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Svensen, C, Vernet M.  2016.  Production of dissolved organic carbon by Oithona nana (Copepoda: Cyclopoida) grazing on two species of dinoflagellates. Marine Biology. 163   10.1007/s00227-016-3005-9   AbstractWebsite

Production of dissolved organic carbon (DOC) by sloppy feeding copepods may represent an important source of DOC in marine food webs. By using the C-14-labeling technique, we quantify for the first time the production of DOC by the small cyclopoid copepod Oithona nana on two species of dinoflagellates, Oxyrrhis marina and Karlodinium sp. We found significant production of DOC when O. nana grazed on O. marina, corresponding to 6-15 % of the carbon ingested. When grazing the smaller Karlodinium sp., no DOC was produced. In additional experiments, we compared O. nana feeding rates on the dinoflagellate species Prorocentrum micans, Akashiwo sanguinea, Karlodinium sp. and O. marina. Clearance rates varied with prey size, with highest and lowest clearance rates on O. marina and Karlodinium sp., respectively. Our study indicates that even though O. nana feed efficiently on dinoflagellates, some of the carbon cleared can be lost as DOC. However, the DOC production by O. nana was lower than rates reported for calanoid copepods. We hypothesize that this is a result of the ambush feeding behavior of O. nana, which is considered a more specialized feeding mode than, for instance, suspension feeding. Due to high abundances and global distribution, we suggest that Oithona can represent an important source of DOC in marine ecosystems. This would particularly be the case during autumn and winter, where they may contribute to maintaining the microbial loop activities during periods of low primary production.

Ross, RM, Quetin LB, Baker KS, Vernet M, Smith RC.  2000.  Growth limitation in young Euphausia superba under field conditions. Limnology and Oceanography. 45:31-43.   10.4319/lo.2000.45.1.0031   AbstractWebsite

Growth rates of late furcilia and juvenile Antarctic krill (Euphausia superba Dana) in the spring and summer were related to food quantity and quality. The 4 yr covered by this study (1991-1992, 1993-1994, 1994-1995, and 1995-1996) were part of the seasonal time series of the Palmer Long-Term Ecological Research program. Chlorophyll a concentrations represented food quantity, and accessory photosynthetic pigments represented phytoplankton community composition or food quality. Instantaneous growth rates reflected the in situ nutritional history of the previous intermolt period. The response of krill to the food environment was seen on temporal scales of days to weeks. Percent growth per intermolt period (percentage growth IMP-1) varied significantly both within and between years, ranging from similar to 2 to 10% IMP-1. Percent growth IMP-1 increased with increasing chlorophyll a (Chl a), reaching a maximum of 9.3% IMP-1 above a critical concentration of about 3.5 mg m(-3). Maximum growth was reached in only 2 yr, 1991-1992 and 1995-1996. In a multiple regression analysis, total Chi a and prymnesiophyte-Chl a explained over 71% of the temporal variance in growth. In general, highest growth was found toward the end of diatom blooms and lowest during periods of low phytoplankton biomass or blooms dominated by cryptophytes and prymnesiophytes. The results of this study support the hypothesis that maximum growth rates are only possible during diatom blooms and that production in Antarctic krill is limited by both food quantity and quality.