23 research outputs found
Influence of the surface roughness of hard substrates on the attachment of selected running water macrozoobenthos
Flowing water can develop an immense force pushing on animals inhabiting the surface of stones in running waters. These animals have developed attachment devices supporting them to maintain their position against current. Some of these attachment devices (e.g. claws, suckers) have been described to require a certain kind of surface roughness. In this thesis, the interplay of attachment devices and surface texture of the hard bottom substrates in running waters was investigated in detail for selected animals of the torrential fauna using scanning electron microscopy, videotaping, attachment experiments, friction measurements, white light profilometry and replication techniques. Moreover, a quantitative description of the range of surface roughness of stones commonly occurring in running waters is given first time.In FlieĂgewĂ€ssern lebende Tiere haben eine Vielzahl von Anpassungen entwickelt, um mit den teilweise enormen StrömungskrĂ€ften umzugehen. Zu solchen Strömungsanpassungen gehören die verschiedenen Haftorgane, welche das Tier unterstĂŒtzen seine Position in der Strömung zu halten. Von einigen dieser Haftorgane (Krallen, SaugnĂ€pfe) wird beschrieben, dass sie eine spezielle OberflĂ€chenrauheit benötigen. Gegenstand dieser Doktorarbeit ist das Zusammenspiel von tierischen Haftorganen und der OberflĂ€chenstruktur der Hartsubstrate, welches fĂŒr ausgewĂ€hlte Makroinvertebraten mittels Rasterelektronenmikroskopie, VideoaufÂŹnahmen, WeiĂlichtprofilometrie, Kraftmessungen, Abformungstechnik und Anhaftungsexperimenten untersucht wurde. Weiterhin wurde erstmalig die Amplitude der OberflĂ€chenrauheit von ĂŒblicherweise in FlieĂgewĂ€ssern vorkommenden Gesteinen quantifiziert. Die OberflĂ€chenrauheit von Steinen aus verschiedenen GewĂ€ssern mit unterschiedlichem geologischen Einzugsgebiet wurde mit Hilfe von profilometrischen Messungen quantifiziert. Bezogen auf den arithmetrischen Mittenrauhwert Ra war der raueste Stein etwa sechs mal rauher als der glatteste. Innerhalb aller nĂ€her untersuchten Gesteinsarten (Andesit, Schiefer, Basalt, Quarz, Grauwacke, Quarzite, Buntsandstein) zeigte die Rauheit der einzelnen Steine signifikante Unterschiede. Folglich kann eine einfache qualitative Unterscheidung zwischen der Rauheit der Gesteinsarten, wie sie in verschiedenen Studien vorgenommen wurde, zu beachtlichen Ungenauigkeiten fĂŒhren. UrsprĂŒnglich hatten wir erwartet, die Taxa in AbhĂ€ngigkeit von der Art ihrer Haftorgane auf Steinen bestimmter OberflĂ€chenrauheit zu finden. Ein solcher Zusammenhang wurde jedoch nur fĂŒr Elmis Larven und Ancylus fluviatilis gefunden. Die Verteilung anderer Taxa (Baetis, Rhyacophila, Chironomidae) war dagegen genau umgekehrt wie erwartet. Hier waren offenbar andere Faktoren, wie z. B. die FutterverfĂŒgbarkeit, dominierend. Sogar Taxa, die sich nur mit Krallen festhalten, wurden zumindest mit wenigen Exemplaren auf glatten Steinen gefunden. Eine ErklĂ€rung dafĂŒr könnten die Bedeckung der Steine mit Biofilm und Sedimentablagerungen sowie Ritzen auf den Steinen sein, welche sich meist unabhĂ€ngig von der mittleren OberflĂ€chenrauheit auf den Steinen befinden. Da unter natĂŒrlichen Bedingungen zu viele mögliche Einflussfaktoren variierten, um das Zusammenspiel von Haftorganen und OberflĂ€chenrauheit zu verstehen, wurden intensive Studien fĂŒr ausgewĂ€hlte Haftstrukturen unter definierten Laborbedingungen durchgefĂŒhrt. Das Hauptuntersuchungsobjekt war die Eintagsfliege Epeorus assimilis, welche in schnell strömenden Bereichen lebt und verschiedene Haftstrukturen aufweist. Neben den krĂ€ftigen Krallen zeigten rasterelektronenmikroskopische Aufnahmen Felder mit spitzen Acanthae auf den Sterniten sowie