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ILLUSTRATED GUIDE ON THE BENTHIC DIATOMS of Kuwait's Marine Environment ILLUSTRATED GUIDE ON THE BENTHIC DIATOMS of Kuwait's Marine Environment I L LU S T R AT E D G U I D E O N T H E B E N T H I C D I ATO M S O f KU wA I T 'S M A R I N E E N v I R O N M E N T INTRODuCTION

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The effects on UVB radiation on a subtidal, cohesive-sediment biofilm dominated by the diatom Gyrosigma balticum (Ehrenberg) Rabenhorst were investigated. Chlorophyll fluorescence parameters (F(v)/F(m), φ(PSII)), pigment concentrations, cell densities, and carbohydrate fractions were measured in four treatments (no UVBR, ambient UVBR, +7%, and + 15% enhancement with UVBR). Enhanced UVBR was provided by a computer-controlled system directly linked to natural diel UVBR levels. Increases in φ(PSII) values in the UVBR-enhanced treatments and a decrease in the steady-state fluorescence yield (F(s)) from the surface of the biofilms during the middle and latter part of daily exposure periods suggested that G. balticum responded to enhanced UVBR by migrating down into the sediment. Diatoms in the + 15% UVBR treatment also had significantly higher concentrations of β-carotene after 5 days of treatment. Although G. balticum responded to enhanced UVBR by migration and increased β-carotene concentrations, significant reduction in maximum quantum yield of PSII (F(v)/F(m)) and in minimal fluorescence (F(o)) and decreases in cell densities occurred after 5 days. Concentrations of different carbohydrate fractions (colloidal carbohydrate, glucan, exopolymers [EPS]) associated with diatom biomass and motility also decreased in the UVBR-enhanced treatments. Short-term responses (migration) to avoid UVBR appear insufficient to prevent longer-term decreases in photosynthetic potential and biofilm carbohydrate concentration and biomass.
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Opephora parva, O. pacifica and O. perminuta are commonly reported from brackish and marine sediments worldwide, but their true identity is unclear. Therefore, isotype material of these three taxa was examined using light microscopy. In addition, several populations from different localities in Europe, Africa, South America and Australasia were investigated with light and scanning electron microscopy. In the isotype slide of O. parva and O. perminuta, four different opephoroid taxa could be distinguished; three new combinations are proposed. The correct name of O. parva is O. mutabilis (Grunow) comb. nov.; this is a distinct, valid species, and is usually reported under the later synonym O. olsenii. O. perminuta is transferred to the genus Pseudostaurosira; P. perminuta (Grunow) comb. nov. The two other taxa were identified as O. naveana Le Cohu and O. guenter-grassii (Witkowski & Lange-Bertalot) comb. nov., which is transferred from the genus Fragilaria. These four taxa were then compared with isotype material of O. pacifica (Grunow) Petit. A detailed description of their taxonomy, morphology and ecology is given. Although Opephora mutabilis, O. naveana and O. guenter-grassii differ in some respects from O. pacifica, the type of the genus, their maintenance in this genus is recommended subject to further research.
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Epipelic diatoms are important constituents of estuarine microphytobenthic biofilms. Field-based investigations have shown that the production of carbohydrates by such taxa is ecologically important. However, limited information exists on the dynamics of carbohydrate production by individual species of epipelic diatoms. The production of low and high molecular weight extracellular carbohydrates in axenic cultures of five species of benthic estuarine diatoms, Cylindrotheca closterium (Ehrenberg), Navicula perminuta (Grun.) in Van Heurck, Nitzschia frustulum (Kütz.) Grunow, Nitzschia sigma (Kütz.) Grunow, and Surirella ovata (Kütz.) Grunow, were investigated. All species produced colloidal (water-soluble) carbohydrates during growth, with maximal production occurring during stationary phase. During logarithmic growth, approximately 20% of extracellular carbohydrates consisted of polymeric material (extracellular polymeric substances [EPS]), but during stationary phase, EPS content increased to 34%–50%. Pyrolysis–mass spectrophotometry analysis showed differences in the composition of EPS produced during logarithmic and stationary phase. All species synthesized glucan as a storage carbohydrate, with maximum glucan accumulation during the transition from log to stationary phase. Short-term labeling with 14C-bicarbonate found that between 30 and 60% of photoassimilates were released as colloidal carbohydrate, with EPS consisting of approximately 16% of this colloidal fraction. When cells were placed in darkness, EPS production increased, and between 85 and 99% of extracellular carbohydrate produced was polymeric. Glucan reserves were utilized in dark conditions, with significant negative correlations between EPS and glucan for N. perminuta and S. ovata. Under dark conditions, cells continued to produce EPS for up to 3 days, although release of low molecular weight carbohydrates rapidly ceased when cells were dark treated. Three aspects of EPS production have been identified during this investigation: (1) production during rapid growth, which differs in composition from (2) EPS directly produced as a result of photosynthetic overflow during growth limiting conditions and (3) EPS produced for up to 3 days in the dark using intracellular storage reserves (glucans). The ecological implications of these patterns of production and utilization are discussed.
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Type specimens of the nine Pleurosigma taxa described by A. Mann (1925) from the Philippine Islands were critically re-investigated as a result of a loan of these slides held in the Albert Mann collection at the United States National Museum, Smithsonian Institution, Washington, D.C., (USNM). Improved photomicrographic documentation and more recent insights into the taxonomy of the genus Pleurosigma lead to some revision of Mann's views. Mann noted a similarity between his P. obtusum and P. prisma and these species are here synonymized under the former name. No specific differences can be demonstrated for P. exemptum and P. obesum and the latter is here synonymized under the former name. Although Mann noted some resemblance between specimens of P. falx and small specimens of P. decorum W. Smith, I have found that P. falx A.Mann, closely resembles specimens of P. normanii Ralfs in Pritchard. Because no specific differences have been detected by light microscopy (LM), P. falx is here synonymized with P. normanii which has priority. On the other hand, Mann considered his P. acus very similar to P. intermedium W. Smith but in reality these species differ in several LM respects. As a result of this study, six of the nine new species P. acus, P. dolosum, P. exemptum, P. obtusum, P. rigens and P. suluense proposed by Mann are considered to be valid.