Abstract
Oligotrich ciliates play a key role in linking microbial food webs to the traditional grazing food chain. Hence, the numerical (growth) and functional (grazing) responses of oligotrich ciliates are very important issues in studies of marine ecosystems. Most oligotrich ciliates feed mainly on nanoflagellates, while some of them also have the ability to consume bacteria. Up until now, studies of ciliates grazing on algae have not specifically excluded the effects of bacteria. In the present study, we found that the presence of bacteria in the algal culture medium affected the growth and grazing rates of ciliates grazing on nanoflagellates, resulting in an overestimate of gross growth efficiency at low relative algal concentrations. Strombidium sp. is prey selective mainly grazing on bacteria at low relative algal concentrations, but on algae at high relative algal concentrations. Carbon obtained from ciliate grazing on bacteria should be taken into account in the coastal zone surveys and especially in culture experiments to avoid unreasonable results of carbon flow.
Highlights
Oligotrichea, which mainly comprise the Choreotrichida and Oligotrichida, are the dominant group of ciliates in the microzooplankton (Agatha, 2011)
In order to understand (1) the grazing selection of ciliates on haptophytes (T-ISO) versus bacteria, and (2) the influence of the presence of bacteria in grazing experiments of ciliates on haptophytes, we studied the growth of the bacterivorous oligotrich ciliate Strombidium sp., isolated from the coastal waters of northeastern Taiwan, under two culture conditions, viz., (I) grazing on the haptophyte Isochrysis galbana (T-ISO) with bacteria present in the water column and (II) grazing only on bacteria isolated from the rice-grain-raised water column
The maximum growth rate of Strombidium sp. on T-ISO was higher than that on bacteria alone, showing that T-ISO is a better prey than bacteria for growing Strombidium sp
Summary
Oligotrichea, which mainly comprise the Choreotrichida and Oligotrichida, are the dominant group of ciliates in the microzooplankton (Agatha, 2011). The growth and grazing responses of oligotrich ciliates are very important issues in studies of marine ecosystems, inasmuch as they are among the factors that affect energy transfer (Verity, 1985; Calbet and Saiz, 2005). Some studies suggest that food size (Fenchel, 1986; Jonsson, 1986; Bernard and Rassoulzadegan, 1990; Hansen et al, 1994) and food quality (Chen et al, 2010; Montagnes et al, 2011) determine the feeding behavior of ciliates (Löder et al, 2011). Size may only be a physical constraint (Thurman et al, 2010) while other features of the prey are likely to play an important role in the ciliates grazing process. Yang et al (2015), for example, suggested that the swimming mode of algal cells is important in affecting the prey selectivity of ciliates
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