The armoured mite fauna (Acari: Oribatida) from a long-term study in the Scots pine forest of the Northern Vidzeme Biosphere Reserve, Latvia

In 1992–2012, a considerable amount of soil micro-arthropods has been collected annually as a part of a project of the National Long-Term Ecological Research Network of Latvia at the Mazsalaca Scots Pine forest sites of the North Vidzeme Biosphere Reserve. Until now, the data on oribatid species have not been published. This paper presents a list of oribatid species collected during 21 years of ongoing research in three pine stands of different age. The faunistic records refer to 84 species (including 17 species new to the fauna of Latvia), 1 subspecies, 1 form, 5 morphospecies and 18 unidentified taxa. The most dominant and most frequent oribatid species are Oppiella (Oppiella) nova, Tectocepheus velatus velatus and Suctobelbella falcata.


INTRODUCTION
Most studies of Oribatida or the so-called armoured mites (Subías 2004) have been relatively short term and/or from different ecosystems simultaneously and do not show longterm changes (Winter et al. 1990, Deleporte & Tillier 1999, Starý 1999, Kuriki 2003, Irmler 2004, Sjursen et al. 2005, Eitminavichiute et al. 2008, Cao et al. 2011).It was not possible to find a single long-term (more than fifteen years) study that presented annual continuous observations of the oribatid fauna in the same sampling plots.
In 1992, a research project started at the National Long-Term Ecological Research Network site in the Northern Vidzeme Biosphere Reserve, Latvia.One of the aims was to investigate complexes of soil arthropod species including oribatid mites in Scots pine forest (Pinaceum myrtilosum) in Mazsalaca municipality.Three forest stands (further mentioned as 'sample plots') with different tree age were selected and a large number of samples was collected in each sample plot once a year.From time to time, some results were presented in relation to fauna of Collembola (Jucevica & Melecis 2002, 2005, 2006, Melecis et al. 2005, Koehler & Melecis 2010) and Mesostigmata (Salmane 2000), but the material of oribatid mites was left without scientific notice and remained unpublished.

MATERIAL AND METHODS
The study was carried out in coniferous forest (Pinaceum myrtilosum), 5 km from the town Mazsalaca (Latvia), Northern Vidzeme Biosphere Reserve (57°53′ N, 24°59′ E) and comprised a part of the monitoring of the National Long-Term Ecological Research Network (Melecis et al. 2005).
Sampling plots were located in three Scots pine (Pinus sylvestris) forest stands of different age: an old stand (160-210 years old), a middle aged stand (60-80 years old) and a young stand (40-50 years old).Soils were sandy podzols with raw humus (mor) layer.Pleurozium schreberi and Hylocomium splendens were the dominant moss species.Common vascular plants were Vaccinium shrubs.Sampling of soil micro-arthropods was started in 1992 and performed annually in the last decade of August until the year 2012.In each forest stand 100 samples were taken using soil borer (area: 5cm 2 , max depth: 15cm).Samples from 1992 to 2005 were collected by Viesturs Melecis.Further collecting was carried out by the author.Soil samples were extracted with a modified high-gradient extractor.A more detailed description of the sampling design and extraction has been published by Jucevica and Melecis (2002).
Regarding to the material that was collected from 1992 to 1997, armoured mites were identified by Voldemārs Spuņģis, who additionally mounted 491 individuals in Hoyer's medium (Krantz & Walter 2009) with the purpose of creating a specimen collection.V. Spuņģis used Bulanova-Zachvatkina (1967) keys to identify Oribatida.Juvenile instars were not counted or identified.Later, the collection and the material (sampled from 1992 to 1997) were verified by the author (Kagainis 2012).
The remaining part of the material containing Oribatida collected in 1998-2012 was recently mounted in Hoyer's medium and identified by the author using Weigmann (2006) keys.Identifications have been also verified, when required, by Dr. Biol.Gerd Weigmann (Germany) and Dr. Biol.Ritva Penttinen (Finland).Juvenile instars have only been counted, but not identified.The material is deposited in the Institute of Biology, University of Latvia.
When writing down the species, the order of oribatid families followed the taxonomical principles by Seniczak et al. (2012) and Weigmann (2006).Genera and species were ordered alphabetically.

