Latitudinal Differences in the Planktonic Biomass and Community Structure Down to the Greater Depths in the Western North Pacific

Abstract

As part of the research program WEST-COSMIC Phase I (1997, vertical profiles down to the greater depths (0-2000 m or 5800 m) of the plankton community structure composed of heterotrophic bacteria, phytoplankton, protozooplankton and metazooplankton were studied at one station in each subarctic (44˚N) and in transitional region (39˚N), and two stations in subtropical region (30˚N and 25˚N); all in 137-155˚E in the western North Pacific Ocean. The biomass of all four taxonomic groups decreased rapidly with increasing depths at all stations, although the magnitude of depth-related decrease differed among the groups. As plankton community structure, metazooplankiton biomass and bacterial biomass occupied >50% of the total in 0-2000 and 2000-4000 or 5000 m strata, respectively, at subarctic and transitional stations, while bacterial biomass contributed to >50% of the total consistently from 0 through 4800 or 5800 m at subtropical stations. Metazooplankton biomass integrated over the greater depths exhibited a clear latitudinal pattern (high north and low south), but this was not the case for those of the other taxonomic groups. As a component of metazooplankton, an appreciable contribution of diapausing copepods to the metazooplankton was noted at subarctic and transitional stations, but they were few or nil at subtropical stations.As protozooplankton assemblages, heterotrophic microflagellates (HMF) and dinoflagellates were two major components at subarctic and transitional stations, but were only HMF predominated at subtropical stations.From biomass ratios between heterotrophic bacteria, HMF and dinoflagellates, "sinking POC-DOC-heterotrophic bacteria-HMF-heterotrophic dinoflagellates" link was proposed as a microbial food chain operative in the deep layer of the western NorthPacific. All results are discussed in the light of latitudinal differences in the structure and functioning of plankton community contributing to the 'biological pump' in the western North Pacific Ocean.

Global abundance of planktonic heterotrophic protists in the deep ocean

“…As expected, at a global level, HP biomass decreased clearly with depth, from 280 pg C ml À 1 in the upper mesopelagic layer to 50 pg C ml À 1 in the lower bathypelagic layer. The average biomass for the bathypelagic realm was one order of magnitude larger than the values estimated by Fukuda et al (2007) and Sohrin et al (2010) but similar to other reports (Tanaka and Rassoulzadegan, 2002;Yamaguchi et al, 2004). The biomass ratio between HP and prokaryotes was 0.21 ± 0.05 in the global bathypelagic realm and 0.39 ± 0.08 in the mesopelagic realm.…”

“…The unprecedented magnitude of our sampling effort (116 stations) and the geographical coverage in our study (Figure 1 prokaryotes, only a handful of studies have enumerated deep HP (Pomeroy and Johannes, 1968;Sorokin, 1985;Tanaka and Rassoulzadegan, 2002;Yamaguchi et al, 2004;Fukuda et al, 2007;Sohrin et al, 2010;Morgan-Smith et al, 2011, 2013, likely because of the time-consuming enumeration techniques required. Here we used FC to estimate the abundance of HP (Christaki et al, 2011), a routine that had not yet been used in large-scale oeanographic surveys.…”

“…Data on HP abundance in deep waters have been reported for a total of about 75 locations across the ocean, mostly in the Northern Hemisphere: one Mediterranean site sampled at different times (Tanaka and Rassoulzadegan, 2002), 4 North Pacific stations (Yamaguchi et al, 2004), 6 Subarctic Pacific stations (Fukuda et al, 2007), 14 Pacific stations (Sohrin et al, 2010), 17 North Atlantic stations (Morgan-Smith et al, 2011) and 33 Equatorial Atlantic stations (Morgan-Smith et al, 2013). In general, these studies used epifluorescence microscopy to quantify HP, which provides useful morphologic information (cell size, nucleus shape and presence of flagella) when involving standard DAPI (4 0 , 6-diamidino-2-phenylindole) counts (Porter and Feig, 1980), and enables identification and enumeration of specific taxonomic groups by fluorescence in situ hybridization (FISH) counts (Pernthaler et al, 2001;Massana et al, 2006).…”

Chemical composition and energy content of deep-sea calanoid copepods in the Western North Pacific Ocean

“…In the mesopelagic, upper-bathypelagic and lower-bathypelagic zones, differences in chemical composition between copepods and net-plankton were not appreciable. Yamaguchi et al (2004) noted that copepods were the major component…”

Biological impact assessment of direct CO2 injection into the ocean

“…Such a project, whether small or large scale, would need to start by accumulating base-line information through a deep-sea field survey of biomass, biodiversity [24] and the trophic structure ( Figure 2) together with collection of physicochemical data, in order to evaluate induced ecosystem alterations. These alterations would be reflected in the food-web structure through changes in the trophic position of organisms.…”