Protist Community Grazing on Prokaryotic Prey in Deep Ocean Water Masses

Abstract

Oceanic protist grazing at mesopelagic and bathypelagic depths, and their subsequent effects on trophic links between eukaryotes and prokaryotes, are not well constrained. Recent studies show evidence of higher than expected grazing activity by protists down to mesopelagic depths. This study provides the first exploration of protist grazing in the bathypelagic North Atlantic Deep Water (NADW). Grazing was measured throughout the water column at three stations in the South Atlantic using fluorescently-labeled prey analogues. Grazing in the deep Antarctic Intermediate water (AAIW) and NADW at all three stations removed 3.79% ± 1.72% to 31.14% ± 8.24% of the standing prokaryote stock. These results imply that protist grazing may be a significant source of labile organic carbon at certain meso- and bathypelagic depths.

A Review of Protist Grazing Below the Photic Zone Emphasizing Studies of Oxygen-Depleted Water Columns and Recent Applications of In situ Approaches

“…That study suggests protist grazing could play an important role in carbon cycling in the mesopelagic environment. Rocke et al (2015) conducted on-board, long-term (24 h) incubation experiments using waters from the epipelagic, mesopelagic and bathypelagic North Atlantic collected via Niskin sampling, and FLP prepared from whole seawater samples from another location (Vineyard Sound, MA, USA). Estimation of grazing rates (prey consumed per eukaryote per hour) were not greatly different between the euphotic, 220 and 750 m. Similar percentages (up to 30%) of the standing stock of prokaryotes were consumed by eukaryotes in the mesopelagic (750 m) and at 2,500 m, despite lower eukaryote and prokaryote concentrations.…”

“…Replication of these comparative studies in the future is warranted to assess reliability of these effects not only at these sites in the ETSP, but in other oceans and at other depths. Potential bottle effects during incubations typically include attachment of eukaryotes to container surfaces, negative responses to changing physicochemical conditions (e.g., temperature or oxygen) within the bottle, or preferential grazing and alteration of the food web (Marrasse et al, 1992;Oikonomou et al, 2014;Rocke et al, 2015). In situ incubations will not eliminate all potential sources of artifacts, but can minimize physico-chemical alterations Lin et al (2007) in the Cariaco Basin, Anderson et al (2012) in the central Baltic Sea, Pachiadaki et al (2014) in the Mediterranean Sea, and Rocke et al (2015) in the western Atlantic.…”

“…Potential bottle effects during incubations typically include attachment of eukaryotes to container surfaces, negative responses to changing physicochemical conditions (e.g., temperature or oxygen) within the bottle, or preferential grazing and alteration of the food web (Marrasse et al, 1992;Oikonomou et al, 2014;Rocke et al, 2015). In situ incubations will not eliminate all potential sources of artifacts, but can minimize physico-chemical alterations Lin et al (2007) in the Cariaco Basin, Anderson et al (2012) in the central Baltic Sea, Pachiadaki et al (2014) in the Mediterranean Sea, and Rocke et al (2015) in the western Atlantic. Cuevas and Morales (2006) also reported similar values of prokaryotic (0.6 ± 0.04 × 10 6 cells mL −1 ) and eukaryotic (0.10 ± 3.84 × 10 3 cells mL −−1 ) abundances for the north coast of Chile over the OMZ at 100 m. We observed a decline in concentration of both prokaryotes and protist communities with depth.…”

Past President's Address: Protists of the Mesopelagic and a Bit on the Long Path to the Deep Sea

“…), the Tropical & South Atlantic (Rocke et al. ), the Eastern and Western Mediterranean Sea (Rocke et al. ; Tanaka and Rassoulzadegan ), and the Ross Sea in Antarctica (Safi et al.…”

“…Abundances (cell counts) of aggregate groups have been reported for a very wide range of localities. From across the world ocean between 30°N and 30°S from the Malaspina program (Pernice et al 2015), to the subarctic Pacific (Fukuda et al 2007), the North West Pacific (Yamaguchi et al 2002(Yamaguchi et al , 2004, the Tropical N Pacific to Arctic (Sohrin et al 2010), the subtropical & tropical Atlantic (Morgan-Smith et al 2011), sites around the Canary Islands (Boras et al 2010), the Tropical & South Atlantic (Rocke et al 2015), the Eastern and Western Mediterranean Sea (Rocke et al 2015;Tanaka and Rassoulzadegan 2002), and the Ross Sea in Antarctica (Safi et al 2012).…”