DNA barcoding uses a short fragment of a DNA sequence to identify a taxon. After obtaining the target sequence it is compared to reference sequences stored in a database to assign an organism name to it. The quality of data in the reference database is the key to the success of the analysis. In the here presented study, multiple types of data have been combined and critically examined in order to create best practice guidelines for taxonomic reference libraries for environmental barcoding. 70 unialgal diatom strains from Berlin waters have been established and cultured to obtain morphological and molecular data. The strains were sequenced for 18S V4 rDNA (the pre-Barcode for protists) as well as rbcL data, and identified by microscopy. LM and for some strains also SEM pictures were taken and physical vouchers deposited at the BGBM. 37 freshwater taxa from 15 naviculoid diatom genera were identified. Four taxa from the genera Amphora, Mayamaea, Planothidium and Stauroneis are described here as new. Names, molecular, morphological and habitat data as well as additional images of living cells are also available electronically in the AlgaTerra Information System. All reference sequences (or reference barcodes) presented here are linked to voucher specimens in order to provide a complete chain of evidence back to the formal taxonomic literature.

We conducted an enclosure study in Lake SmbygBrd, a shallow hypertrophic Danish lake, to examine the impact of metazooplankton on the structure of the microbial food web. Here we present results on ciliate abundance, species composition and trophic interactions during 2 consecutive stages of zooplankton succession. Over a 3 wk period, metazooplankton shlfted from dominance of rotifers to cyclopoid copepods and thereafter to cladocerans. On 2 different dates with contrasting zooplankton assemblages we performed enclosure experiments where we compared the population dynamics of ciliates in size-fractionated [<50 pm) treatments with enclosures containing in situ densities of metazooplankton. The cihate cornmunlty in the lake and in the enclosures was mainly represented [>80% of total abundance) by 3 small-sized taxa: Urotricha spp., Halteria grandinella and Rimostrombidium brachylanetum, which showed Mferent dynamics in response to inetazooplankton. In the first experiment, with dominance of rotifers, zooplankton had only a modest predatory impact on the ciliates, and interactions within the ciliate conlmunity were probably more important. Larger, raptonal ciliates (e.g. Monodinium sp., Lagynophrya sp.) seemed to have been the main predators of the small chates. Dlfferent species-specific responses of cihates within the same size range were observed. In contrast, the second expenment, w t h dominance of crustacean zooplankton (cladocerans, copepods), demonstrated a clear top-down control of the whole ciliate community by metazooplankton. Predation is probably the dominating regulating mechanism for ciliate abundance, biomass and species composition in Lake Subygbrd. In contrast, food limitation is thought to be of minor ~rnportance because of generally high concentrations of edible phytoplankton. This view was also supported In our experiments by very high net growth rates of the dominating clliate species after predator removal [in the range 1.0 to 2.4 d-'). The study revealed 2 characteristics of hypertrophic lakes-first, zooplankton con~position and the resulting predation pattern is the decisive factor for the protozoan community structure, and second, the clliate community is dominated by high densities of a few small-sized species.

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