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It is generally accepted that populations of most species experience some level of density dependence; however, this has rarely been shown for soil-dwelling invertebrate species, in particular for earthworms. Experimental data, mostly obtained at high laboratory densities, suggest intense intraspecific competition for resources and/or living space and density-dependent dynamics in earthworm populations, irrespective of their ecological group affiliation. In the present study performed in large field microcosms, I investigated whether density-dependent responses occur within the earthworm density gradients more realistic for the natural sites. Five lumbricid species from epigeic ( Dendrobaena octaedra , Lumbricus rubellus ), endogeic ( Allolobophora chlorotica , Aporrectodea caliginosa ) and anecic ( Lumbricus terrestris ) ecological groups were tested. Soil systems populated with earthworm monocultures in large (20-L) microcosms were exposed in a beech-oak forest for 4.5 months; each species was represented by two ( L. terrestris ) or three treatments forming gradients of increasing density. In two endogeic species, manifold and generally similar density-dependent responses (a retardation of growth, maturation and reproduction rates, but higher mortality rates with density increase) were revealed, likely explained by spatial competition rather than by direct food competition. In each of epigeic species density-dependent responses were less variable and more species-specific. In contrast to endogeics, direct food competition was presumably a more important cause of density-dependence. In L. terrestris no significant density-dependent responses in adult earthworms were revealed; however, they need to be further investigated in relation to the age and territorial behaviour of individual earthworms. Importantly, in any earthworm species the density variations in the reproducing generation had significant consequences for the advancing generation, affecting either the numbers or/and the size (individual weight) of the cocoons produced. It is suggested that an underestimation of density-dependent processes may cause inaccurate estimates of the activities of local lumbricid populations.

Through their manipulation of soil physical and chemical properties, earthworms have the potential to increase nutrient mineralization and benefit crop production. However, this effect is dependent on numerous factors including earthworm densities and ecological strategies. In addition to impacting density, soil environmental conditions may limit earthworm activity to specific times during the growing season, moderating their effects on nutrient availability and crop growth. The purpose of this study was to determine the active period of earthworms to better assess their potential impact on crop productivity in dryland wheat production systems in the Palouse region of northern Idaho and eastern Washington, U.S.A. Earthworm community density, age structure, diversity, and soil moisture and soil temperature were monitored over a 14-month (April 2014–June 2015) period in six dryland wheat fields. All earthworms collected were exotic species, with the endogeic species, Aporrectodea trapezoides being predominant at all sites (87% of all adults identified). Allolobophora chlorotica, Lumbricus terrestris and Aporrectodea tuberculata were collected at lower frequencies (1.8–6.4% of adults). Mean densities ranged from 14 to 75 individuals m−2, and populations transitioned to aestivation beginning in mid-June of both years. All earthworms were active (no aestivating individuals) on 56.9% of the sampling dates in 2014 and 71% of the days in 2015. A short active period and average densities at most sites of less than 100 individuals per m2 suggest that the impact of earthworms on crop growth may be limited in conventional, dryland agricultural fields of this region.

Earthworm immune-competent cells (coelomocytes) can be adversely affected by soil metal contamination. The aim of the present paper was to perform comparative studies on the coelomocytes of four lumbricid species dermally exposed for 2 days to filter paper soaked with Ni, Cu, Zn, Cd, or Pb chlorides (1 mM). Coelomocytes were expelled by electro-stimulation, counted, and assayed ex vivo by flow cytometry and spectrofluorometry. The coelomocytes of Allolobophora chlorotica and Dendrobaena veneta contain both amoebocytes and riboflavin-storing eleocytes; consequently, they were subjected to assays based on flow cytometric quantification of autofluorescent eleocytes and spectrofluorometric measurement of riboflavin content in coelomocyte lysates. In Al. chlorotica, the number of coelomocytes, the percentage of eleocytes, and the amount of riboflavin were significantly lower in Cu-exposed worms although these cytometric parameters were less affected by Ni, Zn, Cd exposure, and entirely unaffected by Pb exposure. In D. veneta, such cellular effects were also only observed in Cu-exposed worms. The coelomic fluids of Aporrectodea caliginosa and Lumbricus rubellus are constitutionally impoverished of eleocytes; therefore, these species could not be subjected to assays measuring the riboflavin content of these granular cells. Rather, the amoebocytes of Ap. caliginosa and L. rubellus were subjected to flow cytometric measurements of in vitro neutral red uptake (NR). However, the NR uptake assay was technically demanding, requiring a strictly normalized incubation period over all samples to yield useful comparative data. In contrast, the riboflavin content in the coelomocyte lysates of eleocyte-rich species appears to be a robust and convenient immune-function biomarker of environmental stress.

