Mean Total Abundance Research Articles

Copepod assemblages in a highly dynamic equatorial estuary on the Brazilian Amazon Coast

AbstractThis study describes the spatial and temporal dynamics of the copepod fauna in the estuary of the Caeté River, a highly dynamic environment characterized by a unique set of hydrological and hydrodynamic attributes. This ecosystem is part of the Amazon Coastal Zone (ACZ), which sustains one of the world's largest continuous tracts of mangrove forest. In the present study, a predominance of high‐energy conditions characterized by macrotides and strong tidal currents was observed throughout the year. Salinity (0.03 ± 0.05–40.00 ± 0.84) and temperatures (26.43 ± 0.10–30.08 ± 0.43 °C) were higher than during the rainy season at all sampling stations. The highest chl‐a concentration (3.92 ± 1.47–17.63 ± 2.60 mg·m−3) was recorded at the most oligohaline (innermost) station during the rainy season, while no spatial or seasonal pattern was found in dissolved nutrient concentrations, except for phosphates, which exhibited the highest concentrations during the dry season. A total of 22 copepod taxa was identified, of which the most abundant were Oithona hebes, Oithona oswaldocruzi, Acartia tonsa, Paracalanus quasimodo, Euterpina acutifrons and Pseudodiaptomus marshi. Copepodites and nauplii were also recorded. Mean total copepod abundance varied from 710.73 ± 897 individuals (ind.)·m−3 at the inner station to 236,486 ± 398,360 ind.·m−3 near the mouth of the estuary (outermost station). The results reflected rainfall‐influenced oscillations in hydrological variables, mainly salinity, which determined shifts in the distribution of copepods and their community structure within the study area. This pattern may be typical of estuaries in the ACZ with similar hydrodynamic and hydrological attributes that are not influenced by the Amazon River plume.

Spatiotemporal distributions of intestinal helminths in female lesser scaup Aythya affinis during spring migration from the upper Midwest, USA.

We examined the associations between intestinal helminth infracommunity structure and infection parameters and the age, size, and year and region of collection of 130 female lesser scaup (Aythya affinis) during their 2014-2015 spring migrations through the upper Midwest, USA. We identified a total of 647,174 individual helminths from 40 taxa, including 20 trematodes, 14 cestodes, 4 nematodes and 2 acanthocephalans parasitizing lesser scaup within the study area. Lesser scaup were each infected with 2-23 helminth taxa. One digenean, Plenosoma minimum, is reported for the first time in lesser scaup and in the Midwest. Mean trematode abundance and total helminth abundance was significantly less in 2015 than 2014, and we suspect that colder weather late in 2015 impacted the intermediate host fauna and caused the observed differences. Brillouin's species diversity of helminths was greatest in the northernmost region of the study area, which coincides with the range of a non-indigenous snail that indirectly causes annual mortality events of lesser scaup. While host age and size were not determined to be influential factors of helminth infracommunity structure, non-parametric ordination and permutational analysis of co-variance revealed that year and region of collection explained differences in helminth infracommunities. Our results suggest that spatiotemporal variations play an important role in the structure of intestinal helminth infracommunities found in migrating lesser scaup hosts, and may therefore impact host ability to build endogenous reserves at certain stopover locations in the Midwest.

A first description of ciliate assemblages in a subtropical, eutrophic bay, South China Sea: species assemblage and environmental correlates

The ciliate community together with physical-chemical variables was investigated in a subtropical, eutrophic bay of the South China Sea from January 7–10 (dry season) and April 27–30 (wet season), 2012. Both temperature and salinity exhibited typical seasonality. A total of 27 species of ciliates belonging to 19 genera were identified, and the dominant species were Strombidium globosaneum in January and Codonella rapa in April. The composition and abundance exhibited spatial and temporal fluctuations, with total mean abundance of ciliates in April (1219 ± 919 ind l-1 ), was much higher than that in January (283 ± 137 ind l-1 ). Spatially, high species numbers were found mainly near the mouth of the estuary, and the abundance decreased from inside to the mouth of the bay. Statistical analysis showed that ciliate assemblages were closely related to the environmental variables. The distribution patterns of salinity and chlorophyll a concentration were similar, suggesting that, prey abundance may correlate significantly with ciliate abundance, and salinity may not be the main factor explaining the spatial variation in the ciliate community in the study area.

