Long‐term plant community changes in managed fens in Ohio,USA

• 1. Long‐term studies are necessary to describe effects of restoration efforts on plant communities and invasive species in North American fen communities. In 1986, 1999 and 2000, wetland plant communities and abiotic factors were sampled in two fens in Ohio that were actively managed as a state nature preserve since 1986. The correlation between plant species and environmental conditions was examined in 1986 to 2000, and changes in woody plant cover were measured on aerial photographs from 1938 to 1997 to analyse long‐term effects of management practices.
• 2. 142 vascular plant species and 32 bryophyte taxa were found in these rich fens, including 13 rare (i.e. state‐listed as endangered, threatened or potentially threatened) and 14 alien species. TWINSPAN analyses identified nine plant community types, and species distributions were correlated with several abiotic factors (groundwater depth, pH, soil organic content, distance from wetland edge and depth of peat). Communities along the wetland edge in deep peat had higher richness, more woody species, more alien species and fewer rare species than communities in areas near sources of flowing groundwater with more marl and less peat.
• 3. There was little change in species richness, evenness, and Shannon's diversity from 1986 to 2000. However, plant species assemblages changed during the study, and changes were different in unmanipulated transects compared with those where habitat managers removed invasive woody plants. An aerial photograph analysis indicated that woody plant cover increased by about 1% each year during 1938 to 1997 despite current management efforts to remove invasive trees and shrubs. Additional strategies should be directed toward reducing shrub encroachment and invasive species while promoting rare species.

Copyright © 2007 John Wiley & Sons, Ltd.     

Aquatic macroinvertebrates and environmental gradients in Phragmites reedswamps: implications for conservation

1. Aquatic macroinvertebrates were sampled from 22 sites in three contrasting reedswamps in the Burry Inlet, south-west Wales, which were respectively estuarine and tidal (Llangennech), coastal and artificial (Ashpits), and inland freshwater (Ffrwd). Species assemblages were ordinated by DECORANA, classified by TWINSPAN and related to physico-chemical factors using correlation, ANOVA and principal components analysis. 2. Reedswamps were not physico-chemically uniform, but varied in dissolved oxygen, nitrogen species, conductivity, water depth and reed character. 3. Among these factors, invertebrate species characteristic of the TWINSPAN groups suggested that conductivity, due to salinity, was an important influence on community composition; different communities were dominated by stenohaline to facultative euryhaline species, or by those characteristic of freshwater. Also, conductivity varied highly significantly across TWINSPAN groups: saline sites supported a higher abundance of fewer taxa, while freshwater sites were characterized by speciose assemblages with more beetles. 4. While major changes due to salinity occurred between and within reedswamps, different reedswamps nevertheless held distinct communities. This suggestion of ‘island’ effects prompts further data on aquatic invertebrates in reedswamps as part of the ‘SLOSS’ debate on their conservation. 5. These data show how salinity in maritime reedswamps provides strong habitat diversity in what appear superficially to be uniform habitats, with importance for example to general site design or managed retreat. The data also reveal that risks to speciose freshwater communities in such sites might arise from tidal inundation or sea level change. © 1997 John Wiley & Sons, Ltd.     

Contrasting changes in freshwater fish assemblages and food webs follow modification of tropical waterways

Fresh waters are increasingly threatened by flow modification. Knowledge about the impacts of flow modification is incomplete, especially in the tropics where ecological studies are only starting to emerge in recent years. Using presence/absence data dated approximately four decades apart (~1966 to ~2010) from 10 tropical rivers, we assessed the changes in freshwater fish assemblage and food web after flow modification. The sites were surveyed with methods best suited to habitat conditions (e.g., tray/push netting for low‐order forest streams, visual surveys for canalised rivers and net casting for impounded rivers). With the presence/absence data, we derived and compared six measures of fish assemblage and food web structure: species richness, proportion of native species, overall functional diversity, native functional diversity, food web complexity and maximum trophic level. We found that changes in community assemblage and food web structure were not generalisable across modification regimes. In canalised sites, species richness and maximum trophic levels were lower in the second time period while the opposite was true for impounded sites. However, proportion of native species was consistently lower in the second time period across modification regimes. Changes in fish assemblages and food webs appear to be driven by species turnover. We recorded 79 cases of site‐specific extirpation and 117 cases of site‐specific establishment. Our data further suggest that turnover in assemblage is again contingent on flow‐modification regime. While the process was stochastic in canalised rivers, benthopelagic species were more likely to be extirpated from impounded rivers where species lost were replaced by predominantly alien fish taxa.     

