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Vernet, M, Baker KS.  1996.  Palmer Long-Term Ecological Research (LTER): Annual January cruise for 1996 (PD96-1). Antarctic Journal of the United States. 31:157-159. AbstractWebsite
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Smith, RC, Fraser WR, Stammerjohn SE, Vernet M.  2003.  Palmer Long-Term Ecological Research on the Antarctic marine ecosystem. Antarctic Peninsula climate variability : historical and paleoenvironmental perspectives. ( Domack E, Leventer A, Burnett A, Bindschadler R, Convey P, Kirby M, Eds.).:131-144., Washington, DC: American Geophysical Union Abstract
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Smith, RC, Baker KS, Fraser WR, Hofmann EE, Karl DM, Klinck JM, Quetin LB, Prezelin BB, Ross RM, Trivelpiece WZ, Vernet M.  1995.  The Palmer LTER: A Long-Term Ecological Research Program at Palmer Station, Antarctica. Oceanography. 8:77-86.   10.5670/oceanog.1995.01   Abstract

The Antarctic marine ecosystem—the assemblage of plants, animals, ocean, sea ice, and island components south of the Antarctic Convergence—is among the largest readily defined ecosystems on Earth (36 x 106 km2) (Hedgpeth, 1977; Petit et aI., 1991). This ecosystem is composed of an interconnected system of functionally distinct hydrographic and biogeochemical subdivisions (Treguer and Jacques, 1992) and includes open ocean, frontal regions, shelf-slope waters, sea ice, and marginal ice zones. Oceanic, atmospheric, and biogeochemical processes within this system are thought to be globally significant, have been infrequently studied, and are poorly understood relative to more accessible marine ecosystems (Harris and Stonehouse, 1991; Johannessen et al., 1994). The Palmer Long-Term Ecological Research (Palmer LTER) area west of the Antarctic Peninsula (Fig. la) is a complex combination of a coastal/continental shelf zone and a seasonal sea ice zone, because this area is swept by the yearly advance and retreat of sea ice. The Palmer LTER program is a multidisciplinary program established to study this polar marine ecosystem.

Baker, KS, Kozlowski WA, Vernet M, Jones JL, Quetin LB, Ross RM, Smith RC, Fraser WR.  1996.  Palmer LTER: Annual season October 1995 through March 1996. Antarctic Journal of the United States. 31:160-164. AbstractWebsite
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Smith, RC, Jones JL, Quetin LB, Ross RM, Baker KS, Kozlowski WA, Vernet M, Fraser W.  1996.  Palmer LTER: Annual season sampling on station. Antarctic Journal of the United States. 31:164-166. AbstractWebsite
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Quetin, LB, Jones J, Ross R, Smith R, Baker K, Vernet M, Fraser WR, Trivelpiece WZ, Sommerville L, Hardesty BD.  1995.  The Palmer LTER: Observations in foraging areas of Adelie penguins during the January 1995 cruise. Antarctic Journal of the United States. 30:269-271. Abstract
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Kozlowski, W, Lamerdin SK, Vernet M.  1995.  The Palmer LTER: Predominance of cryptomonads and diatoms in Antarctic coastal waters. Antarctic Journal of the United States. 30:267-268. Abstract
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Vernet, M, Kozlowski W, Ruel T.  1995.  The Palmer LTER: Temporal variability in primary production in Arthur Harbor during the 1994/1995 growth season. Antarctic Journal of the United States. 30:266-267. Abstract
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Vernet, M, Kozlowski WA, Rosenfield J, Greaves A.  1996.  Palmer LTER: Temporal variability in primary production in Arthur Harbor during the 1995-1996 growth season. Antarctic Journal of the United States. 31:181-182. AbstractWebsite
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Passow, U, Kozlowski W, Vernet M.  1995.  The Palmer LTER: Temporal variability of transparent exopolymer particles (TEP) in Arthur Harbor during 1994/1995 growth season. Antarctic Journal of the United States. 30:265-266. Abstract
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Hewes, CD, Mitchell BG, Moisan TA, Vernet M, Reid FMH.  1998.  The phycobilin signatures of chloroplasts from three dinoflagellate species: A microanalytical study of Dinophysis caudata, D. fortii, and D. acuminata (Dinophysiales, Dinophyceae). Journal of Phycology. 34:945-951.   10.1046/j.1529-8817.1998.340945.x   AbstractWebsite