Planktonic foraminiferal biogeography in the Indian sector of the Southern Ocean: Contribution from CPR data

Within the framework of the Scientific Committee on Antarctic Research (SCAR) Southern Ocean-Continuous Plankton Recorder (SO-CPR) Survey, the oceanic regions around Crozet and Kerguelen Islands were investigated in February–March 2013. Living planktonic Foraminifera (LPF) were collected in the upper mixed layer with a CPR along a 2160 nautical mile sea transect that crossed main hydrological fronts in the Indian sector of the Southern Ocean. In the SO-CPR database, mean total abundances of Foraminifera occurring during late austral summer are highly variable at an inter-annual scale, from 10 to 250 ind.m−3, representing 10–40% of the total zooplankton abundance, respectively. In the Southern Ocean, major inter-annual changes in zooplankton community structure were already reported. In this study, we describe the large scale distributional pattern of individual planktonic foraminiferal species living in near-surface waters of the Indian sector of the Southern Ocean, and we attempt to explain why major spatial variability in relative species abundances occurs during a late austral summer.In February–March 2013, LPF total abundances recorded between 42.86°S and 56.42°S ranged from 0 to a maximum of 258 ind.m−3. In the Open Ocean Zone, the LPF community was composed of four major species (Globigerinita uvula, Neogloboquadrina pachyderma, Neogloboquadrina incompta, Globigerina bulloides). Generally, LPF total abundances are supposed to mirror primary production induced by hydrological fronts or induced by topography near Crozet and Kerguelen Islands. However, during late austral summer 2013, high foraminiferal abundances in the upper mixed layer did not always match the pattern of near-surface primary production (high Chl-a concentration areas delineated from satellite imagery). Low LPF standing stocks in late austral summer in the Southern Ocean contrasted with the presence of high densities of heavily silicified diatoms. This suggests that the late bloom production is not a suitable resource for planktonic Foraminifera. Consequently, LPF regional distribution in the upper mixed layer cannot be directly reconstructed from Chl-a concentration maps derived from satellite imagery. Knowledge of phytoplankton community composition is needed to understand the impact of primary production on foraminiferal population dynamics. Our results also emphasize that the polar/subpolar foraminiferal assemblages are characterized by high abundances of G. uvula in the iron-enriched waters surrounding the French Sub-Antarctic Islands. This species might react either to coastal or late summer production in high latitudes.

Waders (Aves, Charadriiformes) in a Mediterranean remnant wetland: a year-round pilot study evidences contrasting patterns in diversity metrics

Around a yearly cycle (August 2011 - July 2012), we studied the assemblages of waders (Aves Charadriiformes) occurring in a Mediterranean remnant wetland, obtaining a set of diversity metrics. Mean total abundance shows a complementary pattern when compared to species richness and diversity: the highest values of mean total abundance were observed in December-January, due to high dominance of only one very abundant and gregarious species (the lapwing Vanellus vanellus). On the contrary, in this period, species richness and diversity showed the lowest values. These last metrics were highest in values during the April-September period when a large number of species of conservation concern utilize muddy areas as trophic and stop-over sites, due to the seasonal water stress. The highest values in species turnover index were observed between December-January and February-March when passage migrants (high richness, low abundance) substitute the wintering species (low richness, high abundance). Our data highlight that, in Mediterranean remnant wetlands, strategies should be addressed to increase the muddy suitable areas in the April-September period in order to maximize species richness and diversity. In fact, in these months these habitats host pre- and post-breeding migrant waders of conservation concern.

