The Argentine shelf and its shelf-break (Southwestern Atlantic Ocean) are known for their high biological pro-ductivity, and as an important CO2 sink region. However, many aspects of the carbonate system dynamics in the area, especially those related to the biological activity, deserve further study. Here we investigated the mech-anisms affecting the carbonate system distributions, using in situ physical, chemical and biological observations collected along a section (COSTAL-AR) on the Northern Argentine Continental Shelf during two summer cruises in 2019. Our main goal was to evaluate the role of the microbial communities on the modulation of the carbonate system in the area. For that, we characterized (i) the distribution of the thermohaline properties, chlorophyll a, dissolved oxygen, carbonate system (pH, total alkalinity, dissolved inorganic carbon and high resolution un-derway CO2 fugacity, fCO2), dissolved inorganic nutrients, and (ii) the microbial communities (bacterioplankton, phytoplankton, and protozooplankton). Our results show that the COSTAL-AR section was likely an important CO2 sink and presented high seawater fCO2 spatial variability in both middle (272-430 mu atm) and early (211-365 mu atm) summer conditions. Phytoplankton played a key role in modulating the CO2 uptake and car-bonate system spatial variability during summer, especially in the middle and outer shelf. The main contribution to CO2 fixation was given by small cells, since the microbial community was dominated by autotrophic pico-plankton (<2 mu m; e.g. Synechococcus sp. and coccal picophytoeukaryotes). Moreover, the influence of the Shelf -break front in ruling both the seawater fCO2 distribution and biological processes was evident. These findings provide new insights on the connection between the biology and the carbonate system in this sparsely sampled area of the Southwestern Atlantic Ocean.

The “Estación Permanente de Estudios Ambientales” (EPEA, 38°28´ S 57°41´ W, Argentina) is an ecological time series of in situ observations started in 2000 aiming to assess changes in the marine environment and plankton communities under a global change scenario. Bio-optical properties are studied at EPEA since the color of the ocean undergoes temporal fluctuations, both for natural and anthropogenic causes. Here we assessed whether bio-optical properties at EPEA have changed during 2000-2017, identifying the occurrence of special events and inter-annual trends in these properties. An increasing trend in chlorophyll a concentration, possibly due to an increase in the smaller fraction of phytoplankton was observed. Although the absorption coefficient of phytoplankton did not follow a significant trend, it represented the occurrence of special events of high biomass suggesting that satellite information should be useful for the study site. The specific absorption coefficient of phytoplankton and the blue to red absorption ratio showed high values in summer and low in winter, according to the probable dominance of different size cells and their expected acclimation to the light regime. These results emphasize the relevance of periodic bio-optical in situ observations in understanding coastal ecosystems in a context of climate change.

Primary production hotspots in the marine environment occur where the combination of light, turbulence, temperature and nutrients makes the proliferation of phytoplankton possible. Satellite-derived surface chlorophyll-a distributions indicate that these conditions are frequently associated with sharp water mass transitions named "marine fronts". Given the link between primary production, consumers and ecosystem functions, marine fronts could play a key role in the production of ecosystem services (ES). Using the shelf break front in the Argentine Sea as a study case, we show that the high primary production found in the front is the main ecological feature that supports the production of tangible (fisheries) and intangible (recreation, regulation of atmospheric gases) marine ES and the reason why the provision of ES in the Argentine Sea concentrates there. This information provides support to satellite chlorophyll as a good indicator of multiple marine ES. We suggest that marine fronts could be considered as marine ES hot spots.