We have shown previously that riboflavin is stored in chloragosomes of chloragocyte-derived earthworm eleocytes what may have an adaptive value for worms vulnerable to soil-derived pathogen invasion. Thus, it is important to determine whether riboflavin stores are also present in earthworm species with low eleocyte counts, especially in the chloragocytes of their chloragogen tissue that surrounds the coelomic site of the intestine, and find out its putative roles in earthworm immunity. Experiments were performed on adult worms from 6 species. Freely floating coelomocytes (consisting of amoebocytes plus species-specific numbers of eleocytes) were extruded by mild electric shock and then chloragocytes from the same anaesthetized worm were mechanically detached into buffer. Both cell suspensions were analyzed by spectrofluorometry for riboflavin content. It turned out that riboflavin is stored in species-specific quantities in all investigated species. Riboflavin storage predominates in free coelomocytes of eleocyte-rich species (Eisenia andrei, Dendrobaena veneta, Allolobophora chlorotica) while in chloragocytes of species with few eleocytes (Lumbricus terrestris, L. rubellus, and Aporrectodea caliginosa). Upon a massive microbial impact, the coelomocytes (both amoebocytes and eleocytes) are involved in the formation of multicellular bodies encapsulating soil-derived pathogens, what is connected with enhanced coelomocyte mobility. Thus the second aim of the present investigation was to check if riboflavin can participate in coelomocyte accumulations. Tests performed in a 48-well chemotaxis chamber revealed that riboflavin behave as chemoattractant for coelomocytes of all investigated earthworm species, which may be one of mechanisms underpinning its immunomodulatory functions.

Summary The soil seed bank functions to escape unfavourable environmental conditions and seed predation. Anecic earthworms are increasingly recognised as important dispersers and predators of plant seeds. In contrast, the role of the usually more abundant endogeic earthworms which live and feed in the soil on plant seeds is largely unknown. We tested whether (A) endogeic earthworms ( Aporrectodea rosea , Allolobophora chlorotica , Octolasion tyrtaeum , Aporrectodea caliginosa ) ingest and digest grassland plant seeds ( Phleum pratense , Bellis perennis , Trifolium repens , Poa trivialis , Plantago lanceolata , Medicago varia ), (B) the passage of seeds through the gut of endogeic earthworms modifies seed germination, and (C) excreta (mucus and casts) of endogeic earthworms modify seed germination. As a reference effects of the well-studied anecic species Lumbricus terrestris were determined. Endogeic earthworms ingested and digested all of the studied plant seeds; however, both ingestion and digestion were earthworm and plant species specific. Moreover, passage through the gut of endogeic earthworms and their excreta modified plant seed germination (gut passage: B. perennis ; excreta: Ph. pratense and Pl. lanceolata ). The results indicate that endogeic earthworms may strongly impact the composition of the soil seed bank and, consequently, plant community assembly via direct and indirect effects on plant seeds. Since post-dispersal seed predation is a key factor for the structure of plant communities, with the effect on seed survival potentially exceeding that of pre-dispersal predation, seed predation and changes in germination of seeds by endogeic earthworm species is likely to drive plant community composition.

