Anabela A. Berasategui

Environmental regulation of the estuarine copepods Acartia tonsa and Eurytemora americana during coexistence period

The seasonal dynamics of Acartia tonsa and the invader Eurytemora americana were analysed in relation to the environmental variability occurring from April to November in the Bahia Blanca Estuary. Twice a month, the abundance of eggs, nauplii, copepodites and adults was examined and some environmental variables were recorded. Multivariate statistics (CCA) was applied to analyse the data of variables. Acartia tonsa eggs and nauplii diminished from April–May and they were almost absent between June and September, although a small larval peak could be detected from the end of July to October. All the stages of this species increased in number through spring. Eurytemora americana was registered as from June and only nauplii larvae were observed, with a peak increase during September. Copepodites and adults were observed as from July, increasing in number until peaking at the end of September. The number of all stages of this species decreased abruptly, the whole population disappearing from the plankton. The A. tonsa developmental stages were most positively correlated with temperature, photoperiod and other light variables whereas those of E. americana showed positive correlations with chlorophyll- a and salinity. The gradients of the main environmental factors likely give rise to a certain niche separation facilitating the coexistence of the two copepod populations within the period studied.

Sewage pollution effects on mesozooplankton structure in a shallow temperate estuary

The effects of a sewage effluent with no treatment on the mesozooplankton structure and the environmental quality were evaluated in the Bahía Blanca Estuary, during June to November 1995. The highest values of particulate organic matter, nutrients and specially phosphate, were observed in the effluent discharge zone. In addition, taxa richness, mesozooplankton abundance and Shannon diversity values were lower in the sewage discharge area compared with the less polluted area. Eurytemora americana and Acartia tonsa as well as larvae of Balanus glandula, Neohelice granulata and Spionidae were found in the discharge area with lower densities. These results highlight the importance of sewage effluent effects on mesozooplankton community providing background data to use in other monitoring programmes.

Planktonic food and foraging of Eubalaena australis, on Peninsula Valdés (Argentina) nursery ground

Se reportan observaciones sobre alimentacion de la ballena franca austral y zooplancton disponible, realizadas en Bahia Piramides (Golfo Nuevo). Se compararon datos de plancton, comportamiento trofico de las ballenas y temperaturasalinidad y clorofila-a registrados los dias 10 y 19 de octubre de 2005. El 19/10 la biomasa zooplanctonica fue significativamente mayor, observandose un numero alto de ballenas filtrando en superficie. Esta conducta se observo desde el 17 al 21/10. El evento de forrajeo descrito, confirma que la ballena franca se alimenta en este zona reproductiva de parches de zooplancton con una adecuada composicion y alta densidad, en primavera.

Seasonal occurrence and hatching success of benthic eggs of calanoid copepods in the Bahía Blanca Estuary, Argentina

Abstract The seasonal abundance and hatching success of calanoid benthic eggs were examined during the coexistence of Acartia tonsa and Eurytemora americana in the Bahía Blanca Estuary (BBE). The dormancy behaviour of eggs extracted from surface sediment layers was tested by simulating seasonal conditions during incubation. There was a greater abundance of benthic eggs of E. americana (≤8.68×106 eggs m−2) than of A. tonsa, the latter consistently showing low egg abundance (≤0.8×106 eggs m−2). The emergence of most E. americana nauplii occurred at 17°C after the experimental warming phase (refractory phase of 280 days), confirming the diapause character of these eggs. The emergence of the first A. tonsa nauplii from initial cold season samples occurred at 9–12°C after 60–70 days of incubation. However, a 180-day delay in hatching at temperatures ≥15°C was also observed in A. tonsa eggs from the last sampling days of the cold season, thus suggesting an intermediate behaviour between diapause and quiescence. The benthic egg bank in the inner zone of the BBE provides a temporary reservoir for both key copepods, thus contributing in their survival.

Mesozooplankton composition and spatial distribution, Nuevo Gulf, Patagonia, Argentina

The composition and spatial distribution of mesozooplankton of Nuevo Gulf, Argentina, were analyzed from surface samples taken on July, 1997. A total of 32 taxa were recorded. The highest abundances were found close to Nueva Bay, which is located nearby a growing urban population, whereas the lowest values were detected in the center of the gulf. Holoplankton dominated at all stations and evidenced a homogeneous spatial distribution. Meroplankton showed a more heterogeneous pattern. Ctenocalanus vanus was the most abundant taxon followed by Paracalanus parvus . Gastropoda veligers dominated the meroplanktonic fraction. Our results showed that the spatial distribution of the mesozooplankton seemed to be mainly influenced by the dominant hydrological circulation pattern of the region. This research establishes the first scientific basis for further studies in zooplankton communities of this important gulf, closely related to a natural protected worldwide known area declared a world heritage site by UNESCO.

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)

ABSTRACT 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.

Mesozooplankton assemblages and their relationship with environmental variables: a study case in a disturbed bay (Beagle Channel, Argentina)

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.

