Flow-seaweed interactions of Saccharina latissima at a blade scale: turbulence, drag force, and blade dynamics

Abstract

Physical interactions between seaweed blades of Saccharina latissima and unidirectional turbulent flow were examined in an open-channel flume, focussing on flow velocities, drag force acting on a blade, and blade reconfiguration. The data reveal that seaweed blades adjust to high-energy flow conditions relatively quickly, efficiently reducing flow-induced drag via compaction, a mechanism of blade reconfiguration. The drag coefficient of blades of S. latissima varied between 0.02 and 0.07 over a range of mean flow velocities from 0.1 to 0.55 m/s. Both flow action and blade biomechanical characteristics influenced the blade dynamics, with the flow role being predominant in highly energetic conditions. The interaction mechanisms and their strength were found to be scale-dependent, with the combined effect of reduced mean flow velocity and enhanced turbulence in blade wakes. The thickness of the diffusive boundary layer, an important factor in nutrient uptake from the surrounding water, was estimated to be in the range from 0.010 to 0.067 mm. Mechanisms of blade adjustment to the flow and scale-dependent dynamic interactions between blades and turbulent eddies have direct implications for seaweed growth, acclimation, and survival. The estimates of the drag coefficient and the thickness of the diffusive boundary layer will be useful for the development of bio-physical models, environmental assessments, and design of seaweed farms.

A spanwise oscillating plate in a crossflow: Implication for mass transfer and locomotion

“…Dashed lines are for power regression fit to the data (Macrophytes: St = 558 Re −0.56 , R 2 = 0.45, n = 22; Fish: St = 5.91 Re −0.11 , R 2 = 0.24, n = 202; present study: St = 3 × 10 6 Re −1.50 , R 2 = 0.44; n = 7). Macrophyte data compiled from Koehl and Alberte (1988) for Nereocystis luetkeana , Stevens and Hurd (1997) for Macrocystis integrifolia , Denny and Roberson (2002) for Eisenia arborea , Koehl et al (2008) for N. luetkeana , Huang et al (2011) for N. luetkeana , and Vettori and Nikora (2019) for Saccharina latissimi at peak. Fish data compiled from Bainbridge (1958) for Leuciscus leuciscus, Oncorhynchus mykiss irideus , and Carassius auratus , Pyatetskiy (1970) for Sarda sarda and Pomatomus saltatrix , Hunter and Zweifel (1971) for Trachurus symmetricus , Webb (1971) for O. mykiss gairdneri , Webb and Keyes (1982) for Triakis semifasciata , Sphyrna tiburo , and Carcharhinus melanopterus , Videler and Hess (1984) for Pollachius virens and Scomber scombrus , Webb et al (1984) for O. mykiss gairdneri , Videler and Wardle (1991) for Acipenser fulvescens and Gadus morhua , Triantafyllou et al (1993) for Abramis brama and P. saltatrix , and Tytell and Lauder (2004) for Anguilla rostrata .…”

Advancing understanding of kelp aquaculture in Wales: tests across multiple life stages and environmental contexts

“…Water motion affects growth, morphology, and survival of seaweeds. A boundary layer develops around the thallus of kelp, limiting the uptake of nutrients and CO2 (Hurd 2000;Vettori and Nikora 2019). The blades of Saccharina latissima adjust to both flow conditions as well as nutrient conditions by changing the morphology of their blade (Zhu et al 2021).…”