Distribution of Oikopleura Dioica (Tunicata, Appendicularia) associated with a coastal frontal system (39°- 41°s) of the SW Atlantic ocean in the spawning area of Engraulis Anchoita anchovy

Among tunicates, the small planktonic appendicularians generally comprise a significant fraction of the mesozooplankton in frontal systems. The summer 2011 distribution (vertical and spatial) of Oikopleura dioica was studied in terms of abundance, biomass, estimation of egg production and population structure in the different sectors of the El Rincón coastal front, in the light of thermal and salinity gradients. Peaks of abundance of Engraulis anchoita larvae were compared to O. dioica patterns. Samples were collected with plankton nets of 67 µm and 200 µm at two layers, below and above the thermocline depth. CTD data profiles were also recorded. During this campaign high salinity waters were predominant in the estuarine area. Conversely, a thermal stratification was found, being more marked at the external stations of the front where the highest densities and biomass of O. dioica coincided with the highest E. anchoita larvae densities. The size structure of O. dioica was also associated with the thermal gradient. The smaller sizes were found in the homogeneous area at the coast where the temperature was higher around 22ºC. This front constitutes a suitable environment for O. dioica reproduction enhancing the survival rate and growth of several small pelagic fishes such as E. anchoita.Entre os tunicados, as pequenas apendiculárias planctônicas geralmente compreendem uma fração significativa do mesozooplâncton nos sistemas frontais. Foi estudada a distribuição (vertical e espacial) durante o verão de 2011 de Oikopleura dioica, em termos de abundância, biomassa, estimativa da produção de ovos e estrutura da população em diferentes setores da frente costeiro de El Rincón, segundo os gradientes de temperatura e salinidade. Picos de abundância de larvas de Engraulis anchoita foram comparados com os padrões de O. dioica. As amostras foram coletadas com redes planctônicas de 67 e 200 µm em duas profundidades, acima e abaixo da termoclina. Também foram registrados perfis de dados obtidos com CTD. Durante essa campanha, aguas de alta salinidade foram predominantes na área estuarina. No entanto, foi encontrada uma estratificação térmica, sendo mais acentuado nas estações externas da frente, onde as maiores densidades e biomassa de O. dioica foram registradas, coincidindo também com as maiores densidades de larvas de E. anchoita. A distribuição de tamanhos de O. dioica também foi associada ao gradiente térmico. Os menores tamanhos foram encontrados na região mais homogênea da costa, onde a temperatura apresentou cerca de 22ºC. Essa frente é um ambiente propício para a reprodução de O. dioica o que favorece também o aumento da sobrevivência e o crescimento de muitas espécies de pequenos peixes pelágicos, tais como E. anchoita.Fil: Spinelli, Mariela Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; ArgentinaFil: Guerrero, Raul Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Pajaro, Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; ArgentinaFil: Capitanio, Fabiana Lia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentin

Ontogeny versus environmental forcing off the Southwest Atlantic Ocean: Nutritional condition of Fuegian sprat (Sprattus fuegensis) early stages

The Fuegian sprat, Sprattus fuegensis, plays a key trophic role in the Southwest Atlantic Ocean. Growth and survival of small pelagic fishes like sprat are strongly affected by environmental variability and can determine recruitment success. We estimated the nucleic acid composition and assessed with a standardized RNA/DNA index (sRD) the nutritional condition of 273 larvae, metamorphosing, and juvenile Fuegian sprat from two environmentally distinct habitats: the waters off Tierra del Fuego (TDF) and the Marine Protected Area Namuncurá/Burdwood Bank (MPAN/BB). A similar ontogenetic pattern, in which nucleic acid concentrations decreased and sRD increased with increasing standard length (SL) among larval stages was observed in both habitats. A higher percentage of preflexion larvae were under the sRD threshold for growth and optimal growth performance, with sRD values being significantly higher in TDF. Postflexion larvae in both habitats showed maximum sRD values, suggesting that both habitats are suitable nursery grounds. In contrast, metamorphosing and juvenile sprat (only captured in TDF) had consistently low nucleic acid concentrations and sRD values despite increasing SL. Environmental forcing (temperature, salinity, and station depth) was assessed over size-corrected larval sRD. The best model included a negative response to station depth, and the effect of processes associated with this factor are discussed. Although further analyses are needed to reveal underlying dynamics determining early development, these results comprise a baseline for future monitoring approaches on Fuegian sprat life traits and factors affecting their recruitment in this region.Fil: García Alonso, Virginia Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; ArgentinaFil: Diaz, Marina Vera. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Pajaro, Marcelo. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Capitanio, Fabiana Lia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentin

