The rapid increase in atmospheric temperature detected in the last decades in the Western Antarctic Peninsula was accompanied by a strong glacier retreat and an increase in production of melting ...water, as well as changes in the sea-ice dynamic. The objective of this study was to analyze the succession of micro- and mesozooplankton during a warm annual cycle (December 2010-December 2011) in an Antarctic coastal environment (Potter Cove). The biomass of zooplankton body size classes was used to predict predator-prey size relationships (i.e., to test bottom-up/top-down control effects) using a Multiple Linear Regression Analysis. The micro- and mesozooplanktonic successions were graphically analyzed to detect the influence of environmental periods (defined by the degree of glacial melting, sea-ice freezing and sea-ice melting) on coupling/uncoupling planktonic biomass curves associated to possible predator-prey size relationship scenarios. At the beginning of the glacial melting, medium and large mesozooplankton (calanoid copepods, Euphausia superba, and Salpa thompsoni) exert a top-down control on Chl-a and microzooplankton. Stratification of the water column benefitted the availability of adequate food-size (Chl-a <20) for large microzooplankton (tintinnids) development observed during fall. High abundance of omnivores mesozooplankton (Oithona similis and furcilia of E. superba) during sea-ice freezing periods would be due to the presence of available heterotrophic food under or within the sea ice. Finally, the increase in microzooplankton abundance in the middle of spring, when sea-ice melting starts, corresponded to small and medium dinoflagellates and ciliates species, which were possibly part of the biota of sea ice. If glacier retreat continues and the duration and thickness of the sea ice layer fluctuates as predicted by climate models, our results predict a future scenario regarding the zooplankton succession in Antarctic coastal environments.
Península Valdés (PV) is the most austral calving ground for the SW Atlantic population of Eubalaena australis. Recent studies indicate that E. australis often feeds in PV mainly in late September ...and October. A microscopic analysis of food chitin remains found in five whale faeces was performed in the present study in an attempt to obtain baseline knowledge about trophic ecology and degree of use of plankton food available for whales in PV during spring (September–December). The remains in faeces from stranded and live individuals included copepods, other zooplankton and centric diatoms, all of which were characterized. Copepod remains were found to be dominant. Scanning electron and confocal laser scanning microscopes were used for comparative analyses between the mandibular gnathobases found in whale faeces and those obtained from preserved specimens. Mandibular gnathobases were the same in structure and morphometry as those obtained from preserved Calanus australis (copepodites 4–6). The positive relationship observed between the total length and width of the mandibular gnathobases edge of C. australis and those found in faeces allowed us to infer the developmental stages of the copepods ingested by E. australis. Our results indicate – for the first time – the relevant role of C. australis copepodite 5 as main prey for E. australis in PV during the calving season. Copepodite 5 of C. australis accumulates energy-rich lipids. This is energetically attractive for whales and it is the potential reason why E. australis feeds mainly on dense patches dominated by this developmental stage of C. australis.
•Península Valdés (PV) is an important calving ground for Eubalaena australis.•E. australis has experienced high calf mortality events in recent years at PV.•The deaths of E. australis calves in PV ...could be related to phycotoxins.•Evidence of transfer of domoic acid (DA) through pelagic food web to E. australis was documented.•Results indicate that DA could be associated with recent calf deaths at PV.
The gulfs that surround Península Valdés (PV), Golfo Nuevo and Golfo San José in Argentina, are important calving grounds for the southern right whale Eubalaena australis. However, high calf mortality events in recent years could be associated with phycotoxin exposure. The present study evaluated the transfer of domoic acid (DA) from Pseudo-nitzschia spp., potential producers of DA, to living and dead right whales via zooplanktonic vectors, while the whales are on their calving ground at PV. Phytoplankton and mesozooplankton (primary prey of the right whales at PV and potential grazers of Pseudo-nitzschia cells) were collected during the 2015 whale season and analyzed for species composition and abundance. DA was measured in plankton and fecal whale samples (collected during whale seasons 2013, 2014 and 2015) using liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS). The genus Pseudo-nitzschia was present in both gulfs with abundances ranging from 4.4×102 and 4.56×105 cell l−1. Pseudo-nitzschia australis had the highest abundance with up to 4.56×105 cell l−1. DA in phytoplankton was generally low, with the exception of samples collected during a P. australis bloom. No clear correlation was found between DA in phytoplankton and mesozooplankton samples. The predominance of copepods in mesozooplankton samples indicates that they were the primary vector for the transfer of DA from Pseudo-nitzschia spp. to higher trophic levels. High levels of DA were detected in four whale fecal samples (ranging from 0.30 to 710μgg−1 dry weight of fecal sample or from 0.05 and 113.6μgg−1 wet weight assuming a mean water content of 84%). The maximum level of DA detected in fecal samples (710μg DA g−1 dry weight of fecal sample) is the highest reported in southern right whales to date. The current findings demonstrate for the first time that southern right whales, E. australis, are exposed to DA via copepods as vectors during their calving season in the gulfs of PV.
