Engineers analyze fluid physics of movement in sea snails

In the world’s oceans, small sea snails (a form of plankton) move daily between surface waters, where they feed at night, several hundred meters during the day to rest to avoid predators. To depth. Sea snails play an important role in geochemical cycles and climate: 12–13% of global carbonate flux occurs when calcium carbonate shells of dead snails sink to depths, where they contribute to atmospheric carbon and oceanic refining. . But because they are difficult to study and cannot be kept in the laboratory, the behavior of these animals – which bear poetic names such as sea butterflies – is poorly known, especially for subtropical and tropical regions where their Diversity is the largest.

Here, a team of oceanographers and engineers who specialize in research at the intersection of fluid physics and biology, film the movements of tropical sea snails and analyze them both from a fluid physics and ecological point of view. They show that each species has a different style of swimming and sinking, beautiful to look at, depending on their shell shape (spiral, elongated or round), body shape, the appearance and motion of the fluttering “wings”. Smaller, slowest species have more difficulty swimming and are more viscous due to seawater being “sticky” – technically, with a “Reynolds number” – that is, the angle, trajectory, and stability of their movement Affects the

“We wanted to answer how the swimming behavior of these beautiful animals is influenced by their different shell shapes and sizes. We found that species with a wing-shaped shell of an airplane swam faster and compared to those Have more maneuvers with ‘snail-like’. Shells. Understanding the swimming potential of these animals is helping us to better understand their ecological importance and distribution in the ocean. In addition, engineers As, we hope to learn from the swimming style of these organisms to design a new generation of bio-inspired underwater vehicles. “, The same author, Dr. Says David Murphy, assistant professor in the Department of Mechanical Engineering of the University of South Florida, Tampa, Florida.

Kuviarina atlantica, an aschomatous teropod with a long shell. Credit: David Murphy and coauthors

Between 2017–2019, researchers caught several individuals of nine species of sea snails (0.9–13.1 mm long) from Bermuda at night, including 7 types of Thiosomas teropods (“sea butterflies”), a species of Gymnosmatus teropods ( “Sea angels”), which lack a shell as adults), and a species of Atlantic heteropods. They transported them to the laboratory, where they demonstrated their behavior in salt-water aquariums with high-speed stereophotogrammetry Recorded with, a technique that tracks motion in 3-D with a pair of cameras. For each species, they calculated absolute and normal speed (relative to body length) during active swimming and passive drowning. Ki, frequency of wing movement, angle of descent during drowning, torture of climbing route during swimming, and Reynolds number.

They state that each species has a different swimming pattern, which typically climbs in a jagged spiral at 12–114 mm / sec, or an average-sized human up to 1-24 body lengths – 40 m per second. Male corresponds to swimming. per second. The snails sink at similar speeds, but in a straight line, at an angle of 4–30 ° relative to the vertical.

Hyalocylis striata, an acosomatous pteropod with a long shell. Credit: David Murphy and coauthors

“We conclude that the swimming and sinking behavior of these pelvic snails coincides strongly with shell size and shape. Smaller snails with coiled shells swim more slowly while bottle-shaped or wing-shaped shells. Larger snails swim faster as their larger size allows them to. Remove the effect of water viscosity. However, swimming speed is not associated with how far these animals go each day, which suggests That light and temperature levels and the presence of predators and prey also have a role. We also found that the sea butterfly. Murphy states that the wing-shaped shell of its shell to ‘hang-glide’ downward. Uses.

Heliconoids infatus, an Aschomatous teropod with a coiled shell. Credit: David Murphy and coauthors

To study the depth preferences of each species, Murphy et al. Also a large number of snails with computer-driven nets, a multiple opening / closing net and environmental sensing system, 0–1000 m below the surface. They used machine learning (based on images) and ribosomal DNA barcoding to determine species. Based on these results, researchers estimate that these species travel 50–300 m per day, in a daily vertical “commute”, which takes a total of 1–3.7 hours per day.

“It’s totally mesmerizing to see these tiny, fragile animals. To fly through the water has to flap its wings in really intricate motions. We’re fortunate to have high-speed cameras that speed this Can slow down enough for us to see it. And it is amazing to think that these sea butterflies are using the same fluid dynamics principles to fly through the water that insects use to fly through the air. Are, “Murphy concludes.

Bizarre snail that swims like a flying insect

more information:
Ferhat Karakas et al, Warming and Sinking Behavior of Warm Water Pelagic Snails Frontiers in Marine Science (2020). DOI: 10.3389 / fmars.2020.556239

Quotes: Poetry in motion: Analysis of fluid physics of movement in engineered sea snails (2020, 7 September), obtained from on 7 September 2020 We do. Html

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