Summary The population dynamics of earthworms and potworms (Oligochaeta: Lumbricidae, Enchytraeidae) were recorded in three floodplain meadows differing in soil type in Northern Germany during 2 years of contrasting hydrological extremes: 2002 with high precipitation, extended winter inundations and summer floods in two of the sites, and 2003 with an extraordinarily dry summer. In all sites, earthworms dominated the biomass of soil fauna, the dominant species being Octolasion tyrtaeum in marsh soil, Octolasion cyaneum in peat soil, Allolobophora chlorotica in gley soil, and Lumbricus rubellus in all three sites. The enchytraeid communities composed of 7–10 species, differed widely between sites. While the summer flood of 2002 reduced annelid populations in peat soil to zero, in gley soil only enchytraeids were sharply reduced. The earthworms there probably were less affected because of shorter duration of the flood, the lower air temperatures and SOM contents and the diapause of the dominant A. chlorotica . During summer drought in 2003, earthworms and enchytraeids were absent from gley soil, while they had maximum abundances in peat soil. The marsh soil, structured by a microrelief of shallow ditches and ridges, had highest densities of annelids. As it was not subjected to summer flooding in 2002, populations of both earthworms and potworms were stable. The drought in 2003 led to a sharp decrease in earthworm abundance in July, while the enchytraeids reached maximum values. Dynamics and survival strategies of different annelid species are discussed. The water holding capacity as well as the organic matter content of the soil are important factors for annelids in sites subjected to such hydrological extremes. To promote terrestrial annelids, controlled flooding should be kept short, especially in winters following natural summer floods. If possible, recovery times for annelids should be guarenteed, that is 2–3 months without inundations for enchytraeids and about half a year for earthworms. A microrelief with drier refuge sites can be judged as favourable for earthworms. An artificially raised groundwater table will favour annelids during drought periods.

Summary Developments in ecotoxicology and soil restoration have led to an increase in earthworm research over the past 20 years. Rearing of earthworms under laboratory conditions has therefore become desirable, but perceived difficulties have beset this practice. A review of recent research on the development of earthworm culture techniques for temperate, soil dwelling (anecic and endogeic) species is presented. Critical abiotic and biotic factors including soil moisture, organic matter, temperature, pH, earthworm density and species composition are considered, and optimal values provided for four species ( Allolobophora chlorotica, Aporrectodea caliginosa, Aporrectodea longa and Lumbricus terrestris ). Published figures relating to growth to maturity, cocoon production and cocoon viability, for these frequently studied species are collated and advice offered for culture of other soil dwelling species.

Earthworms dominate the animal biomass in moist floodplain soils. They are known to survive long periods in aerated water, but little is known about earthworm population dynamics in floodplain systems with changing inundation frequencies. This study determined earthworm population dynamics in a floodplain system, in relation to frequency and duration of flooding events. From October 2000 to May 2003 earthworms were hand sorted in the 'Afferdensche en Deestsche Waarden', a floodplain on the south bank of the river Rhine, near Druten, The Netherlands. Earthworm numbers and biomasses per age class (adult, subadult, juvenile) were recorded. Numbers and biomasses tend to decrease during flooding. Lumbricus terrestris was found in high numbers (>10/m2) only at the end of a flooding period. Allolobophora chlorotica was hardly affected by flooding; their biomass remained stable during the year. Aporrectodea caliginosa showed fluctuating numbers and biomasses during the sampling period that did not correlate with flooding frequency. Numbers and biomasses of Lumbricus rubellus were strongly reduced at the end of each flooding event, but their population densities fully recovered until next flooding event. Earthworm populations in floodplains fluctuate in time, depending on the season and on the time, duration and frequency of flooding. Different earthworm species react differently towards these flooding dynamics. © 2004 Elsevier GmbH. All rights reserved.

Summary Earthworms are sensitive bioindicators of soil pollution. The aim of present investigations was to study the effects of heavy metals on earthworms and on their coelomocytes involved in the defence reactions. Adult individuals of Allolobophora chlorotica collected in Krakow (K) soil were kept in the laboratory either in the K soil, or were transferred to unpolluted soil from the rural area Sierbowice (S) or to the heavily polluted (Zn>Pb>Cd>Cu) soil from the industrial area, Bukowno (B). They were kept there at 22C for up to 8 weeks. Cocoons and juveniles appeared in S and K soil samples. The number and activity of the coelomocytes of worms maintained in S and K soils were unaffected despite some accumulation of heavy metals in the earthworm tissues. In contrast, in the B soil samples, bioaccumulation of metals was strongest, high mortality of adults was recorded, body mass was reduced, and reproduction completely inhibited. Coelomocytes retrieved from the B soil survivors exhibited significant impairment of pinocytosis and plastic adherence. Perhaps impairment of immune functions contributed to the poor survival under conditions of heavily polluted B soil samples.

