The naupliar forms are important intermediaries between microbial and classical food web as they can efficiently graze on autotrophic picophytoplankton and heterotrophic bacteria in diverse aquatic ecosystems. Current knowledge on feeding behavior of the naupliar grazing on picophytoplankton is limited and need to be explored. Nauplii (NII and NIII instar) of Amphibalanus amphitrite and Artemia salina were used as candidate grazer organisms in feeding experiments in the presence of picophytoplankton Synechococcus. Substantial grazing was observed from these two instars, and feeding behavior exhibited typical Holling type III functional response. At low prey concentration, the adapted foraging technique during food acquisition by the nauplii of both grazers pointing toward sigmoid type III is best suited than the other functional response types. However, lower carbon ingestion rate of NIII than NII and survival only up to NIV instar indicate that picophytoplankton are unable to meet the energy requirement for advanced instar stages of both the grazers. These inferences suggest that picophytoplankton occupy a key position in naupliar diet and should be taken into consideration when assessing mesozooplankton grazing and food web dynamics.
Suchandan Bemal, A. C. Anil