Seasonal abundance of the demersal copepod <i>Pseudodiaptomus cokeri</i> (Calanoidea: Pseudodiaptomidae) in a Caribbean estuarine environment

Seasonal abundance variations of the demersal copepod Pseudodiaptomus cokeri were examinated at three locations (center, north shore and south shore) in Phosphorescent Bay, Puerto Rico, throughout an annual cycle. Nocturnal oblique tows ( 2 1 :00-2 3 :00 hr) were taken biweeldy (three replicates) at each location with a coDicaI net (mouth diamcter = 0.5 m; mesh size = 1 35 11m) and a standard calibrated flowmeter. Water temperature and salinity measurements were taken at the surface and near the bottom in each location before towing activities using a SCT meter. o Chlorophyll-a concentrations were fluorometricaIly determined. The adult and copepodite stages of this species accountcld for approximately 1 .6% of the annual mean total zooplankton abundance of the bayo Higher abundance of P. cokeri (mean:l:l SD = 4 1 9 1 :!: 1 444 iÍldividuals m-3) was associated with ool water temperatures and dry conditions (cooVdry season) which prevailed betw'een December and March relative to the period between April and November (wann/wet seasón) with lower abundance. F1uctuations of this population followed progressive increments in chlorophyll- a concentrations at the three sampling statigns (One-way ANOVA)

Annual variation of parasite communities of deep-sea macrourid fishes from the western Mediterranean Sea and their relationship with fish diet and histopathological alterations

Parasite communities of three abundant benthopelagic macrourid species (Hymenocephalus italicus, Nezumia aequalis and Trachyrincus scabrus) of the upper slope from the western Mediterranean were analysed seasonally. Histopathological, dietary and environmental information (temperature, salinity, O2 and turbidity) were also obtained. The three fish hosts shared only three parasite species (the nematodes Raphidascaris macrouri and Hysterothylacium aduncum and the acanthocephalan Echinorhynchus trachyrinci). H. italicus, the most benthopelagic fish, showed low parasite richness and diversity. The highest total mean abundance of parasites was found in spring for H. italicus and T. scabrus, coinciding with the highest prevalence/abundance of the majority of parasites whereas parasites of N. aequalis exhibited the highest richness, mean abundance and diversity in winter. Parasites related with benthic or infaunal preys were linked to autumn and summer samples off Besós (Barcelona). Some parasites were also linked to high turbidity, which may be due to higher abundances of the intermediate hosts, such as near-bottom zooplaktonic or suprabenthic preys. Few histopathological alterations (e.g. cysts of unknown aetiology) were observed restricted to the two most benthic-feeding fish species inhabiting more closely the near-bottom/sediment level, especially in autumn.

Macrozoobenthos communities in the area of marine pipeline route at Piltun-Astokhskoye oil field (shelf of northeastern Sakhalin) and their long-term variability

Results of macrozoobenthos surveys (in total 86 stations, 432 sediment samples) in the area of marine pipeline route at Piltun-Astokhskoye oil field in July of 2007-2010 are presented. The sediment samples were collected by van Veen sampler (1-3 samples per site from the area 0.05 m 2 , 0.11 m 2 , or 0.25 m 2 ) at the depth 0-45 m. The samples were washed by sea water through the sieve with mesh 1 mm, and the residues including macrobenthos were preserved by 4 % buffered formaldehyde for later processing with total identification of macrozoobenthos (species composition, abundance and biomass) in the laboratories of Far-Eastern Research Hydrometeorological Institute and Institute of Marine Biology in Vladivostok, following to standard techniques. The data were analysed using the PRIMER software including multidimensional cluster analysis of samples by hierarchical agglomerative method of group-average linking based on Bray-Curtis similarity of the macrozoobenthos species composition by biomass. In total, 272 species of macrozoobenthos are identified at the surveyed area, with the highest species number for amphipods (86 species) and polychaetes (72 species). Mean total abundance of macrozoobenthos is 26556.4 ± 2660.9 ind/m 2 , its mean total biomass is 669.7 ± 40.3 g/m 2 . Cumaceans and amphipod crustaceans are the most numerous groups; sea-urchins, bivalves and cumaceans have the highest biomass. Five benthic communities are defined by cluster analysis. There is concluded that the bottom sediments and depth are the main factors determining the characteristics and distribution patterns of benthic assemblages at present time.