RESULTS
The study presents a species diverse fauna described in a local long-term investigation, which includes 84 species, 1 subspecies, 1 form, 5 morphospecies and 18 unidentified taxa among 215 103 specimens examined.(Table 1).
Seventeen oribatid species were registered in Latvia for the first time.The species Phthiracarus boresetosus Jacot, 1930 has been registered during previous studies, yet mistakenly left unmentioned as a new species for the fauna of Latvia (Kagainis 2012).Presently, 227 oribatid species are known for the fauna of Latvia  Network project (1992Network project ( -2012) ) with remarks on their density (ind/m 2 ) and constancy (total number of individuals of the particular species divided by number of collected samples).Sample plots: Y -young pine forest stand (40-50 years old), M -middle aged pine forest stand (60-80 years old), O -old pine forest stand (160-210 years old).Species new to the fauna of Latvia are marked with asterisk (*).Absent calculations are abbreviated with N.

DISCUSSION
In Latvia armoured mites have been studied irregularly, until the revised checklist was published (Kagainis 2011).Soon after, a few more articles were prepared (Kagainis & Eitminavichute 2011, Kagainis & Spungis 2011, 2013) and the status of 209 oribatid species for the fauna of Latvia was proposed.Considering that the Lithuanian fauna of Oribatida consists of 312 species (Eitminavichute 2003), the author expects a large increase in the number of Latvian species in future investigations.
A considerable amount of oribatid mites have been sampled during the twenty one years of the National LTER Network project.This study indicates high regional species diversity.According to latest keys of Weigmann (2006), all 80 named species (including subspecies and forms) from this local study represents 12.9% of the known species diversity of Central Europe, and thus can be considered as high local species diversity.This long-term study has provided biologists also with valuable ecological data (Jucevica & Melecis 2002, 2005, 2006, Melecis et al. 2005, Koehler & Melecis 2010).The identified material of oribatid mites represents 37% of recently known species diversity of the oribatid fauna of Latvia.
Because of the lack of comparable literature showing annually obtained long-term data, further detailed comparisions can not be made.However, there are a few long-term investigations dealing with various ecosystems but not with the pine forest (Winter et al. 1990, Deleporte & Tillier 1999, Starý 1999, Irmler 2004, Sjursen et al. 2005, Eitminavichiute et al. 2008, Cao et al. 2011).Nevertheless, individuals from T. velatus velatus and O. (Oppiella) nova species have been described as the most abundant also in coniferous forest (Eitminavichiute et al. 2008) in Lithuania and oak forest (Starý 1999) in Czech Republic similarly to our study.Cao et al. (2011) mentioned T. velatus velatus also as a recedent species, but agroecosystems were investigated in that study.Some of the literature on long-term studies unfortunately does not characterize fauna by species level and much higher taxa e.g.families or orders are discussed (Winter et al. 1990, Deleporte & Tillier 1999, Sjursen et al. 2005).Investigations of Irmler (2004) showed different dominance strategies of oribatid species.
Several publications exist on short-time investigations in choosing Scots pine forest.Similar to our study, high preference to pine forest stand was observed for O. (Oppiella) nova (37 800 ind/m 2 ) and T. velatus velatus (64000 ind/m 2 ), in comparision of other habitats, and these two species also were registered as dominants (Seniczak et al. 2006).Sylwestrowicz-Maliszewska et al. (1993) described T. velatus velatus (3 593-13 304 ind/m 2 ) as dominant in pine forest ecosystems of Poland.
Additional remarks on oribatid mite densities and constancies attached to the species list of this article can be useful for valuable comparisons during further studies of the fauna (Table 1).The material has been carefully prepared and stored; it can be used as both illustrative material and as a valuable specimen collection for taxonomical research, species verification, and educational purposes during international collaborations.
The National LTER Network project in Mazsalaca forest was closed in 2012, representing a 21 year-long period of collecting data.Moreover, in 2009 intensive forestry has been started at the middle aged forest stand.In this regard, more publications on oribatid mite fauna and ecology are planned to be prepared.

Table 1 .
Oribatid taxa collected at three different sample plots in Mazsalaca pine forest during the National LTER