To evaluate whether alterations in the multidrug-resistance (MDR)-1 gene correlate with intestinal MDR-1 expression and uptake of orally administered P-glycoprotein (PGP) substrates, we analyzed the ...MDR-1 sequence in 21 volunteers whose PGP expression and function in the duodenum had been determined by Western blots and quantitative immunohistology (n = 21) or by plasma concentrations after orally administered digoxin (n = 8 + 14). We observed a significant correlation of a polymorphism in exon 26 (C3435T) of MDR-1 with expression levels and function of MDR-1. Individuals homozygous for this polymorphism had significantly lower duodenal MDR-1 expression and the highest digoxin plasma levels. Homozygosity for this variant was observed in 24% of our sample population (n = 188). This polymorphism is expected to affect the absorption and tissue concentrations of numerous other substrates of MDR-1.
Menéndez, M.C.; Delgado, A.L.; Berasategui, A.A.; Piccolo, M.C., and Hoffmeyer, M.S., 2016. Seasonal and tidal dynamics of water temperature, salinity, chlorophyll-a, suspended particulate matter, ...particulate organic matter, and zooplankton abundance in a shallow, mixed estuary (Bahía Blanca, Argentina). Estuaries are characterized by a variety of interrelated, abiotic and biotic, structural components and intensive physical, chemical, and biological processes. The aim of this study was to investigate the seasonal- and tidal-mediated variability in water temperature, salinity, suspended particulate matter (SPM), particulate organic matter (POM), chlorophyll-a (Chl-a), and zooplankton abundance in the Bahía Blanca estuary, Argentina. The underlying mechanisms responsible for the observed variability are also discussed. Sampling was carried out every two months (December 2004–April 2006) during 14-h tidal cycles in a fixed station located in the inner zone of the estuary. Vertical profiles of temperature and salinity and water samples were obtained at the surface and the bottom to determine SPM, POM, Chl-a, and zooplankton. SPM (97.3 ± 6.9 mg L−1) showed a strong seasonality, mainly attributed to biological activity. POM concentration (1539 ± 107.6 mgC m−1) was high, possibly derived from vascular plants and benthic microalgae. Chl-a (6.91 ± 0.73 mg m−3) and zooplankton (2024.23 ± 9.16 individuals m−3) also showed a seasonal pattern, with higher concentrations in the summer. During the tidal cycle, the highest amounts of the measured variables were observed during the ebb tide. The results highlight the strong variability in the physicochemical and biological variables at different time scales in mesotidal, temperate estuaries. It is essential to take into account this variability in any monitoring program performed in a temperate system dominated by such a tidal regime.
This study focused on the seasonal and spatial analysis of the mesozooplankton community in a human-impacted subantarctic bay in Argentina and aimed to detect assemblages associated with ...environmental variability. Mesozooplankton samples and environmental data were obtained in the Ushuaia Bay (UB) seasonally, from August 2004 to June 2005, and spatially, from coastal (more polluted), middle (less influenced) and open sea water (free polluted) sampling stations. Remarkable seasonal changes on the mesozooplankton community were observed. Nitrogenated nutrients, chlorophyll a, salinity and temperature were the prevailing environmental conditions likely associated with the different mesozooplankton assemblages found in the bay. The copepods Eurytemora americana, Acartia tonsa, Podon leuckarti and Nematoda were particularly observed on the northwest coast of the bay, characterized by the highest level of urban pollution, eutrophicated by sewage and freshwater inputs from the Encerrada Bay which is connected to it. The stations situated in the northeast area, mostly influenced by freshwater input from rivers and glacier melting, showed low mesozooplankton abundances and an important contribution of adventitious plankton. The copepods Ctenocalanus citer, Clausocalanus brevipes and Drepanopus forcipatus were mostly observed at the stations located near the Beagle Channel, characterized by open sea and free polluted waters. Our findings suggest that the variations observed in the mesozooplankton assemblages in the UB seem to be modulated by environmental variables associated with the anthropogenic influence, clearly detected on the coast of the bay. Certain opportunistic species such as A. tonsa and E. americana could be postulated as potential bioindicators of water quality in subantarctic coastal ecosystems.