The absorbance and fluorescence emission spectra for three species of Dinophysis, D. caudata Saville-Kent, D. fortii Pavillard, and D, acuminata Claparede et Lachmann, were obtained through an in vivo microanalytical technique using a new type of transparent filter. The pigment signatures of these Dinophysis species were compared to those of Synechococcus Nageli, a cryptophyte, and two wild rhodophytes, as well as those of another dinoflagellate, a diatom, and a chlorophyte. Phycobilins are not considered a native protein group for dinoflagellates, yet the absorption and fluorescence properties of the three Dinophysis species were demonstrated to closely resemble phycobilins and chloropylls of Rhodomonas Karsten (Cryptophyceae). Analyses of Dinophysis species using epifluorescence microscopy found no additional nucleus or nuclear remnant as would be contributed by an endosymbiont.

Smith, RC, Dierssen HM, Vernet M.  1996.  Phytoplankton biomass and productivity in the Western Antarctic Peninsula region. Foundations for ecological research West of the Antarctic Peninsula. ( Ross RM, Hofmann E, Quetin LB, Eds.)., Washington, D.C.: American Geophysical Union Abstract
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Cefarelli, AO, Vernet M, Ferrario ME.  2011.  Phytoplankton composition and abundance in relation to free-floating Antarctic icebergs. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 58:1436-1450.   10.1016/j.dsr2.2010.11.023   AbstractWebsite

Free-drifting icebergs in the Weddell Sea are expected to affect the surrounding marine ecosystem. Sampling associated with iceberg C-18a, a large tabular, free-drifting iceberg in the NW Weddell Sea, carried out from 10 March to 7 April 2009, was designed to test the hypothesis that the iceberg's presence modified phytoplankton composition and abundance. Areas that define a gradient of possible iceberg influence were sampled for phytoplankton: stations close ( < 1 km) and far (18 km) from iceberg C-18a, an area with numerous small icebergs, Iceberg Alley, and a control site 74 km away. Quantitative samples were obtained from Niskin bottles and counted with an inverted microscope for species abundance. Qualitative samples were collected with nets from the ship's seawater intake. Taxonomic determinations were performed with light and electron microscopy. Overall, diatoms dominated in the mixed layer (surface-similar to 40 m) and unidentified small flagellated and coccid cells at depth (similar to 100 m). Fragilariopsis nana, a diatom 2.4-15.5 mu m in length, dominated numerically the phytoplankton and was most abundant at the control area. The iceberg's effect on phytoplankton composition was consistent with the hypothesis that they facilitate phytoplankton communities enriched in diatoms, as found in other productive areas of Antarctica. Near the iceberg, diatoms were most abundant, principally at depth, while small flagellate concentration diminished. However, total phytoplankton abundance was lowest at Iceberg Alley in the area of highest meltwater contribution, as indicated by low mean temperature in the mixed layer, and highest at the control site. These results suggest that during austral fall, low growth or high zooplankton grazing could be counteracting the positive effect by icebergs on phytoplankton biomass, otherwise observed in summer months. (C) 2010 Elsevier Ltd. All rights reserved.

