The macrofaunal assemblages of a soft-bottom intertidal area invaded by the Pacific oyster Crassostrea gigas (Thunberg, 1793) were studied at the site where reef formation was first reported for the Atlantic coast of South America (Los Pocitos; 40° 25′ 59.5″ S, 62° 25’ 23.2” W). Seasonal random sampling (winter, spring and summer) was conducted on oyster reefs and the nearby bare sediment and cordgrass areas. The habitat showed different structures with a wide size range of available spaces for macrofaunal colonization. Fifty-three macrofaunal species were recorded. Thirty-five percent of them were native, 3% were cryptogenic, 5% were exotic, and 54% need further taxonomic determination. All of the exotic species were found in reefs; though the amphipod Monocorophium insidiosum (Crawford, 1937) also settled on soft and cordgrass sediments. Species assemblages changed across seasons. Diversity was higher in reefs than in cordgrass or bare sediments during the warm season. There were no differences in the proportion of trophic groups. Our results suggest that C. gigas restructures the macrofaunal species assemblages and that this effect is driven by seasonality. In Los Pocitos, oyster reefs currently show a primary role as a suitable habitat for many species, but the net impacts of the invasion of this ecosystem engineer, including the cascading effects on the food web or the facilitation of further invasions remain unclear. The mechanisms and net effects of this restructuring force need further attention.

Understanding reproductive traits of invasive species and their modulation by different invaded habitats is crucial for monitoring invasive processes. The invasive ecosystem engineers (IEE) affect their habitat structure, generating cascading effects that may modulate their own or other species' reproductive traits. In this study, we aim to evaluate the reproductive activity of a nonindigenous species (NIS), the amphipod Melita palmata, in a SW Atlantic coastal lagoon whose habitat structure has been modified by the IEE (reef builder) Ficopomatus enigmaticus. Experiments showed that: (1) the frequency of M. palmata mate pairings (reproductive rate) is higher in reefs built by the IEE than in the facies formed by sediment and valves in reef-free areas (namely sediment); (2) the ratio of mate pairings relative to receptive available females (mate access ratio) is higher in sediment; (3) higher density of M. palmata increases its reproductive rate in both habitats, and (4) lower M. palmata density and reduced habitat structure enhance the mate access ratio. Results suggest that M. palmata reproduction is either density- or habitat-dependent at higher or lower population densities, respectively. This reproductive plasticity might contribute to the permanence of NIS in new systems, the recognition of new habitats, and counteract potential reproductive isolation.

The variability of some population (demo) parameters of the gammarid amphipod Melita palmata was associated with contrasting habitat structures created by the non-indigenous reef-builder polychaete Ficopomatus enigmaticus in the Mar Chiquita coastal lagoon (37 degrees 40 S, 57 degrees 23 W, Argentina). Sampling of M. palmata was conducted biweekly during the reproductive period in F. enigmaticus reefs and sediment from reef-free areas, accounting for the vertical distribution and the presence/absence of macroalgae. Males, females (non-ovigerous and ovigerous), and juveniles are present in both reefs and sediment, but the abundance of M. palmata is several orders of magnitude higher in reefs. Reefs' M. palmata population (demo) displays variations in: (a) abundance, (b) mean size, and (c) proportions of demographic categories. In reefs, females show a higher proportion of ovigerous specimens and a female-biased sex ratio, contrasting the 1:1 ratio observed in sediment. Individuals are more abundant in the surface layer covered with macroalgae in reefs (small sizes) and macroalgae or valves in sediment. The association of M. palmata to F. enigmaticus reefs drives its permanency in the system, enhancing its reproductive potential via different reproductive traits and habitat use, with a reduced potential to spread to marginal areas.

The aims of this study were to compare the richness and the population traits of exotic and native peracarid species in two ports of the Southwestern Atlantic (Mar del Plata: MDP, Puerto Madryn: PMY), in order to discuss the vulnerability of these environments to biological invasions, to explore the current status of these assemblages and to study the life history traits that could favour the establishment of exotic species in these ports. Five biofouling samples were taken each season from 2016 to 2017. The present study showed that exotic species were dominants in both ports but profound differences were registered between environments: MDP port is characterized by the absence of native species and highest richness of exotic species (n = 7 spp.); while in PMY port two native species were registered and exotic species (n = 2 spp.) showed lower richness than MDP port. The analysis of species assemblages and life history traits allows us to discuss the potential invasive pattern of peracarids in the Southwestern Atlantic, suggesting that factors, such as propagule pressure, port infrastructure, pollution levels are closely related to the differences in vulnerability of these artificial environments to biological invasions. In addition, the population dynamics and the reproductive traits of exotic species could explain their establishment and proliferation in the marine environments studied.

