策勒绿洲-沙漠过渡带风成沉积物粒度的空间变化

为了探讨绿洲-沙漠过渡带对绿洲可持续发展的环境效应,本研究对策勒绿洲西缘绿洲-沙漠过渡带、防护林带和绿洲内部的各种风成沉积物及策勒河谷沉积物粒度特征进行比较.结果表明: 绿洲-沙漠过渡带风成沉积物粒度特征(包括粒度分布特征、粒度参数、各粒级含量等)在空间上基本一致,其粒度范围为0.3～200 μm,分选性良好,主峰众数为67 μm,主要为悬浮组分和变性跃移组分,未出现>200 μm的跃移和蠕移组分,表现出典型的大气沙尘近距离传输沉积的特点.与外围(上风向)的策勒河谷(粒度范围0.3～800 μm)和沙漠地区的沉积物比较,过渡带粒度明显偏细,但与过渡带、防护林带和绿洲内部现代尘暴降尘(下风向)各种粒度特征基本一致.策勒绿洲-沙漠过渡带由于存在较高植被覆盖度,能够有效地抑制沙漠地区较粗颗粒组分(>200 μm)通过变性跃移或蠕移方式输送进入过渡带和绿洲内部.绿洲-沙漠过渡带与防护林体系一样,可有效抑制沙漠入侵绿洲,二者形成一个整体,共同维护策勒绿洲生态环境的稳定.     

Donax trunculus (Bivalvia: Donacidae) as a potential biological indicator of grain-size variations in beach sediment

Donax trunculus (Linnaeus, 1758) is one of the most common bivalve molluscs inhabiting the sandy shores of the Mediterranean Sea. This species, which is preferentially distributed on sediments at depths between 0 and about 2 m, is considered to be a substrate-sensitive organism because of its sensitivity to sediment grain size variations during its life cycle, in particular during its early growth stages. This study aims at investigating the relationship between D. trunculus’ density distributions and sediment grain size, in order to evaluate its use as a biological indicator of grain-size variations in beach sediment. For this purpose, a specific environmental study was performed by ISPRA (Italian National Institute for Environmental Protection and Research) along six beaches located in the Central Tyrrhenian Sea between Ladispoli and Anzio (Rome, Italy). On each beach, samples of D. trunculus and superficial sediments were collected in the infra-littoral zone at 3 different depths (0, 0.5, and 1 m) between June 2002 and March 2004. The results pointed out that the distribution of D. trunculus populations is strongly influenced by the sediment's grain size variations. A significant positive correlation was found between species density and the 2.00-phi and 2.50-phi grain size classes; but, in particular, the predominance of the 2.00-phi grain size class in the beach's sediment seems to positively influence the species density and distribution.This study suggests that sediment grain size is the chief factor controlling the distribution of D. trunculus populations; suitable grain sizes allow the settlement and the subsequent growth of well-structured populations. Generally, species density declined in areas subjected to grain-size variations in beach sediments, suggesting a predictable biological response to both natural and human-caused stressors. The present study also highlighted that where nourishment was carried out using suitable sediments, the species reappears on the beach after a few months, as it finds an optimal substrate for settlement. In this case, finding D. trunculus specimens a few months after replenishment indicates that the nourishment operations have been successful from an environmental point of view. As reported by Carignan and Villard (2002), a species that is strongly associated with particular habitat features could be a useful indicator; in particular, a species – like D. trunculus – that is negatively associated with human disturbances could be considered a “positive” indicator of ecological integrity.Long-term monitoring of D. trunculus abundance or density on sandy beaches (adequately carried out during the species’ recruitment period, e.g. between July and September), could help pinpoint the presence of natural or human-made phenomena that are leading to grain-size variations in the sediment. In conclusion, we can assume that D. trunculus can be used as a practical biological indicator to detect grain size variations on sandy beaches in coastal monitoring programmes; it could be a useful tool for researchers, managers and administrators to assess erosion phenomena while minimizing times and costs, also in view of an integrated coastal zone management.     

