Academic journal article Estonian Journal of Ecology

Estonian Enchytraeidae 4. Sublittoral Enchytraeidae (Annelida, Oligochaeta) in the Eastern Baltic Sea/Eesti Valgeliimuklased (Enchytraeidae) 4. Laanemere Idaosa Sublitoraali Valgeliimuklased (Annelida, Oligochaeta)

Academic journal article Estonian Journal of Ecology

Estonian Enchytraeidae 4. Sublittoral Enchytraeidae (Annelida, Oligochaeta) in the Eastern Baltic Sea/Eesti Valgeliimuklased (Enchytraeidae) 4. Laanemere Idaosa Sublitoraali Valgeliimuklased (Annelida, Oligochaeta)

Article excerpt

INTRODUCTION

In three papers of this series (Dozsa-Farkas et al. 1998, Schmelz et al. 2005, Timm 2007), the Estonian terrestrial and freshwater enchytraeids were surveyed. As a small addition to the last paper, Dr K. Dozsa-Farkas (Budapest) identified two amphibious species, Cernosvitoviella immota (Knollner, 1935) and C. tatrensis (Kowalewski, 1917) from the Estonian streams. Two more species, new for science (Marionina deminuta Rota, 2012 and M. mendax Rota, 2012) were recently found from the Estonian soil (Rota 2012), increasing the total number of nominal species of the Enchytraeidae known in Estonia to 54. This fourth paper is dedicated to the enchytraeids living in the brackish waters adjacent to Estonia, Latvia, and Lithuania.

The Baltic Sea has many lacustrine features (limited connection with the ocean, lack of tides, very low salinity, poor fauna with a large proportion of freshwater organisms). Fresh-and brackish-water periods have alternated during its short history of 13 000 years. There is a gradual decline of salinity, from 8-10%o in the SW corner to 2-3[per thousand] in the inner parts of the Bothnian Bay and the Gulf of Finland (Jarvekulg 1979).

Earlier studies on Enchytraeidae in the Baltic Sea have been limited to the pseudolittoral, i.e. the shore and near-shore shallows (Knollner 1935; Backlund 1946; Bulow 1955, 1957; Jansson 1961; Nurminen 1965, 1967; Giere 1976; Tynen & Nurminen 1969; Rota et al. 1998; Erseus et al. 1999; Rota & Healy 1999).

In zoobenthos samples from the open Baltic Sea, enchytraeids are usually either not found or ignored. Bagge & Ilus (1973) registered unidentified enchytraeids at 5 stations of 28, located at depths of 38.5-81 m along the western coast of Finland. Ankar & Elmgren (1976) noted them in 3 of 40 zoobenthos samples taken from a depth of 19 m or more in the Asko-Landsort area, Sweden. Both collections are no longer available.

Rich oligochaete material, including Enchytraeidae, was collected by late Dr Arvi Jarvekulg during extensive zoobenthos studies in the Baltic Sea region bordering with the former USSR (Fig. 1). These worms were studied by me (Timm 1965, 1970, 1987; Jarvekulg 1979). Most Enchytraeidae remained on the family level in these papers; one taxon was erroneously identified as Marionina spicula sensu Nielsen & Christensen (1959). Now, many years later, revision of this family in the Baltic Sea benthal is feasible by using additional material and improved taxonomic knowledge.

STUDY AREA, MATERIAL, AND METHODS

The study area includes the eastern part of the Central Baltic together with the Gulf of Riga, Gulf of Finland, and smaller straits and bays in the Estonian Western Archipelago (Fig. 1). Salinity is usually 3-8[per thousand] in the homohaline (mixing) water layer reaching a depth of 50-80 m. The same depth at the bottom is considered the lower limit of the sublittoral zone. There occur different sediments from stones to mud, but sand and clay prevail. Summer water temperatures can be higher than 20 [degrees]C in small bays and about 15 [degrees]C near the surface in the open sea, but seldom exceed 5 [degrees]C in the lower sublittoral. The deepest zone, pseudobathyal, is covered with more saline, periodically anoxic water and is devoid of oligochaetes. The shallowest zone (pseudolittoral) and the bays with very low salinity (1-2[per thousand] or less) usually reveal no enchytraeids.

[FIGURE 1 OMITTED]

The bulk of the material was obtained from zoobenthos surveys compiled by Dr Arvi Jarvekulg and his team, in the last years including Dr Ado Seire (former institutions: Tallinn Marine Ichthyological Laboratory, renamed as the Estonian Branch of the Baltic Institute of Fisheries and Oceanography; later the Institute of Zoology and Botany, Tartu), on their expeditions during 1959-1981 (Fig. 1). A detailed description of the area and sampling methods is available in a Russian-languague monograph (Jarvekulg 1979). …

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