We report the occurrence of the invasive amphipod Monocorophium acherusicum in Mar del Plata port, Argentina, using morphological and molecular analysis and estimated mean abundance to detect monthly variations of this population. We compared M. acherusicum morphology with that of M. insidiosum and Crassicorophium bonelli, the two most similar locally occurring species, to establish the diagnostic characteristics for the correct identification of them; moreover, we provide some taxonomic notes about others corophiids regionally distributed. M. acherusicum were collected in a subtidal biofouling community and its mean abundance was maximum in summer. In the molecular analysis, the maximum-likelihood tree showed that specimens from Mar del Plata were clustered with M. acherusicum specimens from GenBank and Boldsystems. We support and confirm the species identity in Mar del Plata port using DNA barcoding and with taxonomic methods.

Toxic exotic organisms can have profound effect as new vectors of keystone compounds in non-native areas. In recent years the invasive sea slug Pleurobranchaea maculata has been reported as thriving along the oriental coasts of South America. The same species had been previously found to contain high levels of tetrodotoxins (TTXs) in its native range. With the aim of determining toxin contents for the introduced individuals we performed mouse bioassays (MBA) and liquid chromatography tandem–mass spectrometry analyses (LC–MS/MS) in three distant populations (− 38°02′11″, − 57°31′28″; − 40°29′59″, − 60°14′09″; − 42°44′15″, − 65°01′40″) and followed the temporal variation in toxin contents in one of them, from June 2014 to January 2015. Relative low levels of TTXs were detected jointly with high levels of PSTs. This is the first identification of TTXs in the temperate coasts of the southwestern Atlantic and the first detection of PSTs in a pleurobranch, in both adults and eggs. Concentrations of PSTs and TTXs varied widely among individuals and populations, and through time. Our results provide new hints on the origin and acquisition mechanisms of these toxins in P. maculata and highlight the risk posed by the introduction of this new vector of potent neurotoxins for seafood safety and marine communities in the invaded area.

The Southwestern Atlantic is often perceived as remote region, yet it is not immune to biological invasions. Patchy information on historical community composition hinders our ability to identify introductions to coastal ecosystems in this region. Hull fouling is an under-managed shipping vector that likely continues to transport large numbers of marine species worldwide. The port of Mar del Plata is a comparatively well-studied shipping and commercial hub that may serve as an observatory to monitor new introductions to the Argentine coast. Following detection of nonindigenous isopods during preliminary port sampling in 2007-2008, we organized regular port surveys aimed at assessing the level of population establishment and evaluated hull fouling as a potential introduction vector in the Port of Mar del Plata. In 2011-2012, we conducted 12 monthly dive surveys of port isopod communities in combination with three opportunistic surveys (two in-water, one in dry-dock) of hull fouling communities attached to a domestic research vessel during consecutive port calls at its base in this port. Replicate biofouling samples from underwater dock structures and the vessel's hull were collected by scraping invertebrates in 20 x 20 cm quadrats (even surfaces) and 1000 cm(3) of biofouling organisms (uneven surfaces). Both in port- and hull-fouling communities, we discovered the presence of the nonindigenous isopods Dynamene edwardsi and Paracerceis sculpta. This report constitutes the first detection of these two global marine invaders in American and Argentine waters, respectively. They likely represent relatively recent introductions to this corner of the world's oceans, yet our data indicate that both species are currently well established in Mar del Plata. These results demonstrate (for the first time in the case of D. edwardsi) the potential for hull fouling to disperse both species, and raise a warning on their potential expansion to other Southwestern Atlantic ports and Antarctica in a near future. Research on the marine communities of the Southwestern Atlantic is pressingly needed to establish pre-invasion communities and detect new introductions. Simultaneous surveillance of ports (invasion hubs) and vessels (vectors) can effectively detect invaders and inform prevention efforts in this region.

Non-indigenous species (NIS) are prominent constituents of fouling communities. NIS can cause biodiversity loss and change community structure through the local elimination of native species. Ports are the main focus of NIS and artificial structures are becoming spots of introduction. Community composition can vary with depth and time. In this context, this work aimed to assess substrate (concrete and wood), vertical position (near-surface and near-bottom) and month variations on the abundance of fouling invertebrates' assemblages represented by native, NIS and cryptogenic species within the Mar del Plata port, Argentina. Monthly subtidal samples were taken scraping from fouling assemblages on substrates and vertical position in the port. Assemblages on substrate, depth and time showed similar species composition patterns. Native, NIS and cryptogenic species vary in mean abundances on each substrate, depth and month. Diversity indices on concrete and on near-bottom revealed higher values. High species specific response of NIS (compared to native), found in this study along the temporal fluctuations in fouling communities was registered. A long term monitoring and future studies might consider including more substrates type and an intermediate depth, since they will provide better knowledge about the fouling invasions.