Fish assemblages structure and function along environmental gradients in rivers of Gabon (Africa)

Abstract –  We examined patterns in fish species assemblages structure and function along environmental gradients in rivers of Gabon. Species presence–absence data from 52 sites were first analysed by canonical correspondence analysis. Results showed that the position of sites along the upstream–downstream gradient, together with elevation and water conductance were the most important predictors of local fish assemblage composition. Assemblage richness and trophic structure were further investigated using regression tree analysis. Results revealed a general increase in species richness from upstream to downstream areas and a transition from insectivorous to omnivorous, herbivorous and piscivorous species along this longitudinal gradient. There were several similarities between these previous patterns and those observed in other temperate streams suggesting a potential convergence in fish assemblage along environmental gradients in tropical and temperate riverine systems. From a conservation standpoint, these results highlight the need to evaluate all habitat types along rivers longitudinal gradient to integrate the full spectrum of species assemblages within conservation plans.     

Function of meiobenthos and microorganisms in cellulose breakdown in sediments of wetlands with different origins in Hokkaido

To validate the mechanism of cellulose breakdown in cold climate wetlands, we investigated cellulase activity in sediments collected from 17 wetland sites in Hokkaido, the northern area of Japan. We evaluated cellulase activity by quantitative analysis of glucose released from carboxymethyl cellulose and found that sediments from peat fens demonstrated high activity, followed by sediments from lagoons and estuaries. Sediments from peat fens also contained greater amounts of organic matter, followed by lagoons and estuaries, thereby suggesting a strong positive correlation between organic matter content and cellulase activity. Evaluation of cellulase activity by qualitative cellulose zymographic analysis showed that various cellulases with different molecular sizes were implicated in cellulose breakdown in wetlands. Among them, cellulose breakdown in Meguma Pond (peat fen), Notsuke Gulf (peat fen), and Lake Utonai (lagoon) was potentially due to microorganism cellulase, while that in Lake Chobushi (lagoon) was ascribed to meiobenthos (Oligochaeta species) cellulase. The findings presented herein suggest that the origin and activity level of cellulase vary depending on the type of cold climate wetland.     

Dependence of fish on subtropical riverine mangroves as habitat in the Ryukyu Islands,Japan

To examine whether fish were dependent on mangrove habitat in the Ryukyu Islands (southern Japan), fish assemblage structures were compared on the downstream side between mangrove-rich and mangrove-free rivers on Ishigaki and Okinawa Islands in 2014 and 2015. The mean species richness and abundance of fish were significantly higher in mangrove-rich rivers than in mangrove-free rivers. Mangrove-related food feeders (e.g., benthic invertebrate and detritus) were more abundant in mangrove-rich than mangrove-free rivers while mangrove-unrelated food feeders (e.g., zooplankton feeders) showed no difference between river types. Cluster and ordination analyses demonstrated that fish assemblage structures were clearly different between mangrove-rich and mangrove-free rivers. Of all of the fish species collected (88 species), half of the species (45 species, 51%) occurred exclusively in the mangrove-rich rivers, 9 species (10%) in the mangrove-free rivers and 34 species (39%) were common in both types of rivers. Commercially important fish (e.g., Lutjanus fulvus and L. argentimaculatus) showed greater abundance of juveniles in mangrove-rich rivers than in the mangrove-free rivers, indicating that mangrove-rich rivers can provide important habitat for a variety of fish, including those commercially important to fisheries.     