Vernet, M.  1991.  Phytoplankton dynamics in the Barents Sea estimated from chlorophyll budget models. Polar Research. 10:129-145.   10.1111/j.1751-8369.1991.tb00640.x   AbstractWebsite

Pigment budgets use chlorophyll a and phaeopigment standing stock in combination with their photooxidation and sedimentation rates in the euphotic zone to estimate phytoplankton growth and grazing by micro- and macrozooplankton. Using this approach, average phytoplankton growth in the euphotic zone of thc Barents Sea was estimated at 0.17 and 0.14 d-1 during spring of 1987 and 0.018 and 0.036 d-1 during late- and postbloom conditions in summer of 1988. Spring growth was 65% lower than the estimates from radiocarbon incorporation, supporting a 33% pigment loss during grazing. Macrozooplankton grazing and cell sinking were the main toss terms for phytoplankton during spring while microzooplankton grazing was dominant in summer. In contrast to tropical and temperate waters, Arctic waters are characterized by a high phaeopigment:chlorophyll a ratio in the seston. Photooxidation rates of phaeopigments at in situ temperatures (0 +/- 1-degrees-C) are lower than in temperate waters and vary by a factor of 2 for individual forms (0.009 to 0.018 m-2 mol-1). The phaeopigment fraction in both the suspended and sedimenting material was composed of seven main compounds that were isolated using high-performance liquid chromatography and characterized by spectral analysis. The most abundant phaeopigment in the sediment traps, a phaeophorbide-like molecule of intermediate polarity (phacophorbide a3), peaked in abundance in the water column below the 1% isolume for PAR (60-80 m) and showed the highest rate of photooxidation. This phaeopigment was least abundant in the seston when phytoplankton was dominated by prymnesiophytes but increased its abundance in plankton dominated by diatoms. This distribution suggests that larger grazers feeding on diatoms are the main producers of this phaeopigment.

Montes-Hugo, MA, Vernet M, Smith R, Carder K.  2008.  Phytoplankton size-structure on the western shelf of the Antarctic Peninsula: a remote-sensing approach. International Journal of Remote Sensing. 29:801-829.   10.1080/01431160701297615   AbstractWebsite

Remote-sensing models based on total (b(b)) and particle (b(bp)) backscattering are proposed for estimating phytoplankton size-structure characteristics over the Western Antarctic Peninsula (WAP) waters. It is hypothesized that phytoplankton assemblages with larger cells will have lower spectral b(b) and b(bp) slopes (gamma). Likewise, a higher concentrations of total chlorophyll a (chl(T)) will coincide with larger phytoplankton cells. Values of gamma(bbp), derived from satellite and in situ remote-sensing reflectance (R-rs) measurements were matched up with field determinations of chlorophyll a concentration fractions (chl((>20 mu m)) and chl((0.45-20 mu m))) collected between 1997 and 2006 as part of the Palmer-LTER project. Functionalities between in situ measurements of gamma(bb) and chlorophyll a fractions were also investigated. A consistent inverse relationship between chl((>20 mu m))/chlT and gamma (b(b) and b(bp)) values was found and verified with two approaches: spatial matchup of satellite monthly composites and time-space matchup of photosynthetic pigment markers. Based on satellite data, a gamma(bbp) value of 1.668 was a fair predictor to differentiate WAP waters dominated by 'large' (chl((>20 mu m))/chl(T)>= 0.5, gamma(bbp)<= 1.668) vs 'small' (chl((>20 mu m))/chl(T)<0.5, gamma(bbp)>1.668) phytoplankton cells. A significant negative linear relationship between 19'-butanoyloxyfucoxanthin, fucoxanthin, and gamma(bbp) values suggest that Phaeocystis aggregates and large diatoms (>20 mu m) would explain most of the chl((>20 mu m))/chl(T)-gamma variability. No relationships were evident between chl(T) values and gamma values. Although our results cannot be generalized to other oceanic regions, this work is the first to provide evidence about the significant influence of phytoplankton size distributions on spectral backscattering of WAP waters. Furthermore, and based on chlorophyll a fraction analysis, it was the >20 mu m phytoplankton cells that were responsible for such gamma variations seen on satellite and in situ values.

