Exotic Earthworms Research Articles

Chemical and microbiological changes during vermicomposting of coffee pulp using exotic (Eudrilus eugeniae) and native earthworm (Perionyx ceylanesis) species

Coffee pulp is the main solid residue from the wet processing of coffee berries. Due to presence of anti-physiological and anti-nutritional factors, coffee pulp is not considered as adequate substrate for bioconversion process by coffee farmers. Recent stringent measures by Pollution Control authorities, made it mandatory to treat all the solid and liquid waste emanating from the coffee farms. A study was conducted to evaluate the efficiency of an exotic (Eudrilus eugeniae) and a native earthworm (Perionyx ceylanesis) from coffee farm for decomposition of coffee pulp into valuable vermicompost. Exotic earthworms were found to degrade the coffee pulp faster (112 days) as compared to the native worms (165 days) and the vermicomposting efficiency (77.9%) and vermicompost yield (389 kg) were found to significantly higher with native worms. The multiplication rate of earthworms (280%) and worm yield (3.78 kg) recorded significantly higher with the exotic earthworms. The percentage of nitrogen, phosphorous, potassium, calcium and magnesium in vermicompost was found to increase while C:N ratio, pH and total organic carbon declined as a function of the vermicomposting. The plant nutrients, nitrogen (80.6%), phosphorus (292%) and potassium (550%) content found to increase significantly in the vermicompost produced using native earthworms as compared to the initial values, while the calcium (85.7%) and magnesium (210%) content found to increase significantly in compost produced utilizing exotic worms. Vermicompost and vermicasts from native earthworms recorded significantly higher functional microbial group's population as compared to the exotic worms. The study reveals that coffee pulp can be very well used as substrate for vermicomposting using exotic (Eudrilus eugeniae) and native earthworm (Perionyx ceylanesis).

Exploring chemical analysis of vermicompost of various oil palm fibre wastes

The aim of this work was to study the physical and chemical properties of different oil palm wastes, viz. empty fruit bunch (EFB), oil palm frond (OPF) and oil palm trunk (OPT). A study (84 days duration) was conducted to evaluate the efficiency of an exotic earthworm species (epigeic-African Nightcrawler (Eudrilus euginae)) for the decomposition of different types of oil palm wastes (EFB, OPT and OPF) into valuable vermicompost. The decrease in earthworm’s biomass gain for EFB, OPT and OPF may be due to exhaustion of worm feed in vermicomposters. The percentage of nitrogen, phosphorous and potassium in vermicompost was found to increase while pH and total organic carbon declined as a function of the vermicomposting period. The vermicompost obtained showed an increase in heavy metal content for all the reactors, but levels were still in the range of nutrient in the vermicompost. The data reveal that vermicomposting (using African Nightcrawler) is a suitable technology for the decomposition of oil palm wastes, especially EFB into value-added material.

Do non-native earthworms in Southeast Alaska use streams as invasional corridors in watersheds harvested for timber?

Exotic earthworms from Europe and Asia have invaded previously earthworm-free areas of North America where they consume leaf litter, mix soil horizons, and alter nutrient cycling. Primarily, earthworm introductions occur through human activities; we hypothesized that the combination of logging (i.e., road construction and soil disturbance) and stream transport (i.e., hydrochory) allows earthworms to invade new ecosystems and spread within watersheds. On Prince of Wales Island, AK, we surveyed riparian zones in 11 watersheds with varying timber harvest intensity for terrestrial oligochaetes. Additionally, common invasive earthworms were experimentally submerged in a local stream to test for tolerance to prolonged immersion: all taxa survived immersion for at least 6 days. Using principal components analysis, watershed and harvest variables describing the watersheds upstream of our sampled riparian areas were reduced to two principal components describing harvest intensity (PC1) and harvest style (PC2). Logistic models successfully predicted earthworm abundance (r2 = 0.70) from PC1, which indicated that watersheds with older, intense upstream timber harvest contained larger earthworm populations. Earthworm species richness was best predicted by PC2 (r2 = 0.39), which suggested that earthworm communities in watersheds containing large clear-cut stands were more species-rich. Collectively, these results suggest that (1) invasive earthworms may use streams for dispersal and (2) upstream introductions via timber harvest can initiate downstream earthworm invasions. Hydrochory would allow invasive earthworms to spread at rates (tens of km d−1) that are much greater than previously reported rates of terrestrial spread (5–10 m y−1). Effective control of exotic earthworms in riparian zones will require watershed-level management and surveillance.