Dynamics of clupeiform fish populations such as anchovy are frequently impacted by environmental variations which can affect the success of the species recruitment. Herein, we have analyzed recent otolith growth rate, RNA/DNA nutritional condition index (sRD), and mortality rate of argentine anchovy larvae Engraulis anchoita from three different nursery areas in the Southwest Atlantic. We have evaluated the relationship between the environmental variables (abundance of copepod nauplii, temperature, chlorophyll-a concentration, and abundance of E. anchoita larvae) and larval endogenous variables (size, weight, age, and otolith radius) to sRD and recent growth rate. Fast larval growth rates were observed toward the northern sector of the studied area, characterized by higher temperature. High values of sRD were associated with higher nauplii abundance in the proximity of coastal fronts. The larvae with the lowest growths and lowest minimum values of nutritional condition coincided with the area where there was less abundance of nauplii and higher larval mortality. Larval size and nauplii abundance were positive explanatory factors for both recent growth rate and sRD index. Temperature had a positive effect on recent growth rate and a negative effect on sRD index. This condition index was poorly explained in terms of model fit in comparison with the growth model. The results herein provided could be significant to better understand the recruitment of the species, as to determining favorable areas for the growth and survival of anchovy larvae.

Eutrophication is the most widespread effect of urban development in coastal areas. To elucidate how nutrient loading affects the carbon pathways at the base of food chains, we quantified the carbon transfer among microbial components, from prokaryotes to microzooplankton. For this purpose, we performed two size-fractionation feeding experiments during late summer under moderate (N: 28.5 μM, P: 0.92 μM, Si: 45.8 μM) and severe (N: 173.9 μM, P: 3.5 μM, Si: 67.2 μM) cultural eutrophication in the Bahía Blanca Estuary (Argentina). In both experiments, prokaryotes were largely dominated by heterotrophic forms, small diatoms dominated among autotrophs, and heterotrophic nanoflagellates were the most abundant among protistan grazers. Under severe eutrophication, however, the average biomass was 75% lower for all autotrophic and heterotrophic components. Nutrient loading sustained a higher growth rate of heterotrophic bacteria and phytoplankton but implied poorer trophic transfer. Under moderate eutrophication, daily productivity of nanoplankton and bacteria grazed was 157% and 154%, respectively, while under severe eutrophication, this percentage dropped to 3.54% and 33.7%, respectively. In addition, under excess nutrient conditions, microzooplankton evidenced an active prey switching toward the most abundant prey (diatoms). Weak top-down control of bacterial biomass along with trophic decoupling between microzooplankton and nanoflagellates, constituted a dead-end of bacterial biomass under severe cultural eutrophication. This inefficient carbon transfer can potentially produce a positive feedback by exacerbating organic matter accumulation.

The Straits of Magallanes at the tip of South America connects the Atlantic and Pacific Oceans. The variability in the absorption characteristics by phytoplankton (aph(440)), non-pigmented particles, NPP (aNPP(440)), and chromophoric dissolved organic matter, CDOM (ay(440)), measured along the Straits in late summer 2011 (R/V Melville MV1102 cruise), was analyzed. Satellite-derived monthly PAR data showed that at the time of the cruise the western sector was exposed to a low-light environment (~ 16mol quanta m−2d−1) while the eastern sector received higher irradiance (~ 28mol quanta m−2d−1). In the Patagonian Shelf total absorption was dominated by phytoplankton (up to 76%; aph(440)=0.265m−1), while in the Atlantic Sector of the Straits, the major contributor was NPP (up to 42%; aNPP(440)=0.138m−1), and in the Pacific Sector of the Straits CDOM contributed up to 80% of the total absorption (ay(440)=0.232m−1). These changes could be related in part to the input of fresh water from glacier melting and rain in the Pacific Sector (ay(440) vs salinity rs=−0.98). The carbon biomass (C) was composed in its majority by pico-phytoplankton and secondly by nano-phytoplankton, with exception of the Atlantic Sector where the micro-phytoplankton dominated. Carbon to chlorophyll-a ratios (C:Chla) were very low throughout the Straits (average of ~ 6) because of photoacclimation to the extremely low light. Complementary pigments data obtained in spring 2003 by the BEAGLE expedition indicated the predominance of diatoms all along the Straits, but the bio-optical trend resembled the one found in late summer 2011, i.e., NPP dominated the absorption in the well mixed Atlantic Sector, phytoplankton in the Middle Sector, and CDOM in the Pacific Sector. These results emphasize that underwater light is the major factor affecting phytoplankton growth and physiology, and that prevalent physical and geochemical conditions play an important role regulating the bio-optical properties in this heterogeneous area. These effects should be considered to adjust parameters (such as C:Chla) when running biogeochemical models for this region.