•Anthropogenic eutrophication alters microplankton abundance and structure through changes in nutrient stoichiometry.•Microplankton showed lower reactivity potential to nutrient pulses in heavily ...eutrophic systems.•Effects of climate-related variables are magnified in heavily eutrophic systems.
Quantifying biotic feedbacks in response to environmental signals is fundamental to assess ecosystem perturbation. We analyzed the joint effects of eutrophication, derived from sewage pollution, and climate at the base of the pelagic food web in the Bahía Blanca Estuary (SW Atlantic Ocean). A two-year survey of environmental conditions and microplankton communities was conducted in two sites affected by contrasting anthropogenic eutrophication conditions. Under severe eutrophication, we found higher phytoplankton abundance consistently dominated by smaller sized, non siliceous species, while microzooplankton abundance remained lower and nutrient stoichiometry showed conspicuous deviations from the Redfield ratio. Phytoplankton growth in such conditions appeared controlled by phosphorous. In turn, microplankton biomass and phytoplankton size ratio (<20μm:>20μm) displayed a saturation relationship with nutrients in the highly eutrophic area, although mean phytoplankton growth was similar in both eutrophic systems. The strength of links within the estuarine network, quantified through path analysis, showed enhanced relationships under larger anthropogenic eutrophication, which fostered the climate influence on microplankton communities. Our results show conspicuous effects of severe sewage pollution on the ecological stoichiometry, i.e., N and P excess with respect to Si, altering nutrient ratios for microplankton communities. This warns on wide consequences on food web dynamics and ultimately in ecosystem assets of coastal pelagic environments.
Dutto, M. S., López Abbate, M. C., Biancalana, F., Berasategui, A. A., and Hoffmeyer, M. S. 2012. The impact of sewage on environmental quality and the mesozooplankton community in a highly eutrophic ...estuary in Argentina. – ICES Journal of Marine Science, 69: 399–409. Eutrophication caused by human sewage is a growing phenomenon along coasts. Mesozooplankton abundance, community structure, and environmental quality were compared at two sites in the inner Bahía Blanca Estuary (BBE), Argentina, one receiving regional sewage discharge (Canal Vieja), and the other a non-impacted area (Bahía del Medio). Comparisons of mean abundance and multivariate analyses were performed to detect spatial and temporal variations in both environmental and biotic variables. Significantly higher amounts of nitrogen and phosphorus and lower oxygen and pH were recorded at Canal Vieja. Larvae of the detritivorous crab Neohelice granulata were more abundant at Canal Vieja, whereas the common estuarine copepod species Acartia tonsa was more abundant at Bahía del Medio, where the mesozooplankton community was typical for the estuary. Although mesozooplankton is likely to be adapted to the high organic matter content in the BBE, the environmental conditions at Canal Vieja appear to favour Neohelice granulata, and this species should be considered as a potential indicator of the impact of sewage in future monitoring programmes. Particulate organic carbon and chlorophyll a were not influenced by organic loading in this naturally eutrophic estuary.
Rapid climate-driven melting of coastal glaciers may control plankton dynamics in the Western Antarctic Peninsula. It is known that in Potter Cove, 25 de Mayo/King George Island, phytoplankton is ...tightly coupled to meltwater input. However, no information on zooplankton is available in this regard. The aim of this study was therefore to examine the structure and dynamics of microzooplankton and mesozooplankton in two zones (the inner and outer Potter Cove) differently impacted by glacier melting during two contrasting austral summers (2010 and 2011). Microzooplankton composition differed between the two zones and years analyzed, and its total biomass was observed to be highest far from the glacier influence and during 2010. Mesozooplankton composition and biomass were similar in the two zones and years analyzed. Colder than usual conditions in the summer of 2010 prevented glacier melting, thus favoring the development of an exceptional micro-sized diatom bloom (~190 µg C l
−1
and >15 µg l
−1
chlorophyll
a
), which was tightly followed by a maximum in large copepod abundance. After the bloom and in coincidence with intense glacier melting, large diatoms and large copepods were observed to be replaced by nanophytoplankton and microzooplankton (aloricate ciliates and dinoflagellates), respectively. In 2011, low phytoplankton abundance, probably controlled by high tintinnid biomass, was observed as a result of warmer temperatures than 2010 and low-salinity waters. Large copepods appeared to have exerted a high grazing pressure on aloricate ciliates and heterotrophic dinoflagellates in 2011. Our results suggest that whereas the joint effect of water temperature, salinity and phytoplankton availability as well as composition could be of primary relevance in structuring micro- and mesozooplankton community, zooplankton could be of secondary relevance in controlling phytoplankton biomass in Potter Cove during the two summers analyzed.
PDF
