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Water Currents (water + current)

Distribution by Scientific Domains

Life Sciences	60%
Earth and Environmental Science	30%

Selected Abstracts

Experimental Assessment of Coral Reef Rehabilitation Following Blast Fishing

CONSERVATION BIOLOGY, Issue 1 2005
HELEN E. FOX
arrecifes de Indonesia; recuperación de arrecife de coral; restauración de arrecifes Abstract:,Illegal fishing with explosives has damaged coral reefs throughout Southeast Asia. In addition to killing fish and other organisms, the blasts shatter coral skeletons, leaving fields of broken rubble that shift in the current, abrading or burying new coral recruits, and thereby slowing or preventing reef recovery. Successful restoration and rehabilitation efforts can contribute to coral reef conservation. We used field experiments to assess the effectiveness of different low-cost methods for coral reef rehabilitation in Komodo National Park (KNP), Indonesia. Our experiments were conducted at three different spatial scales. At a scale of 1 × 1 m plots, we tested three different rehabilitation methods: rock piles, cement slabs, and netting pinned to the rubble. Significantly more corals per square meter grew on rocks, followed by cement, netting, and untreated rubble, although many plots were scattered by strong water current or buried by rubble after 2.5 years. To test the benefits of the most successful treatment, rocks, at more realistic scales, we established 10 × 10 m plots of rock piles at each of our nine sites in 2000. Three years after installation, coverage by hard corals on the rocks continued to increase, although rehabilitation in high current areas remained the most difficult. In 2002 rehabilitation efforts in KNP were increased over 6000 m2 to test four rock pile designs at each of four rubble field sites. Assuming that there is an adequate larval supply, using rocks for simple, low-budget, large-scale rehabilitation appears to be a viable option for restoring the structural foundation of damaged reefs. Resumen:,La pesca ilegal con explosivos ha dañado a arrecifes de coral en el sureste de Asia. Además de matar a peces y otros organismos, las explosiones destruyen esqueletos de corales, dejando campos de escombros rotos que se mueven con la corriente, erosionando o enterrando a reclutas de coral nuevos y por lo tanto disminuyen o previenen la recuperación del coral. Esfuerzos exitosos de restauración y rehabilitación pueden contribuir a la conservación de arrecifes de coral. Usamos experimentos de campo para evaluar la efectividad de diferentes métodos de bajo costo para la rehabilitación de arrecifes de coral en el Parque Nacional Komodo (PNK), Indonesia. Desarrollamos nuestros experimentos en tres escalas espaciales diferentes. A una escala de parcelas de 1 x 1 m, probamos tres métodos de rehabilitación: pilas de rocas, losas de cemento y redes sobre el escombro. Crecieron significativamente más corales por metro cuadrado sobre rocas, seguido por el cemento, redes y escombro sin tratamiento, aunque muchas parcelas fueron dispersadas por la fuerte corriente de agua o enterradas por escombros después de 2.5 años. Para probar los beneficios del tratamiento más exitoso, rocas, a escalas más realistas, en 2000 establecimos parcelas de 10 x10 m con pilas de rocas en cada unos de nuestros nueve sitios. Tres años después, la cobertura de corales duros sobre las rocas continuó incrementando, aunque la rehabilitación en áreas con corrientes fuertes fue la más difícil. En 2002, los esfuerzos de rehabilitación en PNK se incrementaron a 6000 m2 para probar cuatro diseños de pilas de rocas en cada uno de los cuatro sitios con escombros. Asumiendo que hay una adecuada existencia de larvas, la utilización de rocas para rehabilitación simple, de bajo costo y gran escala parece ser una opción viable para la restauración de la base estructural de arrecifes dañados. [source]

Expression of one sponge Iroquois homeobox gene in primmorphs from Suberites domuncula during canal formation