Azaspiracid toxins (AZAs) have been identified in marine invertebrates and are of wide geographical distribution, but have not been reported in Argentina or ...

The demographic characteristics of marine zooplankton make it especially suitable for examining the variability of marine ecosystems. The zooplankton annual succession was studied at a permanent coastal station in the Argentine Sea (38 degrees 28S, 57 degrees 41W) in relation to physical conditions and phytoplankton size fractions. Small copepods (<1 mm total length), mainly represented by Oithona nana (Cyclopoida) and adults and copepodites of Calanoida, numerically dominated the metazooplankton throughout the year. In summer, small copepods also exceeded large copepods in biomass. Larvaceans (mostly <1 mm total length) were the second most important metazooplankton group, with strong dominance of Oikopleura dioica. The zooplankton succession exhibited two main periods throughout the year: (1) a cold winterspring period characterized by a dominant classical herbivore food web in which the large copepod Calanoides carinatus and lamellibranch larvae were associated with the lowest temperatures and highest Chl-a and microphytoplankton, and (2) a warm summer period dominated by a microbial food web in which microbial filter-feeders such as Oithona nana, Paracalanus spp., Oikopleura dioica and Penilia avirostris predominated and the highest density of picophytoplankton and lowest concentrations of Chl-a were recorded. The implications of the present findings for the growth and survival of fish larvae distributed in the study area are discussed.

Several satellite models classify phytoplankton functional types (PFT) based on cell size. In this study we used field data from the Argentine Sea on both the photosynthetic and the bio-optical properties of phytoplankton to distinguish photosynthetic and bio-optical phytoplankton types (PBPT). Cluster analyses were run using data from 70 stations sampled during 3 periods to distinguish different PBPT, and principal component analysis was used to describe them. We examined the main taxonomic composition and percentage of chl a in the <5 mu m size fraction found within the PBPT. The distribution of PBPT in relation to hourly primary production and environmental conditions was also investigated. The results showed a high degree of variability in biooptical and photosynthetic properties, e. g. the specific absorption coefficient of phytoplankton, a(ph)(B)(440), varied between 0.015 and 0.067 m(2) (mg chl a)(-1), and the maximum production at light saturation, P-m(B), varied between 0.68 and 10.05 mg C (mg chl a)(-1) h(-1). This resulted in the discrimination of 11 PBPT. Some had similar average cell sizes but differed in their bio-optical or photosynthetic characteristics, e. g. PBPT1 (with diatoms <5 mu m and Emiliania huxleyi 2-5 mu m) and PBPT6 (with diatoms <5 mu m and coccal cells similar to 2 mu m) had markedly different P-m(B) values (PBPT1: 1.20 mg C (mg chl a)(-1) h(-1) and PBPT6: 6.71 mg C (mg chl a)(-1) h(-1)). This variability in the bio-optical and physiological properties is most likely the result of adaptation by phytoplankton communities to the high heterogeneity in environmental conditions in this region. These results indicate that satellite models describing the distribution of PFT based on cell size alone will not provide a realistic representation of the phytoplankton composition in this highly productive and heterogeneous area.