The importance of exposed riverine sediments for phytophagous beetles (Coleoptera) in Scotland and northern England

• 1. The distribution of phytophagous beetle assemblages on exposed riverine sediments (ERS) was investigated using 164 species lists from sites in four river catchments in Scotland and northern England.
• 2. The major influences affecting assemblage distribution were differences in highland and lowland catchment types and within these catchments the amount of vegetation cover. The position of sites within catchments was also important, with differences between tributary and upstream ERS and sites further downstream. Sediment composition had little influence.
• 3. River straightening and impoundments had a significant effect on the distribution of species assemblages.
• 4. A number of nationally rare and scarce species were recorded indicating that ERS appear to be important areas of relatively natural habitat within highly managed landscapes. The habitat diversity of phytophagous assemblages throughout the four catchments differed from that with other beetle groups sampled on the same sites.
• 5. ERS appear to be important sites for phytophagous beetles and the presence of nationally rare and scarce species increases ERS conservation value on sites usually considered important for other invertebrate groups.

Copyright © 2002 John Wiley & Sons, Ltd.     

Estuarine fishes in two large eastern Australian coastal rivers—does prawn trawling influence fish community structure?

Fish communities were sampled quarterly over a 2-year period at sites along the estuarine gradient of two large coastal rivers, the Richmond and Clarence, located in eastern Australian (NSW). A total of 175 582 fish from 73 species was captured, with two species making up 65% of this total. Many fish species of economic importance in local coastal waters were captured, predominantly as juveniles. Multivariate analysis revealed three significantly different groupings of sites corresponding to the marine, brackish and tidal-freshwater zones of the two rivers. The two rivers were remarkably similar in terms of overall abundance and diversity of fish, and structuring of fish communities, despite a large-scale and intensive prawn trawling industry operating on the Clarence River. Dependency of fishes on estuarine habitats and the distribution of some of the dominant fish species in relation to estuarine gradients are discussed.     

A North African–European transition fauna: water beetles (Coleoptera) from the Ebro delta and other Mediterranean coastal wetlands in the Iberian peninsula

1. The aquatic Coleoptera of some major wetlands in the Mediterranean coast of Spain were surveyed, with the aim of assessing their conservation value and the status of some coastal species in the Iberian Peninsula. 2. Classification of 59 species from 13 sites between the deltas of the rivers Ebro and Llobregat using TWINSPAN suggested that water origin and amount and structure of vegetation were major factors influencing the composition of the coastal water beetle communities. 3. The Ebro delta is considered to be a key biogeographical area, being the limit of the distribution of a number of north African and European species. Coastal sites in the Iberian peninsula sustain the only known populations in continental Europe of at least three Ethiopian species, although two of them may have become extinct. Some European species known to have reached the north of Catalonia were also considered to be possibly extinct in the Iberian peninsula owing to the destruction of their habitats. Three circum-Mediterranean coastal species were recorded for the first time in the Iberian peninsula, one of them in a genus new to its fauna. 4. Despite the scarcity of true endemics—the result of the recent geological origin and the temporal dynamics of coastal systems—some species were exclusive to temporary habitats, and had very restricted distributions. 5. Although most of the areas studied have some form of protection, this is mainly focused in large, permanent lagoons and on the vertebrate fauna. The need to include marginal areas and invertebrates in the protection plans for the area is stressed.     