mit Setae bestandene Haftkissen auf der Unterseite der KiemenblĂ€ttchen. Letztere Ă€hneln in ihrem Erscheinungsbild stark den Haftstrukturen terrestrischer Insekten, welche fĂŒr ihre auĂergewöhnlichen FĂ€higkeiten bekannt sind. Die gleichen Haftstrukturen wurden auch bei der verwandten Art Iron alpicola gefunden. Die Setae dieser Art haben die gleiche GröĂe wie bei Epeorus, die Dichte war dagegen signifikant höher. Letzteres könnte eine gröĂere Haftkraft bedingen, welche eine Anpassung an die höhere FlieĂgeschwindigkeit im Habitat dieser Eintagsfliege sein könnte. In verschiedener Literatur wird angenommen, dass die KiemenblĂ€ttchen beider Arten einen Saugnapf bilden um der Strömung zu wiederstehen. Unsere Videoaufnahmen zeigten jedoch, dass die KiemenblĂ€ttchen keinen dichten Randkontakt zum Untergrund ausbilden und somit kein Unterdruck aufrecht erhalten werden kann. Messungen der Reibungskraft zeigten einen signifikanten Effekt der Haftkissen auf den KiemenblĂ€ttchen auf glatten und einigen rauen Substraten. Der Reibungskoeffizient der KiemenblĂ€ttchen hing von der OberflĂ€chenrauheit und Zugrichtung ab. Diese Ergebnisse weisen darauf hin, dass sowohl Verklammerungseffekte mit OberflĂ€chenunregelmĂ€Ăigkeiten als auch molekulare AdhĂ€sion eine Rolle bei der Anhaftung spielen. In weiteren Experimenten waren lebende Larven jedoch nicht in der Lage, sich auf glatten Substraten zu halten. Dies war ĂŒberraschend, da Epeorus Larven bereits auf glatten OberflĂ€chen beobachtet worden waren. Da die in diesen Versuchen verwendeten Substrate ohne Biofilmbewuchs waren, nehmen wir an, dass der Biofilm einen bedeutenden Einfluss auf die Haftbedingungen hat. Auf diesen sterilen Substraten hielten sich die Larven nur auf den rauesten Substraten. Die Krallen benötigten eine OberflĂ€chenrauheit von minimal 6 ”m (Ra). Eine von zwei Einstellungen zur Rauheitsmessung erwies sich als empfehlenswert fĂŒr weitere Untersuchungen. Das Zusammenspiel der beiden nĂ€her untersuchten Haftorgane der Epeorus Larven war in AbhĂ€ngigkeit von der OberflĂ€chenrauheit verschieden. Auf glatten Substraten, wo die Krallen nur in wenigen Ritzen einhaken können, bewirken die Haftkissen einen zusĂ€tzlichen Vorteil wĂ€hrend sich auf rauen Substraten die HaftkrĂ€fte beider Haftstrukturen aufsummieren
Air Retention under Water by the Floating Fern Salvinia: The Crucial Role of a Trapped Air Layer as a Pneumatic Spring
The ability of floating ferns Salvinia to keep a permanent layer of air under water is of great interest, e.g., for dragâreducing ship coatings. The airâretaining hairs are superhydrophobic, but have hydrophilic tips at their ends, pinning the airâwater interface. Here, experimental and theoretical approaches are used to examine the contribution of this pinning effect for airâlayer stability under pressure changes. By applying the capillary adhesion technique, the adhesion forces of individual hairs to the water surface is determined to be about 20 ”N per hair. Using confocal microscopy and fluorescence labeling, it is found that the leaves maintain a stable air layer up to an underpressure of 65 mbar. Combining both results, overall pinning forces are obtained, which account for only about 1% of the total airâretaining force. It is suggested that the restoring force of the entrapped air layer is responsible for the remaining 99%. This model of the entrapped air acting is verified as a pneumatic spring (âairâspringâ) by an experiment shortcircuiting the air layer, which results in immediate air loss. Thus, the plant enhances its airâlayer stability against pressure fluctuations by a factor of 100 by utilizing the entrapped air volume as an elastic spring
Elasticity of the hair cover in air-retaining Salvinia surfaces
