Home About us Contact
|
Home About us Contact | ||
|
|
||
Hard Substrates (hard + substrate)
Selected AbstractsSPECIES COMPOSITION AND SEASONAL PERIODICITY OF MACROALGAL SPECIES IN CORPUS CHRISTI BAY, TEXASJOURNAL OF PHYCOLOGY, Issue 2000J.C. Agan Benthic algal sampling from selected sites along Corpus Christi Bay and from one site at the Port Aransas, Texas south jetty was completed between April 1999 and February, 2000. Species composition, seasonal periodicity, and fluctuations in temperature and salinity were determined. This is the first comprehensive study of benthic macroalgae conducted in Corpus Christi Bay, which is shallow, turbid, and lacks natural hard substrate. Man-made jetties are necessary for suitable floral attachment. Macroalgae are affected by changes in salinity as freshwater inflows are followed by periods of drought, which increase salinity. These effects are most notable where freshwater enters at the south end near Oso Bay and at the north end at Nueces Bay. Previous Texas algal collections described species of Enteromorpha, Ulva, Gelidium, and Gracilaria as the most dominant plants of the area. This supports the current study with the additions of Hypnea musciformis and Centroceras clavulatum. Dominant plants at the Port Aransas jetty include Ulva fasciata, Padina gymnospora, and Hypnea musciformis. The Rhodophyta including Gracilaria, Gelidium, and Centroceras clavulatum dominate the bay and do so throughout the year. Chlorophytes, although few in species richness, are important to benthic coverage and biomass. Phaeophyta are found predominantly at the Port Aransas jetty with Sargassum, Dictyota dichotoma, and Petalonia fascia being most abundant. A transition occurs in species composition as the water temperature changes seasonally. Hincksia, Ectocarpus, and Petalonia fascia are found only during the cooler months. [source] Effects of substrate stiffness on cell morphology, cytoskeletal structure, and adhesionCYTOSKELETON, Issue 1 2005Tony Yeung Abstract The morphology and cytoskeletal structure of fibroblasts, endothelial cells, and neutrophils are documented for cells cultured on surfaces with stiffness ranging from 2 to 55,000 Pa that have been laminated with fibronectin or collagen as adhesive ligand. When grown in sparse culture with no cell-cell contacts, fibroblasts and endothelial cells show an abrupt change in spread area that occurs at a stiffness range around 3,000 Pa. No actin stress fibers are seen in fibroblasts on soft surfaces, and the appearance of stress fibers is abrupt and complete at a stiffness range coincident with that at which they spread. Upregulation of ,5 integrin also occurs in the same stiffness range, but exogenous expression of ,5 integrin is not sufficient to cause cell spreading on soft surfaces. Neutrophils, in contrast, show no dependence of either resting shape or ability to spread after activation when cultured on surfaces as soft as 2 Pa compared to glass. The shape and cytoskeletal differences evident in single cells on soft compared to hard substrates are eliminated when fibroblasts or endothelial cells make cell-cell contact. These results support the hypothesis that mechanical factors impact different cell types in fundamentally different ways, and can trigger specific changes similar to those stimulated by soluble ligands. Cell Motil. Cytoskeleton 60:24,34, 2005. © 2004 Wiley-Liss, Inc. [source] Contaminated suspended sediments toxic to an Antarctic filter feeder: Aqueous- and particulate-phase effectsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2009Nicole A. Hill Abstract Disturbances such as dredging, storms, and bioturbation result in the resuspension of sediments. This may affect sessile organisms that live on hard substrates directly above the sediment. Localized sediment contamination exists around many Antarctic research stations, often resulting in elevated contamination loads in marine sediments. To our knowledge, the potential impact of resuspended contaminated sediments on sessile fauna has not been considered, so in the present study, we assessed the sensitivity of Antarctic spirorbid polychaetes to aqueous metals and to metal-contaminated sediments that had been experimentally resuspended. Worms were first exposed to aqueous metals, both singly and in combination, over 10 d. Spirorbid mortality was tolerant to copper (median lethal concentration [LC50], 570 ,g/L), zinc (LC50, >4,910 ,g/L), and lead (LC50, >2,905 ,g/L); however, spirorbid behavior responded to copper concentrations as low as 20,g/L. When in combination, zinc significantly reduced mortality caused by copper. A novel technique was used to resuspend sediments spiked with four concentrations of three metals (up to 450 ,g/g dry wt of copper, 525 ,g/g dry wt of lead, and 2,035 ,g/g dry wt of zinc). The response of spirorbids to unfiltered suspended sediment solutions and filtered solutions (aqueous metal exposure) was measured. Suspended sediments were toxic to filter-feeding spirorbids at concentrations