EVOLUTION AND DEVELOPMENT, Issue 3 2003
Sanja Perovi
SUMMARY Sponges (Porifera) represent the evolutionary oldest multicellular animals. They are provided with the basic molecules involved in cell,cell and cell,matrix interactions. We report here the isolation and characterization of a complementary DNA from the sponge Suberites domuncula coding for the sponge homeobox gene, SUBDOIRX-a. The deduced polypeptide with a predicted Mr of 44,375 possesses the highly conserved Iroquois-homeodomain. We applied in situ hybridization to localize Iroquois in the sponge. The expression of this gene is highest in cells adjacent to the canals of the sponge in the medulla region. To study the expression of Iroquois during development, the in vitro primmorph system from S. domuncula was used. During the formation of these three-dimensional aggregates composed of proliferating cells, the expression of Iroquois depends on ferric iron and water current. An increased expression in response to water current is paralleled with the formation of canal-like pores in the primmorphs. It is suggested that Iroquois expression is involved in the formation of the aquiferous system, the canals in sponges and the canal-like structures in primmorphs. [source]

Scared fish get lazy, and lazy fish get fat

JOURNAL OF ANIMAL ECOLOGY, Issue 4 2009
Frank Johansson
Summary 1Many biological textbooks present predator-induced morphological changes in prey species as an example of an adaptive response, because the morphological change is associated with lower predation risk. Here we show that the adaptive morphological response observed in many systems may actually be an indirect effect of decreased activity , which reduces the predation risk , rather than a direct adaptive response. 2One of the classical examples comes from crucian carp, where the presence of pike leads to a deeper body. We manipulated pike cues (presence and absence) and water current (standing and running water) and found that both standing water and pike cues similarly and independently induced a deeper body. 3Since the presence of pike cues as well as standing water might be associated with low swimming activity, we suggest that the presence of pike causes a reduction in activity (antipredator behaviour). Reduced activity subsequently induces a deeper body, possibly because the energy saved is allocated to a higher growth rate. 4Our result suggests that even if morphological change is adaptive, it might be induced indirectly via activity. This important conceptual difference may be similar in many other systems. [source]

Effect of sandy and muddy substrates on the growth and survival of the freshwater clam Galatea paradoxa (Born 1778)

AQUACULTURE RESEARCH, Issue 9 2010
Daniel Adjei-Boateng
This study was conducted to determine the effect of a sandy and muddy substrate on the growth and survival of three size-classes of Galatea paradoxa (Born 1778). The experiment was conducted over a 6-month period in a 1000 m2 pond at the research farm of the Faculty of Renewable Natural Resources. Three size classes (shell length) of G. paradoxa categorized as small (20,30 mm), medium (31,40 mm) and large (>40 mm) were used to ascertain the effect of a sandy and muddy substrate on growth performance. Growth in general was very slow, between 1.4 and 2.4 mm over the 6-month experimental period. The lengths measured at the end of the experiment were also significantly different. However, the mean length gained and the specific growth rate for the three size classes in the two substrates (sandy and muddy) were not significantly different (P>0.05). The results of this study indicate that the pond environment is not suitable for the culture G. paradoxa as the species is adapted to life in a river with its filter-feeding activity dependent on the water current. The effect of the substrate type on growth was not significant. However, the substrate type did affect survival, with sandy substrates yielding in better survival than muddy ones. [source]

Gliding movement in Peranema trichophorum is powered by flagellar surface motility

CYTOSKELETON, Issue 4 2003
Akira Saito
Abstract A colorless euglenoid flagellate Peranema trichophorum shows unique unidirectional gliding cell locomotion on the substratum at velocities up to 30 ,m/s by an as yet unexplained mechanism. In this study, we found that (1) treatment with NiCl2 inhibited flagellar beating without any effect on gliding movement; (2) water currents applied to a gliding cell from opposite sides caused detachment of the cell body from the substratum. With only the anterior flagellum adhering to the substratum, gliding movement continued along the direction of the anterior flagellum; (3) gentle pipetting induced flagellar severance into various lengths. In these cells, gliding velocity was proportional to the flagellar length; and (4) Polystyrene beads were translocated along the surface of the anterior flagellum. All of these results indicate that a cell surface motility system is present on the anterior flagellum, which is responsible for cell gliding in P. trichophorum. Cell Motil. Cytoskeleton 55:244,253, 2003. © 2003 Wiley-Liss, Inc. [source]

