Observations of large-scale fluid transport by laser-guided plankton aggregations

Abstract

Diel vertical migration of plankton has been proposed to affect global ocean circulation to a degree comparable to winds and tides. This biomixing process has never been directly observed, however, due to the inability to predict its occurrence in situ or to reproduce it in a laboratory setting. Furthermore, it has been argued that the energy imparted to the ocean by plankton migrations occurs at the scale of individual organisms, which is too small to impact ocean mixing. We describe the development of a multi-laser guidance system that leverages the phototactic abilities of plankton to achieve controllable vertical migrations concurrently with laser velocimetry of the surrounding flow. Measurements in unstratified fluid show that the hydrodynamic interactions between neighboring swimmers establish an alternate energy transfer route from the small scales of individually migrating plankton to significantly larger scales. Observations of laser-induced vertical migrations of Artemia salina reveal the appearance of a downward jet, which triggers a Kelvin-Helmholtz instability that results in the generation of eddy-like structures with characteristic length scales much larger than the organisms. The measured energy spectrum is consistent with these findings and indicates energy input at large scales, despite the small individual size of the organisms. These results motivate the study of biomixing in the presence of stratification to assess the contribution of migrating zooplankton to local and global ocean dynamics. The laser control methodology developed here enables systematic study of the relevant processes. C 2014 AIP Publishing LLC.

Intentional introduction of Artemia sinica (Anostraca) in the high-altitude Tibetan lake Dangxiong Co: the new population and consequences for the environment and for humans

“…Laboratory experiments have shown diurnal vertical migrations of Artemia aggregations in an unstratifi ed water column through the hydrodynamic interactions between neighboring swimmers may establish an alternate energy transfer route from the small scale of individually migrating plankton to signifi cantly larger scales (Wilhelmus and Dabiri, 2014). The authors of that study proposed that Artemia aggregation may affect water body circulation to a degree comparable to winds.…”

Can small zooplankton mix lakes?

“…Zooplankton aggregation density is important and may have emergent effects on biomixing: higher concentrations can enable interactions of wakes originating from single organisms and enhance shear and mixing in the same fashion as observed by Wilhelmus and Dabiri (2014). The form of the relationship between zooplankton density and biomixing is currently not known e.g., there may be a concentration threshold over which biomixing is enhanced.…”

Pilot‐scale open‐channel raceways and flat‐panel photobioreactors maintain well‐mixed conditions under a wide range of mixing energy inputs

“…PIV measures fluid velocity by measuring neutrally buoyant particle travel distances over short time periods (Adhikari & Longmire, 2012a; Foeth, Van Doorne, Van Terwisga, & Wieneke, 2006; Jeon & Sung, 2011; Khalitov & Longmire, 2002; Kiger & Pan, 2000). Biological applications include aquatic predator–prey interactions (Adhikari & Longmire, 2012b), three‐dimensional fluid motion around fish (Gemmell, Adhikari, & Longmire, 2014), and effects of plankton motion to ocean dynamics (Wilhelmus & Dabiri, 2014). ADV calculates fluid velocity using the speed of sound of an acoustic pulse (Kraus, Lohrmann, & Cabrera, 1994; Lohrmann, Cabrera, & Kraus, 1994).…”

“…Biological applications include aquatic predator-prey interactions (Adhikari & Longmire, 2012b), three-dimensional fluid motion around fish (Gemmell, Adhikari, & Longmire, 2014), and effects of plankton motion to ocean dynamics (Wilhelmus & Dabiri, 2014). ADV calculates fluid velocity using the speed of sound of an acoustic pulse .…”