Benthic invertebrates in the surf zone of exposed sandy beaches represent important links for energy circulation between benthic and pelagic food webs. This work assesses the trophic ecology of co-occurring epi- and hyper-benthic invertebrates inhabiting the surf zone of sandy beaches located close to an estuarine mouth. It illustrates that different sources of organic matter induce changes in resource utilization. The trophic positions, and the niche width and overlap of species were described using δ13C and δ15N stable isotope analysis. The contribution of different sources to the particulate organic matter was quantified through stable isotopes analysis and fatty acids profiles. Shifts in the trophic niches of dominant species reflected a decrease in the contribution of estuarine carbon to the diets along the coast. This change in contribution of estuarine carbon also influenced trophic niche properties: more diverse resources availability resulted in narrower niches without overlap while less diverse resources resulted in broad isotopic niches and a highest overlap. Results show that spatial variations in the availability of resources can modify carbon pathways and trophic interactions in coastal food webs. Whenever resources are abundant, species display a more specialized diet while food scarcity leads to broader diets, a pattern consistent with the optimal foraging theory. This resource maximization behavior commonly observed in nature is also occurring in surf zone ecosystems.

Estuarine copepods are considered ecological relevant components in the marine trophic webs and have high phenotypic plasticity and adaptability to face the environmental variations coastal marine ecosystems typically show. This work aims to assess the Acartia tonsa food availability, egg production, and female survival in an urban-industrial sewage discharge site (Canal Vieja, CV) and a non-disturbed site by sewage (Bahía del Medio, BM) from the Bahía Blanca Estuary, Argentina. Acartia tonsa females and microplankton samples, used as natural food, were taken during the austral warm season 2008–2009. The experimental incubations of the females were performed in a laboratory simulating the in situ environmental conditions. The microplankton showed different composition and abundance values between both studied sites. The survival of females showed significant differences between the sites, but the egg production did not show clear differences between them. A positive correlation was found among egg production, diatom, and tintinnid-ciliate abundances. A low female survival (16.5%) was observed when high ammonium concentrations (35.15μM) were recorded at CV. The concentration of nitrogenous nutrients, especially ammonium, along with pH and turbidity, were the drivers explaining the variation in the reproductive performance and survival of A. tonsa. Our findings further understand the reproductive performance, plasticity, and survival of key planktonic organisms in polluted coastal areas.

Ctenophora are important components of marine ecosystems. However, the South-western Atlantic and Sub Antarctic region are still one of the least studied region in the world. We report the species composition and spatial distribution of Ctenophora and reviewed the studies performed in this region. New data obtained between 1910 and 2019, encompassing an area of c. 7 million km(2)(32-60 degrees S, 34-70 degrees W) were presented and published information was added. We confirm the occurrence of nine taxa, seven of which have been previously reported in the region.Mnemiopsis leidyiandPleurobrachia pileuswere the most frequent and numerous species.Beroe ovatawas frequently observed but reaching high numbers only occasionally.Beroe cucumiswas always observed in low numbers.Callianira antarctica,Lampea pancerinaandMertensia ovumhave been reported few times as single individuals.EurhamphaeaandBeroesp. were found for the first time in the study region. This overview represents the state of the art in ctenophore research for the studied region, providing new knowledge on species composition and patterns of spatial distribution in the area.

