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 Fließgewässern lebende Tiere haben eine Vielzahl von Anpassungen entwickelt, um mit den teilweise enormen Strömungskräften umzugehen. Zu solchen Strömungsanpassungen gehören die verschiedenen Haftorgane, welche das Tier unterstützen seine Position in der Strömung zu halten. Von einigen dieser Haftorgane (Krallen, Saugnäpfe) wird beschrieben, dass sie eine spezielle Oberflächenrauheit benötigen. Gegenstand dieser Doktorarbeit ist das Zusammenspiel von tierischen Haftorganen und der Oberflächenstruktur der Hartsubstrate, welches für ausgewählte Makroinvertebraten mittels Rasterelektronenmikroskopie, Videoauf¬nahmen, Weißlichtprofilometrie, Kraftmessungen, Abformungstechnik und Anhaftungsexperimenten untersucht wurde. Weiterhin wurde erstmalig die Amplitude der Oberflächenrauheit von üblicherweise in Fließgewässern vorkommenden Gesteinen quantifiziert. Die Oberflächenrauheit von Steinen aus verschiedenen Gewässern 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 näher 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 führen. Ursprünglich hatten wir erwartet, die Taxa in Abhängigkeit von der Art ihrer Haftorgane auf Steinen bestimmter Oberflächenrauheit zu finden. Ein solcher Zusammenhang wurde jedoch nur für 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 Futterverfügbarkeit, dominierend. Sogar Taxa, die sich nur mit Krallen festhalten, wurden zumindest mit wenigen Exemplaren auf glatten Steinen gefunden. Eine Erklärung dafür könnten die Bedeckung der Steine mit Biofilm und Sedimentablagerungen sowie Ritzen auf den Steinen sein, welche sich meist unabhängig von der mittleren Oberflächenrauheit auf den Steinen befinden. Da unter natürlichen Bedingungen zu viele mögliche Einflussfaktoren variierten, um das Zusammenspiel von Haftorganen und Oberflächenrauheit zu verstehen, wurden intensive Studien für ausgewählte Haftstrukturen unter definierten Laborbedingungen durchgeführt. Das Hauptuntersuchungsobjekt war die Eintagsfliege Epeorus assimilis, welche in schnell strömenden Bereichen lebt und verschiedene Haftstrukturen aufweist. Neben den kräftigen Krallen zeigten rasterelektronenmikroskopische Aufnahmen Felder mit spitzen Acanthae auf den Sterniten sowie mit Setae bestandene Haftkissen auf der Unterseite der Kiemenblättchen. Letztere ähneln in ihrem Erscheinungsbild stark den Haftstrukturen terrestrischer Insekten, welche für ihre außergewöhnlichen Fähigkeiten bekannt sind. Die gleichen Haftstrukturen wurden auch bei der verwandten Art Iron alpicola gefunden. Die Setae dieser Art haben die gleiche Größe wie bei Epeorus, die Dichte war dagegen signifikant höher. Letzteres könnte eine größere Haftkraft bedingen, welche eine Anpassung an die höhere Fließgeschwindigkeit im Habitat dieser Eintagsfliege sein könnte. In verschiedener Literatur wird angenommen, dass die Kiemenblättchen beider Arten einen Saugnapf bilden um der Strömung zu wiederstehen. Unsere Videoaufnahmen zeigten jedoch, dass die Kiemenblättchen 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 Kiemenblättchen auf glatten und einigen rauen Substraten. Der Reibungskoeffizient der Kiemenblättchen hing von der Oberflächenrauheit und Zugrichtung ab. Diese Ergebnisse weisen darauf hin, dass sowohl Verklammerungseffekte mit Oberflächenunregelmäßigkeiten als auch molekulare Adhäsion 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 überraschend, da Epeorus Larven bereits auf glatten Oberflächen 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 Oberflächenrauheit von minimal 6 µm (Ra). Eine von zwei Einstellungen zur Rauheitsmessung erwies sich als empfehlenswert für weitere Untersuchungen. Das Zusammenspiel der beiden näher untersuchten Haftorgane der Epeorus Larven war in Abhängigkeit von der Oberflächenrauheit verschieden. Auf glatten Substraten, wo die Krallen nur in wenigen Ritzen einhaken können, bewirken die Haftkissen einen zusätzlichen Vorteil während sich auf rauen Substraten die Haftkräfte 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 drag‐reducing ship coatings. The air‐retaining hairs are superhydrophobic, but have hydrophilic tips at their ends, pinning the air–water interface. Here, experimental and theoretical approaches are used to examine the contribution of this pinning effect for air‐layer 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 µN 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 air‐retaining 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 (“air‐spring”) by an experiment shortcircuiting the air layer, which results in immediate air loss. Thus, the plant enhances its air‐layer 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 air–water interface and prevent rupture of contact. It has been proposed that these trichomes can oscillate with the air–water 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 chiton’s 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 chiton’s adhesive tenacity decreases significantly upon rougher textures