approximating those found in contaminated Antarctica areas. Toxicity resulted both from aqueous metals and from metals associated with the suspended sediments, although suspended clean sediments had no impact. To our knowledge, the present study is the first to show that resuspension of contaminated sediments can be an important pathway for toxicity to Antarctic hard substrate organisms. Based on the present results, current sediment-quality guidelines used in the evaluation of Australian sediments may be applicable to Antarctic ecosystems. [source] Consequences of introducing the invasive amphipod Gmelinoides fasciatus into large shallow Lake Peipsi: present distribution and possible effects on fish foodJOURNAL OF APPLIED ICHTHYOLOGY, Issue 2010K. Kangur Summary The objective of the study was to assess the effect of the Baikalian amphipod Gmelinoides fasciatus, a successful invader into Europe, as a fish food source in Lake Peipsi to where it was introduced in the 1970s. In 2002,2006, the littoral macrozoobenthos was studied along 17 transects (0.1,4 m depth, 384 quantitative samples) to determine the recent distribution of G. fasciatus and its share in the benthic community. Earlier records on the littoral macrozoobenthos from the years 1970, 1980, 1990 and 2000 were also used for comparison. Our results indicate that the invasive G. fasciatus is the dominant species (about 43% of total macrozoobenthos abundance) in the littoral zone of Lake Peipsi, while the native gammarids Gammarus lacustris and Pallasea quadrispinosa appear to be extinct and oligochaetes seem to have declined. G. fasciatus preferred hard substrates and it was mainly distributed close to water shallow beach areas (water depth <0.2 m), where its abundance reached locally up to 29 000 ind. m,2 (97% of total macrozoobenthos abundance). This distribution pattern of the invader in summer makes it mostly inaccessible for adult fish and increases its survival rate. Being highly mobile, G. fasciatus is not sensitive to water level fluctuations in shallow lakes. These behavioural characteristic increase its population success. [source] In situ deformation of thin films on substratesMICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2009Marc Legros Abstract Metallic thin-film plasticity has been widely studied by using the difference between the coefficients of thermal expansion of the film and the underlying substrate to induce stress. This approach is commonly known as the wafer curvature technique, based on the Stoney equation, which has shown that thinner films have higher yield stresses. The linear increase of the film strength as a function of the reciprocal film thickness, down to a couple hundred nanometers, has been rationalized in terms of threading and interfacial dislocations. Polycrystalline films also show this kind of dependence when the grain size is larger than or comparable to the film thickness. In situ TEM performed on plan-view or cross-section specimens faithfully reproduces the stress state and the small strain levels seen by the metallic film during wafer curvature experiments and simultaneously follows the change in its microstructure. Although plan-view experiments are restricted to thinner films, cross-sectional samples where the film is reduced to a strip (or nanowire) on its substrate are a more versatile configuration. In situ thermal cycling experiments revealed that the dislocation/interface interaction could be either attractive or repulsive depending on the interfacial structure. Incoherent interfaces clearly act as dislocation sinks, resulting in a dislocation density drop during thermal cycles. In dislocation-depleted films (initially thin or annealed), grain boundaries can compensate for the absence of dislocations by either shearing the film similarly to threading dislocations or through fast diffusion processes. Conversely, dislocations are confined inside the film by image forces in the cases of epitaxial interfaces on hard substrates. To increase the amount of strain seen by a film, and to decouple the effects of stress and temperature, compliant substrates can also be used as support for the metallic film. The composite can be stretched at a given temperature using heating/cooling straining holders. Other in situ TEM methods that served to reveal scaling effects are also reviewed. Finally, an alternate method, based on a novel bending holder that can stretch metallic films on rigid substrates, is presented. Microsc. Res. Tech., 2009. © 2009 Wiley-Liss, Inc. [source] The genus Leptophytum (Melobesioideae, Corallinales, Rhodophyta) in NW SpitsbergenNORDIC JOURNAL OF BOTANY, Issue 4 2004Athanasios Athanasiadis Three species of the genus Leptophytum, viz. the generitype L. laeve, L. foecundum and the new Arctic endemic L. jenneborgii nov. sp. are described from localities in NW Spitsbergen. A fourth species, related to L. laeve, may also be present and its status requires further comparative studies with Lithothamnion tenue described from western Greenland. Leptophytum