Editor: Rubens M. Lopes Marine invasions are a growing threat challenging the preservation of ocean biodiversity. These invasions occur in a context of global change due to increasing anthropogenic activities, with maritime transport being the main mechanism of introduction of aquatic invertebrates (Grigorovich et al., 2003). Shipping serves as a vector for the dispersal of organisms through ballast water, sediment, or hull fouling (Minchin & Gollash, 2002). Aquaculture and aquarium trade are also vectors of transfer and introduction of alien species (Minchin, 2007; Grosholz et al., 2015). Among marine species, hydrozoans are considered successful invaders due to their environmental flexibility, small size, wide variety of life cycles, and reproductive processes that allow them to be easily transported and to establish in new regions (Graham & Bayha, 2008; Rilov and Crooks, 2009; Folino-Rorem et al., 2008). However, due to their relatively inconspicuous and seemingly low environmental impact on ecosystems, hydrozoans may be overlooked in invasion biology (Miglietta and Lessios, 2008). Nevertheless, there are several examples of invasions by hydromedusa species in different ecosystems around the world, including the cases of Maeotias marginata, Moerisia lyonsi, Gonionemus vertens, and Blackfordia virginica, among others (Ma & Purcell, 2005, Gaynor et al., 2016, Harrison et al., 2013). Blackfordia virginica (Hydrozoa, Leptomedusae) is thought to be native to the Black and Caspian Sea and is recognized to be a successful invader of estuarine coastal waters around the world (Europe, North America, Asia, and Central America) (Bayha & Graham, 2014). In the Southwestern Atlantic, it was recorded for the first time in the northeast of Brazil (Paranaguá, 1963) and then, nearly four decades later, in the Rio de la Plata estuary on the Argentine shelf (Genzano et al., 2006) and in different estuarine ecosystems along the southern and southeastern Brazilian coast (Nogueira & Oliveira, 2006). This hydromedusa is considered an euryhaline species, which has been shown to tolerate a wide range of salinity, from 2.2 to 36 (Moore, 1987). It displays a metagenetic life cycle comprised of a benthic polyp phase, which reproduces asexually, and a planktonic sexual phase, the medusa. Pelagic medusae and benthic polyps have been observed in brackish water ecosystems, and polyps have also been found in estuaries and coastal saltwater swamps (Bardi & Marques 2009). In several tropical and temperate estuaries, B. virginica occurs seasonally, developing higher biomasses and abundances at temperatures ≥ 14 ° C (e.g. Wintzer et al., 2013; Freire et al., 2013; Jaspers et al., 2018). It feeds on adults and nauplii of copepods, barnacle nauplii (Mills & Sommer, 1995), and fish larvae (Wintzer et al., 2013). Morais et al. (2015) demonstrated that it also feed on phytoplankton and ciliates and is able to maintain a good nutritional condition during periods of low availability of metazooplanktonic prey, basing its diet on sources of particulate organic matter. © 2021 The authors. This is an open access article distributed under the terms of the Creative Commons license. Ocean and Coastal Research http://doi.org/10.1590/2675-2824069.20013vmvm Brief CommuniCation

The variability of the zooplankton community over a spatial and a tidal scale, the relationship between physico-chemical variables, and the abundance of zooplankton were studied in the temperate and turbid Bahía Blanca Estuary (Southwestern Atlantic, Argentina). Samples were taken by pumps during 12-h tidal cycles, at 3-h intervals, from two depths and three sites across the main channel in the inner and middle estuary zones. The zooplankton was dominated by the copepods Acartia tonsa and Euterpina acutifrons, and larvae of the invasive Pacific oyster Crassostrea gigas. The physico-chemical variables that most influenced the zooplankton community were salinity, temperature, suspended particulate matter, and chlorophyll a Most taxa showed higher abundances in the inner estuary, which corresponds to a turbid and shallow area. The abundance of A. tonsa was higher in the inner estuary while that of E. acutifrons was higher in the middle estuary. This spatial distribution is consistent with the tidal distribution of these species as in the inner estuary the abundance of A. tonsa peaked at ebb tide and that of E. acutifrons peaked at flood tide. Significant differences in the zooplankton community structure both across the channel and between depths were detected by multivariate analyses, but no clear patterns were found in the abundance of each taxon by a species-level analysis. The results provide insight into the patterns of zooplankton distribution and abundance in a temperate, turbid, and human-impacted coastal ecosystem, considering different spatial and short-term scales. These results will be useful to design efficient sampling programmes in highly dynamic environments.

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.

