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Photic Zone (photic + zone)
Selected AbstractsDynamics of the SAR11 bacterioplankton lineage in relation to environmental conditions in the oligotrophic North Pacific subtropical gyreENVIRONMENTAL MICROBIOLOGY, Issue 9 2009Alexander Eiler Summary A quantitative PCR assay for the SAR11 clade of marine Alphaproteobacteria was applied to nucleic acids extracted from monthly depth profiles sampled over a 3-year period (2004,2007) at the open-ocean Station ALOHA (A Long-term Oligotrophic Habitat Assessment; 22°45,N, 158°00,W) in the oligotrophic North Pacific Ocean. This analysis revealed a high contribution (averaging 36% of 16S rRNA gene copies) of SAR11 to the total detected 16S rRNA gene copies over depths ranging from the surface layer to 4000 m, and revealed consistent spatial and temporal variation in the relative abundance of SAR11 16S rRNA gene copies. On average, a higher proportion of SAR11 rRNA gene copies were detected in the photic zone (< 175 m depth; mean = 38%) compared with aphotic (> 175 m depth; mean = 30%), and in the winter months compared with the summer (mean = 44% versus 33%, integrated over 175 m depth). Partial least square to latent structure projections identified environmental variables that correlate with variation in the absolute abundance of SAR11, and provided tools for developing a predictive model to explain time and depth-dependent variations in SAR11. Moreover, this information was used to hindcast temporal dynamics of the SAR11 clade between 1997 and 2006 using the existing HOT data set, which suggested that interannual variations in upper ocean SAR11 abundances were related to ocean-climate variability such as the El Niño Southern Oscillation. [source] High vertical and low horizontal diversity of Prochlorococcus ecotypes in the Mediterranean Sea in summerFEMS MICROBIOLOGY ECOLOGY, Issue 2 2007Laurence Garczarek Abstract Natural populations of the marine cyanobacterium Prochlorococcus exist as two main ecotypes, inhabiting different layers of the ocean's photic zone. These so-called high light- (HL-) and low light (LL-) adapted ecotypes are both physiologically and genetically distinct. HL strains can be separated into two major clades (HLI and HLII), whereas LL strains are more diverse. Here, we used several molecular techniques to study the genetic diversity of natural Prochlorococcus populations during the Prosope cruise in the Mediterranean Sea in the summer of 1999. Using a dot blot hybridization technique, we found that HLI was the dominant HL group and was confined to the upper mixed layer. In contrast, LL ecotypes were only found below the thermocline. Secondly, a restriction fragment length polymorphism analysis of PCR-amplified pcb genes (encoding the major light-harvesting proteins of Prochlorococcus) suggested that there were at least four genetically different ecotypes, occupying distinct but overlapping light niches in the photic zone. At comparable depths, similar banding patterns were observed throughout the sampled area, suggesting a horizontal homogenization of ecotypes. Nevertheless, environmental pcb gene sequences retrieved from different depths at two stations proved all different at the nucleotide level, suggesting a large genetic microdiversity within those ecotypes. [source] Internal loading: A new solution to an old problem in aquatic sciencesLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 1 2004Lars Håkanson Abstract Internal loading has long been regarded as an ,Achilles heel' in aquatic science and management. Internal loading is of fundamental importance in large and shallow lakes, where even low wind velocities can cause a considerable resuspension of matter deposited on the lake bed. The resuspended matter, and the chemical substances bound to the resuspended matter, will influence almost all processes in the aquatic ecosystem, such as water clarity and depth of the photic zone, and hence, primary and secondary production. If the sediments are contaminated, it will increase the concentrations of harmful substances in water and sediments and the potential ecosystem effects related to such concentrations. This paper presents an overview of the processes regulating bottom dynamic conditions in lakes (erosion, transport, accumulation), provides examples on the role of internal loading within the context of limnology and water management, and presents a new, general approach to quantify internal loading from sediments in lakes. The new approach has been critically tested, being a key factor behind the increase in predictive power of a new generation of lake models meant to be used for practical water management. Internal