Oligochaete distribution patterns in two German hardwater lakes of different trophic state

AbstractWe investigated the effect of contrasting trophic conditions on the distribution and dominance patterns of Oligochaeta species assemblages in lake sediments and their relation to the environmental variables depth, season, and substrate. The study was performed on the highly eutrophic Lake Haussee and the oligotrophic Lake Stechlin, both hardwater lakes in the Baltic Lake District of Northern Germany. Quantitative monthly and seasonal sampling took place over one year at 14 representative sites, covering littoral and profundal sediments of both lakes. Between-lake differences in the profundal were clearcut with an absence of any zoobenthos in Lake Haussee and a peculiar meiobenthic species assemblage in Lake Stechlin (Collado et al. 1999). Between-lake differences in the littoral, however, were small and mainly attributable to a small number of species exclusive to Lake Stechlin and an overall higher abundance of oligochaetes, especially naidids, in Lake Haussee. Species-richest family in both lakes were Naididae; Tubificidae were dominant in Lake Stechlin; in Lake Haussee Tubificidae and Naididae were equally abundant. Most striking were diversity of habitat types and species distribution patterns in the littoral. Multivariate analysis (CA, CCA) showed that the distribution patterns of oligochaete species assemblages are significantly correlated with depth, season and substrate. Depth is the major factor when the whole water body is considered. When confining to the littoral, species abundance and distribution are strongly related to seasonality and substrate type. Naididae show, in general, maximal abundances in autumn and summer and a preference for plants, plant debris and soft sediments; Tubificidae are more abundant in spring and prefer mineral substrate. The relation between seasonality, substrate and food availability is discussed

Description of Enchytronia pygmaea sp. n. (Enchytraeidae, Clitellata), a very small enchytraeid in European soils

A new and very small European species of terrestrial enchytraeids is described, Enchytronia pygmaea sp. nov. (Enchytraeidae, Oligochaeta). It differs from all enchytraeids known so far in the chaetal pattern: lateral bundles have 2 chaetae from segment II to V, 0 from segment VI to XII–XV, and only 1 chaeta in lateral postclitellar bundles; ventral bundles have 2 chaetae. A further peculiarity is the presence of only 1 pair of preclitellar nephridia. The species must be considered as widespread as it is recorded here from 17 different localities distributed over seven European countries ranging from the Atlantic to the Mediterranean zone

On a collection of enchytraeids (Oligochaeta) from first order streams in São Paulo State, Brazil

A collection of 21 ethanol-preserved specimens of enchytraeids collected in first order streams in São Paulo State, Brazil, was whole-mounted on slides and investigated under light microscope. Eight species taxa were distinguished, belonging to Achaeta, Guaranidrilus, and Marionina. Five species could be named, one of them tentatively: Achaeta neotropica Černosvitov, 1937, Achaeta singularis Schmelz, 2008, Guaranidrilus oiepe Righi, 1974, Marionina argentea (Michaelsen, 1889) s.l., Marionina cf. seminuda Xie & Rota, 2001. Three further unnamed species taxa of Guaranidrilus were distinguished; two of them may be new species. The presence of sexually mature specimens of A. singularis allowed an emendation of the original description which was based on juvenile specimens. The rod-shaped crystals in the coelom of A. singularis are similar to raphides in plants and sponges, an

Effects of organic pesticides on enchytraeids (Oligochaeta) in agroecosystems: laboratory and higher-tier tests

Enchytraeidae (Oligochaeta, Annelida) are often considered to be typical forestliving organisms, but they are regularly found in agroecosystems of the temperate regions of the world. Although less known than their larger relatives, the earthworms, these saprophagous organisms play similar roles in agricultural soils (but at a smaller scale), e.g., influencing soil structure and organic matter dynamics via microbial communities, and having a central place in soil food webs. Their diversity is rarely studied or often underestimated due to difficulties in distinguishing the species. New genetic techniques reveal that even in anthropogenically highly influenced soils, more than 10 species per site can be found. Because of their close contact with the soil pore water, a high ingestion rate and a thin cuticle, they often react very sensitively to a broad range of pesticides. Firstly we provide a short overview of the diversity and abundance of enchytraeid communities in agroecosystems. Afterwards, we explore the available data on enchytraeid sensitivity toward pesticides at different levels of biological organization, focusing on pesticides used in (mainly) European agroecosystems. Starting with non-standardized studies on the effects of pesticides on the sub-individual level, we compile the results of standard laboratory tests performed following OECD and ISO guidelines as well as those of higher-tier studies (i.e., semi-field and field tests). The number of comparable test data is still limited, because tests with enchytraeids are not a regulatory requirement in the European Union. While focusing on the effects of pesticides, attention is also given to their interactions with environmental stressors (e.g., climate change). In conclusion, we recommend to increase the use of enchytraeids in pesticide risk assessment because of their diversity and functional importance as well as their increasingly simplified use in (mostly standardized) tests at all levels of biological organization

Neon Lights Up a Controversy: the Solar Ne/O Abundance

The standard solar model was so reliable that it could predict the existence of the massive neutrino. Helioseismology measurements were so precise that they could determine the depth of the convection zone. This agreement between theory and observation was the envy of all astrophysics -- until recently when sophisticated three-dimensional hydrodynamic calculations of the solar atmosphere reduced the metal content by a factor of almost two. Antia & Basu (2005) suggested that a higher value of the solar neon abundance, Ne/O = 0.52, would resolve this controversy. Drake & Testa (2005) presented strong evidence in favor of this idea from a sample of 21 Chandra stars with enhanced values of the neon abundance, Ne/O = 0.41. In this paper, we have analyzed solar active region spectra from the archive of the Flat Crystal Spectrometer on Solar Maximum Mission, a NASA mission from the 1980s, as well as full-Sun spectra from the pioneering days of X-ray astronomy in the 1960s. These data seem consistent with the standard neon-to-oxygen abundance value, Ne/O = 0.15 (Grevesse & Sauval 1998). If these results prove to be correct, than the enhanced-neon hypothesis will not resolve the current controversy.Comment: submitted to ApJ Letter

The Transparency of Solar Coronal Active Regions

Resonance scattering has often been invoked to explain the disagreement between the observed and predicted line ratios of Fe XVII 15.01 A to Fe XVII 15.26 A (the ``3C/3D'' ratio). In this process photons of 15.01, with its much higher oscillator strength, are preferentially scattered out of the line of sight, thus reducing the observed line ratio. Recent laboratory measurements, however, have found significant inner-shell Fe XVI lines at 15.21 and 15.26 Angstroms, suggesting that the observed 3C/3D ratio results from blending. Given our new understanding of the fundamental spectroscopy, we have re-examined the original solar spectra, identifying the Fe XVI 15.21 line and measuring its flux to account for the contribution of Fe XVI to the 15.26 flux. Deblending brings the 3C/3D ratio into good agreement with the experimental ratio; hence, we find no need to invoke resonance scattering. Low opacity in Fe XVII 15.01 also implies low opacity for Fe XV 284.2, ruling out resonance scattering as the cause of the fuzziness of TRACE and SOHO EIT 284-Angstrom images. The images must, instead, be unresolved due to the large number of structures at this temperature. Insignificant resonance scattering implies that future instruments with higher spatial resolution could resolve the active region plasma into its component loop structures.Comment: accepted to Ap J Letter