Plant community,primary productivity,and environmental conditions following wetland re-establishment in the Sacramento-San Joaquin Delta,California

Wetland restoration can mitigate aerobic decomposition of subsided organic soils, as well as re-establish conditions favorable for carbon storage. Rates of carbon storage result from the balance of inputs and losses, both of which are affected by wetland hydrology. We followed the effect of water depth (25 and 55 cm) on the plant community, primary production, and changes in two re-established wetlands in the Sacramento San-Joaquin River Delta, California for 9 years after flooding to determine how relatively small differences in water depth affect carbon storage rates over time. To estimate annual carbon inputs, plant species cover, standing above- and below-ground plant biomass, and annual biomass turnover rates were measured, and allometric biomass models for Schoenoplectus (Scirpus) acutus and Typha spp., the emergent marsh dominants, were developed. As the wetlands developed, environmental factors, including water temperature, depth, and pH were measured. Emergent marsh vegetation colonized the shallow wetland more rapidly than the deeper wetland. This is important to potential carbon storage because emergent marsh vegetation is more productive, and less labile, than submerged and floating vegetation. Primary production of emergent marsh vegetation ranged from 1.3 to 3.2 kg of carbon per square meter annually; and, mid-season standing live biomass represented about half of the annual primary production. Changes in species composition occurred in both submerged and emergent plant communities as the wetlands matured. Water depth, temperature, and pH were lower in areas with emergent marsh vegetation compared to submerged vegetation, all of which, in turn, can affect carbon cycling and storage rates.     

Fish Communities and Their Associations with Environmental Variables, Lower San Joaquin River Drainage, California

Twenty sites in the lower San Joaquin River drainage, California, were sampled from 1993 to 1995 to characterize fish communities and their associations with measures of water quality and habitat quality. The feasibility of developing an Index of Biotic Integrity was assessed by evaluating four fish community metrics, including percentages of native fish, omnivorous fish, fish intolerant of environmental degradation, and fish with external anomalies. Of the thirty-one taxa of fish captured during the study, only 10 taxa were native to the drainage. Multivariate analyses of percentage data identified four site groups characterized by different groups of species. The distributions of fish species were related to specific conductance, gradient, and mean depth; however, specific conductance acted as a surrogate variable for a large group of correlated variables. Two of the fish community metrics – percentage of introduced fish and percentage of intolerant fish – appeared to be responsive to environmental quality but the responses of the other two metrics – percentage of omnivorous fish and percentage of fish with anomalies – were less direct. The conclusion of the study is that fish communities are responsive to environmental conditions, including conditions associated with human-caused disturbances, particularly agriculture and water development. The results suggest that changes in water management and water quality could result in changes in species distributions. Balancing the costs and benefits of such changes poses a considerable challenge to resource managers.     

Fish Communities of the Sacramento River Basin: Implications for Conservation of Native Fishes in the Central Valley, California

The associations of resident fish communities with environmental variables and stream condition were evaluated at representative sites within the Sacramento River Basin, California between 1996 and 1998 using multivariate ordination techniques and by calculating six fish community metrics. In addition, the results of the current study were compared with recent studies in the San Joaquin River drainage to provide a wider perspective of the condition of resident fish communities in the Central Valley of California as a whole. Within the Sacramento drainage, species distributions were correlated with elevational and substrate size gradients; however, the elevation of a sampling site was correlated with a suite of water-quality and habitat variables that are indicative of land use effects on physio-chemical stream parameters. Four fish community metrics – percentage of native fish, percentage of intolerant fish, number of tolerant species, and percentage of fish with external anomalies – were responsive to environmental quality. Comparisons between the current study and recent studies in the San Joaquin River drainage suggested that differences in water-management practices may have significant effects on native species fish community structure. Additionally, the results of the current study suggest that index of biotic integrity-type indices can be developed for the Sacramento River Basin and possibly the entire Central Valley, California. The protection of native fish communities in the Central Valley and other arid environments continues to be a conflict between human needs for water resources and the requirements of aquatic ecosystems; preservation of these ecosystems will require innovative management strategies.     

