Aquatic versus terrestrial attachment: Water makes a difference

Abstract

SummaryAnimal attachment to a substrate is very different in terrestrial and aquatic environments. We discuss variations in both the forces acting to detach animals and forces of attachment. While in a terrestrial environment gravity is commonly understood as the most important detachment force, under submerged conditions gravity is nearly balanced out by buoyancy and therefore matters little. In contrast, flow forces such as drag and lift are of higher importance in an aquatic environment. Depending on the flow conditions, flow forces can reach much higher values than gravity and vary in magnitude and direction. For many of the attachment mechanisms (adhesion including glue, friction, suction and mechanical principles such as hook, lock, clamp and spacer) significant differences have to be considered under water. For example, the main principles of dry adhesion, van der Waals forces and chemical bonding, which make a gecko stick to the ceiling, are weak under submerged conditions. Capillary forces are very important for wet adhesion, e.g., in terrestrial beetles or flies, but usually do not occur under water. Viscous forces are likely an important contributor to adhesion under water in some mobile animals such as torrent frogs and mayflies, but there are still many open questions to be answered. Glue is the dominant attachment mechanism of sessile aquatic animals and the aquatic realm presents many challenges to this mode of attachment. Viscous forces and the lack of surface tension under submerged conditions also affect frictional interactions in the aquatic environment. Moreover, the limitation of suction to the pressure difference at vacuum conditions can be ameliorated under water, due to the increasing pressure with water depth.

Intra‐ and inter‐specific morphological diversity of amphidromous gobies influences waterfall‐climbing performance

“…Waterfall-climbing occurs at the interface between air and water as the individuals generally use a water layer that is only a few millimeters thick. While climbing, fish thus encounter both the constraints of drag from flowing water, and the force of gravity (Maie et al, 2007(Maie et al, , 2012Ditsche & Summers, 2014). As juvenile S. lagocephalus returning to freshwaters are generally bigger and heavier than the other sicydiine species previously studied, both of these forces should be relatively greater than in smaller taxa, because gravitational force scales with animal mass and drag scales with surface area (Maie et al, 2007(Maie et al, , 2012.…”

Mechanotransduction as an Adaptation to Gravity

“…These flow forces vary in magnitude and direction, and under specific conditions, can even reach higher values than gravity. In addition, viscous forces and the lack of surface tension under immersed conditions are also important in the aquatic environment (1). Some aquatic species may still sense gravity.…”

Functional morphology of suction discs and attachment performance of the Mediterranean medicinal leech (Hirudo verbanaCarena)

“…suction), although both upside-down crawling along metal wire meshes and reduced attachment performances under dry conditions indicate that leeches possibly employ additional attachment principle(s) (figure 5a). Here mechanical interlocking, capillary and viscous forces or van der Waals forces (especially, in the case of dry conditions) could contribute to adhesion [39]. For example, higher friction forces especially between the furrowed sucker margins and rough surfaces could improve the leech attachment by counteracting their inward movement in pull-off measurements [36].…”