Ciliate (Euplotes sp.) predation by Pseudodiaptomus annandalei (Copepoda: Calanoida) and the effects of mono-algal and pluri-algal diets

Background: Pseudodiaptomus annandalei is an estuarine species and being cultured as live feed for grouper fish larvae and other planktivores. We examined the predation behavior of P. annandalei adults when preying on ciliated protists (Euplotes sp.) and the effects of mono-and pluri-algal diets on ciliate predation by P. annandalei under laboratory conditions. The algal food comprised the pigmented flagellate Isochrysis galbana (4 similar to 5 mu m) and Tetraselmis chui (17 similar to 20 mu m). Results: Males and females of P. annandalei consumed 8 similar to 15 ciliate cells/h. The probability of ciliate ingestion following an attack was a direct function of the copepod's hunger level. Conversely, the probability of prey rejection after capture was a negative function of the copepod's hunger level. Starved and poorly fed females showed a significantly lower rate of prey rejection compared to similarly treated males. The duration of handling a ciliate prey did not significantly differ between males and females of P. annandalei. Starved copepods spent less time handling a ciliate prey than fed copepods. Prey ingestion rates showed a negative relation with the feeding duration, whereas the prey rejection rate increased as the feeding duration increased. The ciliate consumption rate of P. annandalei was significantly lower in the presence of mixed algae. Neither I. galbana nor T. chui alone had any significant effect on ciliate consumption by P. annandalei. Conclusions: The results confirmed that P. annandalei ingests bacterivorous heterotrophic protists even in the presence of autotrophic protists. Therefore, our results point to the role of P. annandalei in the transfer of microbial carbon to the classical food chain in estuarine and brackish water ecosystems.