Many members of Archaea, a group of prokaryotes recognized three decades ago, colonize extreme environments; however, new research has shown that Archaeans are also abundant components of plankton in the open sea, where they play a key role in the biogeochemical cycles. Although the widespread distribution of Archaea in the marine environment is well documented there are no reports on the detection of Archaea in the Southwest Atlantic Ocean. During the search for picophytoplankton sequences using eukaryotic universal primers, we retrieved archaeal rDNA sequences from surface samples collected during the spring at a fixed monitoring station (EPEA) in the Argentine Sea. From environmental DNA and using PCR methodology, two DNA fragments of about 1700 and 1450 bp were visualized after electrophoresis in agarose gels, and separately purified, cloned, and sequenced. BLAST analysis showed that sequences of the highest size corresponded to eukaryotic organisms and, unexpectedly, those of about 1460 bp corresponded to archaeal organisms. Phylogenetic analysis showed that archaeal sequences belong to Euryarchaeota of marine group II, characterized as a methanogenic lineage. This is the first report on the presence of group II Euryarchaeota sequences in environmental water samples of the Argentine Sea. The fact that Archaea sequences were amplified with primers non-specific for this group may suggest an unexpected abundance of these organisms in the early spring in the Argentine Sea.

Fil: Covacevich, Fernanda. Fundacion para Investigaciones Biologicas Aplicadas. Centro de Estudios de Biodiversidad y Biotecnologia; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina

Azadinium spinosum has been identified as a species producer of azaspiracids (AZAs), marine toxins reported to cause human poisoning etiologically similar to diarrheic shellfish poisoning. AZAs are accumulated by molluscs via food web which, in turn, may cause human poisoning after consumption of contaminated shellfish. In this study, the presence of a species of the genus Azadinium, A. cf. spinosum, is reported for the first time in the Southwest Atlantic ocean, and two blooms in northern shelf waters of Argentina are analysed. Both blooms occurred during spring in succesive years and developed along extensive areas (up to 60km transection) of the middle shelf and near the shelf break in 1990, and also near the shelf break during 1991. The extended shelf break front of the Argentine Sea developed during spring and summer is a highly productive area rich in exploited marine resources. In November 1990, a first bloom (up to 9.03×106cellsL−1) produced heavy discolorations, and morphological and taxonomical studies showed that the causing organism was a new dinoflagellate genus. During September 1991 plankton composition and abundance along a transect from the coast to the Malvinas Current were analysed. Results showed that this dinoflagellate was the most important species in middle shelf waters, with high biomass and abundance values (up to 3×106cellsL−1) surpassing those of various chain-forming diatom Thalassiosira species, typical of the spring bloom. The description of this new taxon, according to the thecal analysis performed at that time by light and scanning electron microscopy, corresponds with little morphological differences to the thecal tabulation, cell morphology and dimensions of the recently described Azadinium spinosum. Taking into account these minor differences and due to the lack of both DNA sequence data and AZAs production, we decided to name it A. cf. spinosum. The phagotrophic dinoflagellate Gyrodinium fusus has shown to be an important grazer of A. cf. spinosum during the first bloom, suggesting that its grazing activity could have acted as a modeling factor in population levels of its prey. The presence of A. cf. spinosum in this area opens several questions as that related to toxin production given the regional importance of bivalve commercial fisheries.