Benthic conditions around a historic shipwreck: Vrouw Maria (1771) in the northern Baltic proper

Since her shipwreck in 1771, the wooden vessel Vrouw Maria has been lying on the seabed at 41m depth on the border between the Archipelago Sea and the northern Baltic proper, off the southern coast of Finland. The wreck lies in an upward position in a right angle to the dominating bottom current, which is potentially affecting seabed topography, sediment characteristics and zoobenthic communities both upstream (NE) and downstream (SW) of the wreck. This multidisciplinary study attempts to clarify abiotic and biotic patterns and processes in the vicinity of the wreck by combining field investigations with physical simulation studies in the field and in the laboratory. Multibeam echo-sounder techniques were utilised to generate a map of the wreck area and sediment grab samples were taken to characterize the sediment type and its zoobenthic community. A medium-sized field experiment generated data on the accumulation of sediment organic matter in the presence and absence of a current and/or a barrier on the seafloor and a small-scaled laboratory study was conducted to simulate scour forming processes.The results showed that a deeper basin, scour area, with the dimensions 150×300m, was present downstream of the wreck and there was also a smaller scour area upstream of the wreck. Similar traces on the bottom were simulated in the laboratory. The organic content (recent mud) and the proportion of finer sediment were more pronounced in areas closer to both sides of the wreck. These results were in turn imitated in a field experiment, where the accumulation of organic matter in the sediment increased significantly downstream, when a current was interrupted by a barrier. Regarding zoobenthos in the wreck area, 11 taxa and a mean total abundance of 773 individuals per m2 were registered. The dominant species were Macoma balthica and Marenzelleria sp., which together made up >80% of the total number of individuals. Multivariate data analyses showed significant differences in community structure between upstream and downstream sides of the wreck and these differences were basically expressed as more individuals upstream of the wreck of the seven most common species. Univariate data analyses also showed significantly more species and higher total abundance in the scour area upstream of the wreck compared to the downstream scour area. The weakened communities downstream of the wreck were possibly due to accumulation of organic matter and more frequent occurrence of hypoxia. The results are useful for describing bottom areas around long-term physical barriers/artificial reefs, as background measurements ahead of possibly increased archaeological diving activities, sediment excavations or measures taken to raise the wreck to the surface, as well as for any attempts to preserve the wreck in situ.

An ecological assessment of Foul and Folly Bays, Morant wetlands area, Jamaica using Ecopath with Ecosim

The Morant wetlands bays (Foul and Folly Bays) are contiguous with the Great Morass, a large wetland located at the extreme eastern end of the island of Jamaica. A multidisciplinary ecological assessment of the bays was conducted from April 2007–May 2008 aimed at generating a baseline of conditions to confirm the trophic status and importance of the area thus providing support for its designation as a protected area. Water column assessment included zooplankton and phytoplankton collections for 12 months at 11 stations. Zooplankton tows were conducted using a 200 μm net (0.5 m hoop diameter) contemporaneous with 5 l Niskin bottle casts for phytoplankton. Zooplankton abundances were determined for nine functional groups (calanoids, cyclopoids, harpacticoids, nauplii, copepodites, carnivores: medusa and chaetognaths, larvaceans and larvae) for which equivalent biomass was generated using conversion factors based on previous studies in Jamaica. Total phytoplankton biomass (mg Chl a m−3) was determined directly using filtration (onto a 0.7 μm filter) and fluorometry while detritus was estimated using the model. Ecopath with Ecosim 5.1 was then used to model the trophic interactions of the planktonic community in the Morant wetlands bays. 116 different taxa of zooplankton were identified with a mean total abundance ranging from 282 ± 56 to 3459 ± 752 animals m−3 across the annual cycle. Total phytoplankton biomass (Chlorophyll a) ranged from 0.14 ± 0.04 to 0.34 ± 0.2 mg m−3 across the annual cycle. A similar study in a pristine bay (Discovery Bay) on the north coast of Jamaica indicated mean zooplankton abundances between 1077 ± 191 and 3794 ± 87 animals m−3 and phytoplankton biomass between 0.4 and 0.8 mg m−3. The plankton parameters suggest that Foul and Folly Bays are even more pristine than Discovery Bay and the Ecopath model indicated that unlike Discovery Bay, these Morant wetlands bays were far more resilient and therefore able to recover from stresses (e.g. eutrophication). However, there is still need for protection of this pristine area as the high abundance of larvae coupled with fast flowing currents through the bays provides evidence that this area could be an important source of larvae to other areas of Jamaica's south coast.

