Detection and abundance estimation of euphausiids using an optical plankton counter

Abstract

An optical plankton counter (OPC) mounted on a towed Batfish vehicle was used to detect and estimate the abundance of euphausiids in the Emerald and La Have Basins of the Scotian Shelf, northwest Atlantic Ocean. Euphausiids (Meganyctiphanes norvegica and Thysanoessa inermis) were identified from their characteristic diameter distributions measured by the OPC. The diameter distributions containing euphausiid peaks were compared to several depth strata known to contain these animals. The depth strata containing euphausiids were established from acoust~cal tows made on the same cruise and the identification of animals was accomplished by sampling these acoustical layers with the BIONESS net sampler. The die1 migration patterns of the euphausiids were also identified from these diameter distributions. Euphausiid reaction to artificial lights mounted on Batfish and BIONESS showed increases in abundance estimates by a factor of 2 x and 50x respectively. Experiments with artificial lights mounted on a remotely operated vehicle and camera platforms are also described. An artificial light mounted on a towed Batfish resulted in a distinct increase in euphausiid abundance estimates as measured by the OPC. Abundance estimates from the OPC are also compared to results from acoustical tows and showed agreement to within a factor of 2 and better.

Zooplankton population dynamics: measuring in situ growth and mortality rates using an Optical Plankton Counter

“…Technical details of the OPC can be found in Herman (1988 and1992), and Herman et al (1993). Briefly, the optical sensors situated on each side of the flow tunnel count the number and measure the equivalent spherical diameter (ESD) of particles in 3431 digital sizes within a range from 0.25 to 14 mm.…”

“…In Sørfjorden, Thysanoessa inermis, T. raschii, and T. longicaudata were present as 1-(GI) and 2-yr-olds (GII). The ESD of T. inermis varies from 2 to 3 mm, and the ESD of Meganyctiphanes norvegica varies from 3 to 6 mm (Herman et al 1993). Chaetognaths have a relatively long, transparent body, and a small but dark gut.…”

Causes of under- or overestimation of zooplankton biomass using Optical Plankton Counter (OPC): effect of size and taxa

“…Zooplankton biomass has been measured using various methods: that include the plankton net, coulter counter (Maddux & Kanwisher 1965), optical plankton counter (Herman 1988), video plankton recorder (Davis et al 1992), and acoustics (Backus & Barnes 1957). Within these, the optical plankton counter (OPC) has been used in numerous studies (Sprules et al 1998, Labat et al 2002, Nogueira et al 2004, Huntley et al 2006, because it can measure rapidly and with ease, and can be used for in situ measurements also (Herman et al 1993). The OPC provides particle count data in equivalent spherical diameter (ESD) size units.…”

Capturing quantitative zooplankton information in the sea: Performance test of laser optical plankton counter and video plankton recorder in a Calanus finmarchicus dominated summer situation

“…The Optical Plankton Counter (OPC) was one response to 26 this challenge. It was designed to provide continuous real-time information on the size 27 and abundance of zooplankton (Herman 1988;Herman et al 1993). The OPC has since 28 been carried on many different platforms, and has been successfully applied in numerous 29 oceanographic studies (Herman et al 2004, and references therein).…”