Pelagic Marine Environments Research Articles

Identification of Culturable Oligotrophic Bacteria within Naturally Occurring Bacterioplankton Communities of the Ligurian Sea by 16S rRNA Sequencing and Probing.

> Abstract Typical marine bacteria (i.e., obligately oligotrophic) that were numerically dominant members of naturally occurring marine communities were identified by cloning and sequencing the amplified 16S rRNA genes obtained from dilution cultures of the original samples. The data reported here refer to two different habitats of a marine pelagic environment (28 miles offshore, in the northwestern Mediterranean Sea). The samples were taken from the water column at two representative layers, i.e., the 30-m depth, corresponding to the chlorophyll maximum layer, and the 1800-m depth, representative of a deep, oligotrophic environment. Three major lineages were found in the 16S rDNA clone libraries prepared from the two samples, two of which could be assigned to the Vibrio and the Rhodobacter groups. The third lineage was a distant relative of the genus Flavobacterium, but it was not closely related to any marine isolate. Six oligonucleotide probes, either complementary to the conserved sequence domains or selectively hybridizing to the clone sequences, were designed for use as hybridization group-specific and strain-specific probes. A single-mismatch discrimination between certain probes and nontarget sequences was demonstrated by detecting the probes' specificity at different hybridization and washing conditions. The screening of the clone libraries with the obtained probes revealed that neither the 30-m sample higher dilution nor the 1800-m one were pure cultures. While some representatives of the Vibrio group were found in both the surface and the deep sample, the members of the Flavobacterium and Rhodobacter lineages were detected only in the deep and the euphotic layers, respectively. We suggest an approach for analyzing autochthonous marine bacteria able to grow in unamended seawater.

Impact of temperature, salinity and light on hatching of eggs ofAnisakis simplex(Nematoda, Anisakidae), isolated by a new method, and some remarks on survival of larvae

Abstract A new efficient method of isolating large number of eggs from anisakid worms is described. The method involves blending the worms in an electric mixer and isolating the eggs by centrifugation. Eggs were used to study factors affecting egg hatching and survival of emerged larvae of Anisakis simplex. The hatching time (range 3–21 days) varied inversely with temperature (5-21 0q, but did not differ significantly with salinity (0–28 psu). The final proportions of eggs which hatched, increased with salinity. This proportion was highest at 13 °C and lowest at 21°C; larvae which emerged in fresh water died within a few hours irrespective of temperature. The mean survival time of larvae was in the range of92-131 days. The survival time increased with salinity but decreased with temperature. Light exposure (at 13°C) was found to reduce significantly the time needed for the hatching of eggs. The results support the hypothesis that A. simplex is adapted to off-shore pelagic marine environments.

Interannual variability in krill abundance at South Georgia

Interannual variability within the pelagic marine environment around South Georgia is a well-recognised phenomenon. A key aspect of this variability is interannual fluctuation in the abundance of Antarctic krill Euphausia superba. Here we describe a new acoustic survey programme to monitor krill abundance in the South Georgia region. We present biomass estimates for 2 survey boxes, located over the shelf-break to the northeast and northwest of the island, derived from the first of these surveys conducted in January 1996. We contrast these with the most recent previous estimates for the region obtained in January 1994. Weighted mean krill density (and weighted variances) estimates for the 1996 surveys were 40.57 g m-2 (13.37) and 26.48 g m-2 (54.30) for the eastern and western boxes respectively. These are high compared with those obtained in January 1994, when estimates for similar areas were 1.87 g m-2 (0.14) and 7.43 g m-2 (1.33) respectively. The greater than 20-fold difference between surveys reveals a very large interannual variability in krill abundance at South Georgia. In 1994 the low abundance resulted in greatly reduced breeding success in most habitual krill predator species there. In the 1996 season, however, breeding success of these species was normal. Instantaneous estimates of krill abundance using acoustic techniques are therefore consistent with measurements from predators, whose breeding performances provide a longer-term indication of prey abundance in the surrounding pelagic ecosystem in a particular season.

Phylogeny of Prosthecobacter, the fusiform caulobacters: members of a recently discovered division of the bacteria.