Sediment preferences and size-specific distribution of young-of-the-year Pacific halibut in an Alaska nursery

A combination of laboratory experiments and field surveys was used to test the hypotheses that responses to sediments change with fish size and that sediment grain-size is the predominant environmental factor affecting small-scale distribution in young-of-the-year (yoy) Pacific halibut Hippoglossus stenolepis . Laboratory tests showed that the smallest fish (31–40 mm L _T) chose fine sediments (muddy and fine sands), fish 51–70 mm had high selectivity (primarily medium sand), and the largest fish (80–150 mm) were not selective although they avoided the largest grain-sizes (pebbles and granules). Sediment preferences were correlated with size-dependent burial capabilities. Beam trawl collections were made over a 6 year period in Kachemak Bay, Alaska, to examine the distribution of yoy Pacific halibut (14–120 mm L _T) using small size classes (e.g. 10 mm intervals). Canonical correlation analysis showed that the per cent of sand in the sediment was a highly significant variable for all but one size and date combination. Catch per unit of effort (CPUE) for newly settled fish (<30 mm L _T) was highest on very fine sand, fish 41–80 mm were most abundant on fine sand, and the largest yoy fish (81–120 mm) were abundant over a range of sediments from fine sand to mud. Except for the smallest fish, Pacific halibut in the field were associated with sediments somewhat finer than predicted from the laboratory experiments; however, virtually all were captured where they could bury easily. The ability of flatfish to bury and shelter in sediment is related to fish size; consequently, habitat associations shift rapidly during the first year of life. Habitat models for yoy flatfishes should consider size-dependent shifts in capabilities and preferences.     

Polymorphism in recent ostracods of southwestern Spain: an environmental approach

The analysis of the surface ornamentation permits us to differentiate two morphotypes in the recent populations of the ostracod Urocythereis oblonga collected in shallow marine sediments of the Huelva littoral (SW Spain). An environmental analysis was made and its abundances were compared with different environmental parameters. Morph 1 (reticulated or “normal”) is almost always dominant, characterizing microenvironments with low salinity water changes, low to moderate energy levels, poorly sorted bottom sediments with high percentages of fine grain sizes (very fine sands, silts and clays) and moderate to high ostracod diversity. Morph 2 (punctuated or “degraded”) is significantly represented (> 10%) in stressing conditions, i.e., moderate salinity fluctuations, moderate to high hydrodynamic levels, low organic matter contents, moderate to well-sorted sediments with high percentages of medium sands and low to very low ostracod diversity. These differences make clear the potential of these microcrustaceans as environmental tracers in these transitional areas.     

Genetic structure of three populations of the 'living fossil' brachiopod Lingula from Queensland, Australia

An electrophoretic survey of enzyme variation demonstrates that the genomes of three populations of the inarticulate brachiopod Lingula contain a higher level of variability than the average for marine, tropical invertebrates, and for other brachiopods. Genetic distances between populations from localities up to 1200 km apart were very small, indicating that the populations belong to a single species, L. anatina Lamarck. These data suggest that larval dispersal is capable of maintaining a homogeneous gene pool over this range. It is predicted that the dispersal mechanism is sufficiently efficacious to ensure gene-flow throughout most of the Indo-West Pacific distribution of Lingula. Further investigations of genetic distance should support the hypothesis, based on studies of adult and larval morphology, that many presently recognized species should be reassigned to L. anatina.     

An illustrated key to the soft-bottom caprellids (Crustacea: Amphipoda) of the Iberian Peninsula and remarks to their ecological distribution along the Andalusian coast

The soft-bottom caprellids of the Iberian Peninsula are revised. Nineteen species have been reported so far, 42 % being endemic to the Mediterranean Sea. The lateral view of all of them is provided, together with an illustrated key for all the species. An ecological study was also conducted during 2007–2010 along the Andalusian coast to explore the relationships of caprellids with abiotic data. A total of 90 stations (0–40 m deep) were sampled and 40 contained caprellids. Along the Atlantic, caprellids were present in only 20 % of the stations, while along the Mediterranean coast, caprellids were present in the 75 % of the sampling sites. Furthermore, the abundance of caprellids was also higher in the Mediterranean coast. The dominant species was Pseudolirius kroyeri (present in 24 stations and showing the highest abundances with 1,780 ind/m²), followed by Phtisica marina (22 stations) and Pariambus typicus (11 stations). According to CCA and BIO-ENV, sediment type, P, pH and oxygen were the parameters that better explained the distribution of caprellids. Although the three dominant species were found in all types of sediment, the univariate approach showed that P. kroyeri was significantly more abundant in fine sediments (silt–clay and very fine sands) than in gross sediments (coarse and very coarse sands). The majority of studies dealing with caprellids from the Iberian Peninsula have been focused on shallow waters and further efforts are needed to explore biodiversity of deeper areas.     