A strong interest in the southern Patagonian shelf has emerged in recent years, along with the increasing recognition of its high biological productivity. Knowledge of the pelagic food web structure that supports the richness of this system is still developing, but there are indications that mesozooplankton occupy a pivotal position, as consumers of smaller plankton and as vital prey for fish and squid. All plankton communities in the size 2μm–20mm, total and size-fractioned chlorophyll a (Chl a), nutrients and hydrology were surveyed simultaneously in October 2005 between 47°S–55°S. Picoplankton, nanoplankton and microplankton were taxonomically and functionally (autotrophs, heterotrophs) sorted within each size fraction. Plankton data and trophic relationships were examined through multivariate statistics. At that time fairly homogeneous thermal conditions prevailed over most of the shelf but weak saline horizontal gradients were evident. N/P ratios indicated no N or P limitation for phytoplankton. Surface concentrations of total Chl a were particularly high in the Grande Bay area at ca. 51°S near shore (28.6mgm−3) and at ca. 47°S on the shelf-break (7.7mgm−3). At both locations the contribution of the Chl a>5μm fraction was remarkably high. The dinoflagellate Prorocentrum minimum (10·106cellsL−1) and the diatom Thalassiosira cf. oceanica (1.3·106cellsL−1) were respectively blooming at these sites. Otherwise <10μm plankton prevailed overall. Copepods largely dominated the >200μm fraction. Three mesozooplankton assemblages typical of the inner, middle, and outer shelf were identified. The inner and middle shelf assemblages overlapped slightly but were spatially separated from the outer shelf community. Adults and late copepodids of Drepanopus forcipatus were typical of the inner shelf assemblage. Middle-shelf species included the copepod Ctenocalanus vanus, the amphipod Themisto gaudichaudii and the chaetognath Sagitta tasmanica, while an assortment of taxa characterized the outer sector. Latitudinal patterns in mesozooplankton community composition were less noticeable than cross-shelf patterns. No clear distribution of phytoplankton and protozooplankton assemblages was apparent when the whole <200μm plankton community structure was considered. In contrast, communities in the optimal size food for copepods (>10–200μm) were slightly different across shelf. Overall, spatial patterns of mesozooplankton and food availability matched weakly, suggesting a poor coupling between consumers and their prey communities at the time. Significant correlations were found particularly with large autotrophs and heterotrophs.

Oithona nana (Copepoda: Cyclopoida) is a widely distributed but poorly known species. The objective of this study was to estimate the seasonal variation of O. nana secondary production in temperate coastal waters off Argentina, South West Atlantic. The species occurred throughout the year, with higher abundances in spring and winter (9692-10132 ind m(-3)) than in summer and autumn (5537-8635 ind m(-3)). Sex ratio was highly skewed toward females. Total length of adults and immature stages was inversely related with temperature. Clutch size (mean +/- SD = 12 +/- 2 eggs sac(-1)) and egg diameter (mean +/- SD = 45 +/- 2 mu m) did not change throughout the year. Embryonic duration was inversely related to temperature (r(2) = 0.99). Mean (+/- SD) population-specific egg production rate (0.07 +/- 0.03 day(-1)) did not show a clear seasonal pattern; however, slightly higher values were observed in the warmest months. Oithona nana integrated annual production was 9.8 mg C m(-3), 94% of which was represented by copepodite somatic growth. The key role played by O. nana in the coastal waters of the Argentine Sea warrants further ecological studies under different oceanographic conditions.

Ultraphytoplankton (< 5 mu m) are important members of food webs in any pelagic system. Temporal succession in their community structure was studied at a coastal station (38 degrees 28'S-57 degrees 41'W), "Estacion Permanente de Estudios Ambientales (EPEA)", during summer 2001-2002. Prokaryotic and eukaryotic algae of this fraction, and small protozoa were identified, enumerated and optically characterized using a combination of methods: classic and fluorescence microscopy, flow cytometry and absorption spectra. Ultraphytoplankton contributed up to 90% of total chlorophyll a during this summer. Synechococcus dominated the community and their highest biomass was related to high temperature and stability during January. Chlorophyta coccal algae had a maximum biomass in February, when the water column was weakly stratified. Cryptophyceae, Prymnesiophyceae, Prasinophyceae, Bacillariophyceae and Chrysophyceae ultra-algae were present in variable proportions throughout the period. Variations in optical properties were significantly related to the shift from prokaryotic to eukaryotic coccal cells, which would allow the possibility of inferring phytoplankton types bio-optically. The ultraphytoplankton succession was mainly driven by physical forces, especially the degree of stability. Algae with coccal life-form strategies seem to be a major source of biogenic carbon supporting the functioning of this pelagic coastal ecosystem during summer.

