Uncovering hidden biodiversity in the Cryptophyta: New picoplanktonic clades from clone library studies at the Helgoland time series site in the southern German Bight.

Cryptophyceae are important group in marine phytoplankton, but little is known about the occurrence and distribution of individual species. Recently, with use of molecular probes and microarray technology, it has been shown that species related to Teleaulax spp. or Chroomonas spp. (clades 4 and 6) contributed most to cryptophyceam biomass in the North Sea. The probe for clades 4 and 6 cannot separate them and the single probe recognises members of both clades. Here, we increase the genetic diversity of our investigations of cryptophycean diversity in the North Sea by sequencing 18S rRNA clone libraries made from fractionated water samples to examine specifically the picoplanktonic fraction and to determine whether clade 4 or 6 were the dominant cyrptophytes. We focused on samples from the spring phytoplankton bloom in 2004 because the microarray signals were the strongest at this time. Excluding chimeric sequences, we detected nine cryptophycean OTUs, seven of which fell into the Teleaulax/ Plagioselmis branch, whereas two grouped with Geminigera spp. Our results indicate that these OTUs, affiliated with clade 4, may be an important component of cryptophyte community during spring bloom in the North Sea

Uncovering hidden biodiversity in the Cryptophyta: Clone library studies at the Helgoland Time Series Site in the Southern German Bight indentifies the cryptophycean clade potentially responsible for the majority of its genetic diversity during the spring bloom.

Cryptophyceae are important group in marine phytoplankton, but little is known about the occurrence and distribution of individual species. Recently, with use of molecular probes and microarray technology, it has been shown that species related to teleaulax spp. or Chroomonas spp. (clades 4 or 6) contributed the most to cryptophycean biomass in the north Sea. for the microarray study, the single probe (clade 4/6) recognizes members of both clades 4 and 6 and thus cannot separate them. Therefore, it was unknown as to whether the cryptophyte community was composed of clade 4, clade 6 or both of them. Here, we addressed this question and increased the genetic diversity of our investigations of cryptophycean diversity in the north Sea by sequencing 18S rRnA clone libraries made from fractionated water samples to examine specifically the picoplanktonic fraction because that fraction was studied in detail in the earlier microarray study. We focused on samples from the spring phytoplankton bloom in 2004 because the microarray signals were the strongest at this time. Excluding chimeric sequences, we detect- ed nine cryptophycean oTUs, seven of which fell into the teleaulax/Plagioselmis branch, whereas two grouped with Geminigera spp. our results indicate that these oTUs, affiliated with clade 4, may be an important component of cryptophyte community during spring bloom in the north Se

Status and trends in the structure of Arctic benthic food webs

Ongoing climate warming is causing a dramatic loss of sea ice in the Arctic Ocean, and it is projected that the Arctic Ocean will become seasonally ice-free by 2040. Many studies of local Arctic food webs now exist, and with this review paper we aim to synthesize these into a large-scale assessment of the current status of knowledge on the structure of various Arctic marine food webs and their response to climate change, and to sea-ice retreat in particular. Key drivers of ecosystem change and potential consequences for ecosystem functioning and Arctic marine food webs are identified along the sea-ice gradient, with special emphasis on the following regions: seasonally ice-free Barents and Chukchi seas, loose ice pack zone of the Polar Front and Marginal Ice Zone, and permanently sea-ice covered High Arctic. Finally, we identify knowledge gaps in different Arctic marine food webs and provide recommendations for future studie

Enrichment of Omnivorous Cercozoan Nanoflagellates from Coastal Baltic Sea Waters

Free-living nano-sized flagellates are important bacterivores in aquatic habitats. However, some slightly larger forms can also be omnivorous, i.e., forage upon both bacterial and eukaryotic resources. This hitherto largely ignored feeding mode may have pronounced implications for the interpretation of experiments about protistan bacterivory. We followed the response of an uncultured group of omnivorous cercozoan nanoflagellates from the Novel Clade 2 (Cerc_BAL02) to experimental food web manipulation in samples from the Gulf of Gdańsk (Southern Baltic Sea). Seawater was either prefiltered through 5 µm filters to exclude larger predators of nanoflagellates (F-treatment), or prefiltered and subsequently 1∶10 diluted with sterile seawater (F+D-treatment) to stimulate the growth of both, flagellates and bacteria. Initially, Cerc_BAL02 were rapidly enriched under both conditions. They foraged on both, eukaryotic prey and bacteria, and were highly competitive at low concentrations of food. However, these omnivores were later only successful in the F+D treatment, where they eventually represented almost one fifth of all aplastidic nanoflagellates. By contrast, their numbers stagnated in the F-treatment, possibly due to top-down control by a concomitant bloom of other, unidentified flagellates. In analogy with observations about the enrichment of opportunistically growing bacteria in comparable experimental setups we suggest that the low numbers of omnivorous Cerc_Bal02 flagellates in waters of the Gulf of Gdańsk might also be related to their vulnerability to grazing pressure