Garibotti, IA, Vernet M, Ferrario ME, Smith RC, Ross RM, Quetin LB.  2003.  Phytoplankton spatial distribution patterns along the western Antarctic Peninsula (Southern Ocean). Marine Ecology-Progress Series. 261:21-39.   10.3354/meps261021   AbstractWebsite

This paper describes spatial distribution patterns of the phytoplankton community (composition, cell abundance and biomass concentration) in relation to local environmental conditions in the Southern Ocean. Sampling was performed during summer 1997 off the coast of the western Antarctic Peninsula between Anvers Island and Marguerite Bay. Phytoplankton was characterized by relatively low biomass throughout most of the study area and was dominated by nanoalgae (<20 mum). Phytoplankton varied along an on-offshore gradient, with decreasing total cell abundance, chlorophyll a (chl a) concentration and carbon biomass toward the open ocean. Chl a concentration showed surface or subsurface maxima in coastal and middle-shelf waters, and deep maxima between similar to40 and 100 m in oceanic waters. Across-shelf variability in phytoplankton correlated with vertical stability in the water column, which appears to be the major parameter affecting phytoplankton community structure in the area. We hypothesize that the deep chl a maximum offshore may be associated with iron limitation in near-surf ace waters and higher iron concentration in 'winter waters' (subsurface remnant of Antarctic Surface Waters). On a smaller spatial scale, a cluster analysis showed great regional variability in phytoplankton assemblages. The area was divided into 4 main regions based on differences in the phytoplankton composition and concentration. Three peaks in phytoplankton abundance were found on a north-to-south gradient in near-shore waters: a Cryptomonas spp. bloom near Anvers Island, a small unidentified phytoflagellate bloom in Grandidier Channel, and a diatom bloom in Marguerite Bay. These assemblages resemble different stages of the phytoplankton seasonal succession, and may be related to the progressive sea-ice retreat, which might have regulated the timing of the onset of the phytoplankton seasonal succession in a north-south gradient. Biological environmental factors, such as seeding of the water column by epontic algae and selective zooplankton herbivory, are hypothesized to affect community composition in coastal regions. We conclude that large-scale variability in phytoplankton community structure is related to water column physical conditions and possibly iron availability, while mesoscale variability, as seen in coastal waters, is more likely due to seasonal succession of different algae groups.

Johnsen, G, Sakshaug E, Vernet M.  1992.  Pigment composition, spectral characterization and photosynthetic parameters in Chrysochromulina polylepis. Marine Ecology-Progress Series. 83:241-249.   10.3354/meps083241   AbstractWebsite

The photobiological response of an isolate of the prymnesiophyte Chrysochromulina polylepis, obtained from a bloom in the Skagerrak in May-June 1988, was evaluated with respect to pigment composition, spectral dependence of light harvesting, and photosynthetic parameters of cultures grown at 75 to 120-mu-mol m-2 s-1 irradiance, 16 h day length and 15-degrees-C. Results were compared to similarly grown cultures of the diatom Skeletonema costatum that appeared before and after the C. polylepis bloom. Chl a-specific absorption of light (degrees-a(c)) and chl a-specific absorption of quanta transported to photosystem II, estimated by means of a scaled fluorescence excitation spectrum (degrees-F), were 1.7 to 2.1 times larger in C. polylepis than in S. costatum in the visible spectrum. C. polylepis harvested blue-green light (450 to 500 nm) particularly efficiently. This is related to a high proportion of 19'-hexanoyloxyfucoxanthin and chl c3 relative to chl a. Nonetheless, both C polylepis and S. costatum absorb light more efficiently in 'clearest' blue ocean water than in 'clearest' green coastal water according to calculations based on spectrally corrected absorbed quanta transported to photosystem II (degrees-FBAR). Carbon-specific light absorption was about the same in the 2 species since the chl a: C ratio in S. costatum was twice as high as in C. polylepis. C. polylepis had a much smaller maximum carbon uptake (P(m)B) than S. costatum. Differences between the 2 species in terms of photosynthetic parameters, pigment composition, and spectral characteristics normalized to chl a, carbon, and cell are discussed.