Plankton composition and density, and domoic acid (DA) content in microplankton and mesozooplankton were assessed over the northern Patagonian coastal shelf in late austral summer 2013. Maximum values of DA in these two plankton fractions as well as maximum densities of both Pseudo-nitzschia spp. (mainly the toxigenic P. australis) and DA potential vectors were only detected on the southern coast of San Matías Gulf and the eastern coast of Valdés Peninsula. In this zone, waters were characterized by low temperature, high nitrate, and intermediate values of silicic acid and phosphate. Based on the high association between the DA values recorded and the values of either micro- and mesozooplankton grazer density or biomass, we inferred that DA transfer from Pseudo-nitzschia spp. occurred largely through the small copepods Euterpina acutifrons and Oithona nana, Calanidae nauplii and Calanidae copepodites, Noctiluca scintillans, and euphausiid developmental stages. Small copepods, Calanidae nauplii and copepodites, and cladocerans were proposed as novel DA vectors although this suggestion requires experimental confirmation. This study provides the first lines of evidence of the co-occurrence of Pseudo-nitzschia spp. blooms with DA production and accumulation in mesozooplanktonic grazers at the base of the food web and of the environmental and oceanographic conditions that seem to favor these processes over the northern Patagonian shelf coasts.

[This corrects the article DOI: 10.1371/journal.pone.0217628.].

Solitary macroscopic polyps are rare, and ecological information about them, such as diet and feeding rates is scarce worldwide. Here we describe the population of the solitary and seasonal polyps of Corymorpha januarii found in the Bahía Blanca Estuary, Argentina, and provide one of the first approaches to define their feeding ecology by gut content analysis. We analyzed the substrate and the accompanying benthic components, and provided in situ observations as well as observations on polyps kept in aquarium. A mean of 4 types of trophic items per polyp and 13.33 consumed prey items per polyp were obtained, representing a daily carbon consumption of 1.8 mg C per polyp per day and 75 mg C per square meter per day when considering polyp densities. The daily mass-specific ingestion rate was 20.5 % of polyp biomass. Polyps of C. januarii showed a variable diet composed mainly of organic matter and zooplanktonic prey, and probably selected copepods, mysids, and other zooplanktonic prey of lower or no swimming capacity (e.g., barnacle larvae and invertebrates, and fish eggs). The diversity of the prey ingested indicates that C. januarii is highly adaptable to changing environmental conditions, and this organism may have a significant role in energy transfer in estuarine waters.

Fluctuations in abundance of dominant species can cause competitive release of resources with consequences on community structure and functioning. In the present study, changes in the intertidal macroinfauna community of an exposed sandy beach were evaluated during two contrasting periods characterized by low and high densities of the yellow clam Amarilladesma mactroides. The increase in clam abundance and biomass was associated with a significant decrease in abundance of the rest of the community. In particular, a decline was observed for the pea crab Austinixa patagoniensis, a commensal species that lives in the burrows of the shrimp Sergio mirim. Our study demonstrates that fluctuations in clam abundance lead to long-term changes in community structure, suggesting the presence of competitive interactions. The environmental stability over the two periods strengthens the hypothesis that the competition between species is crucial for shaping the ecological community. Stable isotope analysis allows discarding trophic competition as mechanism of exclusion. Image maps reveal complementary distribution of species, showing the relevance of the spatial competition, which is mediated by changes in abundance of a third species. Indeed, high densities of A. mactroides reduce the available area for the establishment of the S. mirim burrows, limiting the foraging behavior of its commensal, the pea crab. Such an interaction drives density-dependent exclusion of the pea crab from the intertidal zone following the establishment of the yellow clam population. This study illustrates that spatial competition triggered by the increase of a bed-forming species can have community-wide consequences in exposed sandy beaches.

