AME 74:59-71 (2015)  -  DOI: https://doi.org/10.3354/ame01729

ABSTRACT: We studied the numerical and functional responses of the marine oligotrichous ciliate Strombidium cf. sulcatum on 4 prey organisms to assess which prey properties affect the grazing response and food ingestion of this taxon. The predator exhibited higher growth rates when feeding on Dunaliella sp. than on Pyramimonas sp., Prorocentrum sp. or a small cryptophyte species. The ingestion rate of the predator when feeding on Dunaliella sp. increased with increasing prey concentrations. However, no significant ingestion was detected for the other prey organisms. By measuring important properties of the prey organisms, we found that (1) cellular carbon and nitrogen contents and fatty acid composition of the prey organisms are likely unimportant factors affecting food ingestion of oligotrichous ciliates; (2) although the essential fatty acids EPA, DPA and DHA were not detected in Dunaliella sp., low amounts of EPA and DHA were detected in the predator, indicating that this ciliate can synthesize these fatty acids at a slow rate by itself; and (3) the swimming velocity of Dunaliella sp. was much slower and its swimming behaviour was different from that of the other prey organisms, indicating that the swimming motility of prey species may play a pivotal role in determining the food ingestion of oligotrichous ciliates. This study provided new insight into the mechanism of grazing response and food ingestion of oligotrichous ciliates, which aids in our understanding of how this important ciliate group shapes the composition and functioning of phytoplankton communities in situ.

KEY WORDS: Grazing response · C:N ratio · Fatty acid · Swimming behaviour · Microbial food web · Helgoland Roads