The class Cryptophyceae (Division Cryptophyta) contains ecologically relevant species, which are widespread in aquatic environments. However, classification, identification, and enumeration of cryptophytes are challenged by a morphology that must be usually examined with EM to permit species identification. The quantitative importance of this group has been revealed by HPLC data. But ecological information assessing the occurrence or seasonality of cryptophytes in the marine environment is still scarce. Molecular techniques allow for a refined assessment of taxonomically challenging taxa, such as the cryptophytes. In our laboratory, a PHYLOCHIP was developed to facilitate and refine the assessment of cryptophyte microalgae. Here, we present the results of an environmental study that took advantage of the PHY-LOCHIP. The study was designed to elucidate the seasonality and contribution of cryptophytes to phytoplankton structure in the German Bight. The occurrence of cryptophytes in total plankton versus the picoplankton fraction was assessed with the PHYLOCHIP between the years 2004 and 2006. Our data indicate that cryptophytes are an important and constant contributor to phytoplankton structure of the German Bight, especially in the picoplankton fraction.

The microalgal class Prasinophyceae (Chlorophyta) contains several picoeukaryotic species, which are known to be common in temperate and cold waters and have been observed to constitute major fractions of marine picoplankton. However, reliable detection and classification of prasinophytes are mainly hampered by their small size and few morphological markers. Consequently, very little is known about the abundance and ecology of the members of this class. In order to facilitate the assessment of the abundance of the Prasinophyceae, we have designed and evaluated an 18S rRNA gene-targeted oligonucleotide microarray consisting of 21 probes targeting different taxonomic levels of prasinophytes. The microarray contains both previously published probes from other hybridization methods and new probes, which were designed for novel prasino- Phytoplanktonic cells between 0.2 and 2 m are termed picoplankton, and in spite of their small size, they can contribute greatly to the global carbon cycle, biomass, and productivity in the sea (6,8). The prokaryotic picophytoplankton consists of two cyanobacterial genera, Synechococcus (23, 48) and Prochlorococcus (4); in contrast, the eukaryotic part of the picophytoplanktonic community is less well known. Recently, several new classes have been described (2,16,37). As one of the key taxa in the marine eukaryotic picoplankton, the Prasinophyceae are an exceptionally interesting group (36).

In studies on the biochemical compounds in phytoplankton, water samples generally are (pre-) filtered to retain the organisms for extraction. Such filters can be used for further investigations in microscopic or chromatographic (for example HighPerformance-Liquid-Chromatography, HPLC) methods, while the filtrates can be used for nutrient or fluorometric measurements as well as for microscopic examinations. Which filter is chosen for a study often depends on its pore size, the costs and, in particular for HPLC measurements, on its chemical compatibility. In our study we compared the chlorophyll-a retention on the filters by HPLC as well as the fluorescence before and after filtration, and nutrient content of the filtrates. The filters we tested were of different material and with various pore sizes. Although Whatman GF/C and GF/F filters are preferred in phytoplankton studies, we found that the Nylon Membrane filter of 0.2 μm pore size provided the most consistent results in chlorophyll-a retention and the one of 0.45 μm pore size in nutrient investigations.

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