夏季大亚湾鱼类群落结构与多样性

根据2018年8月大亚湾海域底拖网鱼类资源调查数据,分析了大亚湾夏季鱼类群落结构特征。结果表明:2018年大亚湾夏季渔获鱼类56种,隶属9目、34科、47属。其中,鲈形目(Perciformes)最多(39种,69.64%);物种组成以短吻鲾(Leiognathus brevirostris)、黄斑蓝子鱼(Siganus oramin)、拟矛尾鰕虎鱼(Parachaeturichthys polynema)、六指马鲅(Polynemus sextarius)和二长棘犁齿鲷(Evynnis cardinali)等小型低值鱼类为主;鱼类物种多样性存在明显的空间差异,表现为湾口海域最大,沿岸海域次之,湾中部海域最小。鱼类群落结构大体分为咸淡水湾内和海水广布湾口两个鱼类群组;对比1985—2017年夏季调查资料可知,30多年来大亚湾夏季鱼类群落物种多样性减小;优势种组成更替显著,由以大型中上层的经济鱼类为主演变为以小型底层、近底层的低值鱼类为主,其主要原因是人类活动对大亚湾生态系统的干扰,尤其是捕捞致使鱼类群落结构发生改变、趋向简单化。     

Characteristics and habitats of non-native plant species in the city of Chonju,southern Korea

Investigations on non-native organisms have become an important task of modern ecology throughout the world. The major objective of this study was to identify the characteristics and habitats of non-native plant species in Korean cities in order to derive conclusions on the success of biological invaders. The city of Chonju in southwest Korea was selected as a representative investigation area. All wild-growing vascular plants were recorded in the city on a total of 106 sample plots located in representative land-use types and within various distances of the city center. Frequency, origin, life forms, and plant families of non-native species were analyzed. Additionally, the percentage of non-native species along a gradient from the city center to the outskirts was investigated. We found that most common non-native species of the flora of Chonju are: (i) native to the Northern hemisphere; (ii) belong to the annuals; (iii) belong to the plant families of the Compositae or Leguminosae; and (iv) they perform best on sites that are continuously disturbed by human impact. In conclusion, non-native species play a significant role in enhancing biological diversity in urban areas.     

Assessing fern diversity: relative species richness and its environmental correlates in Uganda

Techniques for the rapid quantification of tropical biodiversity are of critical importance in deciding where to invest scarce conservation resources. Here we describe a simple survey method for assessing species-level richness of a poorly known plant group, the pteridophytes. We then illustrate the use of a powerful, rarefaction- based technique of controlling for inevitable differences in sampling effort to calculate the relative species richness of our study sites. Lastly, we explore how closely observed patterns of relative species richness of Ugandan forests are correlated with a suite of simple environmental variables. We find that fully 75% of the variance in our estimate of fern diversity can be predicted from just two measures: soil fertility (scored as C/N ratio, itself related to rainfall); and distance from the nearest putative Pleistocene refugium.     

枸杞岛潮下带沙地生境鱼类群落结构和季节变化

为了解岛礁水域沙地生境的鱼类群落结构特征,评估该生境对鱼类资源养护的潜在作用,于2009年采用多网目组合刺网对枸杞岛潮下带沙质区域进行了逐月采样,同步设置岩礁为对照生境.应用α和β多样性指数结合相对重要性指数、相对渔获率、ABC曲线和聚类排序方法对两种生境中的鱼类组成、多样性变化和群落格局与变化进行了全面探讨.全年在沙地和岩礁生境共采集鱼类63种,隶属11目38科56属,2种生境各自出现的鱼类皆为46种.受暖水种频繁出现在沙地生境的影响,潮下带沙质区域鱼类区系比岩礁生境略显丰富,且春夏季的渔获量普遍高于岩礁生境;由于种类组成均匀度较低,沙地生境各季节的α多样性普遍较低,夏季显著低于岩礁生境.日本须鳎是沙地生境的指示种,为早春、夏末和秋冬季沙地底层优势鱼种.5-7月鳀、多数月份鲻和10月份鳗鲇等种类对沙地生境的阶段性利用,使其形成了区别于以趋礁性鱼类为优势类群的岩礁生境的群落格局和季节动态.沙地是多种鱼类幼鱼阶段的庇护所和饵料场,是鲆鲽类的良好栖息地.沙地生境在维持鱼类区系和养护鱼类资源方面具有重要作用.     