jenneborgii is restricted to sublittoral sites around Vasahalvøya, between 8 and 30 m depth growing on hard substrates (usually on Lithothamnion glaciale) and forming encrusting to foliose thalli up to 10 cm in diameter. New lamellae develop in an unattached-superimposed pattern, overgrowing the parent thallus, so that individuals can reach at least 1.5 cm in thickness. Thallus organization is dorsiventral, with a noncoaxial hypothallium (producing rare patches of coaxial cells) and an ascending perithallium with short subepithallial and flattened epithallial cells. Multiporate conceptacles have convex or flattened roof and develop specialized (thinner-wider) pore cells lining the canals. This character combination supports a position in the genus Leptophytum, as recently emended by Athanasiadis & Adey (2006), and simultaneously distinguishes L. jenneborgii from its Arctic and North Atlantic congeners. Like Leptophytum arcticum nov. comb., that is only known from Uddebay on the east coast of Novaja Zemlya, L. jenneborgii shows a restricted distribution on the presumed north periphery of maximum ice cover during the latest glaciation. It is suggested that these two species represent the first evidence of algal glacial survivals in this part of the Arctic. [source] Palaeocology of Hard Substrate Faunas from the Cretaceous Qahlah Formation of the Oman MountainsPALAEONTOLOGY, Issue 1 2001Mark A. Wilson Skeletal encrusters and carbonate hardgrounds are rare in siliciclastic sands and gravels because of high levels of abrasion and sediment movement. An exception to this is the Maastrichtian Qahlah Formation of the Oman Mountains, a sequence of coarse siliciclastic sediments deposited on a shallow marine shelf above wavebase and at an equatorial palaeolatitude. This unit contains intercalated carbonate hardgrounds and other hard substrates which were encrusted and bored. The hard substrates, comprising carbonate and silicate clasts, calcareous bioclasts (mollusc shells and coral fragments) and wood, supported a diverse encrusting and boring fauna dominated in biomass by the oyster Acutostrea. There are twelve bryozoan species and at least two serpulid worm species, most living cryptically. Other encrusters on exposed surfaces include the agglutinated foraminiferan Placopsilina and several species of colonial corals. Borings in the carbonate clasts and shells are predominantly those of bivalves (Gastrochaenolites), with subsidiary clionid sponge (Entobia) and acrothoracican barnacle (Rogerella) borings. The woodgrounds are thoroughly bored by teredinid bivalves (Teredolites). Of the common substrate types, carbonate hardground clasts support the greatest number of taxa, followed by chert clasts, with limestone rockground pebbles being depauperate. Clast composition and relative stability probably explain these differences. Individual clasts probably had variable and typically long colonisation histories. Detailed palaeoecological interpretation is constrained by taphonomic loss, time-averaging and clast transportation and reorientation. Evidence from the Qahlah Formation shows that tropical rocky-shore biotas in the Cretaceous were not impoverished as previously believed. [source] Influence of different substrates on the evolution of morphology and life-history traits of azooxanthellate solitary corals (Scleractinia: Flabellidae)BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2010YUKI TOKUDA Sessile organisms are influenced considerably by their substrate conditions, and their adaptive strategies are key to understanding their morphologic evolution and traits of life history. The family Flabellidae (Cnidaria: Scleractinia) is composed of the representative azooxanthellate solitary corals that live on both soft and hard substrates using various adaptive strategies. We reconstructed the phylogenetic tree and ancestral character states of this family from the mitochondrial 16S and nuclear 28S ribosomal DNA sequences of ten flabellids aiming to infer the evolution of their adaptive strategies. The Javania lineage branched off first and adapted to hard substrates by using a tectura-reinforced base. The extant free-living flabellids, including Flabellum and Truncatoflabellum, invaded soft substrates and acquired the flabellate corallum morphology of their common ancestor, followed by a remarkable radiation with the exploitation of adaptive strategies, such as external soft tissue [e.g. Flabellum (Ulocyathus)], thecal edge spine, and transverse division (e.g. Placotrochus and Truncatoflabellum). Subsequently, the free-living ancestors of two genera (Rhizotrochus and Monomyces) invaded hard substrates independently by exploiting distinct attachment apparatuses such as tube-like and massive rootlets, respectively. In conclusion, flabellids developed various morphology and life-history traits according to the differences in substrate conditions during the course of their evolution. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 184,192. [source] | |||||||||||||