The diversity and seasonal variations of two assemblages of marine benthic peracarids were studied between a natural rocky shore and an artificial harbour area over a 12-month period. Samples were obtained monthly in La Estafeta, a rocky intertidal zone with low human impact, and Mar del Plata Harbour, a polluted environment, between March 2011 and March 2012. The two sites differed markedly in the composition and abundance of species across all seasons: the tanaid Tanais dulongii was most abundant in La Estafeta rocky shore, followed by the amphipods Monocorophium acherusicum, Hyale grandicornis, Ampithoe valida, the isopod Idotea balthica, the tanaid Leptochelia sp. and the isopod Sphaeroma serratum. In contrast, M. acherusicum was most abundant in the harbour area, followed by T. dulongii, S. serratum, Ericthonius punctatus, I. balthica, Caprella equilibra and C. dilatata. Total density of peracarids varied between months in La Estafeta rocky shore and Mar del Plata Harbour. In La Estafeta rocky shore mean density increased from March to May 2011 (autumn in the southern hemisphere; ca. 45,000 ind/m(2)), decreased sharply until August and then increased in January 2012. In Mar del Plata Harbour the mean density was lower from March to October (ca. 500,000 ind/m(3)), then increased and reached a maximum in January 2012 (more than 1,500,000 ind/m(3)), and decreased until the following March. This study suggests that the differences in peracarid assemblages, diversity and seasonality could be related to an effect of temperature, but we should not rule out a synergistic effect of other factors, such as pollution, food availability and hydrodynamic factors.

We studied the population dynamics and reproductive biology of Caprella dilatata and Caprella equilibra in order to provide the basis for understanding the ecological role of both species in Mar del Plata Harbour. Caprellids and organisms from the fouling community were obtained by sampling in the harbour, monthly from April 2014 to March 2015. Mean density of C. dilatata was homogeneous during most of the study period (ca. 50-200 ind/100 g) and reached their maximum in May (ca. 650 ind/100 g), while C. equilibra did not show any differences during the sampling period (ca. 30 ind/100 g). Juveniles of C. dilatata reached their highest densities in May, while ovigerous females were at their maximum values in late spring, summer and early autumn, and no correlation was found between seawater temperature and monthly density. On the other hand, C. equilibra reached its maximum juvenile and ovigerous female densities in summer, and showed a positive correlation with seawater temperature. Sex-ratio was female biased in C. dilatata, but in C. equilibra it was equal between sexes. The number of eggs carried by females was positively correlated to the size in both species. The present study suggests that the population dynamics of C. equilibra are intimately related to seawater temperature, while for C. dilatata no relationship was found. Future studies of ecology and behaviour traits in caprellid species are needed in order to determine the ecological role and the environmental factors that could affect both species.

Harbours are important sites for the containment and dispersal of invasive species throughout the world, so the study of life history traits of species is important to understand the success of their invasion and their potential effects on the habitat. In recent years several invasive species have been reported in Argentinian harbours; however, studies of the ecology and life history of these species are scarce. We studied the population dynamics and reproductive biology of Monocorophium acherusicum and Ericthonius punctatus, in order to update the published information on the introduced amphipods in Mar del Plata harbour. Both species showed a seasonal pattern characterized by high densities in warmer months, related to the highest reproductive activity and the increase of recruitment in summer and early autumn, and lower densities in the cold season. The sex ratio was always female-biased and the number of eggs carried by females was positively correlated to the size. The present study suggests that both species have colonized Mar del Plata harbour successfully, showing viable populations (cohorts of juveniles, males, females and ovigerous females). This work provides the basis for monitoring the impact generated by introduced amphipods over the existing fauna.

Tanais dulongii (Audouin, 1826) is a small benthic crustacean with separate sexes and a marked sexual dimorphism characterized by a cephalothorax narrowed anteriorly, larger chelae (claws) and a pair of tiny genital cones in males, and ovisacs that form chambers for carrying embryos in females. Recent studies have described the existence of intersexual individuals with a cephalothorax similar to males, large chelae and ovisacs, but, due to their small size, it has not been possible to confirm the presence of genital cones under normal light microscopy. The present study analyses and compares external reproductive structures under scanning electron microscopy, of male and female T. dulongii, to corroborate the presence of both ovisacs and genital cones in potentially intersex individuals. The possible causes, such as hermaphroditism, environmental sex determination, parasitism, genetic aberration or endocrine-disrupting pollutants, are discussed.