Long-term Developments in Ecological Rehabilitation of the Main Distributaries in the Rhine Delta: Fish and Macroinvertebrates

Significant anthropogenic pressure in the Dutch part of the River Rhine is present from the 12th century. River engineering and water pollution were the main stress factors for flora and fauna. From the middle of the 20th century measures were taken to reduce water pollution. Recently, from 1987 onwards, these activities were put into a wider context of ecological river rehabilitation. Effects of improvements on fish and macroinvertebrates in the main distributaries in the Rhine delta are reviewed. The conclusions are that (a) most of the alterations in the Rhine delta are irreversible due to hard socio-economic boundary conditions (e.g. safety, navigation); (b) chances for the development of riverine biotopes have therefore to be found in the forelands and not in the main channels of the Rhine delta; (c) further reduction of pollutants, especially thermal pollution, is needed to help original species to colonise the Rhine delta again; (d) non-indigenous species clearly leave a mark on recolonisation possibilities of original species.     

Zooplankton and environmental characteristics of Shiroro Lake at the extremes of its hydrological cycle

We studied the newly-created Shiroro lake, Nigeria, at the extremes of its hydrological cycle: high water level (HWL) and low water level (LWL). Temperatures reflected prevailing weather conditions; pH, dissolved oxygen, turbidity and suspended solids were highest during HWL, but transparency, conductivity, NO ₃ ^– -N, PO ₄ ^3– -P and Na⁺ were higher during LWL. A total of twenty-six species of pelagic zooplankton were identified: five species of cladocerans, eight species of copepods, and thirteen species of rotifers. The freshwater medusa (Limnocnida) and Daphnia longispina were absent during HWL but present at LWL, suggesting seasonality of the zooplankton community. Thermocyclops consimilis and T. emini are new records for Nigeria, bringing to nine the number of known Thermocyclops species in Nigeria.     

Integrating environmental and spatial processes in ecological community dynamics

The processes controlling the abundances of species across multiple sites form the cornerstone of modern ecology. In these metacommunities, the relative importance of local environmental and regional spatial processes is currently hotly debated, especially in terms of the validity of neutral model. I collected 158 published data sets with information on community structure, environmental and spatial variables. I showed that approximately 50% of the variation in community composition is explained by both environmental and spatial variables. The majority of the data sets were structured by species-sorting dynamics (SS), followed by a combination of SS and mass-effect dynamics. While neutral processes were the only structuring process in 8% of the collected natural communities, disregarding neutral dispersal processes would result in missing important patterns in 37% of the studied communities. Moreover, metacommunity characteristics such as dispersal type, habitat type and spatial scale predicted part of the detected variation in metacommunity structure.     

Influence of environmental heterogeneity on genetic diversity and structure in an endemic southern Californian oak

Understanding how specific environmental factors shape gene flow while disentangling their importance relative to the effects of geographical isolation is a major question in evolutionary biology and a specific goal of landscape genetics. Here, we combine information from nuclear microsatellite markers and ecological niche modelling to study the association between climate and spatial genetic structure and variability in Engelmann oak (Quercus engelmannii), a wind-pollinated species with high potential for gene flow. We first test whether genetic diversity is associated with climatic niche suitability and stability since the Last Glacial Maximum (LGM). Second, we use causal modelling to analyse the potential influence of climatic factors (current and LGM niche suitability) and altitude in the observed patterns of genetic structure. We found that genetic diversity is negatively associated with local climatic stability since the LGM, which may be due to higher immigration rates in unstable patches during favourable climatic periods and/or temporally varying selection. Analyses of spatial genetic structure revealed the presence of three main genetic clusters, a pattern that is mainly driven by two highly differentiated populations located in the northern edge of the species distribution range. After controlling for geographic distance, causal modelling analyses showed that genetic relatedness decreases with the environmental divergence among sampling sites estimated as altitude and current and LGM niche suitability. Natural selection against nonlocal genotypes and/or asynchrony in reproductive phenology may explain this pattern. Overall, this study suggests that local environmental conditions can shape patterns of genetic structure and variability even in species with high potential for gene flow and relatively small distribution ranges.     

