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Vernet, M, Hunter JR, Vetter RD.  1988.  Accumulation of age pigments (lipofuscin) in 2 cold-water fishes. Fishery Bulletin. 86:401-407. AbstractWebsite
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Vernet, M, Mitchell BG, Holmhansen O.  1990.  Adaptation of Synechococcus in situ determined by variability in intracellular phycoerythrin-543 at a coastal station off the Southern California coast, USA. Marine Ecology-Progress Series. 63:9-16.   10.3354/meps063009   AbstractWebsite

Concentrations of extracted phycobiliproteins were measured at a station off the Southern California coast, USA, from November 1985 to March 1986. The main pigment found was phycoerythrin-543 (PE) from Synechococcus spp. as described by Alberte et al. (1984). Concentrations of PE in water column, between 3 and 40 m, varied between 0.01 and 1.60 microg/l. Maximum values were found between 3 and 22 m. In situ concentrations of PE were positively correlated with cell numbers of Synechococcus spp., which ranged from 1.4 to 116 X 10^6cells/l, and showed maximal values between 3 and 13 m. Because no other types of PE were detected, all PE measured was considered to come from Synechococcus-type cells. Cellular concentrations of PE varied between 2.1 and 40.3 X 10^-9 microg PE/cell, with an average value of 10 5±4.1 X 10^-9 microg PE/cell above the 1 % isolume for PAR (Photosynthetically Available Radiation). Pigment per cell increased consistently with depth dunng autumn and spring and had low and relatively constant values in the winter. High PE:cell (>20 X 10^-9 microg PE/cell) was observed only below the 1 % isolume for PAR. For all samples, cellular concentration of PE was inversely correlated with incident PAR and was positively correlated to dissolved inorganic nitrogen (nitrate) concentration. Cyanobactena were not a dominant component of phytoplankton standing stock during this study, contributing an estimated 4 to 15 % of total chlorophyll in the water column, but had high specific growth rates, with maximal values of >0.75 d^-1 close to the surface. Absorption of light at 540 nm, as measured by in vivo absorption spectra of phytoplankton, was not correlated with PE concentration in the water column.

Robison, BH, Vernet M, Smith KL.  2011.  Algal communities attached to free-drifting, Antarctic icebergs. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 58:1451-1456.   10.1016/j.dsr2.2010.11.024   AbstractWebsite

Disintegration of the Antarctic Peninsula's eastern ice shelves has increased the population of icebergs traversing the Weddell Sea, but until recently little was known about their ecological impact on the pelagic environment. Here we describe a class of algal communities that occur on the submerged flanks of large, free-drifting, glacially-derived tabular icebergs. We used remotely operated vehicles to examine these icebergs directly for the first time, to survey the algal communities and collect material for shipboard laboratory studies. The communities, principally diatoms, were associated with a characteristic cupped configuration of the ice surface, and they served as feeding sites for aggregations of Antarctic krill. Production rate measurements indicate that these communities are providing a substantial contribution to regional primary production in summer. As the number of icebergs grows, the number of algae communities may also be increasing, along with their cumulative contribution to organic carbon flux. (C) 2010 Elsevier Ltd. All rights reserved.

Moline, MA, Claustre H, Frazer TK, Schofield O, Vernet M.  2004.  Alteration of the food web along the Antarctic Peninsula in response to a regional warming trend. Global Change Biology. 10:1973-1980.   10.1111/j.1365-2486.2004.00825.x   AbstractWebsite

In the nearshore coastal waters along the Antarctic Peninsula, a recurrent shift in phytoplankton community structure, from diatoms to cryptophytes, has been documented. The shift was observed in consecutive years (1991-1996) during the austral summer and was correlated in time and space with glacial melt-water runoff and reduced surface water salinities. Elevated temperatures along the Peninsula will increase the extent of coastal melt-water zones and the seasonal prevalence of cryptophytes. This is significant because a change from diatoms to cryptophytes represents a marked shift in the size distribution of the phytoplankton community, which will, in turn, impact the zooplankton assemblage. Cryptophytes, because of their small size, are not grazed efficiently by Antarctic krill, a keystone species in the food web. An increase in the abundance and relative proportion of cryptophytes in coastal waters along the Peninsula will likely cause a shift in the spatial distribution of krill and may allow also for the rapid asexual proliferation of carbon poor gelatinous zooplankton, salps in particular. This scenario may account for the reported increase in the frequency of occurrence and abundance of large swarms of salps within the region. Salps are not a preferred food source for organisms that occupy higher trophic levels in the food web, specifically penguins and seals, and thus negative feedbacks to the ecology of these consumers can be anticipated as a consequence of shifts in phytoplankton community composition.

Garibotti, IA, Vernet M, Ferrario ME.  2005.  Annually recurrent phytoplanktonic assemblages during summer in the seasonal ice zone west of the Antarctic Peninsula (Southern Ocean). Deep-Sea Research Part I-Oceanographic Research Papers. 52:1823-1841.   10.1016/j.dsr.2005.05.003   AbstractWebsite