The present study shows the results of laboratory experiments addressing the effects of different water qualities on E. americana's fecundity and survival. The study was carried out with cultured females, incubated under different water qualities and controlled conditions during ten days (7 +/- 2 degrees C, 14 h light, salinity of 32 +/- 2, Tetraselmis sp. and Nannochloropsis sp. as food). Four treatments were established: P = subsurface water from sewage plume of Bahia Blanca city, D = the dissolved phase of P, I = bottom water in the sewage discharge point of Bahia Blanca city, and C = water from the low-impacted area of Monte Hermoso, used as a control treatment. Egg production, number of nauplii, number of faecal pellets, survival and fertility-state of females were evaluated. The differences and relationships among copepod factors, environmental variables and pollutants levels (cadmium, lead, copper, zinc, chrome and ammonium-phosphate dissolved), were analysed among treatment using non-parametric multivariate analysis. The copepod factors showed a negative association with pollutants levels and the turbidity. No mortality was observed in C, P and D treatments, whereas 100% mortality was observed in treatment I. Females from C, showed the highest egg production (22.6 +/- 6.5 eggifemale.clutch), as well as gonads regeneration and a second egg laying. Egg production, number of nauplli and faecal pellets were similar for P and D treatments, but significantly lower than those registered in C. In P treatment, only 40% of females showed regeneration of their gonads for a second egg laying (12.4 +/- 2.9 eggifemale.clutch) and in D treatment, no female regenerated their gonads for a second egg laying (12.5 +/- 3 egg/female.clutch). The results indicate that bioavailable contaminants from dissolved phase of sewage effluent reduce the fertility in Eurytemora americana, while the bottom water at the sewage discharge site is undoubtedly lethal for this species. (C) 2017 Elsevier Ltd. All rights reserved.

A combined approach merging stable isotopes and fatty acids was applied to study anthropogenic pollution in the Río Negro estuary. Fatty acid markers of vegetal detritus indicated considerable allochthonous inputs at freshwater sites. Correlative evidence of diatom fatty acids, δ13C, chlorophyll and particulate organic matter suggested the importance of diatoms for the autochthonous organic matter production at the river mouth. Low δ15N values (~0‰) and high fatty acid 18:1(n-7) concentrations in the suspended particulate matter, in combination with the peaks of coliforms and ammonium, indicated a strong impact of untreated sewage discharge. The 15N depletion was related to oxygen-limited ammonification processes and incorporation of 15N depleted ammonium to microorganisms. This work demonstrates that the combined use of lipid and isotopic markers can greatly increase our understanding of biogeochemical factors and pollutants influencing estuaries, and our findings highlight the urgent need for water management actions to reduce eutrophication.

In this study, we reported the species composition and spatial distribution of Scyphomedusae and Cubomedusae from the southwestern Atlantic and Subantarctic region and reviewed the available knowledge of life history traits of these species. We gathered the literature records and presented new information collected from oceanographic and fishery surveys carried out between 1981 and 2017, encompassing an area of approximately 6,7 million km(2) (32-60 degrees S, 34-70 degrees W). We confirmed the occurrence of 15 scyphozoans and 1 cubozoan species previously reported in the region. Lychnorhiza lucerna and Chrysaora lactea were the most numerous species, reaching the highest abundances/biomasses during summer/autumn period. Desmonema gaudichaudi, Chrysaora plocamia, and Periphylla periphylla were frequently observed in low abundances, reaching high numbers only occasionally. Phacellophora camtschatica, Aurelia sp., Drymonema gorgo, Atolla chuni, Stygiomedusa gigantea and Pelagia cf. noctiluca were observed always in low numbers. Atolla wyvillei, Stomolophus meleagris, Desmonema comatum and Tamoya haplonema were reported just a few times and mostly individually. Although new species/reports can be found as surveys are undertaken, these results are considered to be the reliable baseline for further ecological studies seeking to understand the ecological role that these jellyfish play in marine ecosystems.