An investigation of the relationship between sediment particles size and the development of green algal mats (Ulva prolifera) on the intertidal flats of Muan, Korea

The relationship between median grain size of sediments and the abundance in the wild of green algal mats (Ulva prolifera) on the intertidal flats of Muan, Korea, were investigated. The impact of substratum particle size on the growth and survival of germlings was examined in the laboratory. In the wild, the average annual density of algal mats was 7,950 ind m⁻². The algal mats mainly occurred in sands and exhibited patchy distribution. Statistical analysis indicates significant spatial analysis differences and a significant relationship between density and the ratio of sands to silts, suggesting that the distribution and density of this species were related to particle size. In laboratory experiments, the survival rate of U. prolifera germlings was the lowest value (22%) on sediments with a median grain size of 63–125 μm. Laboratory experiments have generally shown a positive relationship between attachment or survival of the alga and substratum particles size. Our laboratory results indicate a clear link between germling settlement/survival and substratum particle size. These results explain the spatial differences in abundance observed in the field in relation to the distribution and ratio of sands to silt on the Muan flats.     

Composition and Distribution of Recent Marine Ostracod Assemblages in the Bottom Sediments of Central Aegean Sea (SE Andros Island,Greece)

The present study provides a thorough analysis of the composition of recent marine ostracod populations from the bottom sediments of the central Aegean Sea, as well as their distribution patterns. In particular, a detailed qualitative and quantitative study of living ostracod assemblages was carried out in the marine environments of SE Andros Island. Sampling took place at Kastro and Korthi Gulf, both located at the southeastern coast of the Andros Island and from depth of 1.5 to 18 m, while additional samples were collected outside the gulfs at a depth of 120–180 m. Only ostracods considered to have been living at the time of collection were picked from the samples. A total of 51 species belonging to 34 genera were identified and four main ostracod assemblages, representing different biotopes, were distinguished. The results produced from the application of Q‐mode cluster analysis in the data set, the calculated assemblage structure indices for each sample, as well as the bathymetric and granulometric data are as follows: Hiltermannicythere rubra assemblage (occurs in substrates of sandy mud and at a water depth ranging from 40–60 m to the depth of 100 m or even more), Loxoconcha affinis, Xestoleberis sexmaculata assemblage (occurs in substrates of muddy very fine to fine sands and shallower environments), Semicytherura incogruens assemblage (occurs in very fine sands at a water depth from 10 to 28 m), Loculicytheretta pavonia and Neocytherideis fasciata, Pontocythere turbita assemblages (occurs mainly in fine sands and at a water depth between 3.5 and 15 m) and Urocythereis neapolitana assemblage (occurs in substrates of medium to coarse sand and at a water depth of less than 20 m). (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Correlation of shape and habit with sediment grain size for selected species of the bivalve Anadara

Burrowing ability was experimentally determined for a range (3–150 g) of sizes of the blood ark, Anadara ovalis , in sieved sediments ranging from very coarse sand (-1 φ) to silt (>4 φ). Small individuals (<5 g) could penetrate the complete range of sieved sediments, but the ability to reburrow apparently decreases with size (age) so that adults larger than 50 g can only reburrow in fine sands (2.5–3.0φ). This semi-infaunal species has a length/height ratio of 1.16 and is most commonly found in sand. The infaunal A. cheninitzi and A. braziliana , with L/H values of 1.10 and 1.18, respectively, are also most common in sands. The ovate (L/H ratio = 1.07–1.25) forms of the Pliocene A. trilineata from the Kettleman Hills of California are inferred to have been infaunal, based on the absence of muricid boreholes and the infrequent occurrence of epizoans. Ovate specimens are restricted to fine sands (2–3φ) in the Etchegoin and San Joaquin Formations, sediment textures into which the adults could probably reburrow. Elongated shell morphotypes (L/H = 1.5–1.67) have muricid boreholes and epizoans concentrated posterodorsally on the inferred exposed portion of the shells in life position. Populations of elongated shells were associated with gravelly, sandy and silty sediments, as is the living epibyssate A. lienosa (L/H = 1.72) and A. transversa (L/H = 1.48).□ Anadarids, burrowing, epifounal, infaunal, Pliocene, sediment influence .     

