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2016
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.

2000
Whitehead, K, Vernet M.  2000.  Influence of mycosporine-like amino acids (MAAs) on UV absorption by particulate and dissolved organic matter in La Jolla Bay. Limnology and Oceanography. 45:1788-1796.   10.4319/lo.2000.45.8.1788   AbstractWebsite

Experimental work with cultures of the red tide dinoflagellate Lingulodinium polyedrum suggested mycosporine-like amino acids (MAAs) are a component of the organic matter excreted by cells. MAAs in dissolved organic matter (DOM) also may have it large influence on absorption of ultraviolet (UV) light through the water column. To test these hypotheses in a natural setting, data were collected from March 1995 through April 1996 in coastal waters off California, U.S.A. During this time, a large red tide of L. polyedrum occurred in March and April 1995. In this field study, we show that MAAs are a quantifiable component of DOM, particularly during the period following the red tide events. Absorption spectra of particulate organic matter (POM) and DOM samples revealed disproportionately high levels of UV absorption relative to visible wavelengths. UV absorption by POM at 330 nm was linearly related to phytoplankton biomass (between 0-10 mug chlorophyll [Chl] a L-1), measured as Chi a, accounting for 71% of the variability in absorption. Chromatographic analyses revealed the presence of various MAAs in both POM and DOM pools. MAAs were observed in 83% (n = 53) and 47% (n = 13) of the samples analyzed with concentrations ranging from 0 to 2.75 muM (0-696.00 mu mol mug(-1) Chi a) in the POM and 0 to 111.40 nM in the DOM fraction. Absorption by dissolved MAAs, as calculated from the measured concentrations, correlated with DOM UV absorption (r(2) = 0.77) and accounted for up to 10% of the total DOM absorption at 330 nm. Thus, MAAs are a small but quantifiable component of the DOM pool in the field and contribute to UV absorption.