Influence of water flow velocity, water depth and colony distance on distribution and foraging patterns of terns in the Wadden Sea

FISHERIES OCEANOGRAPHY, Issue 3 2009
PHILIPP SCHWEMMER
Abstract Surface-feeding seabirds, such as Common (Sterna hirundo) and Arctic Terns (Sterna paradisaea) in the German Wadden Sea, are dependent on biological and physical processes that affect prey availability close to the water surface. We proposed the following four hypotheses: (i) relationships should exist between high water flow velocity and foraging activity of terns, as turbulence should enhance prey availability at the surface; (ii) the areas of highest foraging success should be located within areas of low water depth, due to enhanced biological productivity; (iii) as terns are known to have small foraging radii, the location of their breeding grounds should be related to the location of their foraging grounds; (iv) terns should forage intensely in river estuaries, as these should hold ample food supplies. The time between terns leaving the colony and their first foraging attempt differed significantly among different tidal stages: the time was shortest during flood and ebb tides (i.e., highest water flow velocities). Modelling of a long-term data set revealed the highest probability of foraging activity in conditions of high water currents, in both shallow areas and in areas of around 15,20 m depth. Foraging activity was negatively correlated with distance from colony. The distance to the closest estuary had no significant effect on foraging behaviour. Our findings emphasize the physical,biological coupling in the Wadden Sea and highlight the overall importance of small-scale physical processes in directly influencing prey availability for surface-feeding seabirds. [source]

Influence of lateral gradients of hydrologic connectivity on trophic positions of fishes in the Upper Mississippi River

FRESHWATER BIOLOGY, Issue 3 2009
KATHERINE A. ROACH
Summary 1. Riverscapes consist of the main channel and lateral slackwater habitats along a gradient of hydrological connectivity from maximum connection in main channel habitats to minimum connection in backwaters. Spatiotemporal differences in water currents along this gradient produce dynamic habitat conditions that influence species diversity, population densities and trophic interactions of fishes. 2. We examined the importance of lateral connectivity gradients for food web dynamics in the Upper Mississippi River during spring (high flow, moderately low temperatures) and summer (low flow, higher temperatures). We used literature information and gut contents analyses to determine feeding guilds and stable isotope analysis to estimate mean trophic position of local fish assemblages. During June and August 2006, we collected over 1000 tissue samples from four habitats (main channel, secondary channels, tertiary channels and backwaters) distributed within four hydrologic connectivity gradients. 3. Mean trophic position differed among feeding guilds and seasons, with highest values in spring. Mean trophic position of fish assemblages, variability in trophic position and food chain length (maximum trophic position) of the two dominant piscivore species (Micropterus salmoides and M. dolomieu) in both seasons were significantly associated with habitat along the lateral connectivity gradient. Food chain length peaked in tertiary channels in both seasons, probably due to higher species diversity of prey at these habitats. We infer that food chain length and trophic position of fish assemblages were lower in backwater habitats in the summer mainly because of the use of alternative food sources in these habitats. 4. A greater number of conspecifics exhibited significant among-habitat variation in trophic position during the summer, indicating that low river stages can constrain fish movements in the Upper Mississippi River. 5. Results of this study should provide a better understanding of the fundamental structure of large river ecosystems and an improved basis for river rehabilitation and management through knowledge of the importance of lateral complexity in rivers. [source]

Behavior and physiology of mechanoreception: separating signal and noise

INTEGRATIVE ZOOLOGY (ELECTRONIC), Issue 1 2009
John C. MONTGOMERY
Abstract The mechanosensory lateral line is found in all aquatic fish and amphibians. It provides a highly sensitive and versatile hydrodynamic sense that is used in a wide range of behavior. Hydrodynamic stimuli of biological interest originate from both abiotic and biotic sources, and include water currents, turbulence and the water disturbances caused by other animals, such as prey, predators and conspecifics. However, the detection of biologically important stimuli often has to occur against a background of noise generated by water movement, or movement of the fish itself. As such, separating signal and noise is "of the essence" in understanding the behavior and physiology of mechanoreception. Here we discuss general issues of signal and noise in the lateral-line system and the behavioral and physiological strategies that are used by fish to enhance signal detection in a noisy environment. In order for signal and noise to be separated, they need to differ, and we will consider those differences under the headings of: frequency and temporal pattern; intensity discrimination; spatial separation; and mechanisms for the reduction of self-generated noise. We systematically cover the issues of signal and noise in lateral-line systems, but emphasize recent work on self-generated noise, and signal and noise issues related to prey search strategies and collision avoidance. [source]