Earthworms are sensitive bioindicators of soil pollution. The aim of present investigations was to study the effects of heavy metals on earthworms and on their coelomocytes involved in the defence reactions. Adult individuals of Allolobophora chlorotica collected in Krakow (K) soil were kept in the laboratory either in the K soil, or were transferred to unpolluted soil from the rural area Sierbowice (S) or to the heavily polluted (Zn>Pb>Cd>Cu) soil from the industrial area, Bukowno (B). They were kept there at 22 °C for up to 8 weeks. Cocoons and juveniles appeared in S and K soil samples. The number and activity of the coelomocytes of worms maintained in S and K soils were unaffected despite some accumulation of heavy metals in the earthworm tissues. In contrast, in the B soil samples, bioaccumulation of metals was strongest, high mortality of adults was recorded, body mass was reduced, and reproduction completely inhibited. Coelomocytes retrieved from the B soil survivors exhibited significant impairment of pinocytosis and plastic adherence. Perhaps impairment of immune functions contributed to the poor survival under conditions of heavily polluted B soil samples.

Summary Coelomocytes (extruded via dorsal pores of earthworms subjected to 5V electric shock) of adult Allolobophora chlorotica, Lumbricus terrestris, Dendrobaena veneta and Eisenia fetida consisted of species-specific proportions of hyaline amoebocytes, granular amoebocytes, and eleocytes. In all species a significant increase of granular amoebocytes with a parallel decrease of hyaline amoebocytes was recorded by the end of Spring and beginning of Summer, both in animals from the natural environment and in those kept in the laboratory at the room temperature. It indicates that coelomocyte proliferation/maturation is dependent mainly on the annual endogenous rhythm, which is relatively stable even at atypical ambient temperatures. During four successive seasons viability and functions (plastic adherence or neutral red pinocytosis) were recorded in coelomocytes of A. chlorotica assayed at various in vitro temperatures. In coelomocytes retrieved from animals freshly collected from their natural environment, coelomocyte activity was better at low temperatures (0 °C and 10 °C) during the Winter, while during other seasons (especially in the Summer) it was best at 22 °C. Such seasonal effects were abolished in coelomocytes from animals tested after one-month acclimation to the room temperature, as in all seasons cell functions were best at 22 °C. These observations indicate that earthworm coelomocytes can thermally adapt. This phenomenon was also recorded in L. terrestris, D. veneta and E. fetida . In conclusion, earthworm coelomocyte proliferation/maturation seems to be endogenously controlled while coelomocyte activity seems to be more plastic and subjected to thermal adaptation.

In the alluvial plain of Scarpe-Escault, in northern France, past emissions from a Zn smelter resulted in a notable Zn, Cd, and Pb-contamination of soils. The aim of this study was to assess the response of earthworm communities to a gradient of metal pollution. In 11 sites located within 4 kilometers of the smelter, according to the dominant wind direction, characteristic soil parameters and total metal contents were determined and 9 earthworm species were collected. The Kmeans clustering method, applied to the first two axes extracted by Principle coordinate analysis on species abundances, allowed to separate the 11 sites into 6 groups depending on their pollution status and the type of vegetation cover (cultivated soils, grasslands, poplar plantations). Significant differences were found between the 6 groups for the total density of earthworms, which varied from 392 ind.m - 2 in unpolluted grassland to 2 ind.m - 2 in the metallophyte grassland, where soil pollution was higher than in the other sites. Intermediate densities were found in unpolluted poplar plantations with 271 ind.m - 2 (but only 57 ind.m - 2 in polluted stands), and 52 ind.m - 2 in unpolluted cultivated soils. Metal pollution also reduced species richness (from 6 to 1 species). Aporrectodea caliginosa and Allolobophora chlorotica appeared to be the most sensitive to heavy metals. A. caliginosa was dominant in unpolluted grassland (about 45 ind.m - 2 ), absent in the most polluted site (35000, 8271 and 190 mg kg - 1 for Zn, Pb, and Cd, respectively), and present in polluted poplar plantation (1112, 616 and 12 mg kg - 1 for Zn, Pb, and Cd, respectively) although at a very low density (less than 1 ind.m - 2 ).