Exotic Ecosystem Engineers Change the Emergence of Plants from the Seed Bank of a Deciduous Forest

The anthropogenic spread of exotic ecosystem engineers profoundly impacts native ecosystems. Exotic earthworms were shown to alter plant community composition of the understory of deciduous forests previously devoid of earthworms. We investigated the effect of two exotic earthworm species (Lumbricus terrestris L. and Octolasion tyrtaeum Savigny) belonging to different ecological groups (anecic and endogeic) on the emergence of plants from the seed bank of a northern North American deciduous forest using the seedling emergence method. We hypothesized that (1) exotic earthworms change the seedling emergence from the plant seed bank, (2) L. terrestris increases the emergence of plant seedlings of the deeper soil layer but decreases that of the upper soil layer due to plant seed burial, and (3) O. tyrtaeum decreases plant seedling emergence due the damage of plant seeds. Indeed, exotic earthworms altered the emergence of plant seedlings from the seed bank and the functional composition of the established plant seedlings. Surprisingly, although L. terrestris only marginally affected seedling emergence, O. tyrtaeum changed the emergence of native plant species from the seed bank considerably. In particular, the number of emerging grass and herb seedlings were increased in the presence of O. tyrtaeum in both soil layers. Moreover, the impacts of earthworms depended on the identity of plant functional groups; herb species benefited, whereas legumes suffered from the presence of exotic earthworms. The results highlight the strong effect of invasive belowground ecosystem engineers on aboveground ecosystem characteristics and suggest fundamental changes of ecosystems by human-spread earthworm species.

Long-term effects of lime on earthworm abundance and biomass in an acidic soil on the south-western slopes of New South Wales, Australia

Earthworm populations were monitored annually over 10 years in an acidic soil on the south-western slopes of New South Wales, Australia. The Typic Fragiochrept soil at the experimental site has a strong texture-contrast profile with a soil pH of 4.0–4.2 in 0.01 M CaCl 2 in the 0–20 cm horizon. We found that the site was dominated by two native species, the megascolecids Spenceriella macleayi and Spenceriella montana, and accompanied by three exotic species, the lumbricid Aporrectodea trapezoides, and the acanthodrilids Microscolex dubius and Microscolex phosphoreus. Total earthworm abundance varied from 61 to 188 m −2. Lime, applied as a treatment, favoured all exotic earthworm species; their abundance was 3 times greater in limed soil than in unlimed soil. This strongly indicated that severe soil acidity was the most likely factor limiting, directly and indirectly, these species at this site. In contrast, the responses of the two native species to lime varied from negative ( S. montana) to non-responsive ( S. macleayi), suggesting that these native species are well adapted to acidic soil conditions, and perhaps to the dry seasonal conditions experienced during 5 of the 10 years the site was sampled.

An updated earthworm list for the British Isles and two new ‘exotic’ species to Britain from Kew Gardens

Exotic earthworms have previously been recorded in the UK. Many of those records are from the Royal Botanical Gardens, Kew. Earthworms were collected from Kew on two separate occasions in 2007 (March and August). In total 6 species were found, of which two are new species records for the British Isles. When updating the British earthworm species list it became apparent that many species are not inhabitants of UK soils but are transitory visitors in greenhouses. Their status in soils is currently unknown. A new system of recording earthworm species in the British Isles is proposed and consists of two parts. Part 1 lists those species found living freely in soils, part 2 lists those species whose status is unknown, many of which are likely to be imported visitors found in greenhouses. The need for systematic sampling of earthworms throughout the UK is highlighted and the possible effects of climatic change on earthworm populations are commented on.