Immersed in water superhydrophobic surfaces (e.g., lotus) maintain thin temporary air films. In certain aquatic plants and animals, these films are thicker and more persistent. Floating ferns of the genus Salvinia show elaborated hierarchical superhydrophobic surface structures: a hairy cover of complex trichomes. In the case of S. molesta, they are eggbeater shaped and topped by hydrophilic tips, which pin the airâwater interface and prevent rupture of contact. It has been proposed that these trichomes can oscillate with the airâwater interface, when turbulences occur and thereby stabilize the air film. The deformability of such arrays of trichomes requires a certain elasticity of the structures. In this study, we determined the stiffness of the trichome coverage of S. molesta and three other Salvinia species. Our results confirm the elasticity of the trichome coverage in all investigated Salvinia species. We did not reveal a clear relationship between the time of air retention and stiffness of the trichome coverage, which means that the air retention function is additionally dependent on different parameters, e.g., the trichome shape and surface free energy. These data are not only interesting for Salvinia biology, but also important for the development of biomimetic air-retaining surfaces
Comparison of drag forces acting on different benthic body shapes in marine molluscs
The marine intertidal is an area prone to high wave energy and flow velocities,
and the organisms living there are subjected to large hydrodynamic forces, such as drag.
These forces acting to dislodge organisms may result in reduced foraging efficiency and
depressed overall growth. In this study the body shape of a snail, chiton, and limpet are
subjected to flume testing to observe how drag forces and drag coefficients change with a
range of Reynolds numbers simulating currents up to 6 m/s. In higher flow velocities the
snail body shape experienced drastically higher drag forces than the limpet and chiton
body shape. The drag coefficients for the limpet and chiton both were relatively high at
low flow velocity, and quickly decreased at higher speeds. The snail however
experienced an opposite change in drag coefficient, with a lower drag coefficient at low
flow speeds and increased with higher flow speeds. When compared to Reynolds number
drag coefficients for the limpet and chiton show little change at higher Reynolds number,
contrast to the snail body shape in which the drag coefficient appears to fluctuate with
increasing Reynolds number
Characteristics of the Habitat of the Northern Clingfish
The Northern Clingfish, Gobiesox maeandricus, has many well-studied morphological
adaptations to help it cope with the harsh environment that it lives in: the intertidal zone.
Lab studies have shown that this fish can adhere to smooth and rough surfaces as well as
slippery and non-slippery surfaces. Now, the aim of the current study is to define the
habitat of the Northern Clingfish and compare habitat parameters with these previous lab
studies. We show that the clingfish is presented with a challenging, slippery habitat We
find that nearly 90% of the rocks present in the habitat of the clingfish are covered in
biofilm and are consequently slippery. Clingfish cope with their habitat by seeking
shelter under rocks within a specific size range (15-45 cm in width) and they are most
commonly found under rocks that have gravel as the main substrate. Rocks that clingfish
were found under possessed a wide range of aufwuchs (periphyton) cover. Rock size did
not correlate to fish length, but a bimodal distribution was found in the transect area
Characteristics of the Habitat of the Northern Clingfish
The Northern Clingfish, Gobiesox maeandricus, has many well-studied morphological
adaptations to help it cope with the harsh environment that it lives in: the intertidal zone.