The inverse relationship between the particle size of food resources and earthworm growth rate is widely recognised. The aim was to determine the effects of the particle size of food on interactions between combinations of adult and hatchling A. chlorotica and L. terrestris under laboratory conditions. Treatments were set up in 1 litre mesocosms, maintained in darkness at 15 ′ 1 °C. Separated cattle solids (SCS) were used as food either unmilled or milled to < 1 mm. The latter led to a 185 and 54 % increase in the mass of A. chlorotica and L. terrestris respectively, compared with unmilled SCS. Intra-specific competition in A. chlorotica was detected in adult and hatchling pairings. A positive inter-specific interaction was recorded with hatchling A. chlorotica and mature L. terrestris fed unmilled SCS with growth of the former significantly greater (P

Summary The inverse relationship between the particle size of food resources and earthworm growth rate is widely recognised. The aim was to determine the effects of the particle size of food on interactions between combinations of adult and hatchling A. chlorotica and L. terrestris under laboratory conditions. Treatments were set up in 1 litre mesocosms, maintained in darkness at 15 ± 1 °C. Separated cattle solids (SCS) were used as food either unmilled or milled to A. chlorotica and L. terrestris respectively, compared with unmilled SCS. Intra-specific competition in A. chlorotica was detected in adult and hatchling pairings. A positive inter-specific interaction was recorded with hatchling A. chlorotica and mature L. terrestris fed unmilled SCS with growth of the former significantly greater (P A. chlorotica were only recorded in unmilled SCS treatments when paired with L. terrestris (week 18). In milled treatments, 100% maturation was achieved in monoculture and in pairings with hatchling and mature L. terrestris by week 14. The final mass of initially hatchling L. terrestris (3.23 g) fed milled SCS in monoculture was significantly greater (P A. chlorotica and mature conspecifics. With unmilled SCS, lowest initially hatchling L. terrestris mean mass (1.04 g) was recorded when paired with mature conspecifics. Growth of both species was significantly enhanced by decreased food particle size and this effect was size specific. The intensity of competitive interactions was influenced by food particle size and stage of earthworm development. Results suggested a positive association between the two species and mechanisms for this are proposed.

Summary In the alluvial plain of Scarpe-Escault, in northern France, past emissions from a Zn smelter resulted in a notable Zn, Cd, and Pb-contamination of soils. The aim of this study was to assess the response of earthworm communities to a gradient of metal pollution. In 11 sites located within 4 kilometers of the smelter, according to the dominant wind direction, characteristic soil parameters and total metal contents were determined and 9 earthworm species were collected. The Kmeans clustering method, applied to the first two axes extracted by Principle coordinate analysis on species abundances, allowed to separate the 11 sites into 6 groups depending on their pollution status and the type of vegetation cover (cultivated soils, grasslands, poplar plantations). Significant differences were found between the 6 groups for the total density of earthworms, which varied from 392 ind.m–2 in unpolluted grassland to 2 ind.m–2 in the metallophyte grassland, where soil pollution was higher than in the other sites. Intermediate densities were found in unpolluted poplar plantations with 271 ind.m–2 (but only 57 ind.m–2 in polluted stands), and 52 ind.m–2 in unpolluted cultivated soils. Metal pollution also reduced species richness (from 6 to 1 species). Aporrectodea caliginosa and Allolobophora chlorotica appeared to be the most sensitive to heavy metals. A. caliginosa was dominant in unpolluted grassland (about 45 ind.m–2), absent in the most polluted site (35000, 8271 and 190 mg kg–1 for Zn, Pb, and Cd, respectively), and present in polluted poplar plantation (1112, 616 and 12 mg kg–1 for Zn, Pb, and Cd, respectively) although at a very low density (less than 1 ind.m–2).