Exotic earthworms of great lakes forests: A search for indicator plant species in maple forests

The invasion of exotic earthworms in previously earthworm-free northern deciduous forests has been linked to the disappearance of forest floor litter, declines in plant species richness, and the development of monotypic stands of Carex pensylvanica. However, the impact of exotic earthworms on the regeneration of trees and understory plants is largely unknown. We examined the relationships between earthworm density, plant species richness, leaf litter accumulation, number of tree ( Acer) seedlings, and cover of C. pensylvanica at 14 sites in mesic hardwood forests of the Chequamegon-Nicolet National Forest in northern Wisconsin. Earthworm biomass, especially of the genera Lumbricus, Aporrectodea, and Octolasion was negatively associated with leaf litter mass and number of Acer seedlings. Nine plant species, including two spring ephemerals ( Dicentra cucullaria and Osmorhiza claytonii), a sedge ( Carex deweyana), and an invasive mint ( Galeopsis tetrahit) were negatively correlated with exotic earthworm densities. Dryopteris intermedia and Allium tricoccum, on the other hand, were associated with high earthworm densities. The activities of exotic earthworms appear to have significant impacts on Acer regeneration and the persistence of many herbaceous plants. Our findings suggest that the effects of exotic earthworms on litter mass are strongly related to the observed effects on species composition. Sensitive species can be used as indicators of high and low earthworm densities and might be useful for identifying forests of high conservation value where future invasions of exotic earthworms should be prevented.

Influence of Soil Buffering Capacity on Earthworm Growth, Survival, and Community Composition in the Western Adirondacks and Central New York

We examined how buffering capacity affected natural earthworm communities by comparing well-buffered soils in Madison County in central New York and poorly buffered soils in the western Adirondacks. We also investigated how liming and interspecific competition influenced growth and survival of 2 exotic taxa (Eisenia foetida and Amynthas agrestis) in Adirondack and central New York soils using laboratory microcosms. Earthworms were more abundant and diverse in central New York soils than in western Adirondack soils. Interspecific competition had no effect on growth or survival of either species in microcosms. Survival of A. agrestis was low in Adirondack soils without lime, but liming increased survival to that of central New York soils. Growth rates of E. foetida were lowest in Adirondack soils without lime, but highest in Adirondack soils with lime. Our results suggest that high soil acidity may be preventing exotic earthworms from successfully invading the western Adirondacks.

Responses of Earthworms to Organic Matter at Different Stages of Decomposition

This study was conducted to examine the responses of earthworms to soil organic matter and litter at different decomposition stages and their contributions in litter decomposition processes in southern subtropical areas of China. Two plantations were selected as the study sites: Site I was dominated by the exotic endogeic earthworm species Ocnerodrilus occidentalis; Site II was dominated by epigeic species Amynthas corticis. After the fallen litter and earthworms were removed or expelled, four treatments were set up as: reserving the top soil (0–5 cm, equal to H layer) (H), removing the top soil and adding fresh litter (Le), removing the top soil and adding semi-decomposed litter (Li), and a control with no top soil nor any litter (CK). Five randomized blocks that were enclosed with nylon nets on the top were set up in each site, and then the four treatments were arranged randomly in each block. After 2–3 months, earthworms were collected using the formalin method. The results showed that Ocnerodrilus occidentalis preferred Treatment H though it was found in Treatments Le and Li as well; Amynthas corticis preferred Treatment Li though sometimes it also appeared in Treatment H; and Amynthas sp., another epigeic species, was mainly present under Treatment Le and only appeared in Treatment H occasionally. These findings confirmed that earthworm species belonging to different ecological groups had different responses to organic matter at different decomposition stages. The impacts of earthworm communities dominated by O. occidentalis mainly appeared at the later periods of litter decomposition.

