Factors contributing to dwarfing in the mangrove Avicennia marina

BACKGROUND AND AIMS: In Richards Bay, South Africa, Avicennia marina frequently exhibits a distinct productivity gradient, with tree height decreasing markedly from 6-10 m in the fringe zone to <1.5 m in the dwarf zone which is 120 m inland at a slightly higher elevation. In this investigation, soil physico-chemical conditions between fringe and dwarf A. marina were compared and the constraints imposed by any differences on mangrove ecophysiology and productivity determined. METHODS: Soil and plant samples were analysed for inorganic ions using spectrophotometry. Gas exchange measurements were taken with an infrared gas analyser and chlorophyll fluorescence with a fluorometer. Xylem psi was determined with a pressure chamber and chlorophyll content with a chlorophyll absorbance meter. RESULTS: In the dwarf site, soil salinity, total cations, electrical conductivity and soil concentrations of Na(+), K(+), Ca(2+), Mg(2+), Zn(2+), Mn(2+) and Cu(2+) were significantly higher than those in the fringe zone. Soil water potential and the concentration of soil P, however, were significantly lower in the dwarf site. In the leaves, Na(+) was the predominant ion and its concentration was 24 % higher in dwarf than fringe mangroves. Leaf concentrations of K(+), Ca(2+), Mg(2+), Mn(2+) and P, however, were significantly lower in dwarf mangroves. Photosynthetic performance, measured by gas exchange and chlorophyll fluorescence, was significantly reduced in the dwarf plants. CONCLUSIONS: The results suggest that hydro-edaphic factors contribute to high soil salinities, low water potentials, water stress and ion imbalance within tissues including P deficiency, which in interaction, contribute to dwarfing in Avicennia marina.     

Millimeter‐scale genetic gradients and community‐level molecular convergence in a hypersaline microbial mat

To investigate the extent of genetic stratification in structured microbial communities, we compared the metagenomes of 10 successive layers of a phylogenetically complex hypersaline mat from Guerrero Negro, Mexico. We found pronounced millimeter‐scale genetic gradients that were consistent with the physicochemical profile of the mat. Despite these gradients, all layers displayed near‐identical and acid‐shifted isoelectric point profiles due to a molecular convergence of amino‐acid usage, indicating that hypersalinity enforces an overriding selective pressure on the mat community.     

The salt stress-induced LPA response in Chlamydomonas is produced via PLA₂ hydrolysis of DGK-generated phosphatidic acid

The unicellular green alga Chlamydomonas has frequently been used as a eukaryotic model system to study intracellular phospholipid signaling pathways in response to environmental stresses. Earlier, we found that hypersalinity induced a rapid increase in the putative lipid second messenger, phosphatidic acid (PA), which was suggested to be generated via activation of a phospholipase D (PLD) pathway and the combined action of a phospholipase C/diacylglycerol kinase (PLC/DGK) pathway. Lysophosphatidic acid (LPA) was also increased and was suggested to reflect a phospholipase A₂ (PLA₂) activity based on pharmacological evidence. The question of PA''s and LPA''s origin is, however, more complicated, especially as both function as precursors in the biosynthesis of phospho- and galactolipids. To address this complexity, a combination of fatty acid-molecular species analysis and in vivo ³²P-radiolabeling was performed. Evidence is provided that LPA is formed from a distinct pool of PA characterized by a high α-linolenic acid (18:3n-3) content. This molecular species was highly enriched in the polyphosphoinositide fraction, which is the substrate for PLC to form diacylglycerol. Together with differential ³²P-radiolabeling studies and earlier PLD-transphosphatidylation and PLA₂-inhibitor assays, the data were consistent with the hypothesis that the salt-induced LPA response is primarily generated through PLA₂-mediated hydrolysis of DGK-generated PA and that PLD or de novo synthesis [via endoplasmic reticulum - or plastid-localized routes] is not a major contributor.     

