Swimming and Sinking Behavior of Warm Water Pelagic Snails

Abstract

Swimming and sinking behavior by pelagic snails is poorly studied but is important in their ecology, predator-prey interactions, and vertical distributions. We used a low magnification, high speed stereophotogrammetry system to study the swimming and sinking kinematics of nine warm water pelagic snail species (seven thecosomes, one gymnosome, and one heteropod). As different thecosomatous pteropod species may have coiled, elongated, or globular shell morphologies, we focused on how the shell shape, body geometry, and body size affect their swimming behavior from a fluid mechanics perspective. In addition, ZooScan image analysis and metabarcoding of archived vertically stratified MOCNESS samples were used to relate swimming behaviors to night time and daytime vertical distributions. While different large scale swimming patterns were observed, all species exhibited small scale sawtooth swimming trajectories caused by reciprocal appendage flapping. Thecosome swimming and sinking behavior corresponded strongly with shell morphology and size, with the tiny coiled shell pteropods swimming and sinking the slowest, the large globular shelled pteropods swimming and sinking the fastest, and the medium-sized elongated shell pteropods swimming and sinking at intermediate speeds. However, the coiled shell species had the highest normalized swimming and sinking speeds, reaching swimming speeds of up to 45 body lengths s −1 . The sinking trajectories of the coiled and elongated shell pteropods were nearly vertical, but globular shell pteropods use their hydrofoillike shell to glide downwards at approximately 20 • from the vertical, thus retarding their sinking rate. The swimming Reynolds number (Re) increased from the coiled shell species [Re ∼ O(10)] to the elongated shell species [Re ∼ O(100)] and again for the globular shell species [Re ∼ O(1000)], suggesting that more recent lineages increased in size and altered shell morphology to access greater lift-to-drag ratios available at higher Re. Swimming speed does not correlate with the vertical extent of migration, emphasizing that other factors, likely including light, temperature, and predator and prey fields, influence this ecologically important trait. Size does play a role in structuring the vertical habitat, with larger individuals tending to live deeper in the water column, while within a species, larger individuals have deeper migrations.

Genome‐wide phylogeography reveals cryptic speciation in the circumglobal planktonic calcifier Limacina bulimoides

“…Shell shape is likely to have a phenotypically plastic component linked to life history and environmental conditions (Hoffman et al, 2010; Hollander et al, 2006; Mariani et al, 2012; Zieritz et al, 2010). Pteropod shell shape is an important trait that directly affects their sinking and swimming speeds, manoeuvrability, and their resulting ability to navigate the water column for food and evade predators (Karakas et al, 2020). In other molluscs, shell shape has been shown to be correlated with environment, either as genetically inherited differences or phenotypically plastic traits.…”

Barcoding coffee grounds - Exploring pteropod gastropod biodiversity with dregs in collection jars

“…Diel vertical migration is a known phenomenon for most thecosome species, and in our samples we found DNA material in night and day hauls in anticipated quantities. Swimming and sinking behaviour by these pelagic snails is important in their ecology, predator-prey interaction, and vertical distribution (Karakas et al 2020). Despite the costs, benefits like niche partitioning, metabolic advantage due to colder temperatures at depth, avoidance of light, high temperatures and predators seem to advocate this behaviour (Hays 2003, Antezana 2009).…”

The impacts of past, present and future ocean chemistry on predatory planktonic snails

“…The atlantids, however, are fully shelled because their shell is integral to their survival. Not only can they fully retract into the shell and seal themselves in with an operculum for protection, the adult atlantids also use their shell as a swimming appendage, which is paired with their single swimming fin, both being flapped in a coordinated wing-like manner to produce rapid directional propulsion [5,6]. The atlantid shell is already present upon hatching [3] and is likely important at the larval stage for physical protection, and also as ballast to allow rapid escape by sinking.…”