The Dynamic Nature of Protistan Ingestion Response to Prey Abundance

Abstract

ABSTRACT. Ingestion rate of Paraphysomonas imperforata was found to be a hyperbolic function of prey density. But the same flagellate clone had multiple ingestion responses to prey density, depending on its physiological state and physical stress it suffers. The flagellates in a physiological state of higher growth tended to have higher maximum ingestion and clearance rates than ones in a physiological state of lower growth. The same trend was observed for volume‐specific maximum ingestion and volume‐specific clearance rate. In response to changing prey density, the growth rate did not change as quickly as the ingestion rate, suggesting imbalance between the two. The tested physical stresses, including shaking, centrifugation, and filtration, also resulted in reduction of ingestion parameters of the flagellates. But half‐saturation constants did not show any trend in response to either physiological state or physical stress. In light of the dynamic nature of protistan ingestion response to prey abundance, short incubation, which minimizes the physiological change, and careful handling, which prevents the possible physical stress, should be employed in order to avoid underestimation of in situ ingestion rates. Previously reported ingestion parameters of lab‐cultured protists, which are thought to be unrealistic in natural conditions, may represent only one of multiple ingestion responses, probably prey‐rich condition.

Seasonal variations in trophic dynamics of nanoflagellates and picoplankton in coastal waters of the western subtropical Pacific Ocean

“…6). Some studies consider water temperature and prey density to be among the most important factors regulating the seasonal ingestion rate of nanoflagellates (Choi 1994). However, in our study, these correlations were weak between observed grazing rates on bacteria or Synechococcus spp.…”

“…Tsai et al (2005) found a significant diel variation in bacterial growth, but there is a lack of data on the seasonal variation in bacterial growth and of nanoflagellate grazing rates, and on factors controlling the effect of nanoflagellate grazing on bacteria throughout the year. One study (Choi 1994), however, suggested that water temperature and prey density are among the most important factors regulating the seasonal grazing rate on bacteria by protists.…”

“…Tsai et al (2005) found a significant diel variation in bacterial growth, but there is a lack of data on the seasonal variation in bacterial growth and of nanoflagellate grazing rates, and on factors controlling the effect of nanoflagellate grazing on bacteria throughout the year. One study (Choi 1994), however, suggested that water temperature and prey density are among the most important factors regulating the seasonal grazing rate on bacteria by protists.Picophytoplankton, predominantly coccoid cyanobacteria (Synechococcus spp. ), on the other hand, can make up a major proportion of the phytoplankton biomass and production in oceanic waters (Olson et al 1990), and contribute up to 90% of total phytoplankton biomass in oligotrophic waters (Probyn 1985).…”

Relative importance of phototrophic, heterotrophic, and mixotrophic nanoflagellates in the microbial food web of a river-influenced coastal upwelling area

“…Water temperature and prey abundance are usually some of the most important factors regulating HNF phagotrophic activity (Choi 1994, Vaqué et al 1994. Positive correlation between bacterial abundance and MNF and HNF ingestion evidence this strong dependence (Table 2).…”

Significant year‐round effect of small mixotrophic flagellates on bacterioplankton in an oligotrophic coastal system

“…Water temperature and prey abundance are usually considered among the most important factors regulating HF phagotrophic activity (Choi 1994;Vaqué et al 1994). SGRs in both HF size categories were significantly correlated, which suggests that the same environmental factor controls the feeding activity of both HF size categories.…”