Earthworms in a 15 years agricultural trial

Alternative cropping systems have been proposed to enhance sustainability of agriculture, but their mid and long-term effects on soil biodiversity should be studied more carefully. Earthworms, having important agro-ecological functions, are regarded as indicators of soil biological health. Species composition, abundance, and biomasses of earthworms were measured in autumn 2005–2007 (period 1) and 2011–2013 (period 2) in a trial initiated in 1997 near Paris, France. A conventional, an organic and a direct seeded living mulch-based cropping systems were compared. Earthworms were sampled in a wheat crop by combining the application of a chemical expellant and hand-sorting.In period 1, earthworm abundance did not usually differ in the three cropping systems, but sometimes it was higher in the conventional system. Mean total abundance was 122, 121 and 149individualsm−2 in period 1 and 408, 386 and 216 in period 2 in the organic, living mulch and conventional systems respectively. While earthworm abundance and biomass increased slightly in the conventional system between the two periods, they at least tripled in the other two systems. This was mainly due to the species Aporrectodea caliginosa and Aporrectodealonga in the living mulch cropping system, and to A. caliginosa,Lumbricus castaneus, Lumbricus terrestris and A. longa in the organic system.After at least 14 years, organic and living mulch cropping systems contained between 1.5 and 2.3 times more earthworms than the conventional system. Considering the inter-annual variations in earthworm communities due to climatic conditions and cultural practices, earthworm communities should be assessed over several years before conclusions can be drawn. Moreover, since changes in cultural practices may take a long time to affect earthworm communities, mid and long-term trials are needed to assess the effects of cropping systems on soil biodiversity.

Earthworm assemblages as affected by field margin strips and tillage intensity: An on-farm approach

Earthworm species contribute to soil ecosystem functions in varying ways. Important soil functions like structural maintenance and nutrient cycling are affected by earthworms, thus it is essential to understand how arable farm management influences earthworm species. One aim of arable field margin strips and non-inversion tillage is to enhance agrobiodiversity, however their influence on earthworm species assemblages remains unclear. In particular, on-farm studies conducted over multiple years that capture variability across the landscape are rare. The current study monitored earthworm species assemblages on 4 farms in Hoeksche Waard, The Netherlands, from 2010 to 2012. It was hypothesised that arable field margin strips (FM) and non-inversion tillage (NIT; a reduced tillage system that loosens subsoil at 30−35 cm depth) would have higher earthworm species abundances (epigeics and anecics in particular), soil organic matter, and soil moisture than adjacent mouldboard ploughing (MP) fields, and that earthworm numbers would decrease with distance away from FM into arable fields (MP only). FM contained a mean total earthworm abundance of 284 m−2 and biomass of 84 g m−2 whereas adjacent MP arable fields had only 164 earthworms m−2 and 31 g m−2. Aporrectodea rosea, Lumbricus rubellus, Lumbricus terrestris, and Lumbricus castaneus were significantly more abundant in FM than adjacent arable soil under MP. However, no decreasing trend with distance from FM was observed in earthworm species abundances. A tillage experiment initiated on the farms with FM showed that relative to MP, NIT significantly increased mean total earthworm abundance by 34% to 275 m−2 and mean total earthworm biomass by 15% to 51 g m−2 overall sampling dates and farms. L. rubellus, A. rosea, and L. terrestris were significantly more abundant overall in NIT than MP. FM and NIT positively affected earthworm species richness and abundances and it is noteworthy that these effects could be observed despite variation in environmental conditions and soil properties between samplings, farms, and crops. Higher top-soil organic matter and less physical disturbance in FM and NIT likely contributed to higher earthworm species richness and abundances. The anecic species L. terrestris (linked to water infiltration and organic matter incorporation) was more abundant in FM, but densities remained very low in arable soil, irrespective of tillage system.

