Dynamics and vertical distribution of a Hrabeiella periglandulata (Annelida) population in South Moravia, Czech Republic

The objective of this work was to evaluate the density, dynamics and vertical distribution of a Hrabeiella periglandulata population in a forest soil at Brno, Czech Republic. From December 2003 to November 2004, two plots covered by mixed stands and two covered by coniferous stands were sampled monthly. Six soil cores per plot were taken down to 15 cm and subdivided into layers, which were subjected to wet funnel extraction. Missing in one of the coniferous stands H. periglandulata was abundant in the mixed stand with the highest soil pH. In this stand, monthly sampling continued until November 2005, with three additional samplings up to January 2007. Mean annual density was 2,672±1,534 individuals m. Population dynamics differed from those reported from Germany. Highest densities were reached in early summer, lowest between August and December. Due to aggregated horizontal distribution, differences between monthly values were often nonsignifi cant. No signifi cant correlation with climatic data was found. Nevertheless, the observed dynamics corresponded to the climatic conditions, showing particularly the negative effect of drought. The population was evenly distributed in the sampled soil profi le, only avoiding the organic layer. Except for a locality in Poland, this is the easternmost record of the species.

Little is known about its ecology and area of distribution.In all cases, the species has been recorded Pesq. agropec. bras., Brasília, v.44, n.8, p.917-921, ago. 2009 in studies focusing on enchytraeids.Records have been published from Europe only, showing a range from southern Sweden in the north (Erséus & Rota, 1998), across central Europe -Germany (Jans & Römbke, 1989;Graefe, 1989Graefe, , 1990Graefe, , 1993aGraefe, , 1993b;;Purschke, 1999;Beylich & Graefe, 2007), Czechia (Pižl & Chalupský, 1984;Šídová & Schlaghamerský, 2007) and Poland (Dumnicka & Rożen, 2002) -to central Italy in the South (Rota & Lupetti, 1996).It has been found in soils of deciduous and coniferous forests, as well as of meadows and gardens.Graefe & Schmelz (1999) have characterised the species as an indicator of fresh soils (absent in wet habitats) of slight to moderate soil acidity (adapted to acidity stress), and preferring the A h -horizon of soils with mull to moder humus forms.According to Rota (1998), the species cannot endure a prolonged submersion in water, but is also very sensitive to drought.
This work reports on a population found in a municipal forest of the city of Brno (South Moravia, southeastern Czech Republic), during a study on enchytraeids (Clitellata: Enchytraeidae) commenced in late 2003 (Schlaghamerský & Šídová, 2007;Šídová & Schlaghamerský, 2007).Comparable ecological data on H. periglandulata have only been published from a few sites in southwestern Germany (Jans & Römbke, 1989), but even in that study, no proper year-round sampling was conducted.
The objective of the present study is to provide information on the density, population dynamics and vertical distribution of this population of H. periglandulata, based on year-round data.
Hrabeiella periglandulata was studied at this site from December 2003 to January 2007.From December 2003 to December 2004, six randomly positioned soil cores (17 cm 2 area, depth mostly 12 cm or more) were taken at the beginning of each month, in each of the four above mentioned plots.Monthly sampling continued till November 2005 in one of the plots (mixed stand within the game park, with the highest density of H. periglandulata).In March and May 2006, and January 2007, further 6 or 8 cores per date were taken in this plot.All soil cores were cut into layers according to soil horizons (3 cm layers, when horizons were thicker or not well distinguishable).All the subsamples were subjected to wet funnel extraction: 12-hour exposure without heating, then heating of the soil surface up to 43 °C within 3 hours.Extracted specimens were stored in water at 8 °C and, subsequently, counted under a binocular preparation microscope.During 2004, further soil samples were taken for analysis of soil chemistry and texture.