Cape, MR, Vernet M, Kahru M, Spreen G.  2014.  Polynya dynamics drive primary production in the Larsen A and B embayments following ice shelf collapse. Journal of Geophysical Research-Oceans. 119:572-594.   10.1002/2013jc009441   AbstractWebsite

The climate-driven collapses of the Larsen A and B ice shelves have opened up new regions of the coastal Antarctic to the influence of sea ice resulting in increases in seasonal primary production. In this study, passive microwave remote sensing of sea ice concentration and satellite imagery of ocean color are employed to quantify the magnitude of and variability in open water area and net primary productivity (NPP) in the Larsen embayments between 1997 and 2011. Numerical model output provides context to analyze atmospheric forcing on the coastal ocean. Following ice shelf disintegration the embayments function as coastal, sensible heat polynyas. The Larsen A and B are as productive as other Antarctic shelf regions, with seasonally averaged daily NPP rates reaching 1232 and 1127 mg C m(-2) d(-1) and annual rates reaching 200 and 184 g C m(-2) yr(-1), respectively. A persistent cross-shelf gradient in NPP is present with higher productivity rates offshore, contrasting with patterns observed along the West Antarctic Peninsula. Embayment productivity is intimately tied to sea ice dynamics, with large interannual variability in NPP rates driven by open water area and the timing of embayment opening. Opening of the embayment is linked to periods of positive Southern Annular Mode and stronger westerlies, which lead to the vertical deflection of warm, maritime air over the peninsula and down the leeward side causing increases in surface air temperature and wind velocity. High productivity in these new polynyas is likely to have ramifications for organic matter export and marine ecosystem evolution. Key Points Primary production and sea ice dynamics after ice shelf disintegration Larsen embayments function as productive coastal sensible heat polynyas High sea ice interannual variability affects total production

Vernet, M, Lorenzen CJ.  1987.  The presence of chlorophyll b and the estimation of phaeopigments in marine phytoplankton. Journal of Plankton Research. 9:255-265.   10.1093/plankt/9.2.255   AbstractWebsite

A reverse-phase h.p.l.c. technique was used to estimate the concentration of chlorophyll b in phytoplankton cultures, fecal pellets of Calanus pacificus, and suspended paniculate matter from the Central North Pacific, Oregon coastal waters, and Dabob Bay (a temperate fjord in Puget Sound, WA, USA). The purpose was to assess the distribution of this pigment in the euphotic zone and its effect on the fluorometnc estimation of phaeopigments. Analyses of natural waters confirm high chlorophyll b concentrations (median mass ratio of b:a > 0.3) at the depth of the chlorophyll a maximum in tropical waters while values for temperate plankton are relatively low (median mass ratio of chl b:a = 0.05) and patchy. Zooplankton fecal pellets showed a significant enrichment in chlorophyll b, suggesting grazing as a mechanism to explain high concentrations of this pigment at the bottom of the euphotic zone. It is estimated that the presence of chlorophyll b could cause an average overestimation of phaeopigment concentration by the fluorometnc technique of 38% between 0 and 200 m in the Central North Pacific. This effect is more pronounced at the layer of chlorophyll b maximum (120–140 m).

Vernet, M, Kozlowski WA, Yarmey LR, Lowe AT, Ross RM, Quetin LB, Fritsen CH.  2012.  Primary production throughout austral fall, during a time of decreasing daylength in the western Antarctic Peninsula. Marine Ecology-Progress Series. 452:45-61.   10.3354/meps09704   AbstractWebsite

