Feeding selection of heterotrophic marine nanoflagellates based on the surface hydrophobicity of their picoplankton prey

Abstract

Theory suggests that variation in the attractive solvation force associated with cell-surface hydrophobicity can significantly affect contact rates among small cells in aqueous environments and consequently may influence rates and selective impacts of marine nanoflagellate grazers feeding on picoplankton assemblages. To investigate this hypothesis, we assayed the natural range in hydrophobic characteristics of subtropical picoplankton from the oligotrophic subtropical Pacific (Station Aloha, 22Њ45ЈN, 158ЊW) and mesotrophic Kaneohe Bay, Hawaii, using hydrophobic interaction chromatography (HIC) in conjunction with analytical flow cytometry. Variability in a relative index of cell-surface hydrophobicity (HIC index) for heterotrophic bacteria, Prochlorococcus and Synechococcus, exhibited some consistent spatial patterns. The HIC index for Prochlorococcus at Station Aloha varied about threefold, being consistently more hydrophobic in the upper 80 m of the water column and dropping abruptly below this depth. Heterotrophic bacteria were more hydrophobic near the surface and decreased slightly, but steadily, with increasing depth. The hydrophobicity of heterotrophic bacteria steadily increased along a Kaneohe Bay transect extending from oligotrophic to mesotrophic conditions. In experiments involving nanoflagellates grazing on laboratory cultures of Prochlorococcus, cell cultures exhibiting the highest HIC indices were grazed upon at the highest rates. An additional experiment involving mixtures of Prochlorococcus cells exhibiting high and low hydrophobicities showed that the average hydrophobicity of the uningested prey mixture was driven progressively toward lower hydrophobicity as the more hydrophobic cells were selectively removed through time. If these laboratory grazing results hold in nature, the rate at which picoplankton cells are cleared from suspension by nanoflagellates could vary by as much as twofold due solely to natural variation in cell surface hydrophobicity.

Close coupling between phytoplankton growth and microzooplankton grazing in the western South China Sea

“…Although it can be argued that more mortality rate estimates for Synechococcus in Fig. 6B lie above the 1 : 1 comparison line than below, few exceed the approximately 40-50% higher values that would be predicted from rate proportionality to cell radius or r 0.8 (Monger and Landry 1991). The general similarity between contemporaneous rate estimates for these two prey organisms could be indicative of cell properties that affect their relative vulnerabilities to predation independent of size.…”

“…As major consumers of the ultraphytoplankton, nano-sized heterotrophic protists link the grazing mortalities of the component groups. Theory suggests, for example, that relative grazing vulnerabilities should be defined by a fixed size relationship roughly proportional to cell radius (Monger andLandry 1990, 1991), which provides another advantage to small size. Perturbation experiments, such as open-ocean iron fertilization (Landry et al 2000), have shown, for example, that grazers can respond quickly to control or suppress ultraphytoplankton populations, even as other size classes, and phytoplankton biomass as a whole, are strongly increasing.…”

Spatial variability of phytoplankton pigment distributions in the Subtropical South Pacific Ocean: comparison between in situ and predicted data

“…11d). This feature has been observed in other subtropical gyre systems (Claustre and Marty, 1995;Monger et al, 1999), but the reasons for its existence are still unclear. Claustre and Marty (1995) suggest that this deep nanoflagellate population can develop close to the nutricline, which is the case here.…”

Size Selective Feeding in Cyclidium glaucoma (Ciliophora, Scuticociliatida) and Its Effects on Bacterial Community Structure: A Study from a Continuous Cultivation System

“…These changes are caused by selective grazing of protists on specific bacteria, which consequently has an impact on the whole bacterial community (BC). Several characteristics of the bacterial cell, such as motility, cell surface properties, size, and activity state (growth or division), can be criteria for a protistan predator to prefer or avoid it as food [17,32,41]. Until now, most studies in this field focused on the size selective feeding of ciliates and flagellates and its various effects on bacteria.…”