Pandora's Box Contained Bait: The Global Problem of Introduced Earthworms

Introduced exotic earthworms now occur in every biogeographic region in all but the driest or coldest habitat types on Earth. The global distribution of a few species (e.g., Pontoscolex corethrurus) was noted by early naturalists, but now approximately 120 such peregrine species are recognized to be widespread from regional to global scales, mainly via human activities. Species adapted to human transport and to colonization of disturbed habitats are most widespread and are the principal invasive species. We identify a number of endogenous and exogenous factors that may contribute to the successful establishment and spread of peregrine species. Quantification of these factors may help to determine why certain species become invasive while others do not. Recent advances in theory and modeling of biological invasions and in molecular techniques should prove fruitful in improving our understanding of invasive earthworms, as well as in predicting their impacts on ecosystems.

Impact of an exotic earthworm on seed dispersal of an indigenous US weed

Summary Ambrosia trifida L. (giant ragweed), an aggressive weed of US grain crops and indigenous to North America, colonizes no‐tillage crop fields and undisturbed soils despite its large seed size and susceptibility to seed predation. Secondary seed dispersal is critical to seed survival and seedling establishment, yet mechanisms of secondary dispersal are poorly understood for such large‐seeded weedy species. Field experiments were conducted to determine how seed foraging by the European exotic burrowing earthworm Lumbricus terrestris L., affected A. trifida seed burial and seedling recruitment, and to determine seed selectivity by L. terrestris. Earthworms collected and buried over 90% of A. trifida seeds placed on the soil surface at a rate eightfold faster than abiotic seed burial. There was a sixfold higher concentration of seeds in burrows than in surrounding soil and a mean of 127 A. trifida seeds per burrow after a single season of A. trifida seed dispersal. Earthworms buried A. trifida seeds from 0·5 to 22 cm deep and reduced recruitment by 37% compared to seeds buried abiotically and protected from predators, due to burial of some seeds below emergence depth limits. However, seedling biomass was increased by 30%. Earthworms foraged selectively among seeds of 11 large‐seeded species and collected more seeds of A. trifida than of other species. The earthworms buried small (8·5 mm) A. trifida seeds more deeply and reduced their emergence more than large (11·5 mm) A. trifida seeds. Synthesis and applications. The novel interaction of L. terrestris and A. trifida increases seed bank formation of A. trifida. Burrows of L. terrestris provide safe sites for seeds of A. trifida that may increase seedling establishment in environments with a high risk of seed predation. Control measures to prevent reproduction by A. trifida should be increased where L. terrestris is present due to the earthworms’ ability to bury and protect weed seeds. Selective seed caching by this widely distributed earthworm species may change plant community composition in agricultural and natural areas in North America and influence the evolution of seed traits. Land managers should consider the effects of L. terrestris on seedling regeneration of native and exotic plant species in areas undergoing colonization by L. terrestris.

Distribution and impacts of invasive earthworms in Canadian forest ecosystems

In Canada it is generally accepted that most indigenous earthworms did not survive glaciation, and that the majority of the earthworms now inhabiting Canadian soils are relatively recent introductions of European origin. Although these exotic earthworms are generally considered to be beneficial in agricultural soils, their effects can be less benign in forested ecosystems. Studies have shown that invading earthworms can significantly alter the forest floor, affecting the distribution of carbon, nitrogen and other chemicals, roots, microbes and other elements of the soil fauna, and even understory vegetation. This paper summarizes the current distribution of exotic and native earthworm species in Canadian forests and draws on the results of studies of invasion patterns and environmental impacts in northern forests in North America and Europe to discuss potential outcomes for forests in Canada. The potential for variables such as temperature, pH, litter palatability and dispersal, to limit or promote the invasion of exotic earthworms in Canadian forests is discussed, and areas for future research are proposed. The same earthworm species that are invading forests in northern Europe and the US are also invading Canadian forests. Several species of exotic earthworms are already established in a wide range of deciduous and coniferous forest types, including the boreal. Evidence is presented to suggest that further expansion into Canadian forests is likely.