Antarctic phytoplankton is characterized by a pronounced seasonality in abundance, driven mainly by changes in sunlight. We combined measurements and modeling to describe the influence of changing daylength on fall and winter phytoplankton production in coastal waters of the western Antarctic Peninsula (wAP) in 2001 and 2002. The model was parameterized with field observations from the Palmer Long-Term Ecological program in the wAP during summer and early fall and from the Southern Ocean Global Ecosystems Dynamics program fall and winter cruises to Marguerite Bay and shelf waters. Shorter daylength and a deepening of the mixed layer account for most of the decrease in primary production during March, April, and May. At this time, biomass decreases by an order of magnitude and remains low and constant until the end of August. An additional loss rate was added to the primary production model to fit output to observations. This loss rate, estimated at similar to 0.1 to 0.15 d(-1), is due to physical, chemical, and biological processes such as scavenging by sea ice, zooplankton grazing, cell lysis, and cell sedimentation, which are expected to be high at this time of year. Growth and loss rates of phytoplankton populations are similar on 1 March, with growth decreasing rapidly over time while the loss rates remain constant. By the beginning of winter (1 June), growth is low, with minimum rates in July and increasing towards September. During a period of diminishing food supply, preliminary estimates of grazing indicate that fall biomass could support existing macrozooplankton populations, but the timing and concentration of food supply is variable and expected to affect health of zooplankton as they enter the winter.

Vernet, M, Martinson D, Iannuzzi R, Stammerjohn S, Kozlowski W, Sines K, Smith R, Garibotti I.  2008.  Primary production within the sea-ice zone west of the Antarctic Peninsula: I-Sea ice, summer mixed layer, and irradiance. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 55:2068-2085.   10.1016/j.dsr2.2008.05.021   AbstractWebsite

in shelf waters of the western Antarctic Peninsula (wAP), with abundant macro- and micronutrients, water-column stability has been suggested as the main factor controlling primary production; freshwater input from sea-ice melting stabilizes the upper water column by forming a shallow summer mixed layer. Retreating sea ice in the spring and summer thus defines the area of influence, the sea-ice zone (SIZ) and the marginal ice zone (MIZ). A 12-year time series (1995-2006) was analyzed to address two main questions: (1) what are the spatial and temporal patterns in primary production; and (2) to what extent and in what ways is primary production related to sea-ice dynamics. Data were collected on cruises performed during January of each year, at the height of the growth season, within the region bounded by 64 degrees S and 64 degrees W to the north and 68 degrees S and 66 degrees W to the south. Average daily integrated primary production varied by an order of magnitude, from similar to 250 to similar to 1100mg cm(-2) d(-1), with an average cruise primary production of 745 mg C m(-2) d(-1). A strong onshore-offshore gradient was evident along the shelf with higher production observed inshore. Inter-annual regional production varied by a factor of 7: maximum rates were measured in 2006 (1788 mg cm(-2) d-(1)) and minimum in 1999 (248 Mg C m(-2) d(-1)). The results support the hypothesis that primary production in the wAP shelf is related to sea-ice dynamics. To first order, shallower summer mixed-layer depths in the shelf correlated with late sea retreat and primary production. Principal component analysis showed that high primary production in January was associated with enhanced shelf production toward the coast and in the south, explaining 63% of the variability in space and time. This first mode captured the inter-annual variability in regional production. Temporal variability in primary production (time series of anomalies defined for each location) showed spatial dependence: higher primary production correlated with shallow mixed-layer depths only at mid-shelf; in coastal and offshore waters, primary production correlated with deeper mixed layers. Thus, coastal primary production can show a non-linear relationship with summer mixed layers. Under conditions of large biomass (> 20 mg ch1 a m(-3)) and shallow mixed-layer depth (e.g., 5 m) phytoplankton production becomes light limited. This limitation is reduced with a deepening of the summer mixed layer (e.g., 20m). Dominance of diatoms and the ability to adapt and photosynthesize at higher light levels characterized the large phytoplankton blooms. No significant regional trend in primary production was detected within the 12-year series. We conclude that the regional average primary production on the wAP shelf is associated with shallow summer mixed layers in conjunction with late sea-ice retreat. An opposite relationship is observed for the highest production rates in coastal waters, associated with large biomass, where a deepening of the summer mixed layer relieves light limitation. (C) 2008 Elsevier Ltd. All rights reserved.

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.