Molecular approach (PCR-DGGE) to diet analysis in young Antarctic krill Euphausia superba

Antarctic krill Euphausia superba Dana comprise a key component of the Southern Ocean food web, yet despite decades of research, questions concerning the regional, seasonal and ontogenetic differences in their diet remain. All current methods used to characterize krill diet have limitations for identifying the full complement of the diet. Using DNA as a marker molecule, our goal in this study has been to evaluate the efficacy of a PCR-DGGE (denaturing gradient gel electrophoresis) approach targeting the 18S rDNA gene to discriminate among diet constituents in gut and fecal pellet samples from young Antarctic krill relative to their feeding environment-the seawater and sea ice microbial community. We conducted 2 laboratory-based feeding experiments with known food items and 3 field samplings of both the krill and their feeding environment. Sequenced PCR-DGGE phylotypes from laboratory trials clearly distinguished diatom and copepod prey, while in situ feeding analyses revealed that a broad diversity of taxa were ingested, including diatoms (Bacillariophyta, the most prevalent group detected), dinoflagellates, cryptomonads, prasinophytes, ciliates, cercozoans, choanoflagellates, turbellarians and (possibly) sponge larvae. Band image analyses allowed environmental and diet phylotypes to be matched. On average, 32% of those from the environment were present in the diet; conversely, of the phylotypes detected in the diet, an average of 59% were in common with the environment. Changes in environmental phylotypes among sampling dates were reflected by similar changes in the krill diet as potential prey diversity (richness) decreased during a phytoplankton bloom.