Results and Discussion
Except for a locality in southeastern Poland (Dumnicka & Rożen, 2002), the study site presents Table 1.Chemical soil characteristics of the study plots.
the easternmost published record of the species, thus shifting the border of the known range further to the southeast, and by large closing the gap between known localities in the southwest, South Bohemia (Pižl & Chalupský, 1984) and northwest (North Bohemia) of the Czech Republic, and the above mentioned Polish site (Figure 1).While the lack of records from most of Scandinavia, the Netherlands and the British Isles might represent a biological fact, the same is probably not true for further parts of western Europe, where a lack of soil mesofauna studies based on wet extraction techniques (usually used to study enchytraeids) might be responsible for missing records.The same is true for other parts of central, southern and eastern Europe, except for Austria and Hungary, where enchytraeids have been studied rather extensively, but H. periglandulata has not been recorded so far.
From December 2003 to December 2004, H. periglandulata was found in three of the four study plots: mixed forest stand inside Holedná Game Park (344 specimens); mixed forest stand outside Holedná Game Park (31 specimens); coniferous forest stand inside Holedná Game Park (3 specimens).Densities differed substantially along a transect of only ca.400 m (distance between the most remote plots).Over the entire study period until January 2007, 758 specimens were collected in the fi rst plot (characterised by the highest soil pH) (Table 1).The mean annual density, based on two years of monthly sampling, was 2,672±1,534 individuals m -2 .The mean annual density of all enchytraeid species (based on one year of monthly sampling), in the fi rst plot, was 14,500±4,900 individuals m -2 (Šídová & Schlaghamerský, 2007).This shows that H. periglandulata can be a quantitatively important member of the annelid assemblage in soils (with individuals reaching up to 1.5 mm in body length, the biomass of an individual or of a given population will of course stay below that of most enchytraeid species).Annual density maxima were found in May 2004 and June 2005, and low densities from late summer till October or even into the winter as in December 2003 or November 2005 (Figure 2).The lowest mean density recorded in this plot was 196 individuals m -2 in September 2005, and the highest one was 11,863 individuals m -2 in June 2005.Due to the highly aggregated horizontal distribution (also indicated by the high standard errors of the mean), many of the monthly values did not differ signifi cantly.However, the observed trend in population dynamics corresponded to the climatic development during the study period -with low densities at times of low precipitation and partially also low temperatures.This trend showed, particularly, the negative effect of the droughts at the end of the summer.The observed population dynamics differed from those at sites in southwestern Germany, where minima occurred in early summer, and maxima in winter (Jans & Römbke, 1989).This is in rather good agreement with the differences between the more Atlantic climate in southwestern Germany and the more continental climate in southeastern Czech Republic, and shows that one has to be careful in drawing general conclusions on a species' biology based on local phenological data.
was often very dry during samplings.This might have contributed to the low percentage of H. periglandulata in this layer, as observed to some degree also in the case of enchytraeids (Schlaghamerský & Šídová, 2007;Šídová & Schlaghamerský, 2007).However, avoidance of the uppermost organic soil layer by H. periglandulata was also observed elsewhere within its known range (Jans & Römbke, 1989;Graefe & Schmelz, 1999).The high percentage of specimens found in the sampled part of the B-horizon at our site (depending on the soil core these were 12-15 cm and, partially, also 9-12 cm layers) was remarkable, as this consisted of very fi ne, silty mineral soil with very little organic matter.Thus, although the soil at our site seemed rather special, the vertical distribution of H. periglandulata found here was in agreement with that observed by other authors (Jans & Römbke, 1989;Graefe & Schmelz, 1999).It is possible that the proportions of  Pesq.agropec.bras., Brasília, v.44, n.8, p.917-921, ago. 2009 individuals dwelling in greater depths than the sampled ones were not negligible, and the true population densities might be, therefore, higher than those presented.

Conclusions
1. Hrabeiella periglandulata can reach densities of several thousand individuals per square metre, comparable to the densities of other small soil annelids -in particular enchytraeids -in the same soils.
2. The population of H. periglandulata in Brno reaches maximal densities in late spring to early summer and minimal densities in late summer to autumn.
3. At the study site, H. periglandulata is rather evenly distributed in the upper 15 cm of soil, only avoiding the litter layer.
4. The range of H. periglandulata reaches further to the southeast than previously reported.

Figure 2 .
Figure 2. Population dynamics (mean monthly densities±SE) of Hrabeiella periglandulata in the most studied plot (mixed forest stand, inside Holedná Game Park) from December 2003 to January 2007; monthly mean air temperatures and precipitation sums from October 2003 to January 2007 from the closest meteorological station; note that abundance data were collected at the beginning of each month.

Figure 3 .
Figure 3. Vertical distribution (mean percentages of individuals present in individual soil layers) of Hrabeiella periglandulata in the most studied plot (mixed forest stand, inside Holedná Game Park).