Microphytobenthos of Arctic Kongsfjorden (Svalbard, Norway): biomass and potential primary production along the shore line

During summer 2007, Arctic microphytobenthic potential primary production was measured at several stations around the coastline of Kongsfjorden (Svalbard, Norway) at ?5 m water depth and at two stations at five different water depths (5, 10, 15, 20, 30 m). Oxygen planar optode sensor spots were used ex situ to determine oxygen exchange in the overlying water of intact sediment cores under controlled light (ca. 100 ?mol photons m?2 s?1) and temperature (2–4°C) conditions. Patches of microalgae (mainly diatoms) covering sandy sediments at water depths down to 30 m showed high biomass of up to 317 mg chl a m?2. In spite of increasing water depth, no significant trend in “photoautotrophic active biomass” (chl a, ratio living/dead cells, cell sizes) and, thus, in primary production was measured at both stations. All sites from ?5 to 30 m water depth exhibited variable rates of net production from ?19 to +40 mg O2 m?2 h?1 (?168 to +360 mg C m?2 day?1) and gross production of about 2–62 mg O2 m?2 h?1 (17–554 mg C m?2 day?1), which is comparable to other polar as well as temperate regions. No relation between photoautotrophic biomass and gross/net production values was found. Microphytobenthos demonstrated significant rates of primary production that is comparable to pelagic production of Kongsfjorden and, hence, emphasised the importance as C source for the zoobenthos

Seasonal population dynamics and trophic role of planktonic nanoflagellates in coastal surface waters of the Southern Baltic Sea

We investigated the temporal dynamics and trophic role of different nanoflagellates in surface waters of the Gulf of Gdańsk (Baltic Sea) between April and October 2007. Two 18S rRNA gene clone libraries were constructed from samples collected in spring and summer, and weekly changes in the abundances of five phylogenetic groups were studied by fluorescence in situ hybridization with newly designed probes. Stramenopiles affiliated with MAST-6 and Pedinellales were most numerous in spring but rare in summer. Both groups formed short-lived blooms during a sudden drop of salinity due to riverine influx (from 7.1 to 6.2 practical salinity units). The analysis of food vacuole content suggested that MAST-6 nanoflagellates were herbivorous, whereas bacterivory was found both in plastidic and aplastidic pedinellid populations. Members of an uncultured lineage of aplastidic, bacterivorous cercozoans distantly related to Ebria tripartita were more abundant in summer when water temperatures exceeded 17 degrees C. Multicellular trophonts and/or free-living single cell stages of two lineages of Group 1 parasitic Syndiniales (alveolates) were present in spring and early summer. One of these alveolate populations repeatedly peaked before and after the freshwater influx, but was conspicuously absent throughout the period of decreased salinity. Our results indicate that nanoflagellate populations in coastal surface waters may form short-lived blooms that can only be detected by high-frequency sampling, and that may be related both to seasonal development and to sporadic (e.g. mixing) events. In view of their trophic diversity we moreover suggest that nanoflagellates in eutrophic coastal waters should not be regarded as a single functional unit

Seasonal dynamics and activity of typical freshwater bacteria in brackish waters of the Gulf of Gdańsk

While typical freshwater and marine bacteria have been found to co-occur in brackish habitats, it is unknown if they are active members of the local bacterial assemblages or if their presence is the result of passive transport only. We followed the seasonal dynamics of typical freshwater bacteria (R-BT lineage of Betaproteobacteria; Ac1 Actinobacteria; LD12 Alphaproteobacteria) and of marine SAR11 Alphaproteobacteria in the brackish water of the Gulf of Gdańsk (southern Baltic Sea), and we assessed their incorporation of thymidine and leucine at three distinct environmental conditions. The temporal development of bacteria was driven not only by local conditions but also by phenomena resulting from the dynamic hydrology of the site. Both temperature and salinity were important factors influencing bacterial community composition, as reflected by the clear distinction of three assemblages in spring and summer and during a period of enhanced freshwater influx. During spring, high proportions of R-BT Betaproteobacteria and Ac1 Actinobacteria incorporated the radiolabeled tracers, and all three freshwater lineages were most active during the subsequent phase of low salinity. The summer period was characterized by highest abundances of Ac1 Actinobacteria and of both alphaproteobacterial lineages. All studied freshwater lineages were active members of the brackish water communities at specific environmental conditions, including LD12 Alphaproteobacteria, which have so far been considered to thrive exclusively in freshwater habitats. By contrast, the presence of the typical marine SAR11 bacteria seemed to result from passive inflow with more saline waters from the Baltic proper