loading of any water pollutant depends on sedimentation. Sedimentation in this approach is presented as a function of two substance-specific variables, including the fall velocity of the carrier-particles and the particulate fraction (which, by definition, is the only fraction of a water pollutant that can settle out on the lake bed), and three generic variables, including mean depth, suspended particulate matter and ET-areas (areas of erosion and transport). On ET-areas there is, by definition, a discontinuous sedimentation of materials that settles according to Stokes' law. Basically, internal loading is the sum of advective (resuspension) and diffusive transport from the sediments. Resuspension from ET-areas is given as a function of the lake form (a new algorithm based on the volume development) and the age of ET-sediments. [source] Embryonic development of verongid demosponges supports the independent acquisition of spongin skeletons as an alternative to the siliceous skeleton of spongesBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2009MANUEL MALDONADO Approximately 85% of extant sponges (phylum Porifera) belong to the class Demospongiae, which contains 14 taxonomic orders. In the orders Verongida, Dictyoceratida, and Dendroceratida, jointly referred to as ,keratose demosponges', the skeleton does not contain siliceous spicules but only spongin fibres. This shared trait has encouraged placement of these orders together within Demospongiae, although their relationships remain uncertain. The present study documents for the first time embryo development in the order Verongida (Aplysina aerophoba), providing some clues for phylogenetic inference. Spawned eggs were enveloped by a follicle of maternal cells. Embryos and larvae were chimeric organisms, the blastocoel of which was filled with symbionts and maternal cells migrated from the follicle. The ultrastructure of epithelial larval cells revealed: (1) a basal apparatus characterized by a peculiar, angling accessory centriole; (2) a pear-shaped nucleus with a protruding beak connected to the rootlets of the basal body; and (3) a distinctive Golgi apparatus encircling the nuclear apex. Developmental and ultrastructural findings support the concept, in congruence with recent molecular studies, that Verongida are more closely related to Halisarcida (askeletal sponges) and Chondrosida (askeletal sponges + sponges with spongin + spiculate sponges) than to the remaining ,keratose' orders, making a monophyletic ,supra-ordinal unit' equivalent to a subclass (Myxospongia, new subclass). Hence, spongin skeletons have evolved at least twice in Demospongiae. Independent acquisition of ,corneous' materials as an alternative to silica could have been stimulated by the radiation of diatoms at the Cretaceous,Tertiary boundary (approximately 65 Mya), which depleted silicon in the photic zone of the world's ocean. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 427,447. [source] Biogeochemistry of a gypsum-encrusted microbial ecosystemGEOBIOLOGY, Issue 3 2004D. E. CANFIELD ABSTRACT Gypsum crusts containing multicolored stratified microbial populations grow in the evaporation ponds of a commercial saltern in Eilat, Israel. These crusts contain two prominent cyanobacterial layers, a bright purple layer of anoxygenic phototrophs, and a lower black layer with active sulphate reduction. We explored the diel dynamics of oxygen and sulphide within the crust using specially constructed microelectrodes, and further explored the crust biogeochemistry by measuring rates of sulphate reduction, stable sulphur isotope composition, and oxygen exchange rates across the crust,brine interface. We explored crusts from ponds with two different salinities, and found that the crust in the highest salinity was the less active. Overall, these crusts exhibited much lower rates of oxygen production than typical organic-rich microbial mats. However, this was mainly due to much lower cell densities within the crusts. Surprisingly, on a per cell-volume basis, rates of photosynthesis were similar to organic-rich microbial mats. Due to relatively low rates of oxygen production and deep photic zones extending from 1.5 to 3 cm depth, a large percentage of the oxygen produced during the day accumulated into the crusts. Indeed, only between 16% to 34% of the O2 produced in the crust escaped, and the remainder was internally recycled, used mainly in O2 respiration. We view these crusts as potential homologs to ancient salt-encrusted microbial ecosystems, and we compared them to the 3.45 billion-year-old quartz barite deposits from North Pole, Australia, which originally precipitated gypsum. [source] | |||||||||||||