Lab studies have shown that this fish can adhere to smooth and rough surfaces as well as
slippery and non-slippery surfaces. Now, the aim of the current study is to define the
habitat of the Northern Clingfish and compare habitat parameters with these previous lab
studies. We show that the clingfish is presented with a challenging, slippery habitat We
find that nearly 90% of the rocks present in the habitat of the clingfish are covered in
biofilm and are consequently slippery. Clingfish cope with their habitat by seeking
shelter under rocks within a specific size range (15-45 cm in width) and they are most
commonly found under rocks that have gravel as the main substrate. Rocks that clingfish
were found under possessed a wide range of aufwuchs (periphyton) cover. Rock size did
not correlate to fish length, but a bimodal distribution was found in the transect area
Comparison of drag forces acting on different benthic body shapes in marine molluscs
The marine intertidal is an area prone to high wave energy and flow velocities,
and the organisms living there are subjected to large hydrodynamic forces, such as drag.
These forces acting to dislodge organisms may result in reduced foraging efficiency and
depressed overall growth. In this study the body shape of a snail, chiton, and limpet are
subjected to flume testing to observe how drag forces and drag coefficients change with a
range of Reynolds numbers simulating currents up to 6 m/s. In higher flow velocities the
snail body shape experienced drastically higher drag forces than the limpet and chiton
body shape. The drag coefficients for the limpet and chiton both were relatively high at
low flow velocity, and quickly decreased at higher speeds. The snail however
experienced an opposite change in drag coefficient, with a lower drag coefficient at low
flow speeds and increased with higher flow speeds. When compared to Reynolds number
drag coefficients for the limpet and chiton show little change at higher Reynolds number,
contrast to the snail body shape in which the drag coefficient appears to fluctuate with
increasing Reynolds number
Northern Clingfish, Gobiesox maeandricus, habitat, San Juan Island
The Northern Clingfish, Gobiesox maeandricus, has many well-studied morphological
adaptations to help it cope with the harsh environment that it lives in: the intertidal zone.
Lab studies have shown that this fish can adhere to smooth and rough surfaces as well as
slippery and non-slippery surfaces. Now, the aim of the current study is to define the
habitat of the Northern Clingfish and compare habitat parameters with these previous lab
studies. We show that the clingfish is presented with a challenging, slippery habitat We
find that nearly 90% of the rocks present in the habitat of the clingfish are covered in
biofilm and are consequently slippery. Clingfish cope with their habitat by seeking
shelter under rocks within a specific size range (15-45 cm in width) and they are most
commonly found under rocks that have gravel as the main substrate. Rocks that clingfish
were found under possessed a wide range of aufwuchs (periphyton) cover. Rock size did
not correlate to fish length, but a bimodal distribution was found in the transect area
Characteristics of the Habitat of the Northern Clingfish
The Northern Clingfish, Gobiesox maeandricus, has many well-studied morphological
adaptations to help it cope with the harsh environment that it lives in: the intertidal zone.
Lab studies have shown that this fish can adhere to smooth and rough surfaces as well as
slippery and non-slippery surfaces. Now, the aim of the current study is to define the
habitat of the Northern Clingfish and compare habitat parameters with these previous lab
studies. We show that the clingfish is presented with a challenging, slippery habitat We
find that nearly 90% of the rocks present in the habitat of the clingfish are covered in
biofilm and are consequently slippery. Clingfish cope with their habitat by seeking
shelter under rocks within a specific size range (15-45 cm in width) and they are most
commonly found under rocks that have gravel as the main substrate. Rocks that clingfish
were found under possessed a wide range of aufwuchs (periphyton) cover. Rock size did
not correlate to fish length, but a bimodal distribution was found in the transect area
Suction as a Mechanism of Attachment in Chitons
Chitons, like other mollusks, rely upon a variety of adhesive forces to combat factors
such as wave action and predation in the intertidal. In this study, we explore what effect
suction has upon a chitonâs total force of attachment and tenacity, as well the impact of
substrate roughness. In this experiment, we found that suction plays a significant role in
chiton attachment over a range of roughness. We also found that a chitonâs adhesive
tenacity decreases significantly upon rougher textures