A botanical classification of standing waters in Britain: Applications for conservation and monitoring

1. A classification is described based on an indicator species analysis of the vegetation of 1124 fresh and brackish standing water sites in Great Britain. 2. Ten Site Types are recognizable by their assemblages of plants, and these groupings are related to the alkalinity, pH and conductivity of the water. One Type consists of extremely acid water bodies on peat. There are two other nutrient-poor Types, distinguishable from each other largely by size and substrate, as well as by vegetation. These sites lie mostly in the north and west of Britain. There are four distinct Site Types with nutrient-rich water, one characteristic of Scotland, the rest more typical of the lowlands of southern and eastern Britain. A further Site Type is regarded as mesotrophic and is found mainly in northern England and Scotland. Of the remaining two Site Types, one shows an unusual combination of base-poor and base-rich characteristics and the other comprises brackish sites in Scotland. 3. The use of the classification for producing Trophic Ranking Scores, both for individual species and for sites, and the application of these scores for monitoring the nutrient status of fresh waters are explained. 4. The application of the classification to the selection of sites important for nature conservation is discussed, with special reference to north west Scotland. 5. This classification is compared with other classifications of aquatic vegetation in Great Britain.     

Effectiveness of fishing gears to assess fish assemblage size structure in small lake ecosystems

Measurement of fish body‐size distributions is increasingly used as a management tool to assess fishery status. However, the effects of gear selection on observed fish size structure has not received sufficient attention. Four different gear types (experimental gill nets, fine mesh bag seine, and two different sized mesh trap nets), which are commonly employed in the study area for fisheries surveys, were used to fish in five small (< 200 ha) lakes to evaluate differential catch in terms of species composition and assemblage size distributions. Kolmogorov–Smirnov tests revealed that, out of the five lakes and six comparisons, the four gear types captured fish of statistically similar size distributions in only one instance. Non‐metric multi‐dimensional scaling followed by a multi‐response permutation procedure revealed that the species composition of fish captured by these gears also differs. These results support the notion that multiple gear types should be used to assess body‐size distributions as well as fish assemblage composition.     

Morphological variability of Atlantic salmon Salmo salar and brown trout Salmo trutta in different river environments

Abstract – The morphologies of sympatric juvenile Atlantic salmon Salmo salar parr and brown trout Salmo trutta parr were compared between Irish rivers with contrasting hydraulic environments – a high‐gradient and a low‐gradient tributary from the River Barrow catchment, south‐east Ireland and a high‐gradient river from the Burrishoole catchment, west of Ireland. The two catchments differ markedly in mean annual precipitation (849.0 mm year^?1 and 1370.3 mm year^?1 for the Barrow and Burrishoole catchments, respectively). Parr of both species demonstrated morphological variation between and within catchments. Changes in metrics such as pectoral fin length, body depth and body length between and within catchments suggest that hydraulic forces were a major determinant of morphological variation. Both species from the Burrishoole catchment had relatively larger pectoral fins, longer heads, larger eyes and shallower bodies than conspecifics from the Barrow catchment. In rivers subject to frequent rainfall‐driven high discharges, such as those in the Burrishoole catchment, a more fusiform body and head shape coupled with larger pectoral fins may reduce the energetic cost of maintaining position in the water column, as well as increase stability and manoeuvrability. The larger eyes in both parr species in the Burrishoole catchment could further be a response to the lower visibility of the more turbid and peat‐stained waters or to the reduced prey availability. The results of this study demonstrate that local adaptation to flow conditions can yield morphologically distinct populations and that multiple species can exhibit parallel phenotypic responses to changing environmental conditions.     

Influence of artificial headlands on fish assemblage structure in the surf zone of a sandy beach,Kashimanada Coast,Ibaraki Prefecture,central Japan

To determine the effects of artificial headlands (groins with an anchor-shaped head portion) on the surf-zone fish assemblage structure of a sandy beach with strong wave action, three study sites (headland site sheltered behind the head portion, pocket-beach site between two adjacent headlands and exposed reference site without headlands) were sampled on the Kashimanada Coast, central Japan, in summer and autumn in 2012 and 2013. Distinct differences in physical conditions were recognized between the headland site and the other two sites throughout the study period, the former being characterized by lower wave height and turbidity, finer sediment particles and richer detritus. The fish assemblage structures also differed among the sites, the headland site supporting greater species and individual numbers. Cluster analysis showed clear differences in species composition of fish assemblages between the headland site and the other two sites. In addition, small-sized fishes tended to be more abundant at the headland site compared with the other two sites, although no differences were apparent in fish assemblage structure between the pocket-beach and reference sites. These results suggested that the presence of headlands had marked effects on the surf-zone fish assemblage structure in the study area.     