Growing Up Down South: Spatial and Temporal Variability in Early Growth of Fuegian Sprat Sprattus fuegensis From the Southwest Atlantic Ocean

The Fuegian sprat Sprattus fuegensis represents one of the most important pelagic resources in the Southwest Atlantic Ocean (SWAO), exerting a crucial ecological role as an intermediary link in Patagonian food webs. Otolith microstructure of 217 age-0 sprats were analyzed aiming to characterize growth patterns and possible environmental effects over them. Samples were gathered during three oceanographic surveys (spring 2014; autumns 2016, 2017) in Tierra del Fuego (TDF) and the Marine Protected Area Namuncurá-Burdwood Bank (MPAN-BB), the first Argentinian open-sea marine protected area. Daily growths (DG) of larvae and post-larvae were estimated by individually modeling size and otolith radius relationships through back-calculation procedures using potential and linear functions, respectively. Increment widths (IW) and DG values and trajectories were assessed for older sprats (i.e., survivors) sampled in the autumn surveys considering the habitat, year sampled and sprats’ hatching seasons, and were additionally evaluated in relation to sea-surface temperature (SST). IW and DG trajectories differed primarily according to the habitat sampled and sprats’ hatching seasons. Overall, strong coupling was detected between IW and DG trajectories with SST in both habitats. However, statistical assessment on particular comparisons showed that this general trend is not strictly invariant. Even though several results pinpointed a positive correlation between IW and DG with SST, the highest DG were estimated for summer- and autumn-born sprats sampled in 2016 in the MPAN-BB, period and habitat with the lowest SST values. These results unveil a complex relationship between spatial and temporal variability during early growth of Fuegian sprats, supplying relevant information that could be used in the creation of adequate ecosystem based management strategies in the SWAO.Fil: García Alonso, Virginia Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; ArgentinaFil: Brown, Daniel Roberto. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Pájaro, Marcelo. Instituto Nacional de Investigaciones y Desarrollo Pesquero; ArgentinaFil: Capitanio, Fabiana Lia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentin

Diversidad de copépodos en aguas costeras de la Patagonia en el Atlántico a lo largo de un ciclo anual

El objetivo de este estudio es analizar la sucesión anual del zooplancton en una estación costera en la Patagonia (Argentina), con especial énfasis en copépodos y sus posibles presas, en relación con la radiación solar y la temperatura como factores ambientales. El ciclo anual del plancton mostró dos periodos, otoño/invierno y primavera/verano. Durante el periodo otoño/invierno, la baja temperatura y la radiación se correlacionaron con la mayor abundancia de diatomeas y la mayor diversidad de copépodos. Este periodo se caracterizó por la dominancia de la cadena clásica herbívora, y el copépodo grande Calanoides carinatus dominó la comunidad. Por el contrario, durante el periodo de primavera/verano, con alta radiación y mayores niveles de temperatura, los flagelados fueron el alimento disponible para el zooplancton y se correlacionaron con las especies pequeñas de copépodos como el harpacticoideo Euterpina acutifrons. Además, la reproducción intensiva de los copépodos pequeños E. acutifrons y Paracalanus parvus se llevó a cabo principalmente en verano. Por otro lado, se encontró una alta diversidad de especies en invierno, cuando la radiación ultravioleta fue baja. El patrón temporal de los copépodos observado en nuestro estudio fue explicado por la disponibilidad de alimento y los factores ambientales (temperatura y radiación solar), aunque otros factores tales como la abundancia de los depredadores pueden ser también importantes en la modulación de la comunidad. Nuestros resultados muestran la importancia de la dinámica de la abundancia de copépodos y destaca su papel clave en las cadenas tróficas pelágicas de las aguas costeras de la Patagonia norte.The aim of this study is to analyze the annual zooplankton succession at a coastal station in Patagonia (Argentina), with special emphasis on copepods and their potential preys, using solar radiation and temperature as environmental factors. The annual plankton cycle exhibited autumn/winter and spring/summer phases. During the autumn/winter phase, low temperature and radiation were correlated with higher diatom abundance and copepod diversity. This period was characterized by a dominant classical herbivorous food web in which the large copepod Calanoides carinatus dominated the community. On the contrary, during the spring/summer period, with high radiation and temperature levels, flagellates were the dominant food available for zooplankton and correlated with smaller species of copepods such as the harpacticoid Euterpina acutifrons. Also, intensive reproduction of the small copepods E. acutifrons and Paracalanus parvus occurred mainly in summer. On the other hand, high species diversity was found in winter when the ultraviolet radiation was low. The temporal pattern of the copepods observed in our study was explained by food availability and environmental factors (temperature and solar radiation), although other factors such as predator abundance may also be important in modulating the community. Our results show the importance of copepod abundance dynamics and highlights their key role in the pelagic food web in northern Patagonian coastal waters.Fil: Spinelli, Mariela Lorena. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; ArgentinaFil: Gonçalves, Rodrigo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación Playa Unión. Estación de Fotobiología Playa Unión; ArgentinaFil: Villafañe, Virginia Estela. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación Playa Unión. Estación de Fotobiología Playa Unión; ArgentinaFil: Capitanio, Fabiana Lia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentin

Heritability of morphological and life history traits in a pelagic tunicate

Populations may adapt in response to selection pressures imposed by global environmental change. In marine zooplankton, measurements of the heritability of key life history characters, and thus the potential for evolution, are still rare. Here we demonstrate the feasibility of conducting controlled mating experiments with the dioecious appendicularian Oikopleura dioica to explore the narrow-sense heritability and genetic correlation among morphological and life history traits. At our standard laboratory conditions (15 ± 1°C, 100 μg C l–1), mature females were larger (1.213 ± 0.19 mm, mean ± SD) and lived longer (8.5 ± 2.18 d) than did males (1.115 ± 0.15 mm, 7.6 ± 2.07 d). The heritability (±SE) of morphological characters was low (trunk size, 0.37 ± 0.25; house size, 0.39 ± 0.23) to moderate (tail length, 0.50 ± 0.31). In contrast, an important life history trait, lifespan, showed high heritability (0.89 ± 0.47) and may therefore respond rapidly to selection pressure, either in the laboratory or in the wild.Fil: Lobon, Carla M.. Universidad de Oviedo; EspañaFil: Acuña, José L.. Universidad de Oviedo; EspañaFil: López Alvarez, Marcos. Universidad de Oviedo; EspañaFil: Capitanio, Fabiana Lia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Otolith morphology and feeding ecology of an Antarctic 3 nototheniid, Lepidonotothen larseni

This study is based on the analysis of the stomach content and the morphology and morphometry of the three pairs of otoliths (sagitta, asteriscus and lapillus) of Lepidonotothen larseni (Lo¨nnberg) collected at the South Shetland Islands and Antarctic Peninsula during summer, in order to find possible relationships between ontogenetic change of sagittal otolith shape and feeding ecology. Length-weight relationship resulted in a positive allometric growth, with juveniles and adults in good nutritional condition (Le Cren condition index.1), and with a decreasing trend from noon to late evening of the stomach repletion index. The stomach content consisted of several prey, with copepods and amphipods more frequent and abundant in juveniles, whereas euphausiids were in adults. The morphometric analysis of otoliths enabled us to relate different measurements with fish size, and those contributing mostly to separate juveniles from adults were the otolith and rostrum length and their percentage (R index). Juveniles proportionally showed a shorter and wider sagitta than adults reflected in a major E index because of a rounded shape and a minor R index because of a less developed rostrum. This pattern can be tentatively linked to the different habitat of juveniles and adults of this species, being respectively pelagic and epibenthic, as also evidenced by the 24 ontogenetic change of feeding habits.Fil: Curcio, Nadia Soledad. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; ArgentinaFil: Tombari, Andrea. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; ArgentinaFil: Capitanio, Fabiana Lia. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biologia Experimental y Aplicada; Argentin

Spatio-temporal dynamics of mesozooplankton in the subantarctic Beagle Channel: The case of Ushuaia Bay (Argentina)