Temporal and spatial patterns of annelid populations in intertidal sediments of the Quequén Grande estuary (Argentina)

Temporal and spatial patterns of polychaete and oligochaete populations inhabiting intertidal sediments of the Quequén Grande estuary (Buenos Aires Province, Argentina) were analysed monthly during a yearly period. Local sediments are poorly selected, very fine sands, with a high percentage of mud. Two sites, located at both banks of the estuary were studied: (1) Site N, with a comparatively steep slope and percentage of mud increasing with sediment depth; (2) Site Q, with a gentle slope and percentage of mud increasing towards the sediment surface. The assemblage of annelids was characterised by a very low specific richness, being composed just by 4 species: the polychaetes Laeonereis acuta, Boccardiella ligerica and Capitella sp., and the tubificid oligochaete Ilyodrilus cf. frantzi. Density of the nereid L. acuta reached a peak in late summer and a minimum in spring. The population of Capitella sp. also showed maximum densities in summer, but collapsed during early fall, disappearing completely from the study area. Densities of I. cf. frantzi were highly variable in time and space. Three of the 4 species showed maximum densities at site Q, where mud content was highest at the sediment surface. At this sampling site, most of the L. acuta population occurred within the upper 8 cm of the substrate. On the contrary, at site N, where mud and organic matter content increased with depth, this species was more abundant at subsurface layers (8–16 cm) than at the sediment surface.     

Sedimentary facies from the modern coral reefs,Jordan Gulf of Aqaba,Red Sea

Summary Sixty-three sediment samples collected from the modern fringing reefs off the Jordan coast (Gulf of Aqaba, Red Sea) have been analysed in order to determine variations of composition and texture by using correspondence factor analysis. From the shore seawards, the following physiographic zones are recognized: beach; shallower backreef zone; reef flat zone; forereef zone including sandy or coral-built slopes. Eight sediment facies and subfacies can be recognized on the basis of total component composition and foraminiferal assemblages and four sediment facies can be recognized using grain-size data. Wellsorted, fine to medium, quartzofeldspathic sands (terrigenous facies) occur on beaches and outer sandy slopes close to wadi mouths. Backreef areas exhibit relatively well-sorted fine sands of terrigenous-coral and Miliolidae-Soritidae facies. Poorly sorted, coarse sands of coral-coral-line algal and Homotremid facies characterize reef flats and the upper parts of coral-built forereef areas, which respecitively display an Amphistegina-Spirolina subfacies and an Acervulina one. Poorly sorted, medium sands of coralmolluscan-foraminiferal (Amphistegina-Acervulina) facies are restricted to the lower parts of the forereef zone. Latcral limits of the various biofacies coincide with the distribution of the related organic communities.     

Effets de la marée noire de l' ”Amoco Cadiz ” sur le benthos sublittoral du nord de la Bretagne

Effects of the “Amoco Cadiz ” oil spill on the sublittoral benthos, north of Brittany. Effects of hydrocarbons on the sublittoral macrobenthic communities have been observed through (1) studies of population dynamics of selected communities, conducted prior to the spill by the tanker “Amoco Cadiz ” in spring 1978 and (2) comparisons between the situation in summer 1978 with that in earlier years, with continuation of the observations in some selected sites. The effect of the spill has been selective, involving a limited number of species, mainly crustaceans, molluscs and the sand-urchinEchinocardium cordatum. The spill mainly affected communities on fine sediments and, to a lesser degree, those on mixed sediments. Notably, the destruction of the dominant populations ofAmpelisca, in areas of fine sands in the Bay of Morlaix, has led to a marked decrease of biomass and production. Moreover, repopulation will be difficult because of the isolation of such communities on the southern side of the English Channel. The effects evolved with time; after a phase of sharp and selective mortality, which did not last more than a few weeks, secondary effects on the recruitment of the remaining species do not seem to have occurred on a large scale. Nevertheless, a proliferation of polychaetes has been noticed.      