Prosthecobacter fusiformis is morphologically similar to caulobacters; however, it lacks a dimorphic life cycle. To determine the relatedness of the genus Prosthecobacter to dimorphic caulobacters and other prosthecate members of the alpha subgroup of the Proteobacteria (alpha-Proteobacteria), we isolated and sequenced 16S rRNA genes from four Prosthecobacter strains. Surprisingly, the results of phylogenetic analyses placed the fusiform caulobacters in a deeply rooted division of the Bacteria that was most closely affiliated with the Planctomyces-Chlamydia group and only distantly related to the alpha-Proteobacteria. The genus Prosthecobacter shares a common lineage in this division with Verrucomicrobium spinosum, a polyprosthecate, heterotrophic bacterium. Consistent with this phylogenetic placement, menaquinones were isolated from Prosthecobacter strains and menaquinones have been isolated from Verrucomicrobium strains and planctomycetes but not from members of the alpha-Proteobacteria. Thus, the genus Prosthecobacter is a second genus in the recently described order Verrucomicrobiales. Members of the genus Prosthecobacter are susceptible to beta-lactam antibiotics and contain mesodiaminopimelic acid, indicating that they, unlike members of the Planctomycetales or Chlamydiales, have peptidoglycan cell walls. This major phenotypic difference, together with the phylogenetic independence of the verrucomicrobia, indicates that these bacteria and the sources of related 16S ribosomal DNAs obtained from soils, freshwater, and the marine pelagic environment represent an unrecognized division of the Bacteria.

Food-web mediated export of biogenic carbon in oceans:hydrodynamic control

This paper describes an approach to determine, using a small number of food-web or hydrodynamic variables, the partitioning of phytoplankton production among 3 carbon fluxes, i.e. remineralization within the euphotic zone, food-web transfer, and sinking to depth of organic particles. In order to do so, the flows of biogenic carbon in the marine pelagic environment are reduced to 5 broad path\z~ays, which are ordered along a continuum of decreasing export relative to primary production. At one end of the continuum, ungrazed phytoplankton is exported to depth and, at the other, biogenic carbon is remineralized within the bacteria-microzooplankton loop. In the present paper, export of biogenic carbon from the euphotic zone includes food-web transfer of primary production and downward flux of particulate organic carbon (POC) into deep waters. A simple model and data from the literature lead to the conclusions that: (1) the export characteristics of pelagic ecosystems are largely determined by the size structure of primary production and the matching (or, conversely, segregation) between primary production and grazing and (2) total export from the euphotic zone is a function of the delivery of mechanical energy to the upper water column whereas the partitioning of total export between foodweb transfer and sinking of POC is controlled by temporal variations in depth of the surface mixed layer Food-web transfer is significant for marine resources and sinking of POC may contribute to the regulation of climate change (sequestration at depth of biogenic carbon).

Enumeration of viable bacteria in the marine pelagic environment

The low percentage of living bacteria commonly obtained when comparing viable counts with total direct counts in seawater could be due more to inappropriate techniques for appreciating the growth ability of living cells than to unadapted culture conditions. The most-probable-number counts in filtered seawater cultures and the microscopic counts of 4(prm1),6-diamidino-2-phenylindole (DAPI)-stained aggregate-forming units grown on black polycarbonate filters appeared significantly correlated to the direct counts. Both these techniques show that in the superficial and intermediate water masses, the living cells may constitute an important (frequently higher than 20%) but highly variable part of the total populations. These viable counts appear more realistic than the conventional CFU counts, which provide only 0.001 to 0.2% of the total counts.

High abundance of Archaea in Antarctic marine picoplankton.

Archaea (archaebacteria) constitute one of the three major evolutionary lineages of life on Earth. Previously these prokaryotes were thought to predominate in only a few unusual and disparate niches, characterized by hypersaline, extremely hot, or strictly anoxic conditions. Recently, novel (uncultivated) phylotypes of Archaea have been detected in coastal and subsurface marine waters, but their abundance, distribution, physiology and ecology remain largely undescribed. Here we report exceptionally high archaeal abundance in frigid marine surface waters of Antarctica. Pelagic Archaea constituted up to 34% of the prokaryotic biomass in coastal Antarctic surface waters, and they were also abundant in a variety of other cold, pelagic marine environments. Because they can make up a significant fraction of picoplankton biomass in the vast habitats encompassed by cold and deep marine waters, these pelagic Archaea represent an unexpectedly abundant component of the Earth's biota.