土壤温度和湿度对外来种蚯蚓Pontoscolex corethrurus 产茧和幼蚓孵化的影响

Laboratory experiments with split—plot block design were conducted to examine the effects of soil temperature and moisture on cocoon production and hatching of the exotic earthworm Pontoscolex corethrurus under controlled conditions. Results showed that consecutive cocoon production and hatching took place at all three soil temperatures and at the two higher soil moisture conditions, used in this experiment. Cultivation time, soil moisture and temperature had significant effects on cocoon production and hatching of P. corethrurus. Earthworms suffered a diapause or even died when reared in soil with 20% moisture content. The greatest cocoon production and hatching rate were observed at 35% soil moisture content. When soil moisture was preferable (e.g. 35%), cocoon production was greater at higher temperatures than at lower temperatures. Hatching rate increased with soil temperature if the soil moisture content was preferable; however it was restrained if the temperature was too high or too low. The greatest hatching rate only occurred at a combination of 25°C soil temperature and 35% soil moisture content. The results also showed that soil moisture was the primary factor limiting the reproduction of P. corethrurus, the effects of soil temperature on earthworm reproduction was influenced by soil moisture.

Removal of invasive shrubs reduces exotic earthworm populations

Invasive species are a leading threat to native ecosystems, and research regarding their effective control is at the forefront of applied ecology. Exotic facilitation has been credited with advancing the success of several aggressive invasive species. Here, we suggest using the knowledge of exotic facilitations to control invasive earthworm populations. In northern hardwood forests, the invasive shrubs Rhamnus cathartica (buckthorn) and Lonicera x bella (honeysuckle) produce high quality leaf litter, and their abundance is positively correlated with exotic earthworms, which increase nutrient cycling rates. We performed an invasive plant removal experiment in two northern hardwood forest stands, one dominated by buckthorn and the other by honeysuckle. Removal of invasive shrubs reduced exotic earthworm populations by roughly 50% for the following 3 years. By targeting invasive species that are part of positive feedback loops, land managers can multiply the positive effects of invasive species removal.

Evidence for human‐mediated dispersal of exotic earthworms: support for exploring strategies to limit further spread

As potent ecosystem engineers, non-native earthworms are altering the fundamental structure and function of previously earthworm-free cold-temperate hardwood forests in North America. Discarded earthworms used for fishing bait has been presumed to be an important vector for the continued spread of non-native earthworms because epicentres of invasion often include boat landings, lakeshores and roads. However, controversy has remained about the overall importance of human-mediated spread vs. natural expansion of established earthworm populations. In this issue of Molecular Ecology, Cameron et al. explore the continued role of humans in dispersing non-native earthworms.

Disturbance dynamics influence Carex pensylvanica abundance in a northern hardwood forest1

Abstract We examined relationships involving the abundance of Carex pensylvanica Lam., a native sedge that can form dense mats in northern hardwood understories, and three types of disturbances: forest management, deer herbivory, and exotic earthworm activity. Stands managed using even-aged silvicultural systems in areas with high deer densities (> 20 deer km−2) had greater C. pensylvanica cover than stands managed using even-aged silvicultural systems in areas with lower deer densities (10–20 deer km−2), or unharvested second-growth communities. Stands managed using uneven-aged silvicultural systems were not significantly different from any other treatment group, regardless of deer density. There was a significant management × deer × earthworm interaction, and earthworm density had a positive relationship with C. pensylvanica cover in most management history × deer density combinations. High levels of disturbance associated with at least two of the three factors considered in this study were associated w...

Construction of an Electrical Device for Sampling Earthworm Populations in the Field

Methods for the estimation of earthworm population densities range from laborious handsorting, through chemical applications, to electrical extraction. Of these methods, only the electrical extraction allows for sampling of earthworms without detrimental soil disturbance or contamination. However, a device to extract earthworms under controlled electronic conditions is not readily available to researchers. An improved design on the long-established electrical octet extraction device is presented. This improved design allows for hand-built construction of an apparatus that can be connected to external drive controls, including data loggers and PC-controlled drivers. This design also allows for modification of sampling settings to suit specific environmental conditions, with control of voltage, and operation with a static or dynamic electrical field being generated. Operational ability to extract earthworms was validated in field trials in both a forested area and an agricultural field. Earthworm sampling efficiencies calculated in comparison to hand-sorting averaged around 90% for the electrical device; however, because of limited field use in this instance, these efficiencies support the general functioning of the apparatus rather than an absolute assurance of quality. In using this hand-built device we established that this design is capable of extracting both native and exotic earthworms of various age and size class under various soil conditions, that soil disturbance and contamination can be avoided, and that the device can easily be transported into remote locations.