Effects of nutrient replacement on benthic macroinvertebrates in an ultraoligotrophic reach of the Kootenai River, 2003–2010

Large impoundments remove substantial amounts of sediment and nutrients from rivers and often limit production by downstream primary producers and secondary consumers. Nutrient levels and macroinvertebrate and fish abundance in the lower Kootenai River (7th order, mean annual discharge = 454 m3/s) in Idaho and Montana declined dramatically after Libby Dam was built in 1972. A subsequent study implicated ultraoligotrophic conditions (total dissolved P [TDP] ≤ 2 µg/L TDP) as a principal causative agent and prompted an on-going experimental nutrient-addition program for the Kootenai River downstream from Libby Dam, with dosing at the Idaho–Montana border. Pre-treatment monitoring began in 2003 and liquid ammonium polyphosphate fertilizer (10-34-0) was added each year during the growing season from 2006 through 2010 with a target TDP concentration of 3 µg/L and TN∶TP near 20∶1. We studied benthic macroinvertebrate responses to the experimental addition and hypothesized moderate increases in invertebrate richness, abundance, and biomass with little change in assemblage structure. We used a before–after control–impact BACI design with macroinvertebrate samples collected pre- and post-treatment from July to early November 2003–2010 from fertilized and unfertilized reaches. After treatment, mean modified (Oligochaeta and Chironomidae subtaxa excluded) total abundance increased 72%, mean total abundance increased 69%, and mean biomass increased 48%. Abundance of Ephemeroptera, the principal insect order in the study area increased 66%. Filter-feeder abundance also increased, indicating increased suspended organic matter in addition to the attached forms consumed by other benthic macroinvertebrates. The first 5 y of experimental treatment resulted in increased food resources for resident native fishes with no major alteration of macroinvertebrate community structure or trophic pathways.

Reevaluación rápida del estado de eutrofización del puerto de Kingston, Jamaica utilizando la comunidad de zooplancton

Previous extensive studies of zooplankton distribution in the eutrophic Kingston Harbour established that it was being continuously contaminated. We assessed the community in 2011, 17 years after a previous study and five years after the introduction of a tertiary waste water system. Sampling was conducted for four weeks at eight stations identical to those sampled in a previous study. We used horizontal surface tows with a 200µm net. A total of 73 zooplankton taxa were identified and copepods dominated with 20 species. Mean total abundances were high, ranging from a minimum of 2 383 animals m-3 in the southern region of Hunts Bay to 194 166 animals m-3at the Inner Harbour. Five zooplankton taxa (Acartia tonsa, Paracalanus spp., Temora turbinata, Penilia avirostris and Lucifer faxoni) that were previously identified as indicators, were again important in the Harbour. The overall zooplankton abundances were similar and in some cases higher than the previous study. There was no significant improvement in the water quality since the introduction of the treatment system at Soapberry. This may be a result of unknown nutrient inputs or of nutrient remaining in the sediments. Rev. Biol. Trop. 62 (Suppl. 3): 231-239. Epub 2014 September 01.

Fish assemblage patterns in the Elbe estuary: guild composition, spatial and temporal structure, and influence of environmental factors

There is still a great lack of information regarding spatial and temporal gradients of quantitative guild composition of the fish fauna and their relation to environmental variables in European estuaries. To fill parts of this gap in knowledge, fish species densities in the Elbe estuary were estimated with high resolution using samples taken by a commercial stow net vessel monthly between April 2009 and October 2010. Altogether, 61 fish species as well as cyprinid hybrids were recorded. A high number of these species belong to the marine life cycle categories of marine stragglers and marine estuarine-opportunists. However, all marine species contributed only 0.4 % to mean total fish abundance, whereas the anadromous species reached a proportion of more than 98 %. The total contribution of freshwater species to the overall catch was 1.4 %. The mean total fish abundance was about 362,989 individuals 10−6 m−3 between April 2009 and October 2010. According to their abundance proportions, the fish fauna was dominated by the following three species: Osmerus eperlanus (96.1 %), Alosa fallax (1.9 %), and Gymnocephalus cernua (0.9 %). Twenty-nine percent of the species had a boreal distribution and 27.4 % belonged to the lusitanian distribution category, whereas a minority of 3.2 % of the species were of Atlantic origin. An additional 40.4 % of the species were freshwater species which were divided into the following five zoogeographical categories: European (19.3 %), Euro-Siberian (8.1 %), Holarctic (6.4 %), Nordic (3.3 %) and Pale-Arctic (3.3 %). The species composition underwent interannual changes comparing both years of investigation at each of the sampling sites in the Elbe estuary. Using the Bio-Env analysis, the maximum correlation between fish assemblage structure and environmental variables was obtained for a parameter combination comprising salinity, water depth, water temperature, and oxygen concentration.

