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Ziegler, AF, Smith CR, Edwards KF, Vernet M.  2017.  Glacial dropstones: islands enhancing seafloor species richness of benthic megafauna in West Antarctic Peninsula fjords. Marine Ecology Progress Series. 583:1-14.   10.3354/meps12363   AbstractWebsite

The West Antarctic Peninsula (WAP) margin is dominated by glaciomarine fjords and has experienced rapid climate warming in recent de cades. Glacial calving along the peninsula delivers icerafted debris (e.g. dropstones) to heavily sedimented fjord basins and the open continental shelf. Dropstones provide hard substrate, increase habitat heterogeneity, and may function as island habitats surrounded by mud. We used seafloor photographic transects to evaluate the distribution and community structure of Antarctic hard-substrate megafauna and the role of dropstones as island habitats in 3 WAP fjords and at 3 nearby shelf stations. Several lines of evidence indicate that dropstones function as island habitats; their communities adhere to principles of island biogeography theory with (1) a positive correlation between dropstone size and species richness, (2) an increase in the proportion of colonized dropstones with increasing dropstone size, and (3) a species-area scaling exponent consistent with island habitats measured globally. Previous work on the soft-sediment megafauna of this region found strong differences in community composition between fjord and shelf sites, whereas we found that dropstone communities differed within sites at small scales (1 km and smaller). We identified 73 megafaunal morphotypes associated with dropstones, 29 of which were not previously documented in the soft-sediment mega fauna. While dropstones constituted < 1% of the total seafloor area surveyed, they contributed 20% of the overall species richness of WAP megabenthos at depths of 437-724 m. WAP dropstone communities adhere to key principles of island biogeography theory, contribute environmental heterogeneity, and increase biodiversity in the WAP region.

Dierssen, HM, Smith RC, Vernet M.  2002.  Glacial meltwater dynamics in coastal waters west of the Antarctic peninsula. Proceedings of the National Academy of Sciences of the United States of America. 99:1790-1795.   10.1073/pnas.032206999   AbstractWebsite

The annual advance and retreat of sea ice has been considered a major physical determinant of spatial and temporal changes in the structure of the Antarctic coastal marine ecosystem. However, the role of glacial meltwater on the hydrography of the Antarctic Peninsula ecosystem has been largely ignored, and the resulting biological effects have only been considered within a few kilometers from shore. Through several lines of evidence collected in conjunction with the Palmer Station Long-Term Ecological Research Project, we show that the freshening and warming of the coastal surface water over the summer months is influenced not solely by sea ice melt, as suggested by the literature, but largely by the influx of glacial meltwater. Moreover, the seasonal variability in the amount and extent of the glacial meltwater plume plays a critical role in the functioning of the biota by influencing the physical dynamics of the water (e.g., water column stratification, nearshore turbidity). From nearly a decade of observations (19911999), the presence of surface meltwater is correlated not only to phytoplankton blooms nearshore, but spatially over 100 km offshore. The amount of meltwater will also have important secondary effects on the ecosystem by influencing the timing of sea ice formation. Because air temperatures are statistically increasing along the Antarctic Peninsula region, the presence of glacial meltwater is likely to become more prevalent in these surface waters and continue to play an ever-increasing role in driving this fragile ecosystem.

Diaz, SB, Paladini AA, Braile HG, Dieguez MC, Deferrari GA, Vernet M, Vrsalovic J.  2014.  Global and direct UV irradiance variation in the Nahuel Huapi National Park (Patagonia, Argentina) after the eruption of Puyehue-Cordon Caulle (Chile). Journal of Atmospheric and Solar-Terrestrial Physics. 112:47-56.   10.1016/j.jastp.2014.02.006   AbstractWebsite

On June 4th, 2011, the Puyehue-Cordon Caulle volcanic complex (40 degrees 35'25"S 72 degrees 07'02"W, Chile) started eruption, sending ash 45,000 feet into the atmosphere. After the initial period, the eruption continued for several months, with less intensity. Changes in global irradiance in the UV-B and UV-A, and direct irradiance and AOD in the UV-A, as consequence of the eruption, were studied. Global irradiance has been permanently measured at the Laboratory of Photobiology (LPh) (41.13S, 71.42W, 804 msl) since 1998. In addition, in the frame of a project to study altitude effect on direct and global irradiance, field campaigns were performed during September 17th to 23rd, 2010 and September 14th to 18th, 2011, in the region of the Nahuel Huapi National Park, near 100 km from the eruption. In those periods, simultaneous measurements of direct and global irradiance and aerosol optical depth (ACID) were carried out at three sites: Laboratory of Photobiology (LPh), Mt Otto (41.15S, 71.38W, 1386 msl) and Mt Catedral (41.17S, 71.48W, 1930 msl). The analysis of aerosols in 2011, three to four month after the eruption started, showed the presence of larger particles and more variability than in 2010, at all sites. Global irradiance, at LPh, also exhibited larger variability, compared to 1999, when no eruption or any other event that could have produced major changes in aerosols occurred. The mean decrease, as consequence of the volcano activity, at LPh, was around 20%, at 305 nm and closed to 10%, at 320 nm. At 380 nm, the decrease was very small and not statistically significant, although in particular days, with large aerosol load, a significant decrease was observed. Direct irradiance, in the UV-A, showed larger decrease than global irradiance. The effect of the eruption was more pronounced at the low altitude site. (c) 2014 Elsevier Ltd. All rights reserved.

Haberman, KL, Ross RM, Quetin LB, Vernet M, Nevitt GA, Kozlowski W.  2002.  Grazing by Antarctic krill Euphausia superba on Phaeocystis antarctica: an immunochemical approach. Marine Ecology-Progress Series. 241:139-149.   10.3354/meps241139   AbstractWebsite

An enzyme-linked immunosorbent assay (ELISA) for Phaeocystis antarctica was developed and used to determine the extent of grazing by Euphausia superba on this prymnesiophyte. First, a specific antiserum to P. antarctica was produced and tested on phytoplankton cells and extracts. Then, the antiserum was tested on extracts of stomachs from krill fed diets of either Thalassiosira antarctica or P. antarctica, and also on mixtures of these extracts. The antiserum response was a logarithmic function of the percentage of the extract mixture that came from P. antarctica-fed krill. In the field, the antiserum was tested on krill collected during December 1996 to February 1997 in the Palmer Long-Term Ecological Research study region west of the Antarctic Peninsula. The antiserum. response suggested that krill ingested P. antarctica at 20% of the stations tested, most of them in nearshore areas. Krill grazed P. antarctica only at stations where concentrations of the marker pigment for P. antarctica, 19'-hexanoyloxyfucoxanthin, were above 0.150 mug l(-1). At these stations, the percentage of P. antarctica in the krill stomach extracts was positively correlated with chlorophyll a concentrations, but negatively correlated with the proportion of P. antarctica within the phytoplankton community. Overall, P. antarctica appeared to comprise a relatively small proportion of the phytoplankton utilized by krill, both spatially and temporally.

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.