The International Census of Marine Microbes (ICoMM), together with the South American and Caribbean Steering Committees of the Census of Marine Life program (CoML), supported the initiative of launching a regional lCoMM node (LACar ICoMM). This network aims at promoting discussions among scientists currently involved in marine microbial studies carried out at both the South American and the Caribbean regions, in order to evaluate the research capabilities and to identify complementary strengths and/or possibilities for enhanced collaboration, that would improve the knowledge on marine microbes and their biodiversity in both regions. We present an overview and discussion on some of the directions of current research on marine microbes in these regions. Concerning the marine phytoplankton studies, the best known taxonomic groups are diatoms and dinoflagellates. In Mexican marine waters, the number of taxa recorded to date is of about 1400. Studies dealing with bacterial, phytoplankton and/or cyanobacterial dynamics are carried out in the Caribbean coastal and oceanic marine systems, underscoring the importance of various environmental states, modulated by geographic and seasonal patterns as well as by the expression of large South American rivers. One of the main issues of this type of survey is the determination of wet and dry seasonal patterns of bacterial dynamics, in seascapes off Puerto Rico, with moderate to absent river inputs. Phytoplankton and bacterioplankton dynamics are also studied in F. Guiana coastal and shelf systems under direct Amazon influence, well known for their important fisheries resources, as well as in other South American marine systems influenced by important fresh water inputs or under upwelling conditions. Bacterial and/or picoeukaryotes diversity are assessed in particular marine systems such as coastal lagoons in Uruguay, the Rio de la Plata estuary and adjacent areas, as well as in sediments of the Oxygen Minimum Zone (OMZ) off South American Pacific coast, and in anoxic waters of the Cariaco Basin. Findings of a diverse range of pico-autotrophs (Patagonian shelf) and particular communities of big filamentous bacteria (OMZ zone off the South American Pacific) represent recent discoveries in those areas. In polluted coastal systems, bacteria with ability to degrade pesticides and hydrocarbons are currently monitored. In coastal areas of the Colombian Caribbean, 64 native marine bacterial strains were isolated from sediment samples. The oil-degrading bacteria are also studied in the Orinoco Delta, submitted to intensive oil exploitation. Furthermore, the Microbial Observatory of Rio de Janeiro (MoRio) established in Guanabara Bay (Brazil), constitutes a model for the study of threatened tropical coastal systems by exploring microbial biodiversity in different coastal systems (including unpolluted sites). The estimation of the activity and diversity of hydrocarbon and oil-degrading bacteria is assessed also in temperate waters and sediments of coastal systems of Argentina. Sharing knowledge and capabilities in common strategies would allow a better understanding of marine microbial diversity patterns in both regions. Rev. Biol. Trop. 56 (Suppl. 1): 183-214. Epub 2008 May 30.

Temporal fluctuations in appendicularian species composition, abundance, size structure, and biomass, and their relationships with physical and biological factors were studied biweekly to monthly from March 2000 to April 2001 at a coastal station (38 degrees 28'S, 57 degrees 41'W) off Argentina, SW Atlantic Ocean. The highest abundances and biomasses were recorded during spring-summer with a maximum in early January (4369 ind m(-3) = 2321 mu g C m(-3)). Secondary production was 76 mg C m(-3) yr(-1) and house production was 123 mg C m(-3) yr(-1) Abundance of Fritillaria borealis Lohmann, 1896 was related to temperature changes, being more abundant during fall-winter; however, we measured only low biomasses. Appendicularia sicula Fol, 1874 and Oikopleura fusiformis Fol, 1872 appeared during summer and autumn, but their abundances were low. Oikopleura dioica Fol, 1872 was present all year and was the dominant species. When chlorophyll a concentration was high, and copepod abundance was low (fall-winter period), both juvenile and adult O. dioica were abundant in all of the samples. During the spring-summer period (low chlorophyll a concentration) a high predominance of adult animals (up to 1400 mu m TL) was observed, suggesting a strong predation by copepods upon O. dioica eggs and juveniles. However, further field evidence is needed to test this hypothesis.