An updated checklist of medusae and ctenophores is presented for the first time for the area comprised by the Bahía Blanca Estuary, the adjacent shelf El Rincón and Monte Hermoso beach, on the southwest coast of Buenos Aires province (Argentina). The area is highly productive and provides several ecosystem services including fishing and tourism. Updated information on the biodiversity of medusae and ctenophores species is essential for the study area, given that these species can affect ecosystem services. The list includes 23 hydromedusae, 3 scyphomedusae, and 3 ctenophores. Five hydromedusae (Halitiara formosa, Amphinema dinema, Aequorea forskalea, Clytia lomae and Halopsis ocellata) were firstly observed in this area. Three species of medusae, 2 hydromedusae (Olindias sambaquiensis and Liriope tetraphylla) and 1 scyphomedusae (Chrysaora lactea) pose a potential health risk, due to their toxicity to humans. Considering the size of the study area, the Bahía Blanca region has a comparatively high species richness of hydromedusae, higher than larger zones previously studied along the temperate SW Atlantic Ocean. The present report provides the baseline knowledge of gelatinous species for the Bahía Blanca region.

Monte Hermoso (SW Atlantic, Argentina) is a coastal ecosystem highly modulated by wind forcing. Ofshore winds have historically played a leading role in the tourist influx as they are associated with the occurrence of the endemic stinging medusa Olindias sambaquiensis. This species is closely related to warm summers but it could be favored by low temperatures in previous winters. Since summer 2013, a change in the wind pattern was locally perceived coincidently with the absence of the medusa in coastal waters. This work aimed at analyzing if wind pattern and sea surface temperature (SST) showed a measurable change along 2008-2015 and evaluating if this change can be associated to the observed variations in the occurrence pattern of O. sambaquiensis. Winds and SST data were analyzed in periods of high (2008-2012) and low (2013-2015) medusae occurrence, based on media and own observations. A significant change in the wind pattern in Monte Hermoso was detected. Wind speed decreased from 6.3 m s-1 in 2008 to 2.4 m s-1 in 2015 and calms and light winds increased by more than 44.2 and 7.5 %, respectively. This change implied an impediment of coastal upwelling, which is the physical process by which medusae reach the coast, and is associated with persistent (10 h or more) WNW to ENE winds blowing at ≥ 3.3 m s-1. Accordingly, in summer 2008 (period of high medusae occurrence), 45 coastal upwelling-days were detected in contrast to only 8 days in summer 2015 (period of absence of medusae). Also, positive SST anomalies were found over the 8-yr period, suggesting an increasing trend of 0.4 °C. Higher temperatures than normal during recent winters probably afect negatively the polyp reproduction. Our results demonstrate an environmental change in the ecosystem of Monte Hermoso and may explain, in part, the low occurrence of O. sambaquiensis in recent summers. The knowledge of the factors that regulate the occurrence of O. sambaquiensis is fundamental for developing a coastal management plan and/or for determining the first adaptation strategies.

Dilution experiments were conducted during a two-year survey in the Bahía Blanca estuary (SW Atlantic Ocean) to evaluate seasonal variations of microzooplankton grazing (m) and phytoplankton growth (μ). The trophic interactions between these groups were investigated in relation to anthropogenic eutrophication. For this purpose, two sites exposed differently to sewage input in the estuary were selected. The percentage of primary production grazed by microzooplankton averaged 79%, although this percentage showed high seasonal variability. The lowest consumer control was found in winter and summer, and was associated with high density of chain-forming diatoms. Conversely, the microzooplankton grazing exerted heavy control on phytoplankton biomass during spring and fall, in concurrence with the highest density of nanoflagellates. Results showed average differences between μ and m close to zero during most of the annual cycle, suggesting microzooplankton control of autotrophic prey in the two sites. Under high exposure to sewage, however, experimental results evidenced the prevalence of non-linear feeding response, poor trophic phasing at low phytoplankton growth rate and lower reactivity of microzooplankton grazing. Regardless their exposure to sewage input, microzooplankton was an important loss term of phytoplankton in the estuarine system and appear as a primary factor defining phytoplankton biomass accumulation.

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 degrees C and 32-36 salinity) and cold seasons (5-7 degrees C; 32-38) in Baha 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.