Tanais dulongii (Audouin, 1826) is a small benthic crustacean with separate sexes and a marked sexual dimorphism characterized by a cephalothorax narrowed anteriorly, larger chelae (claws) and a pair of tiny genital cones in males, and ovisacs that form chambers for carrying embryos in females. Recent studies have described the existence of intersexual individuals with a cephalothorax similar to males, large chelae and ovisacs, but, due to their small size, it has not been possible to confirm the presence of genital cones under normal light microscopy. The present study analyses and compares external reproductive structures under scanning electron microscopy, of male and female T.dulongii, to corroborate the presence of both ovisacs and genital cones in potentially intersex individuals. The possible causes, such as hermaphroditism, environmental sex determination, parasitism, genetic aberration or endocrine-disrupting pollutants, are discussed.

Tanaidaceans are small benthic crustaceans with a strictly benthic life cycle and low dispersion rates, so they are good candidates to evaluate the effects of environment over life history strategies and reproductive biology. In this work, we studied two populations of Tanais dulongii (Audouin, 1826) that live in two contrasting habitats in order to determine whether they differ in life history traits. The animals were obtained by systematic sampling in a rocky shore with a lower anthropic impact (La Estafeta: LE) and a polluted area (Mar del Plata harbour: MdP) from March 2011 to March 2012. Seawater temperature and salinity did not differ between sites, but MdP showed more acid and hypoxic conditions than LE. Population density was homogeneous and lower in MdP (ca. 20 ind/100 gr) than that in LE where density varied between 250 and 800 ind/100 gr. Reproductive individuals and juveniles were always present, and both populations showed two main recruitment periods: the first in spring in both populations, and the second in summer in MdP but in autumn–winter in LE. In both populations, sex ratio was strongly female-biased. Juveniles, females and males from LE had larger sizes than that from MdP and reached their sexual differentiation at larger sizes. The estimated lifespan was about 9 and 12 months in MdP and LE, respectively. This study suggests that the differences observed between populations of T. dulongii in life history traits are intimately related to environmental differences in pH and dissolved oxygen between habitats, but should not be discarded a synergistic effect of temperature, organic pollution, food availability and predation pressure.

Fil: Rumbold, Carlos Enrique. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina

We evaluated benthic habitat quality along a presumed contamination gradient in the Mar del Plata port (Southwestern Atlantic) by coupling biological and chemical proxies in a multidisciplinary approach. Organic matter and photosynthetic pigment contents were higher in silty-clay bottoms of the inner port sites. Levels of all fecal steroids decreased from the inner sites to the port inlet. High concentrations of coprostanol in the inner sites seemed to derive from a permanent population of sea lions rather than from sewage outfalls due to coprostanol/epicoprostanol ratio (IV) values <2.5. PAHs levels were also higher in the inner sector, related to both biomass combustion and petroleum combustion associated to local marine traffic. High disturbance and low ecological status were reflected in low benthic diversity and high AMBI values in the inner sites.

We studied the life history, reproductive biology and spatial distribution of Tanais dulongii on an intertidal flat near Mar del Plata, Argentina. The animals were obtained by systematic sampling in three intertidal zones (high, mid and low), from October 2008 to September 2009. The population density was low during most of spring and summer, increased during autumn and reached its maximum values at the end of this season (35 000 individuals/m(2)): a second, but lower, density peak occurred at the end of winter (15 000 individuals/m(2)). Male density remained below 1000 individuals/m(2) during most of the year in the three zones, although in September it was higher than 1800 individuals/m(2) in the high and mid intertidal zones. Female and juvenile density was below 5000 individuals/m(2) in spring and summer, with little variation between areas, but it differed among areas during autumn and winter, when both groups reached their maximum densities (20 000-40 000 individuals/m(2)) in the low and mid intertidal zones. Ovigerous females were always present; their maximum occurred in spring and summer but earlier in the low and later in the high intertidal zone. Recruitment was higher in autumn and early winter. The sex ratio was strongly female biased (0.08 +/- 0.01). Individual life time was estimated to be 8-9 months and females developed through more instars than males. This study suggests that the different environmental conditions that T. dulongii faced in the 3 intertidal zones caused an important effect on the population dynamics.

Three species of flatworms, Phrikoceros mopsus (Marcus, 1952), Thysanozoon brocchii (Risso, 1818) and Thysanozoon mirtae sp. nov., are described from specimens collected from shallow rocky shores of Mar del Plata harbour, in the southwestern Atlantic. P. mopsus had been described as living in the coasts of Brazil and southern Patagonia. T. brocchii has a more extensive known distribution, from the Mediterranean to the coasts of Brazil and the Argentinean Patagonia. Their morphological variation is here recorded and discussed. Thysanozoon mirtae sp. nov. is characterized by its colour pattern, colourless tentacles, and the presence of well developed spermiducal vesicles and a strong parenchymatic musculature.