Developmental studies on the loricate choanoflagellate Stephanoeca diplocostata ellis : VII. Dynamics of costal strip accumulation and lorica assembly

Summary The barrel-shaped lorica of S. diplocostata consists of two chambers. The anterior chamber contains between 15–24 regularly spaced longitudinal costae, each costa comprising 3 costal strips arranged end-to-end. Four transverse costae are located within the longitudinal costae; one forms the anterior ring, one forms the waist costa and the other two are equally spaced in between. Costae of the posterior chamber comprise two spirals, the longitudinal spiral being outside the transverse spiral. The posterior chamber terminates in a pedicel. All costal strips in the lorica are curved narrow rods, which are circular in cross section, except the strips of the the waist costa which are thicker and are ovoid in cross section. During interphase the protoplast deposits groups of costal strips individually within silica deposition vesicles. When mature, strips are transferred in subgroupings to the top of the inner surface of the collar. The waist costal strips are produced early in interphase but are not all stored within one subgrouping. Details are presented regarding the spatial and numerical reorganization of the collar tentacles during division. The parent cell tentacles are probably shared out equally between the two daughter protoplasts. On the juvenile protoplast the tentacles received from the parent protoplast form the anterolateral and posterior tentacles whereas on the sister they contribute towards the collar. By the end of cell division approximately equal numbers of new tentacles have developed on each protoplast. The manner in which the subgroupings of costal strips interact with the tentacles during division is discussed. The functional significance of tectiform replication is explored. It is concluded that development of a voluminous lorica in conjunction with tectiform replication has allowed loricate choanoflagellates to adopt a free-floating, planktonic habit independent of a substratum. The acquisition of this habit has resulted in loricate choanoflagellates becoming one of the most successful groups of heterotrophic nanoflagellates to colonise the marine pelagic environment including relatively unproductive waters where particle aggregates are few and far between.

Use of particle-size data to predict potential pelagic-fish yields of some southern African areas

A particle-size spectrum model is used to estimate standing stocks of some pelagic fish from measurements of phytoplankton chlorophyll in two exploited regions in southern Africa (southern Benguela and off South West Africa/Namibia) and in two unexploited regions (the Agulhas Bank and off the eastern Cape Province). The model is based on the assumption that equal biomasses occur in logarithmically equal size classes in the pelagic marine environment. Phytoplankton, with an equivalent spherical diameter ranging from 1 to 128 μm, occupy 21 size classes on the logarithmic scale. Two different size ranges are assumed for some commercial, pelagic fish species, equivalent to exploitation with two different purse-seine mesh sizes. A mesh of 12,7 mm would catch 8 size classes of pilchard, horse mackerel and anchovy whereas a mesh of 32 mm would catch only 3,3 size classes of pilchard and horse mackerel. From the model, the potential biomass of these commercial pelagic fish is estimated, after allowing for the presence of other commercial and non-commercial fish and other taxa in the exploited size range. Total pelagic fish production is estimated by assuming constant turnover rates of 1·y−1 and 1,5·y−1 when exploited with 32 and 12,7 mm mesh nets respectively. Consideration of the maximum and mean reported catches in the exploited areas indicates that only some 25 per cent of pelagic fish production is exploitable by man. On this basis, the unexploited Agulhas Bank region may yield some 400 000 metric tons (wet) of pelagic fish of the species considered, and the East Coast region some 90 000 tons. Exploitation in these regions cannot be recommended, because the Agulhas Bank is an important spawning ground for many pelagic species, and the fish in both regions probably act as a reserve buffer for the heavily exploited pelagic resource of the Western Cape.

Total organic carbon in Lake Superior sediments: Comparisons with hemipelagic and pelagic marine environments1

Seventeen box cores from Lake Superior were analyzed for total organic carbon (TOC), porosity, and 210Pb activity. The data were used to determine relationships among bulk sedimentation rates, TOC sedimentation rates, and TOC degradation rates with depth in the core. Results are compared with predictive equations for TOC sedimentation rates and degradation rates in the oceans and show some striking similarities between the behavior of TOC in Lake Superior and in hemipelagic and pelagic marine environments.