On the occurrence of the thumbnail crab <Emphasis Type="Italic">Thia scutellata</Emphasis> in the inner German Bight

The thumbnail crab Thia scutellata occurs in the German Bight in at least two stable populations: at Borkum Riff and Loreley Bank. The western (Borkum Riff) population is larger than the eastern (Loreley Bank) one, probably because of the more frequent ingression of south-western warmer water along the Dutch coast. The sediments of these two localities are well-sorted middle sands with a very low amount of finer fractions.     

Prospects of flora and vegetation reconstructions dependent on sediment petrological conditions, exemplified by eight Egerian floras of Hungary

Sediments of fossiliferous layers of eight Late Oligocene (Egerian) fossil plant sites located in the Hungarian Egerian basin were analyzed by grain-size distribution (wet sieving and laser grain-size distribution). Based on the previous flora and vegetation reconstructions the region defined by the site studied was covered at that time by relatively continuous and uniform zonal vegetation composed of paleotropical elements. Thus, the selected localities differ from one another only with regard to their stratigraphic setting, i.e. whether the fossils were obtained from deeper, more clayey or shallower, more sandy deposits of the oscillation sequence characteristic of the Egerian deposits. At least 50% of the sediment must belong to the mudstone fraction (<0.063 mm) if the majority of plant species are undoubtedly identifiable, while 70% or more, would be optimal, for which the site at Pomáz is a good example. The carbonate content of fossiliferous sediments significantly reduces the chance of good preservation and thus increases the number of unidentifiable taxa. Based on the comparison of plant fossil taxonomical studies, the grain-size distribution and the mineralogical composition of the fossiliferous sediments, a correlation was pointed out what conditions would be required by each taxon to yield identifiable specimens in the fossil record. According to the results of grain-size distribution the present study gives an opportunity—in the course of floristic studies and vegetation reconstructions—to develop a model reflecting the chance of the occurrence of each fossil taxon.     

THE ECOLOGY OF EPIPELIC ALGAE OF FIVE WELSH LAKES,WITH SPECIAL REFERENCE TO VOLVOCALEAN GREEN FLAGELLATES (CHLOROPHYCEAE)1

The ecology of epipelic algae on the marginal sediments of five Welsh lakes was studied over an annual cycle. The lakes, Llydaw, Cwellyn, Padarn, Maelog and Coron ranged from very oligotrophic to nutrient-rich. Attention was focussed on chlamydomonad flagellates, diatoms, blue-green algae and euglenoids and the different proportions of these in algae in the epipelon of lakes of contrasting water quality. A total of 75 algal taxa was found in the five lakes, 25 were species of volvocalean flagellates. Mean annual population density of these flagellates differed by an order of magnitude between the lakes. The greatest population density was recorded for Chlamydomonas anticontata Schiller in nutrient-rich Llyn Maelog. Twenty species of pennate diatoms were recorded frequently in the epipelon. In the nutrient-rich lakes, Maelog and Coron, pennate diatoms were dominant on the sediments, where they exhibited population maxima in spring and autumn. Increase in numbers of epipelic diatoms was recorded when silica concentrations were minimum in the overlying lake waters. Navicula hungarica Grun. achieved the maximum population density, 260 000 cells · cm^?2. Euglenoids formed large epipelic populations during late-summer and autumn in these nutrient-rich lakes. Blue-green algae were more important, proportionally, in the nutrient-poor mountain lakes, which had sediments of higher organic content. Chlamydomonads were the major algal component of the epipelon in the mountain lakes, Llydaw and Cwellyn, where the sediments were characterized by larger particle size, and higher organic content. In the nutrient-rich lakes, where the sediments had higher calcium content, chlamydomonads formed significant populations only during spring and summer, when nutrient levels were minimal in the overlying lakewaters.     