Effect of tillage on earthworms over short- and medium-term in conventional and organic farming

Earthworms play an important role in many soil functions and are affected by soil tillage in agricultural soils. However, effects of tillage on earthworms are often studied without considering species and their interactions with soil properties. Furthermore, many field studies are based on one-time samplings that do not allow for characterisation of temporal variation. The current study monitored the short (up to 53 days) and medium term (up to 4 years) effects of soil tillage on earthworms in conventional and organic farming. Earthworm abundances decreased one and three weeks after mouldboard ploughing in both conventional and organic farming, suggesting direct and indirect mechanisms. However, the medium-term study revealed that earthworm populations in mouldboard ploughing systems recovered by spring. The endogeic species Aporrectodea caliginosa strongly dominated the earthworm community (76%), whereas anecic species remained <1% of all earthworms in all tillage and farming systems over the entire study. In conventional farming, mean total earthworm abundance was not significantly different in reduced tillage (153m−2) than mouldboard ploughing (MP; 130m−2). However, reduced tillage in conventional farming significantly increased the epigeic species Lumbricus rubellus from 0.1m−2 in mouldboard ploughing to 9m−2 averaged over 4 years. Contrastingly, in organic farming mean total earthworm abundance was 45% lower in reduced tillage (297m−2) than MP (430m−2), across all sampling dates over the medium-term study (significant at 3 of 6 sampling dates). Reduced tillage in organic farming decreased A. caliginosa from 304m−2 in mouldboard ploughing to 169m−2 averaged over 4 years (significant at all sampling dates). Multivariate analysis revealed clear separation between farming and tillage systems. Earthworm species abundances, soil moisture, and soil organic matter were positively correlated, whereas earthworm abundances and penetration resistance where negatively correlated. Variability demonstrated between sampling dates highlights the importance of multiple samplings in time to ascertain management effects on earthworms. Findings indicate that a reduction in tillage intensity in conventional farming affects earthworms differently than in organic farming. Differing earthworm species or ecological group response to interactions between soil tillage, crop, and organic matter management in conventional and organic farming has implications for management to maximise soil ecosystem functions.

Genetic and environmental determinants of insect herbivore community structure in a Betula pendula population

A number of recent studies have shown that intraspecific genetic variation of plants may have a profound effect on the herbivorous communities which depend on them. However less is known about the relative importance of intraspecific variation compared to other ecological factors, for example environmental variation or the effects of herbivore damage. We randomly selected 22 Betula pendula genotypes from a local population (< 0.9 ha), cloned them and planted cloned seedlings on two study sites separated at a regional scale (distance between sites about 30 km) to examine an insect community of 23-27 species on these genotypes. B. pendula genotypes did not differ in their species richness, but the total mean abundance and the structure of the insect herbivore community was significantly affected by the genotype, which could account for up to 27% of the total variation in community structure. B. pendula genotype accounted for two to four times more variation in the arthropod community structure than did environmental (block) variation on a local scale, while on a regional scale, genotypic and environmental (site) variation accounted for 4-14% of the arthropod community structure. The genetic effects were modified by environmental variation on both a local and regional scale over one study year, and locally, the largest part of the variation (38%) could be explained by the genotype × environment (block) interactions. Suppression of insect herbivores during one growing season led to changed arthropod community structure in the following growing season, but this effect was minimal and could explain only 4% of the total variation in insect community structure. Our results suggest that both genetic and environmental factors are important determinants of the community structure of herbivorous insects. Together these mechanisms appear to maintain the high diversity of insects in B. pendula forest ecosystems.

