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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2007.04.018 Byline: Tracy A. Villareal, R.M.L. McKay, M.M.D. Al-Rshaidat, R. Boyanapalli, R.M. Sherrell Keywords: Diatoms; Ethmodiscus; Ferridoxin; Iron; North Pacific gyre; Ratios; Phytoplankton Abstract: The giant diatom Ethmodiscus was examined along an east-west transect at 28-30[degrees]N during 2002 and 2003 to determine if abundance, chemical composition or physiological status of this largest of diatoms varied on the scale of 100's-1000's of km in North Pacific gyre. Abundance ranged from 2.0cellsm.sup.-3 and supported the notion of an abundance mosaic reported previously. However, there was only minimal support for the relationship between abundance and nutrient concentration at 125m reported previously. Cellular chlorophyll varied little along the transect (7.3-10.9ngchlcell.sup.-1) except at the westernmost station. Cellular N and P quotas co-varied 3-4.5 fold (mean=50.8[+ or -]3.7 and 3.7[+ or -]0.8nmol N and Pcell.sup.-1) and yielded N:P ratios that closely clustered around the Redfield ratio (average=14.6[+ or -]1.1). Only low levels of chlorophyll-normalized alkaline phosphatase (APase) activity were observed (0.4-2.5nmolP[mu]gchl.sup.-1 h.sup.-1) with APase activity lower than that in either the bulk water, or co-occurring Trichodesmium spp. and Pyrocystis noctiluca. The active fluorescence parameter F.sub.v:F.sub.m, a property sensitive to Fe stress, was uniformly high at all stations (average=0.73[+ or -]0.04 for 2003, and 0.69[+ or -]0.05 for 2002), indicating sufficient Fe for optimum photosynthetic competence. These results contrasted sharply with results from Rhizosolenia mats reported along the same transect where there was a significant decline westward in F.sub.v:F.sub.m. Both ferredoxin (Fd) and flavodoxin accumulated in cells of Ethmodiscus, resulting in Fd Index values of Author Affiliation: Department of Marine Science, Marine Science Institute, The University of Texas, 750 Channel View Drive, Port Aransas, TX 78373, USA Article History: Received 8 September 2006; Revised 11 April 2007; Accepted 22 April 2007

There is growing recognition that winter is an important season for growth of photoautotrophs in ice-covered freshwater environments. Exemplifying this are expansive under-ice blooms of filamentous diatoms in Lake Erie. Here we describe a metatranscriptome constructed from a phytoplankton community dominated by filamentous diatoms. As expected, a high percentage (> 73%) of the sequences with BLAST hits to nucleotides or proteins in National Center for Biotechnology Information databases were associated with photosynthetic algae of which the majority were diatoms, mainly Aulacoseira spp. and Stephanodiscus spp. which was confirmed by analysis of 18S rRNA gene transcripts and microscopy. Consistent with the winter growth environment, psychrophilic and low-light adaptations were observed. Prominent among adaptations to cold were transcripts for genes involved in biosynthesis of unsaturated fatty acids, which were consistent with expected increased membrane fluidity at low temperatures. Reflecting the combined effect of low winter insolation and high light attenuation were an abundant complement of reads for light-harvesting antennae, mainly genes encoding fucoxanthin chlorophyll a / c proteins. The presence of virulence factors originating from oomycetes offers support for new hypotheses into the eventual decline of Lake Erie's winter diatom bloom. Whereas fungi were identified both through the metatranscriptome and by microscopy, dsRNA viruses of fungi were detected that may indirectly counter against fungal infection. This study demonstrates the utility of an environmental omics approach to yield insights underlying phototrophic life as well as the interactions of the entire microbial community in an extreme environment. [ABSTRACT FROM AUTHOR]

Abstract: The limnology of offshore Lake Erie during periods of extensive (>70%) ice cover was examined from ship borne sampling efforts in 2007 to 2010, inclusive. Dense and discrete accumulations of the centric filamentous diatom Aulacoseria islandica (>10μg Chl-a/L) were located in the isothermal (<1°C) water column directly below the ice and only detectable in the ship wake; viable phytoplankton were also observed within ice. Evidence from these surveys supports the notions that winter blooms of diatoms occur annually prior to the onset of ice cover and that the phytoplankton from these blooms are maintained in the surface waters of Lake Erie and reduce silicate concentrations in the lake prior to spring. The mechanisms by which high phytoplankton biomass rise at this time of year requires further investigation, but these winter blooms probably have consequences for summer hypoxia and how the lake responds to climate change. [Copyright &y& Elsevier]