Characteristics of the ichthyofauna of a temperate microtidal estuary with a reverse salinity gradient,including inter‐decadal comparisons

Data on the fish fauna of the Leschenault Estuary on the lower west coast of Australia were collected and used as a model to elucidate the characteristics of permanently open estuaries with a reverse salinity gradient, which undergo seasonal changes similar to many other estuaries with Mediterranean climate. Focus was placed on determining (1) the relationships of the number of species, density, life cycle category and species composition of fishes with region (within estuary), season and year and salinity, (2) whether species are partitioned along the lengths of such systems and (3) the extent and significance of any inter‐decadal changes in species composition. The analyses and interpretation involved using multi‐factorial permutational multivariate analysis of variance (PERMANOVA) and analysis of similarity (ANOSIM) designs, and three new or recently published visualization tools, i.e. modified non‐metric multidimensional scaling (nMDS) plots, coherent species curves and segmented bubble plots. The base, lower, upper and apex regions of the Leschenault Estuary, along which the salinity increased in each season except in winter when most rainfall occurs, were sampled seasonally for the 2 years between winter 2008 and autumn 2010. Estuarine residents contributed twice as many individuals, but less than half the number of species as marine taxa. While the numbers of marine species and estuarine residents declined between the base or lower and apex regions, the individuals of marine species dominated the catches in the base region and estuarine residents in the other three regions. Ichthyofaunal composition in each region underwent conspicuous annual cyclical changes, due to time‐staggered differences in recruitment among species, and changed sequentially along the estuary, both paralleling salinity trends. Different groups of species characterized the fauna in the different regions and seasons, thereby partitioning resources among species. The ichthyofauna of the apex region, in which salinities reached 54 and temperatures 36° C, recorded the highest maximum density and, in terms of abundance, was dominated (90%) by three atherinid species, emphasizing the ability of this family to tolerate extreme conditions. Comparisons between the data for 2008–2010 and 1994 demonstrate that the spotted hardyhead Craterocephalus mugiloides and the common hardyhead Atherinomorus vaigiensis had colonized and become abundant in the Leschenault Estuary in the intervening period. This represents a southwards extension of the distribution of these essentially tropical species during a period of increasing coastal water temperatures as a result of climate change. The abundance of weed‐associated species, e.g. the western gobbleguts Ostorhinchus rueppellii and the soldier Gymnapistes marmoratus, increased, whereas that of the longfinned goby Favonigobius lateralis decreased, probably reflecting increases in eutrophication and siltation, respectively.     

New Silurian cooksonias from dolostones of north-eastern North America

New specimens of Cooksonia and Hostinella are described from the Bertie Group of Ontario and New York State, which is dated by faunas as latest Silurian (Přídolí). The rare plant fossils are unusual in that they are preserved in fine-grained, slightly argillaceous dolostones ('waterlime') rather than clastic rocks. At least two species of Cooksonia are present, one with ± globular sporangial morphology close to C. hemisphaerica Lang. Those with ellipsoidal/discoidal sporangia are compared with C. pertoni Lang, C .  paranensis Gerrienne et al . and C. bohemica Schweitzer, the latter represented by a single specimen from the Přídolí of the Czech Republic. However, the paucity of specimens, which prevents assessment of taphonomic influences on shape, combined with the absence of any anatomical features and the gross morphological simplicity of the fossils, precludes specific assignment. Specimens of Hostinella include one in which apices and a lateral basal structure resembling a root are preserved. It is concluded that the Laurentian assemblage of Ontario and New York State is less diverse and disparate than coeval assemblages, which are also preserved in marine rocks. Its preservation in limestones may have been facilitated by the hypersalinity inferred from various sedimentary features, which would restrict the activity of many decomposers.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 399–413.     

A microcosm study of nitrogen utilization in the Great Salt Lake,Utah

Microcosms were used to study the effects of two inorganic nitrogen sources (ammonia and nitrate) and two organic nitrogen sources (urea and glutamic acid) on the growth of algae and bacteria found in the Great Salt Lake, Utah. Ammonia, nitrate and urea stimulated bacterial growth indirectly through increased algal production of unknown organic substances. Glutamic acid, representing readily available organic carbon and nitrogen, stimulated the bacteria directly. No nitrification was observed in the microcosms although nitrite was found when the microcosms were supplemented with nitrate. Lake sediment contained a number of anaerobic bacteria producing hydrogen sulfide, methane and other gases. Production of these gases was stimulated in the columns with high algal and bacterial activity.     