A high-resolution diatom record of late-Quaternary sea-surface temperatures and oceanographic conditions from the eastern Norwegian Sea

BOREAS, Issue 4 2002
CHRISTOPHER J. A. BIRKS
Core MD95-2011 was taken from the eastern Vøring Plateau, near the Norwegian coast. The section between 250 and 750 cm covers the time period from 13 000 to 2700 cal. yr BP (the Lateglacial and much of the Holocene). Samples at 5 cm intervals were analysed for fossil diatoms. A data-set of 139 modern sea-surface diatom samples was related to contemporary sea-surface temperatures (SSTs) using two different numerical methods. The resulting transfer functions were used to reconstruct past sea-surface temperatures from the fossil diatom assemblages. After the cold Younger Dryas with summer SSTs about 6°C, temperatures warmed rapidly to about 13°C. One of the fluctuations in the earliest Holocene can be related to the Pre-Boreal Oscillation, but SSTs were generally unstable until about 9700 cal. yr BP. Evidence from diatom concentration and magnetic susceptibility suggests a change and stabilization of water currents associated with the final melting of the Scandinavian Ice Sheet at c. 8100 cal. yr BP. A period of maximum warmth between 9700 and 6700 cal. yr BP had SSTs 3,5°C warmer than at present. Temperatures cooled gradually until c. 3000 cal. yr BP, and then rose slightly around 2750 cal. yr BP. The varimax factors derived from the Imbrie & Kipp method for sea-surface-temperature reconstructions can be interpreted as water-masses. They show a dominance of Arctic Waters and Sea Ice during the Younger Dryas. The North Atlantic current increased rapidly in strength during the early Holocene, resulting in warmer conditions than previously. Since about 7250 cal. yr BP, Norwegian Atlantic Water gradually replaced the North Atlantic Water, and this, in combination with decreasing summer insolation, led to a gradual cooling of the sea surface. Terrestrial systems in Norway and Iceland responded to this cooling and the increased supply of moisture by renewed glaciation. Periods of glacial advance can be correlated with cool oscillations in the SST reconstructions. By comparison with records of SSTs from other sites in the Norwegian Sea, spatial and temporal changes in patterns of ocean water-masses are reconstructed, to reveal a complex system of feedbacks and influences on the climate of the North Atlantic and Norway. [source]

The therapeutic effects of retinal laser treatment and vitrectomy.

ACTA OPHTHALMOLOGICA, Issue 5 2001
A theory based on oxygen, vascular physiology
ABSTRACT. The physiologic mechanism of photocoagulation can been seen in the following steps. The physical light energy is absorbed in the melanin of the retinal pigment epithelium. The adjacent photoreceptors are destroyed and are replaced by a glial scar and the oxygen consumption of the outer retina is reduced. Oxygen that normally diffuses from the choriocapillaris into the retina can now diffuse through the laser scars in the photoreceptor layer without being consumed in the mitochondria of the photoreceptors. This oxygen flux reaches the inner retina to relieve inner retinal hypoxia and raise the oxygen tension. As a result, the retinal arteries constrict and the bloodflow decreases. Hypoxia relief reduces production of growth factors such as VEGF and neovascularization is reduced or stopped. Vasoconstriction increases arteriolar resistance, decreases hydrostatic pressure in capillaries and venules and reduces edema formation according to Starling's law. Vitrectomy also improves retinal oxygenation by allowing oxygen and other nutrients to be transported in water currents in the vitreous cavity from well oxygenated to ischemic areas of the retina. Vitrectomy and retinal photocoagulation both improve retinal oxygenation and both reduce diabetic macular edema and retinal neovascularization. [source]