质基本处于中度污染状态;污染源主要为面源污染,且串场河(6号)、新通扬运河(12号)、喜鹊湖(17号)、兴姜河(18号)受人类活动影响较大。     

Variation in fish assemblages across dry-season pools in a Mediterranean stream: effects of pool morphology, physicochemical factors and spatial context

Pires DF, Pires AM, Collares-Pereira MJ, Magalhães MF. Variation in fish assemblages across dry-season pools in a Mediterranean stream: effects of pool morphology, physicochemical factors and spatial context. Ecology of Freshwater Fish 2010: 19: 74–86. © 2009 John Wiley & Sons A/S
Abstract –  Knowledge of patterns of refuge use by fish is critical for maintaining biodiversity in drought-prone streams. In this study, the fish assemblages of 21 dry-season pools in a Mediterranean stream were characterised and related to three sets of factors reflecting pool morphology, physicochemistry and spatial context. Fish were associated with the three sets of variables, with variation partitioning indicating that overall species richness and abundance were primarily related to pool morphology but relative species abundances were mainly associated with physicochemical contexts. In general, species richness was the highest but overall fish abundance was the lowest in large pools. Pools well shaded by riparian canopy held the highest richness and abundance of native fish, but relative species abundances and assembly structure varied among pools contingent on canopy cover, substrate composition and spatial location. These results suggested that conservation of fish diversity in Mediterranean streams requires networks of pools with diverse sizes and physicochemical contexts.     

Temporal changes in the fish community structure of a small subtropical spring lake: Decadal and seasonal analysis

In spring lakes, which have homogeneous environmental characteristics, it is expected that there will be no significant changes in the composition and structure of communities over time, and fluctuations will generally be related to the ecological attributes of the species. We studied the fish community in a small subtropical spring lake, Lake Zacapu, for two different decades to analyse its structural characteristics. Sampling was performed every 3 months at four sites from January to October 1995 and from May 2019 to May 2020. We determined the temporal variation (seasonal and decadal) in the fish community structure with respect to composition, abundance, diversity and dominance. We evaluated the association between species and water quality. Our results showed spatial homogeneity in most physicochemical variables that remained in the same range across decades, although some nutrients (NO₃) recently increased. All species identified in the early samples were present in the recent surveys (eleven native and two nonnative species), indicating that the fish community composition had significant qualitative stability. However, the dominant littoral cyprinid in 1995 was replaced by the more limnetic atherinopsid in 2019–2020, and the diversity and abundance of sensitive fish decreased in recent samplings. Consequently, the current status of critically endangered species is supported for some restricted and microendemic fish. The changes in the community structure attributes, which show a tendency for reduction in native species, emphasise the need to implement efforts to conserve freshwater fish diversity in small spring lakes.     

流溪河底栖硅藻群落结构的时空异质性及其影响因素

底栖硅藻能够较好地响应河流水环境变化,其群落物种组成与分布已被广泛应用于河流水质与生态状况的指示与评估。为了解流溪河底栖硅藻群落结构的时空异质性及其受河流水文与水质的影响,从上游到下游共设置了 20个样点,于2018年3月、6月、9月和12月进行季节采样和观测,采集底栖硅藻,同步测定了水体理化因子;在分析群落组成的基础上,进一步探究河流环境变量和空间变量对流溪河底栖硅藻群落的影响。结果表明,4次调查共检 出底栖硅藻276种,隶属于2纲、6目、9科、55属,底栖硅藻多样性具有明显的时空差异。在季节上,丰水期的物种丰 富度和真辛普森多样性指数高于枯水期。枯水期曲壳藻科的相对丰度超过50%,高于丰水期;而舟形藻科在丰水期 时相对丰度比枯水期高。在空间上,三级河流物种多样性最高,一级河流物种多样最低;一级河流和二级河流的优 势种主要以曲丝藻属的种类为主,三级河流的优势种主要以菱形藻属的种类为主。随着河流等级增加,曲壳藻科相 对丰度降低,而菱形藻科的相对丰度逐渐升高。冗余分析（RDA）表明,环境选择和空间要素对流溪河硅藻群落结构 均有显著影响,但营养盐水平比空间要素有更高的解释率。     

Spatiotemporal patterns of fish community composition in Great Lakes drowned river mouths

Freshwater river mouths in large lakes are centres of biological activity, yet little is understood about the spatial and temporal dynamics of fish communities in these systems. In the Laurentian Great Lakes, we sampled littoral fishes over 3 years in six drowned (i.e., protected) river mouths to: (i) quantify spatial (among river mouths) and temporal (among years) variation, (ii) evaluate associations with environmental conditions and (iii) assess spatial patterns of community similarity. We sampled 6787 fish representing 43 species over the course of the study. Multivariate analyses indicated that variation in fish species composition was more strongly partitioned among river mouths than among years. Fish communities across the six river mouths were partitioned into three groups, a pattern we attribute to variability in anthropogenic disturbance and environmental conditions. Canonical correspondence analysis showed that fish species composition was associated with specific conductivity, vegetation cover, turbidity and pH, suggesting species–environment relationships are similar to those shown for Great Lakes coastal wetlands. Finally, we found a negative relationship between geographic distance and community similarity, suggesting that dispersal and/or environmental gradients play a role in shaping these river mouth fish assemblages. We conclude that Great Lakes drowned river mouths can harbour diverse and spatially variable fish assemblages that are driven by a combination of local and regional factors.