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1.
The study investigated the global and regional phylogeography of the yellowtail kingfish Seriola lalandi by examining genetic diversity and population genetic structure of this species at inter-and intra-ocean level and on a regional scale. DNA fragments of two mitochondrial genes, cytochrome b (Cytb) and cytochrome c oxidase subunit I (COI) and one nuclear gene, recombination activating gene 1 (RAG1), were sequenced to investigate the global-scale phylogeography of this species. The population genetic structure within the South Pacific, as well as along the South African coastline, was examined further using six microsatellite markers. Three distinct clades were identified for S. lalandi, which correspond with previously described subspecies of the North-East Pacific, North-West Pacific and the Southern Hemisphere. Within the latter, additional divergence was observed between the South Pacific and the South-East Atlantic regions. Divergence estimates were indicative of a Pacific origin for S. lalandi populations, because of Pleistocene vicariant events. Microsatellite analyses revealed overall significant genetic differentiation between South African and South Pacific samples. This corroborates recent findings on the global phylogeography of the species. No population differentiation was observed within South Africa, indicating high levels of gene flow. 相似文献
2.
The discovery of layered, SO4-rich sediments on the Meridiani Planum on Mars has focused attention on understanding the formation of acid–saline lakes. Many salt lakes have formed in southern Australia where regional groundwaters are characterized by acidity and high salinity and show features that might be expected in the Meridiani sediments. Many (but not all) of the acid–saline Australian groundwaters are found where underlying Tertiary sediments are sulfide-rich. When waters from the formations come to the surface or interact with oxidised meteoric water, acid groundwaters result. In this paper examples of such waters around Lake Tyrrell, Victoria, and Lake Dey-Dey, South Australia, are reviewed. The acid–saline groundwaters typically have dissolved solids of 30–60 g/L and pH commonly <4.5. Many contain high concentrations of Fe and other metals, leached from local sediments. The combination of acidity and salinity also releases Ra. Around salt-lakes, these acidic waters often emerge at the surface in marginal spring zones where the low density (ρ ∼ 1.04) regional water flows out over the denser (ρ ∼ 1.16) lake brines. In the spring zones examined, large amounts of Fe are commonly precipitated. In a few places minerals of the alunite-jarosite family are formed which can trap many other metals, including Ra. The studied groundwater systems were discovered by U exploration programs following up radiometric anomalies related to this Ra. Evaporation concentrates the lesser soluble salts (gypsum and some halite) on the surface of the lakes. The lake brines contain most of the more soluble salts and form a column within the porous sediments which is held in place by hydrostatic forces around the salt-lake. These brines are near-neutral in pH. 相似文献
3.
Anammox bacteria are widespread in the marine environment, but studies of anammox in marshes and other wetlands are still
scarce. In this study, the role of anammox in nitrogen removal from marsh sediments was surveyed in four vegetation types
characteristic of New England marshes and in unvegetated tidal creeks. The sites spanned a salinity gradient from 0 to 20 psu.
The impact of nitrogen loading on the role of anammox in marsh sediments was studied in a marsh fertilization experiment and
in marshes with high nitrogen loading entering through ground water. In all locations, nitrogen removal through anammox was
low compared to denitrification, with anammox accounting for less than 3% of the total N2 production. The highest relative importance of anammox was found in the sediments of freshwater-dominated marshes, where
anammox approached 3%, whereas anammox was of lesser importance in saline marsh sediments. Increased nitrogen loading, in
the form of nitrate from natural or artificial sources, did not impact the relative importance of anammox, which remained
low in all the nitrogen enriched locations (<1%). 相似文献
4.
Temporal trends of metals in surficial sediments (1991-1998) at two sites in Boston Harbor were analyzed to evaluate the effect of stopping sludge dumping in December 1991. Metal contents of sediments from the old sludge disposal site were higher than those of a station in the central Harbor. Since 1991, carbon, copper, and lead contents have significantly decreased in sediments from the disposal site. Chromium and Zn have shown smaller decreases while Fe, and Mn, have remained relatively constant. Metal content in the central Harbor station, located in an area of sediment reworking, has been quite variable, but, with the exception of Zn which has shown a large decrease relative to iron, the changes seemed to be well correlated with changes in the organic carbon content at this site due to resuspension. Ratios of metals in the sediments are fairly similar at both sites and similar to those of sewage-derived particles, with the exception of Cr, which appears to be enriched in the sediments. 相似文献
5.
Anne E. Giblin Nathaniel B. Weston Gary T. Banta Jane Tucker Charles S. Hopkinson 《Estuaries and Coasts》2010,33(5):1054-1068
Benthic respiration, sediment–water nutrient fluxes, denitrification and dissimilatory nitrate reduction to ammonium (DNRA)
were measured in the upper section of the Parker River Estuary from 1993 to 2006. This site experiences large changes in salinity
over both short and long time scales. Sediment respiration ranged from 6 to 52 mmol m−2 day−1 and was largely controlled by temperature. Nutrient fluxes were dominated by ammonium fluxes, which ranged from a small uptake
of −0.3 to an efflux of over 8.2 mmol N m−2 day−1. Ammonium fluxes were most highly correlated with salinity and laboratory experiments demonstrated that ammonium fluxes increased
when salinity increased. The seasonal pattern of DNRA closely followed salinity. DNRA rates were extremely low in March, less
than 0.1 mmol m−2 day−1, but increased to 2.0 mmol m−2 day−1 in August. In contrast, denitrification rates were inversely related to salinity, ranging from 1 mmol m−2 day−1 during the spring and fall to less than 0.2 mmol m−2 day−1 in late summer. Salinity appears to exert a major control on the nitrogen cycle at this site, and partially decouples sediment
ammonium fluxes from organic matter decomposition. 相似文献
6.