Heavy Metal Concentrations Found in Seston and Microplankton from an Impacted Temperate Shallow Estuary along the Southwestern Atlantic Ocean

ABSTRACT Fernández Severini, M.D.; Villagran, D.M.; Biancalana, F.; Berasategui, A.A.; Spetter, C.V.; Tartara, M.N.; Menéndez, M.C.; Guinder, V.A., and Marcovecchio, J.E., 2017. Heavy metal concentrations found in seston and microplankton from an impacted temperate shallow estuary along the southwestern Atlantic Ocean. Heavy metal concentrations (Cd, Cu, Cr, Fe, Mn, Ni, Pb, and Zn) were studied in the Bahía Blanca Estuary (BBE), one of the most anthropogenically disturbed estuaries in the SW Atlantic Ocean. This study evaluated metal concentrations in the microplankton and seston for the first time, as well as their role in the transport of contaminants in a disturbed coastal environment of the SW Atlantic. Spatial patterns of metals in suspended particulate matter (SPM; seston > 0.45 μm) and microplankton (20–200 μm) were analyzed at sampling sites located at sewage or industrial discharges and, also far from this area, during warm months in 2012 and 2013. Dissolved inorganic nutrients, particulate organic matter (POM), and chlorophyll a (Chl-a) were also analyzed. The POM and Chl-a concentrations were higher near to the sewage discharges; however, metals showed different concentrations between sampling site stations. Those located far from human disturbances showed similar levels to the sites at the sewage or industrial discharges in some cases. In general, the SPM had higher concentrations of metals than the microplankton. In particular, Cr presented important levels in this fraction, which was potentially associated with industrial discharges. On the other hand, a contrasting partition was found for Pb, Zn, and Cu that exhibited higher levels in the microplankton-net material. The high levels of Pb in the microplankton of the BBE may indicate a high availability of this metal in the environment and high uptake rates, with potential health risks to humans and marine life attributable to its toxic effects.

Phenological Changes of Blooming Diatoms Promoted by Compound Bottom-Up and Top-Down Controls

Understanding phytoplankton species-specific responses to multiple biotic and abiotic stressors is fundamental to assess phenological and structural shifts at the community level. Here, we present the case of Thalassiosira curviseriata, a winter-blooming diatom in the Bahía Blanca Estuary, Argentina, which displayed a noticeable decrease in the past decade along with conspicuous changes in phenology. We compiled interannual field data to assess compound effects of environmental variations and grazing by the invasive copepod Eurytemora americana. The two species displayed opposite trends over the period examined. The diatom decreased toward the last years, mainly during the winters, and remained relatively constant over the other seasons, while the copepod increased toward the last years, with an occurrence restricted to winter and early spring. A quantitative assessment by structural equation modeling unveiled that the observed long-term trend of T. curviseriata resulted from the synergistic effects of environmental changes driven by water temperature, salinity, and grazing. These results suggest that the shift in the abundance distribution of T. curviseriata toward higher annual ranges of temperature and salinity—as displayed by habitat association curves—constitutes a functional response to avoid seasonal overlapping with its predator in late winters. The observed changes in the timing and abundance of the blooming species resulted in conspicuous shifts in primary production pulses. Our results provide insights on mechanistic processes shaping the phenology and structure of phytoplankton blooms.

Reproductive trade-off of the copepod Acartia tonsa in a hypersaline estuary of the Southwestern Atlantic. Temporal variations in the morphology of eggs

ABSTRACT The purpose of the present work was to study the seasonal variations in egg production, morphology and hatching success in the cryptic species Acartia tonsa, taking into account variations in female size, population abundance and environmental factors in a turbid and hypersaline estuary. Sampling was performed during the austral warm (18–23°C and 32–36 salinity) and cold seasons (5–7°C; 32–38) in Bahía Blanca Estuary (BBE), Argentina, during 2007 and 2009. Field-collected females were incubated in the laboratory simulating in situ environmental conditions, and specimens from fixed samples were measured using optical and scanning electronic microscopy. Acartia tonsa’s marked seasonality in its reproductive traits was found to ensure its permanence in the water column all over the year. During the warm season, small-sized females were observed to invest their energy in the production of subitaneous eggs with high hatching success and smooth appearance (12.95 ± 2.38 eggs f−1 day−1 and specific egg production rate (SEP) of 16.57%C f−1 day−1). During the cold season, females invested C in body mass as well as in the production of resting eggs of three different morphotypes (6.56 ± 3.2 eggs f−1 day−1 and SEP of 7.37%C f−1 day−1). Although these morphotypes were found to show differences in surface ornamentation, they exhibited the same delayed hatching behaviour. The eggs with shorter spines were found to integrate the resting egg bank in BBE. Our findings confirming a delayed egg hatching behaviour and a great tolerance to low temperatures and high salinities in the A. tonsa population in BBE suggest that this possible strain is a valuable phenotype for aquaculture.