Diversifying clearcuts with green-tree retention and woody debris structures: conservation of mammals across forest ecological zones

We tested the hypotheses (H) that on newly clearcut-harvested sites, (H1) abundance and species diversity of the forest-floor small mammal community, and (H2) abundance, reproduction, and recruitment of red-backed voles ( Vigors), would increase with higher levels of structural retention via green-tree retention (GTR) and woody debris (dispersed and constructed into windrows). Study areas were located in three forest ecological zones in southern British Columbia, Canada. For H1, mean total abundance did generally increase with the gradient of retained habitat structure. Mean species richness and diversity were similar among treatment sites but did show an increasing gradient with structural compexity. For H2, mean abundance, reproduction, and recruitment of were higher in GTR and windrow sites than those without retained structures. There was a positive relationship between mean abundance of and total volume of woody debris across treatments. This study is the first investigation of the responses of forest-floor small mammals to an increasing gradient of retained habitat structure via GTR and woody debris on clearcuts. Our assessment of a combination of these two interventions suggested a potentially strong additive effect that could be cautiously extrapolated across three forest ecological zones. With the advent of low levels of GTR on clearcuts, woody debris structures should help provide some habitat to conserve forest mammals on harvest openings.Myodes gapperiM. gapperiM. gapperi

Community structure and decadal changes in macrozoobenthic assemblages in Lake Poyang, the largest freshwater lake in China

Lake Poyang is the largest freshwater lake in China and contains unique and diverse biota within the Yangtze floodplain ecosystem. However, knowledge of its macrozoobenthic assemblages remains inadequate. To characterize the current community structure of these assemblages and to portray their decadal changes, quarterly investigations were conducted at 15 sites from February to November 2012. A total of 42 taxa were recorded, and Corbicula fluminea, Limnoperna fortunei, Gammaridae sp., Nephtys polybranchia, Polypedilum scalaenum and Branchiura sowerbyi were found to dominate the community in terms of abundance. The bivalves Corbicula fluminea, Lamprotula rochechouarti, Arconaia lanceolata and Lamprotula caveata dominated the community in biomass due to their large body size. The mean abundance of the total macrozoobenthos varied from 48 to 920 ind·m-2, the mean biomass ranged from 28 to 428 g·m-2. The substrate type affected strongly the abundance, biomass, and diversity of the macrozoobenthos, with muddy sand substrates showing the highest values. Compared with historical data, remarkable changes were observed in the abundance of macrozoobenthos and the identity of the dominant species. The mean total abundance decreased from 724 ind·m-2 in 1992 to 228 ind·m-2 in 2012. The dominant species have shifted dramatically. Large unionids were dominant before 1998, whereas pollution-tolerant species (e.g., Branchiura sowerbyi) increased in dominance after 2008. Our findings should have implications for the conservation of the benthic biodiversity of this large Yangtze-connected lake.

Long-term responses in population dynamics and diversity of small mammals in riparian and upland habitats within an agricultural landscape

Riparian zones in agricultural landscapes provide linear non-crop habitats for a variety of plant and mammal species, and hence are an important component of biodiversity. To date, variable responses of abundance, species richness, and species diversity of small mammals have been recorded in riparian and upland habitats. To address this variability, we provide a detailed analysis of seasonal changes in abundance and diversity of terrestrial small-mammal communities over a 7-year period within an agricultural landscape in south-central British Columbia, Canada. We tested the hypotheses (H) that abundance, species richness, and species diversity of communities of small mammals (H1), and demographic parameters of reproduction, recruitment, and survival of the major species: deer mouse (Peromyscus maniculatus) and montane vole (Microtus montanus) (H2), would be higher in riparian than upland habitats. Mean total abundance of small mammals was higher in summer and winter, and species richness higher in summer, in riparian than hedgerow habitats. Winter population data supported the total and species abundance patterns for small mammals, but species richness was similar, and diversity lower, in riparian than hedgerow sites during winter periods. Deer mice were the dominant species in terms of abundance and reproductive output for pregnancies and recruitment, but not survival, in riparian sites. Montane voles were similar in abundance and demographic parameters in the two habitats. House mice (Mus musculus) preferred hedgerows and wandering shrews (Sorex vagrans) riparian sites. Demographic parameters for deer mice and montane voles indicated that both riparian and hedgerow sites were “source” rather than “sink” habitats, and likely contribute to maintenance of mammal diversity in agricultural landscapes.