The distribution of phytoplankton composition, cell abundance and biomass from an area along the Western Antarctic Peninsula was studied during three summers, with the aim of understanding its dynamics over spatial and interannual scales. The studied area is characterized by seasonal sea-ice retreat and advance. Algae composition and concentration were found to be highly variable through the area as well as from year to year. Small unidentified phytoflagellates, diatoms and cryptophytes were the main phytoplankton groups, contributing the major proportion of total phytoplankton cell abundance and biomass concentration. Three annually recurrent phytoplankton assemblages were recognized in the area according to the algae composition and abundance: a diatom bloom associated with the seaice edge, an assemblage dominated by small unidentified phytoflagellates and cryptophytes, and a diatom-enriched assemblage in open waters. The distribution of these assemblages varied from year-to-year. During the summers preceded by early sea-ice retreat, the diatom bloom was spatially restricted and the other two assemblages occupied extended regions, whereas during the late sea-ice retreat year, the diatom bloom extended over a larger region and the other assemblages occupied smaller regions or were just absent. It was detected that these assemblages resemble different stages of the phytoplankton seasonal cycle, and that their distribution through the area can be related to a latitudinal and longitudinal gradient in the phytoplankton growth onset timing, associated with the progressive sea-ice retreat during spring. The local environmental conditions associated with each assemblage were also analyzed, but further study is needed for understanding the causes of the replacement of one assemblage by another through the area. On the other hand, the interannual variability in the distribution of the assemblages can be related to year-to-year differences in the timing of phytoplankton growth onset, associated with variations in the timing of the sea-ice retreat. (c) 2005 Elsevier Ltd. All rights reserved.

Paulsen, ML, Seuthe L, Reigstad M, Larsen A, Cape MR, Vernet M.  2018.  Asynchronous accumulation of organic carbon and nitrogen in the Atlantic gateway to the Arctic Ocean. Frontiers in Marine Science. 5   10.3389/fmars.2018.00416   AbstractWebsite

Nitrogen (N) is the main limiting nutrient for biological production in the Arctic Ocean. While dissolved inorganic N (DIN) is well studied, the substantial pool of N bound in organic matter (OM) and its bioavailability in the system is rarely considered. Covering a full annual cycle, we here follow N and carbon (C) content in particulate (P) and dissolved (D) OM within the Atlantic water inflow to the Arctic Ocean. While particulate organic carbon (POC), particulate organic nitrogen (PON), and dissolved organic carbon (DOC) accumulated in the surface waters from January to May, the dissolved organic nitrogen (DON)-pool decreased substantially (Delta - 50 mu g N L-1). The DON reduction was greater than the simultaneous reduction in DIN (Delta - 30 mu g N L-1), demonstrating that DON is a valuable N-source supporting the growing biomass. While the accumulating POM had a C/N ratio close to Redfield, the asynchronous accumulation of C and N in the dissolved pool resulted in a drastic increase in the C/N ratio of dissolved organic molecules (DOM) during the spring bloom. This is likely due to a combination of the reduction in DON, and a high release of carbon-rich sugars from phytoplankton, as 32% of the spring primary production (PP) was dissolved. Our findings thus caution calculations of particulate PP from DIN drawdown. During post-bloom the DON pool increased threefold due to an enhanced microbial processing of OM and reduced phytoplankton production. The light absorption spectra of DOM revealed high absorption within the UV range during spring bloom indicating DOM with low molecular weight in this period. The absorption of DOM was generally lower in the winter months than in spring and summer. Our results demonstrate that the change in ecosystem function (i.e., phytoplankton species and activity, bacterial activity and grazing) in different seasons is associated with strong changes in the C/N ratios and optical character of DOM and underpin the essential role of DON for the production cycle in the Arctic.

Diaz, S, Vernet M, Paladini A, Fuenzalida H, Deferrari G, Booth CR, Cabrera S, Casiccia C, Dieguez M, Lovengreen C, Pedroni J, Rosales A, Vrsalovic J.  2011.  Availability of vitamin D photoconversion weighted UV radiation in southern South America. Photochemical & Photobiological Sciences. 10:1854-1867.   10.1039/c1pp05162h   AbstractWebsite

Ultraviolet radiation (UVR) plays a key role in several biological functions, including human health. Skin exposure to UVR is the main factor in vitamin D photoconversion. There is also evidence relating low levels of vitamin D with certain internal cancers, mainly colon, breast and prostate, as well as other diseases. Several epidemiological studies have shown an inverse relationship between the above-mentioned diseases and latitude, in accordance with the ultraviolet radiation latitudinal gradient. The aim of this study is to determine whether UV irradiance levels in the southern South America are sufficient to produce suitable levels of vitamin D year around. For this purpose, vitamin D photoconversion weighted-irradiance was analyzed between S.S. de Jujuy (24.17 degrees S, 65.02 degrees W) and Ushuaia (54 degrees 50'S, 68 degrees 18'W). In addition to irradiance, skin type and area of body exposed to sunlight are critical factors in vitamin D epidemiology. Due to a broad ethnic variability, it was assumed that the skin type in this region varies between II and V (from the most to the less sensitive). All sites except South Patagonia indicate that skin II under any condition of body area exposure and skin V when exposing head, hands, arms and legs, would produce suitable levels of vitamin D year round (except for some days in winter at North Patagonian sites). At South Patagonian sites, minimum healthy levels of vitamin D year round can be reached only by the more sensitive skin II type, if exposing head, hands, arms and legs, which is not a realistic scenario during winter. At these southern latitudes, healthy vitamin D levels would not be obtained between mid May and beginning of August if exposing only the head. Skin V with head exposure is the most critical situation; with the exception of the tropics, sun exposure would not produce suitable levels of vitamin D around winter, during a time period that varies with latitude. Analyzing the best exposure time during the day in order to obtain a suitable level of vitamin D without risk of sunburn, it was concluded that noon is best during winter, as determined previously. For skin type II when exposing head, exposure period in winter varies between 30 and 130 min, according to latitude, except for South Patagonian sites. During summer, noon seems to be a good time of day for short periods of exposure, while during leisure times, longer periods of exposure without risk of sunburn are possible at mid-morning and mid-afternoon. At 3 h from noon, solar zenith angles are almost the same for sites between the tropics and North Patagonia, and at 4 h from noon, for all sites. Then, in these cases, the necessary exposure periods varied slightly between sites, only due to meteorological differences.