Use of Neutral Red in short-term sediment traps to distinguish between zooplankton swimmers and carcasses

Abstract

The presence of zooplankton swimmers and carcasses in sediment trap samples has long been a concern in particle flux studies. We successfully developed a protocol using the vital stain Neutral Red to distinguish between copepod swimmers and carcasses in conventional cylindrical sediment traps. Swimmers were stained red whereas carcasses were pale or unstained. The color distinction allowed easy quantification of the two. We subsequently used the protocol in Otsuchi Bay, Japan, on 4 consecutive days in May and again in July 2013. Carcasses were present in the sediment traps on all occasions, and calanoid and cyclopoid copepods accounted for 60.0− 93.6% of all carcasses. Swimmers were 1−2 orders of magnitude more abundant than carcasses, with cyclopoid copepods accounting for up to 75.6% of all swimmers. Copepod carcass flux was negatively related to current velocity at the trap depth. Overall, inclusion of copepod carcasses added no more than 10% to the total particulate organic flux, whereas inclusion of swimmers increased the particulate carbon flux by as much as 87.4%. The low C:N ratio of the other trap materials suggests that sinking particles were a high-quality food source for the benthos in Otsuchi Bay.

Copepod carcasses as microbial hot spots for pelagic denitrification

“…Growing evidence suggests that zooplankton can suffer considerably from non-predatory mortality (Hirst and Kiørboe 2002) and zooplankton carcasses are widely observed in water column and sediment trap samples Elliot and Tang 2011a;Ivory et al 2014;Tang and Elliott 2014). The observations have been ascribed to parasites, viral infection, injuries, starvation and dynamic environmental conditions (Thor et al 2008;Bickel et al 2011;Elliot and Tang 2011b).…”

Applicability of the vital dyes neutral red and fluorescein diacetate to differentiate between alive and dead non-copepod zooplankton

“…(Giesecke et al, 2017) (Table 1). For some of these taxa, negative results were occasionally obtained, like for polychaete larvae and barnacle nauplii (Tang et al, 2006) and harpacticoids (Ivory et al, 2014). The same problem was with fish eggs (Crippen, Perrier, 1974) for which we have got positive result, as well as with Podon polyphernoides (Leuckart), a cladoceran taxonomically close to well-stained Pleopsis polyphemoides (Dressel et al, 1972).…”

“…Some of our conclusions about the applicability of NR proved to be in a good agreement with earlier published data (Table 1). In particular, positive staining was registered in such taxa as polychaete larvae (Crippen, Perrier, 1974;Elliott, Tang, 2009), rotifers, gastropod larvae, chaetognaths (Crippen, Perrier, 1974), barnacle nauplii (Crippen, Perrier, 1974;Elliott, Tang, 2009;Giesecke et al, 2017) and copepod nauplii (Crippen, Perrier, 1974;Ivory et al, 2014;Giesecke et al, 2017), Oikopleura spp. (Giesecke et al, 2017) (Table 1).…”

“…Methodology to identify and differentiate between alive and dead organisms in marine and freshwater zooplankton is still poorly developed and based mainly on: (i) visual discrimination of carcasses in native (live) and preserved samples (Daase et al, 2014, table 1); (ii) vital or mortal staining protocols. For many decades, the vital dye neutral red (NR) has been successfully used to study live/dead zooplankton, mostly copepods, in marine samples (Tang et al, 2006;Elliott, Tang, 2009Ivory et al, 2014;Giesecke et al, 2017). Use of fluorescein diacetate (FDA), a substrate for active enzymes inside viable Ecologica Montenegrina 23: 70-76 (2019) This journal is available online at: www.biotaxa.org/em cells (Butino et al, 2004), has been recently proposed as an alternative, fluorescent technique for viability assay of marine copepods (Litvinyuk et al, 2009;Litvinyuk et al, 2011;Litvinyuk, Mukhanov, 2012).…”

Dead heat: copepod carcass occurrence along the Japanese coasts and implications for a warming ocean

“…0.1 d -1 at the in situ temperature). Furthermore, Ivory et al (2014) used sediment traps to quantify sinking copepod carcasses in Otsuchi Bay during the same sampling period, and reported an average carcass carbon flux of 6.6 mg C m -2 d -1 . This is also of comparable magnitude to our carcass carbon export estimate on a per day basis, and suggests that 89% of the available export carcass carbon would reach the seafloor, with the remaining 11% potentially lost to necrophagy within the water column (Elliott et al, 2010;Dubovskaya et al, 2015).…”