长江芜湖江段鱼类多样性及其群落结构的时空格局

为制定合理的渔业资源保护措施与管理对策,2009年按季度共4次调查了长江芜湖江段鱼类多样性及其群落结构。结果显示:该江段现有鱼类54种,其中以似鳊(Parabramis pekinensis)、油(Hemiculter bleekeri bleek-eri warpacho)、短颌鲚(Coilia brachygnathus Kreyenberg et Pappenheim)、鲫(Carassius auratus)等中小型鱼类为常见种和优势种,表明了该江段的鱼类组成存在明显的小型化特点。长江干流沿岸浅水区的鱼类多样性最高,江心深水区最低,而青弋江支流、漳河支流和漳河河口的居中,青弋江的鱼类种数和个体数都显著低于沿岸浅水区,但漳河的鱼类数量与沿岸浅水区无明显差异。江心深水区的鱼类群落与其它样点明显不同,而青弋江的鱼类群落与沿岸浅水区、漳河及其河口的鱼类群落也存在部分差异。鱼类群落结构的季节动态无显著性。     

Stable or changing lakes? a classification of aquatic macrophyte assemblages from a eutrophic shallow lake system in the United Kingdom

1. It is proposed that an appreciation of patterns of change and stability in macrophyte floras is an important tool for lake managers. 2. The presence and abundance of aquatic macrophytes was annually monitored (from 1983 to 1995) along permanent transects in 13 shallow lakes in the Broads wetland in eastern England, United Kingdom. 3. Cluster analysis (TWINSPAN) revealed three Broad Macrophyte Types (BMTs) or assemblages. Two of these were sub-divided into four and then again into six sub-types. BMT1 had a constant presence (i.e. in more than 60% of all samples) of charophytes, Potamogeton pectinatus L.,Myriophyllum spicatum L. and Najas marina L. BMT2 had a constant presence of Nuphar lutea (L.) Smith and filamentous algae. BMT3 consisted of sites without macrophytes. 4. The BMTs provided a useful regional classification for aquatic vegetation in shallow, calcareous, and slightly brackish lakes with relatively organic sediments. The BMTs were compared with national and international classifications. The value of BMTs as conservation targets was assessed. 5. Analysis of changes of macrophyte assemblages with time, using ordination (CANOCO) and time-series plots, revealed lakes with stable, drifting, or erratic and unstable macrophyte assemblages. 6. The method of presentation used facilitates the interpretation of year-to-year macrophyte changes. The implication is that management effort can be more effectively directed towards conservation targets. The effects of management on the aquatic flora, such as dredging and biomanipulation, were shown to be easily evaluated using Cockshoot Broad as an example. © 1998 John Wiley & Sons, Ltd.     

Effects of mangrove deforestation on fish assemblage at Pak Phanang Bay,southern Thailand

Daytime sampling using a seine net was conducted at Pak Phanang Bay (Nakhon Si Thammarat Province, Thailand) in February and July 2006, to determine differences in fish assemblage structures between a mangrove site and an adjacent site completely cleared of mangroves. The overall numbers of fish species and individuals were significantly higher at the mangrove site than the cleared site in both months. Although benthic crustacean feeders showed more species and individual numbers at the mangrove site in both months, the opposite was found for zooplankton feeders. A cluster analysis, based on the abundance of each species, demonstrated that the fish assemblage structures were distinctly different between the two sites. In addition, significant differences in length frequency distributions for each of the four most abundant species were found between the sites in February and/or July. Small individuals of Scatophagus argus, Ambassis nalua, and Tetraodon nigroviridis were more common at the mangrove site, and of Chelon subviridis at the cleared site. These results suggest that mangrove deforestation exerts marked effects on fish assemblages.