Exotic earthworm effects on hardwood forest floor, nutrient availability and native plants: a mesocosm study

A greenhouse mesocosm experiment, representing earthworm-free North American Acer-dominated forest floor and soil conditions, was used to examine the individual and combined effects of initial invasion by three European earthworm species (Dendrobaena octaedra, Lumbricus rubellus and Lumbricus terrestris) on the forest floor and upper soil horizons, N and P availability, and the mortality and biomass of four native understory plant species (Acer saccharum, Aquilegia canadensis, Aralia racemosa, and Carex pensylvanica). All the three earthworm species combined caused larger impacts on most variables measured than any single earthworm species. These included loss of O horizon mass, decreased thickness of the O horizon and increased thickness of the A horizon, and higher availability of N and P. The latter finding differs from field reports where nutrients were less available after invasion, and probably represents an initial transient increase in nutrient supply as earthworms consume and incorporate the O horizon into the A horizon. Earthworms also increased mortality of plants and decreased total mesocosm plant biomass, but here the impact of all the three earthworm species was no greater than that of L. terrestris and/or L. rubellus alone. This study corroborates field studies that European earthworm invasions alter North American forest ecosystem processes by initiating a cascade of impacts on plant community composition and soil properties.

Human-facilitated invasion of exotic earthworms into northern boreal forests

Recreational and industrial development is rapidly expanding in the boreal forest of western Canada. Concerns exist that such activity is facilitating the introduction and spread of non-native species such as exotic earthworms. The mechanisms by which earthworms are introduced and spread in forested systems are not well understood. Given the poor intrinsic dispersal abilities of earthworms, we propose 4 major introduction mechanisms: 1) abandonment of worms brought as fishing bait; 2) dispersal via vehicles; 3) dispersal via vertebrate predators; or 4) dispersal via waterways. To test these hypotheses, we sampled earthworms in forest stands near boat launches, roads, seismic lines, forest interiors, and remote shorelines of lakes in the boreal forest of northern Alberta, Canada. Boat launches and roads had a significantly higher probability of earthworm occurrence (54% of plots occupied) compared with the other locations (13% of plots occupied). Species commonly used as fishing bait occurred more often near boat launches (18% of plots occupied) than near roads alone (1% of plots occupied). These results suggest that vehicle transport and bait abandonment may both be mechanisms of earthworm introduction. The consequences of these introductions remain unclear but suggest that reduced road construction and regulations prohibiting the discarding of bait need to be considered to slow earthworm invasions.

The leaf-litter earthworm fauna (Annelida: Oligochaeta) of forests in Limpopo Province, South Africa: diversity, communities and conservation

A qualitative survey of the leaf-litter earthworm fauna of 11 selected indigenous forests in Limpopo Province, South Africa, was conducted to identify the species present, to describe the communities and to assess the relationship between indigenous and exotic species. A total of 8185 individuals from 17 species (five indigenous and 12 exotic species) were recorded. The average earthworm community comprised fewer than five species, but up to seven species were sampled from a single forest. Four of the species recorded are national (one species), regional (one species) or local (two species) endemics. Because these species are not known to live elsewhere, the protection of Limpopo Province forests is critical to their survival. The majority (71%) of the earthworm species sampled was exotic, and differences between exotic and indigenous species richness in forests were mostly significant. At the two spatial scales examined (20 m2 and individual forest) there is no evidence of an association between exotic and indigenous species richness. However, we cannot assume that exotic earthworms do not impact the forest ecosystem.