Molecular detection of algal prey in copepod guts and fecal pellets

Jens C. Nejstgaard, Marc E. Frischer, Caren L. Raule, Rita Gruebel, Kathleen E. Kohlberg, Peter G. Verity

Limnol. Oceanogr. Methods 1:29-38 (2003) | DOI: 10.4319/lom.2003.1.29

ABSTRACT: The ability to obtain information about feeding selectivity and rates in situ for key organisms such as copepods and other zooplankton is vital for understanding the mechanisms structuring marine ecosystems. Copepods feed on a wide range of prey, and there are presently no methods available to directly quantify zooplankton feeding on all different prey types in situ. Therefore, the development of a new nonintrusive direct method is necessary to gain a better understanding of the trophic interactions in aquatic ecosystems. Molecular methods based on the polymerase chain reaction have recently become an important tool to study predation by arthropods, particularly insects. Here we present the first results of successful molecular detection of a specific prey consumed by calanoid copepods from gut and fecal material. Using the calanoid copepod species Calanus finmarchicus consuming the haptophyte alga Emiliania huxleyi as a model system, 18S ribosomal DNA originating from E. huxleyi was unambiguously detected in whole DNA extracts from copepods and from their fecal pellets. The results also suggest that prey DNA may be quantified for determination of prey-specific zooplankton feeding rates. However, significantly more research under controlled laboratory and field conditions will be required to achieve these objectives. We hypothesize that molecular methods will become an important tool with the potential to quantify undisturbed trophic interactions between individual predators and all their prey in the complex natural plankton.