Effects of bacterial treatment at early stages of Atlantic cod (Gadus morhua L.) on larval survival and development

Aims: To assess the effects of bacterial treatment at the earliest stages of cod rearing on the microbial load, larval development and performance, testing three bacterial strains (Carnobacterium divergens V41, Arthrobacter sp. and Enterococcus sp.) in vivo that were previously shown to have inhibitory potential towards fish pathogens in vitro. Methods and Results: A bacterial mixture was added eight times to the rearing water from the prehatch to the mid‐larval stage (a 38‐day period). Microbiological analysis of ova, larvae and rearing water was performed regularly. Larval performance and development were evaluated by survival rate, hypersalinity tolerance and physiological measurements. Different larval survival rates were observed within and between treatments, and possibly explained by variations in larval microflora and established probionts. Larvae from one silo, which had been bathed in the bacterial suspension, showed the highest survival rate (42·1%), lowest Vibrio levels, and were significantly heavier (19·3%) and more stress tolerant than control larvae (P < 0·01). This coincided with the intestinal establishment of two of the tested bacteria. Conclusions: Arthrobacter and Enterococcus strains added regularly to the rearing water from the postfertilized egg stage can become established in larval gastrointestinal tract. The Enterococcus strain was associated with increased larval growth, performance and microflora control, indicating its probiotic nature. Significance and Impact of the Study: Regular application of autochthonous probionts may promote larval welfare, development and stress tolerance at early stages, hence increasing production yield in intensive cod larviculture.     

Molecular indicators of microbial contributions to recent and Tertiary hypersaline lacustrine sediments in China

In this paper, we investigate the molecular characteristics of recent sediment from the Ejinur salt lake (northern China) and eight Tertiary (Eocene) core samples from Qianjiang Formation (Eq1-4) of Jianghan basin, central eastern China, focussing on the distributions and abundances of carboxylic acid isolated from extractable organic matter. n-Alkanoic acids in sediments from both study areas (Ejinur and Jianghan) show a pronounced even over odd predominance (EOP) and a bimodel distribution. In the lower molecular weight range C16 and C_18 components are prominent with the former dominant. For higher homologues (≥ C20), docosanoic (C22) and tetracosanoic (C24) acids dominant the n-alkanoic acid homologues for the Jianghan and Ejinur samples, respectively. Alkanoic acids with an isoprenoid skeleton are more abundant in Jianghan, including C20, C21, C24, C_25 and C30 homologues, with a C25 component (3, 7, 11, 15, 19-pentamethyleicosanoic acid) most pronounced in the lower part of the Qianjiang Fm. The carbon skeletons of these isoprenoid acids are identical to those of isoprenoid hydrocarbons previously recognized in source rocks and petroleums from Jianghan, and attributed to Archaea (formally called archaebacteria; e.g. halophiles, methanogens). The similarity in the distributions of isoprenoid alkanoic acids and alkanes suggests that these isoprenoid acids must derive from comparable biological sources, although they appear to be formed geochemically from biosynthetic precursors (e.g. alkanes, alkenes, alkanols or alkenols). The possibility that these acids are formed as oxidation artifacts from alkanes can be discounted because of the dissimilarity between the distributions of n-alkanoic acids and n-alkanes. Iso and anteiso branched carboxylic acids are prevalent in both the Ejinur sample and the upper portion of the Qiangiang Fm (Eq1-3). They derive from bacteria, perhaps sulfate reducing bacteria, and their abundances may aid assessment of the importance of bacterial contributions of organic matter in different sedimentary environments. The presence of hopanoid acids and a 3-carboxy steroidal acid further attest to contributions from bacterial and eukaryotic sources, respectively. The occurrence of carboxylic acids in the Jianghan samples confirms the potential for these compounds to survive in ancient sediments and source rocks, notably in hypersaline settings. This revised version was published online in July 2006 with corrections to the Cover Date.     

Natural and man-induced changes in a tidal channel mangrove system under tropical semiarid climate at the entrance of the Maracaibo lake (Western Venezuela)

Caño Paijana is a tidal channel that connected, until recently, theUruba bay at the mouth of the Limón river, to the Gulf of Venezuelanorth of Maracaibo, Venezuela. It separated the Island of San Carlos fromthe mainland. In the last 50 years the channel has been drying out rapidly,to the extent that presently there is no water flow into or from the seathrough its mouth opening on the Gulf of Venezuela. This mouth wascovered by healthy mangroves (mainly Avicennia germinans) until atleast 1952. The two extremes of the Paijana water channel differ radicallytoday. At Uruba bay end the channel is fringed by dense mangrovevegetation dominated by Rhizophora mangle, while at the Gulf ofVenezuela mouth the vegetation cover is mostly constituted by scrubby,scattered trees of Avicennia germinans, xerophytic shrubs acting asdune fixers, and halophytic strand vegetation. The process is the result ofcomplex interaction between: a) high frequency of low-rainfall years; b)high dune activity during dry years c) dam construction on tributaries ofthe Limón river that reduced discharge of fresh water into Uruba bay.