Krill feeding on sediment in the Gulf of Maine (North Atlantic)

Krill are key members of many marine ecosystems, serving as a critical trophic link between microscopic organisms and large predators such as whales, fish, and seabirds.Krill feeding is thus important to ecosystem carbon cycling.Traditional approaches to determining in-situ krill feeding require a priori assumptions, and may have prey-type detection biases.We took a DNA-based approach to measuring in-situ feeding by northern krill Meganyctiphanes norvegica.The diversity of prey consumed by M. norvegica in situ was analyzed for 80 krill at 8 stations throughout the Gulf of Maine (North Atlantic) using peptide nucleic acid mediated polymerase chain reaction (PNA-PCR) clone library sequencing of 18S rDNA.Relative abundance of the 2 most common prey types was measured with quantitative PCR (qPCR) in the guts of 16 krill.The 245 prey sequences recovered from krill gut contents included copepods, salps, phytoplankton, and a poorly known organism found to be sediment associated.Calanus finmarchicus and the sediment-associated organism were found most commonly, at 7 and 8 stations, respectively, and their 18S rDNA was present in nearly equal quantities in individual krill guts.M. norvegica, like most krill, are typically considered planktivorous; thus krill feeding on sediment organisms represents an unrecognized pathway for carbon flow from the sediment to the pelagic.Calculations suggest that this unrecognized pathway could potentially bring over 100 000 t of carbon annually back into the Gulf of Maine pelagic ecosystem, equivalent to 4% of annual primary production, or the energy demands of 80% of the region's fin whale population.