Provenance Of Atlantic Lingulid Brachiopods

Living lingulid brachiopods are ubiquitous in low-latitude, marine infaunas. Lingula occurs throughout the Pacific and Indian oceans with the only Atlantic species, L. parva, confined to West Africa. Glottidia is restricted to offshore America from Virginia to California and Peru, and is assumed to have descended from a Pacific Lingula during the early Tertiary. Lingulid organophosphatic shells differ structurally. That of Glottidia is characterizedby trellised rods (baculate); that of Indo-Pacific species of Lingula by spheroidal and rod-like microstructures (virgose); and that of L. parva by apatitic rods arranged as spherulites. A spherulitic fabric is unknown in fossil lingulids, but the distinction between GlottidiaLingula can be traced back to the Carboniferous, which accords with the deep molecular divergence between the two genera. The common occurrence of lingulids with baculate shells in European post-Palaeozoic sediments suggests that ancestral Glottidia entered the Atlantic by the Tethyan Current during the Late Cretaceous/early Cenozoic, and migrated into the Pacific before the formation of the Panama Isthmus. Penecontemporaneously, antecedents of L. parva possibly migrated from east Tethys along the trans-Saharan seaway.     

Genetic diversity and mating system in a tropical tree,Carapa guianensis (Meliaceae)

Carapa guianensis Aublet. (Meliaceae) is an abundant, canopy tree species often exported as fine wood products. The populations in the Atlantic coastal plain of Costa Rica have undergone a wide variety of human-induced changes in distribution and abundance, including isolation due to deforestation. Using protein electrophoretic analysis of seeds, we investigated the genetic variability and population differentiation of nine populations and the outcrossing rate in two populations that differed in density by a factor of 50%. Average polymorphism (35%) and heterozygosity (0.12) across populations were relatively low in comparison with other tropical tree species. Only 4.6% of the total genetic variability could be attributed to population differentiation even though populations were separated by as much as 70 km. However, genetic differentiation did increase with distance between pairs of compared populations. There were no apparent differences in genetic variation between logged and unlogged forests. The outcrossing rate for each population was not significantly different from 1.0, but there was evidence of nonrandom mating in the lower density population. High levels of gene flow are probably maintained by seed dispersal as seeds travel well throughout flooded forests and rivers. High population density and synchronous flowering also contribute to high outcrossing rates. These genetic characteristics suggest that Carapa guianensis is a good candidate for natural forest management where it occurs at high density. However, current management practices need to account for the rapid rate of deforestation occurring around managed natural forest sites that will result in the elimination of intervening populations.     

Late Quaternary climate change and spatial genetic structure in the shrub Banksia hookeriana

Spatial genetic variation within species is influenced by both contemporary and historical factors. We attempted to assess the impact of increased aridity and lower temperatures associated with the last glacial maximum on possible refugia and the structuring of genetic variation in Banksia hookeriana, a shrub species restricted to deep sands on the Eneabba sandplain and adjacent Gingin Scarp/Dandaragan Plateau, centred 300 km north of Perth, Western Australia. We used optically stimulated luminescence (OSL) dating to estimate the last time these sands were mobile, as well as amplified fragment length polymorphisms (AFLP) to infer spatial patterns and the phylogeographical history of genetic variation among 15 populations of B. hookeriana. While genetic variation at the species level was high, with 96.6% of 238 AFLP markers polymorphic, average within population gene diversity was low (H(pop) = 0.16). Of the total genetic variation, an analysis of molecular variance (amova) partitioned 70% within populations, 24% among populations within substrate and 6% between substrates. There was an isolation-by-distance effect among populations within the same substrate, but not across substrates, and ordination highlighted genetic differentiation between the sandplain and scarp/plateau populations. A neighbour-joining tree identified the sandplain populations as a distinct clade, with the exception of the most northern sandplain population, which clustered with two northern and eastern plateau populations. The most southern plateau populations formed a clade sister to the sandplain clade. OSL dating of sand at six extant populations suggested that dunes were last mobile 15,000-35,000 years ago, with no clear difference in the ages of sandplain and plateau dunes. These data are consistent with a historical scenario of (re)colonization from isolated refugia of smaller populations either within the patchily vegetated sandplain and/or refugia at the northern, eastern and southern sandplain/scarp margins following postglacial climate amelioration and dune stabilization. Historic interpretations were confounded by the possible effects of long-distance dispersal, natural selection by substrate, and weak and/or ancient introgression with the sister species, Banksia prionotes.