The Beagle Channel is the southernmost South American fjord. Although it has been the focus of many biological studies, more in-depth knowledge of plankton and their linkage with environmental variables is lacking. The main objective of this study was to analyse the spatio-temporal variations in mesozooplankton assemblages of Ushuaia Bay, an ecologically and economically relevant area in the middle Beagle Channel, on the basis of samples collected during summer (March), autumn (June), winter (September) and spring (December) 2012 from environmentally different sites. Mesozooplankton composition and abundance exhibited strong seasonal variations, closely associated with the late winter–springphytoplankton bloom. The appendicularian Fritillaria borealis and the cyclopoid copepod Oithona similis were the dominant species during summer and autumn, whereas meroplanktonic larvae and the cladocerans Evadne nordmanni and Podon leuckarti dominated during late winter and spring, respectively. Mesozooplankton abundance was lower at coastal sites receiving freshwater and sewage discharges. Contrary to data reported a decade earlier, small-sized omnivorous species were dominant in Ushuaia Bay in 2012. The increased abundance of these species and decrease in the abundance of calanoids (e.g. Drepanopus forcipatus and Eurytemora americana) may reflect the natural year-to-year variability in phytoplankton structure and water physico-chemical properties. However, since this bay suffers from chronic pollution, other explanations, such as the influence of eutrophication on plankton structure, should also be considered. This study provides a baseline for future research on the effects of natural and anthropogenic environmental change on the Beagle Channel, thereby expanding our knowledge of plankton in subantarctic fjords.Fil: Presta, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; ArgentinaFil: Capitanio, Fabiana Lia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; ArgentinaFil: Hoffmeyer, Monica Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentin

Mesozooplankton succession in a sub-Antarctic bay (Beagle channel, Southern tip of South America): distinctive annual patterns between two environmentally different zones

Frequent sampling of zooplankton is essential to understand their annual dynamics. However, in polar and subpolar ecosystems, such sampling is rare. This study comparatively analysed, for the first time, the annual mesozooplankton succession in the northwest nearshore and external zones of Ushuaia Bay in the sub-Antarctic Beagle Channel by monthly sampling over two years. The nearshore zone, with shallow waters and strong continental and anthropogenic influence, was characterised by the year-round occurrence of the euryhaline copepod Eurytemoraamericana and adventitious taxa. The mesozooplankton community exhibited pronounced monthly and year-to-year variability but, as a general seasonal trend, winter assemblages were dominated by the copepod Oithona similis and adventitious nematodes, whereas the spring–summer ones were dominated by E. americana, the cladoceran Podon leuckarti and Cirripedia nauplii. In the external zone, the copepods Drepanopus forcipatus and Ctenocalanus citer were found throughout the year. The annual succession showed a clearer seasonal pattern. Main shifts in community structure occurred in late winter–spring and late summer–autumn, when a high representation of meroplankton and appendicularians was closely associated with phytoplankton blooms. The higher temporal variability in the nearshore community was partially related to variable contributions of adventitious taxa to assemblage composition and may be also reflecting stressful conditions for plankton species linked to freshwater and urban discharges reported within the bay. This study allowed filling the temporal gaps in previous research and providing a more complete picture of the annual mesozooplankton dynamics in the Beagle Channel, generating hypotheses at the community and population levels for future research.Fil: Presta, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; ArgentinaFil: Hoffmeyer, Monica Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Universidad Tecnológica Nacional. Facultad Regional Bahía Blanca; ArgentinaFil: Capitanio, Fabiana Lia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Biodiversidad y Biología Experimental y Aplicada. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Biodiversidad y Biología Experimental y Aplicada; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentin

Population structure and maturity stages of Fritillaria borealis (Appendicularia, Tunicata): seasonal cycle in Ushuaia Bay (Beagle Channel)

AbstractFritillaria borealis is a cosmopolitan species, very frequent in sub-antarctic and antarctic waters. The objective of this paper was to analyze its size structure and maturity stages at two sites in Ushuaia Bay: a coastal site exposed to anthropogenic pressure (E1) and a reference site (E2) located in the external zone of the bay. Zooplankton was collected during the 2012 seasonal cycle. The sampling method involved the use of a 67 µm-mesh net. Appendicularians were classified in four maturity stages: I) undifferentiated gonads, II) testis and ovary differentiated, III) expanded testis, IV) discharged testis, expanded ovary. Our results showed that the highest densities of F. borealisoccurred in spring and summer at both sites; coinciding with high values of chlorophyll-a. The percentage of juveniles (I and II) exhibited a spatial and temporal pattern similar to that observed for chlorophyll-a values. During spring-summer, juveniles and mature specimens (III and IV) showed a greater gonadal development than those individuals found in autumn-winter. In conclusion, the mismatching in the population structure and the pattern of densities of F. borealis between coastal and external zones would suggest the existence of two sub-populations susceptible to the influence of the anthropogenic impact in the bay