黄海山东海域春、秋季鱼类群落多样性

根据2006年春季(5月)和秋季(10月)黄海山东海域疏目变水层双拖网调查数据,作者对该海域鱼类群落多样性、空间分布及长度谱特征进行了研究。调查共捕获鱼类61种,其中鲈形目种类最多(27种),其次为鲱形目(8种)和鲉形目(7种);按摄食类型可分为浮游动物食性、浮游动物/底栖动物食性、底栖动物食性、底栖动物/游泳动物食性、游泳动物食性、杂食性、碎屑食性7个类群,其中浮游动物食性占渔获物重量组成的82.5%。春、秋季鱼类群落均主要由小型种类占优势,春季优势种有3种,为玉筋鱼(Ammodytes personatus)、鳀(Engraulis japonicus)和方氏锦鳚(Pholis fangi),秋季优势种有5种,分别是鳀、青鳞小沙丁鱼(Sardinella zunasi)、玉筋鱼、小黄鱼(Larimichthys polyactis)和赤鼻棱鳀(Thryssa kammalensis)。丰富度指数(D)、Shannon-Wiener多样性指数(H’)、均匀度指数(J’)的空间异质性明显,表现出近岸海域(尤其是青岛-乳山南部近岸海域)较高,深水区较低的态势,但多样性指数的季节间差异不显著。资源量与Shannon-Wiener多样性指数(H’)、均匀度指数(J’)、功能团多样性指数(FD)均呈负相关关系,与种类丰富度指数(D)则无相关关系。春、秋季鱼类群落长度谱曲线斜率均小于-0.2,而截距均大于10,与该海域1985年及2000年的研究结果相比,长度谱斜率显著降低、截距显著增加,这与小型个体种类占优势密切相关。与历史资料相比,黄海山东海域鱼类群落多样性下降,小型个体比例上升,资源呈衰退趋势。     

Long-term dynamics and community structure of freshwater gastropods exposed to parasitism and other environmental stressors

1. Freshwater communities are subject to various abrupt environmental disturbances and increasing pollution levels in their habitat. According to the nature and the periodicity of disturbances (i.e. punctuated, recurrent or continuous), one may expect different kinds of response of the target gastropod communities. 2. The gastropod community of a French lake has been investigated for 10 years to study its responses to three main environmental disturbances: supra‐seasonal droughts, recurrent proliferations of cyanobacteria and parasitism by trematodes. The relationship between this latter factor, considered as a continuous stressor, and the gastropod community was a particular focus. 3. A total of 13 280 gastropods belonging to 17 species (mostly Pulmonata with Planorbidae as the dominant family) have been sampled in the lake over the 10‐year time series. Species composition of the gastropod community varied strongly during the study period as did species richness (0–14, mean of 6.5 ± 0.4 species) and abundance of gastropods (0–4456, mean of 192 ± 72 individuals). Trematode larvae belonging to 11 morphotypes of cercariae were detected in 15 of the 17 species of gastropods and had a total prevalence of 2.9%. 4. Droughts (punctuated stressor) were responsible for the disappearance of nearly all gastropod species, and thus represent a severe environmental stressor for them. Nevertheless, the extent of this stressor was limited since the gastropod community was highly resilient. 5. Recurrent proliferations of toxic cyanobacteria (recurrent stressor) coincided with the large decline of the gastropod community, corresponding to a strong decrease in abundance and species richness. Intoxication of gastropods by toxic cyanobacteria was demonstrated by the bioaccumulation of microcystins in all gastropod tissues. 6. Trematode parasitism (continuous stressor) did not affect the gastropod community despite the possibly strong impact of parasites on some host species (those with monthly prevalence as high as 100% at some times). Indeed, abundance and species richness of gastropods were scarcely influenced by trematode prevalence or species richness.     

