Hydraulic stress parameters of a cased caddis larva (Drusus biguttatus) using spatio-temporally filtered velocity measurements

Abstract

By studying hydraulic stress parameters of larvae of the cased caddisfly Drusus biguttatus (Pictet, 1834) in a tributary of the Schwarze Sulm (Carinthia, Austria), we aimed on (1) detecting the flow properties of the spatio-temporally filtered velocity measurements taken, and (2) on defining the hydraulic niche of this caddisfly larva. For this, we took 31 measurement series lasting 30 to 300 s, yielding 2176 single velocity measurements. The probability density functions of the 31 data series were Gaussian or sub-Gaussian, and the mean recurrent interval between velocity maxima within a data series was only 15.00 s. As a consequence, the Trichoptera larvae studied have to face strong flow accelerations in short intervals which is a much higher stress than conventional mean velocity measurements would suggest. The hydraulic niche of Drusus biguttatus is defined by instantaneous flow velocities ranging from 0.04 to 0.69 m s −1 , by drag forces from 13 × 10 −6 to 3737 × 10 −6 N, by Froude numbers from 0.13 to 1.20, and mostly by Reynolds numbers > 2000. Under such conditions, only 5.1% of the drag force is compensated by submerged weight, whereas the remainder has to be counterbalanced by the active efforts of the larvae to remain attached to the substrate.

Born With Bristles: New Insights on the Kölliker’s Organs of Octopus Skin

“…In this context, the present estimations showed that fully everted KO notably increased the body surface of the young octopus by a mean of 2/3 of the skin surface in comparison with skin areas with retracted KO. This modular body surface extension and accompanying rough texture probably influence flow forces (such as those of drag and propulsion) on the young octopus during specific times or stages of paralarval life, enhancing or restricting passive transport within oceanic currents and saving energy in a similar way as observed in other invertebrate larvae (Emlet, 1991;Ditsche and Summers, 2014;Waringer et al, 2020). Planktonic octopus hatchlings are quite similar to squid hatchlings in size and locomotion mode, both have a rounded mantle of a few mm in length and relatively large funnel apertures to use constantly during jet propulsion in the water column (Villanueva et al, 1997(Villanueva et al, , 2016Dan et al, 2020).…”

Case design and flow resistance in high-alpine caddisfly larvae (Insecta, Trichoptera)

“…In total, 101 data sets were taken for fifth instar larvae. The flow to which larvae are (8) U (gSy) * 0.5 = 2.5ln Rey k + 5.3 − 0.1206(Re − 5) exposed in their natural setting is highly fluctuating (usually turbulent; Waringer et al, 2020) and even the mean velocity profiles (as functions of the distance from the ground) may vary. Furthermore, these flow details are very difficult to measure under field conditions.…”

“…In lotic habitats, a tubular case constructed of mineral particles is the most abundant type (Waringer & Graf, 2011). Even so, tubular cases are very different in length, width, weight, curvature, and roughness.…”

“…From a fluid dynamical perspective, such cases may be abstracted as near-wall, submerged, cylinderlike bodies exposed to a fluid flow where the maximum (anterior) case diameter defines how far the larva extends into the log-law layer in which turbulent fluctuations become important (Hoerner, 1965;Kuhlmann, 2014;Waringer et al, 2020). For the biota in question, the hydraulic stress on a body exposed to a flow is a force per area of the body which results from the fluid dynamical pressure (normal stress) and from viscous effects (normal and tangential [shear] stresses) (Scott, 2005).…”

Habitat Suitability Curves for Freshwater Macroinvertebrates of Tropical Andean Rivers

“…The distribution of taxa in rivers depends on the capacity of its organisms to occupy different habitats, which, in turn, depends on their body structure (i.e., nails, gills, suction cups, etc.) or shape (hydrodynamic, cylindrical or flattened) developed to persist in a particular habitat [60][61][62].…”