To gain insight into the importance of the benthos in carbon and nutrient budgets of Boston Harbor and surrounding bays, we measured sediment-water exchanges of oxygen, total carbon dioxide (DIC), nitrogen (ammonium, nitrate+nitrite, urea, N2O), silicate, and phosphorus at several stations in different sedimentary environments just prior to and subsequent to cessation of sewage sludge disposal in the harbor. The ratio of the average annual DIC release to O2 uptake at three primary stations ranged from 0.84 to 1.99. Annual average DIC:DIN flux ratios were consistently greater than predicted from the Redfield ratio, suggesting substantial losses of mineralized N. The pattern was less clear for P: some stations showed evidence that the sediments were a sink for P while others appeared to be a net source to the water column over the study period. In general, temporal and spatial patterns of respiration, nutrient fluxes, and flux ratios were not consistently related to measures of sediment oxidation-reduction status such as Eh or dissolved sulfide. Sediments from Boston Harbor metabolize a relatively high percentage (46%) of the organic matter inputs from phytoplankton production and allochthonous inputs when compared to most estuarine systems. Nutrient regeneration from the benthos is equivalent to 40% of the N, 29% of the P, and more than 60% of the Si demand of the phytoplankton. However, the role of the benthos in supporting primary production at the present time may be minor as nutrient inputs from sewage and other sources exceed benthic fluxes of N and P by 10-fold and Si by 4-fold. Our estimates of denitrification from DIC:DIN fluxes suggests that about 45% of the N mineralized in the sediments is denitrified, which accounts for about 17% of the N inputs from land. 相似文献
7.
Mineralogical, morphological and isotopic (RbSr and KAr) determinations were made on some detrital smectites of Palaeocene and Cenomanian ages from D.S.D.P. drillings in the Atlantic Ocean. These minerals are not inert in their depositional environment; authigenic laths grow on detrital sheets with sharp borders. This authigenesis could occur slightly after deposition in a closed system, for some of these smectites. It has been tentatively quantified by the RbSr and KAr isotopic methods, which seem also well suited to evaluate the chemical extent of this authigenesis. At least, no preferential loss of 40Ar vs. 87Sr could be detected in the minerals, even in those which are smaller than 0.2 μm. 相似文献
8.
JD Klein AE Bester-van der Merwe ML Dicken A Emami-Khoyi KL Mmonwa 《African Journal of Marine Science》2019,41(1):115-118
Genomic data can be a useful tool in the management and conservation of biodiversity. Here, we report the development of genomic resources for the spotted ragged-tooth shark Carcharias taurus using genome-wide DNA data from Illumina next-generation sequencing. We explored two commonly used genetic marker types: microsatellites and mitochondrial DNA. A total of 4 394 putative microsatellites were identified, of which 10 were tested on 24 individuals and found to have ideal properties for population genetic analyses. Additionally, we reconstructed the first complete mitochondrial genome of a South African spotted ragged-tooth shark, and highlight the most informative gene regions to facilitate future primer design. The data reported here may serve as a resource for future studies and can ultimately be applied in the sustainable conservation and fisheries management of this apex predator. 相似文献
9.
Two sets of hypervelocity impact experiments have been performed in the open using a contact charge technique and recorded using fast-framing cameras. It has been possible to record the uninterrupted ballistic trajectories of fragments from the catastrophically disrupted targets, together with their velocity and rotational properties directly after the impact, as well as their size. By performing these experiments in the open and on fairly soft ground, secondary fragmentation normally caused by impact onto the walls or floor of a test chamber has been minimised. A total of 10 experiments have been performed using targets of artificial rock which were either homogeneous, cored or carefully pre-fractured. We report here on the analysis of some of these data using a computer and special software written and developed by our group, with an indication of the results obtained. 相似文献
10.
The species-rich genus Mustelus (smoothhounds) of the shark family Triakidae is one of the most bio-economically important groups of elasmobranchs in the world’s oceans. Despite the commercial value of Mustelus, the systematics of the group remains largely unresolved and there is no global review or synthesis of knowledge about the conservation status and conservation genetics of smoothhounds across all oceanic regions. Here, we analysed published studies as well as grey literature to gain insight into the biogeographic, ecological and behavioural factors that shape genetic diversity in smoothhounds, and we identify critical knowledge gaps. From a series of molecular phylogenetic studies it can be inferred that the genus Mustelus is paraphyletic and that the aplacental species evolved secondarily from the placental species of the genus. The increasing availability of genetic data aids in disentangling systematic issues, such that more meaningful morphological characters can be chosen for use in practical field-identification keys for co-occurring smoothhounds. An integrative taxonomic approach to the genus Mustelus may offer the best chance of recording and protecting the biodiversity of these sharks. Furthermore, it is evident that different smoothhound species exhibit unique gene-flow patterns, suggesting varying rates within species and hence that species-level conservation approaches would be most appropriate. Molecular studies have advanced our understanding of smoothhound biology (including reproductive traits), ecology and evolution. While many knowledge gaps remain, a crucial lesson from this review is that, when doing assessments on a molecular level, it is important to place genetic results in a broader context, by assimilating biological and ecological data, if definitive conclusions are to be drawn. 相似文献