Spatial and Temporal Ecology of Native and Introduced Fish Larvae in Lower Putah Creek,California

For two years we studied the distribution and abundance of native and introduced fish larvae in Putah Creek (Yolo County, CA), a low elevation regulated stream. We used light traps and conical drift nets to sample the fish larvae at two spatially separated sites from March through July 1997 and at four sites from February through August 1998. Native larvae occurred both earlier in the year and in higher abundance than those of introduced species. Both native larvae and overall numbers of larvae were more abundant at upstream sites in both years. Sampling of larvae appeared to be sensitive to the detection of rare species. Drift nets and light traps collected similar numbers of larvae, but each method tended to select for different taxa. There were significant trends in diel patterns of abundance, with more fish larvae being found during the hours of darkness. We suggest that differences between the sites were due to habitat changes resulting from an upstream dam that has created a refuge of diverse habitat and cool flowing water for native taxa.     

Histopathology, blood chemistry, and physiological status of normal and moribund striped bass (Morone saxatilis) involved in summer mortality ('die-off') in the Sacramento-San Joaquin Delta of California

Summer mortality ('die-off') is common in striped bass, Morone saxatilis (Walbaum), in the San Francisco Bay-Delta region. Tissue and blood samples of moribund and healthy striped bass collected during the summers of 1986–1988 were analysed. Sixteen moribund and 25 healthy reference fish from the Carquinez Strait area and eight fish caught in the Pacific Ocean were studied. Moribund fish plasma was invariably yellow-orange; most of the moribund fish had discoloured livers with haemorrhagic regions, and approximately one-third had haemorrhagic intestines. Piasma levels of aspartale aminotransferase, uric acid, alkaline phosphatase and cortisol were significantly higher than in reference fish from Carquinez Strait and the Pacific Ocean, whereas cholesterol, sodium, chloride, triiodothyronine and glucose levels were significantly lower. Hepatic heavy metal concentrations and bacterial content were similar in moribund and reference fish. Gill Na.⁺, K⁺ -ATPase activity was significantly lower in moribund fish. Liver, kidney, intestine, and thyroid follicles of moribund fish displayed various histopathological changes, and corticosteroidogenic (interrenal) tissue could not be identified positively in moribund fish. These findings are discussed in relation to recent work on the chemical burdens (industrial and agricultural hydrocarbons) found in livers from some of the fish examined in this study.     

Imprint of past environmental regimes on structure and succession of a deep-sea hydrothermal vent community

Dramatic perturbations of ecological communities through rapid shifts in environmental regime do not always result in complete mortality of residents. Instead, legacy individuals may remain and influence the succession and composition of subsequent communities. We used a reciprocal transplant experiment to investigate whether a legacy effect is detectable in communities experiencing an abrupt increase or decrease in hydrothermal fluid flux at deep-sea vents. Vent habitats are characterized by strong gradients in productivity and physico-chemical stressors, both of which tend to increase with increasing vent fluid flux. In our experiments, many species survived transplantation from cool (water temperatures <2°C above ambient) to warm (4–30°C above ambient) habitats, resulting in significantly higher species richness on transplanted than remaining experimental substrata. A legacy effect was much less apparent in transplantation from warm to cool habitat, although a few vestimentiferan tubeworms, normally restricted to warm habitat, survived transplantation. The asymmetry in influence of legacy individuals suggests that productivity enhancement may outweigh potential physiological stress in setting limits to distributions of vent invertebrates. This influence of biological processes contrasts with theory developed in the rocky intertidal that predicts the predominance of physical control at the high-stress end of an environmental gradient. Prediction of successional transitions in vents and other habitats experiencing regime shifts in which remnant species may survive must take into account the possible influence of historical effects.