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The economic costs of non-indigenous species (NIS) are a key factor for the allocation of efforts and resources to eradicate or control baneful invasions. Their assessments are challenging, but most suffer from major flaws. Among the most important are the following: (1) the inclusion of actual damage costs together with various ancillary expenditures which may or may not be indicative of the real economic damage due to NIS; (2) the inclusion of the costs of unnecessary or counterproductive control initiatives; (3) the inclusion of controversial NIS-related costs whose economic impacts are questionable; (4) the assessment of the negative impacts only, ignoring the positive ones that most NIS have on the economy, either directly or through their ecosystem services. Such estimates necessarily arrive at negative and often highly inflated values, do not reflect the net damage and economic losses due to NIS, and can significantly misguide management and resource allocation decisions. We recommend an approach based on holistic costs and benefits that are assessed using likely scenarios and their counter-factual.

Despite significant growth in the information on introduced species (NIS), agreement on their comparative fitness and effects on native (NAT) communities is heterogeneous. Hypotheses aimed at explaining their fitness and impacts are as often supported as challenged. In order to investigate whether origin is associated with fitness or impact, we reviewed 72 meta-analyses of trait differences between NAT and NIS, and impacts of NIS on NAT and the environment, covering terrestrial and aquatic organisms. Interpretation of the trends was based on overall meta-analysis conclusions, and on numbers of point estimates (individual effect sizes) within and across studies. Mixed results were found in 44% of the studies. Higher NIS fitness and significant impacts were found in 31%, and 25% concluded that significant outcomes are largely absent. Point estimates showed that non-significant outcomes (57%) are more common than significant ones. Two thirds yield mixed trait differences and impacts, or do not support the concept that NIS are more fit or have negative effects on NAT. When trait differences or impacts are significant, NAT are usually less fit, or are negatively impacted, but this trend is influenced by the fact that most surveys are based on the most damaging invasive species.

International audience; Siliceous polycystines and phaeodarians are open-ocean planktonic protists found throughout the water column and characterized by complex siliceous skeletons that are formed, at least partly, through the uptake of silicic acid. These protists contribute to the marine organic carbon (C) and biogenic silica (bSi) pools, but little is known about their contribution to the silica (Si) biogeochemical cycle. Here we report the first measurements of the Si uptake rate of polycystine and phaeodarian cells from samples collected in the Mediterranean Sea using the 32 Si-based method. The elementary composition (bSi, particulate organic carbon and nitrogen) of these organisms was also measured. Combining our results with published data on the distribution and abundance of Polycystina and Phaeodaria in the global ocean, we conclude that these organisms could contribute from 0.2 to 2.2 mmol Si m −2 of the marine standing stock of bSi and from 2 to 58 Tmol Si yr −1 (1% to 19%) of the global oceanic biogenic silica production. The implications for the global marine Si cycle are discussed.

The invasive golden mussel Limnoperna fortunei is known to strongly affect benthic communities in South American freshwaters, but the evolution of these effects after the early invasion stages is poorly understood. Using predator exclusion (covered with 15- and 40-mm meshes) and inclusion (unprotected) substrates, we investigated the interaction between golden mussels and benthic invertebrate communities at different levels of exposure to predators in the Paraná River delta. Colonization of the substrates was largely dominated by the mussels. Oligochaeta, Nematoda, and Hirudinea were the most abundant accompanying groups, while Rotifera, Tardigrada, Copepoda, Cladocera, Chironomidae, Gastropoda, Hydracarina, Amphipoda, and nauplii appeared sporadically. Regardless of their different trophic modes and functional attributes, the numbers and biomass of associated invertebrates were not only enhanced by protection against predators, but also by the presence of mussel colonies. Enhancement of invertebrate densities associated with mussel colonies was higher on unprotected than protected substrates, suggesting that invertebrate facilitation increases with increasing predation pressure. Comparisons with a similar study carried out a decade earlier suggest that, after two decades of invasion, the reproductive potential of the mussel, the predation pressure on its colonies, and its facilitation effects on other invertebrates have increased in the Paraná River delta. Fil: Duchini, Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Boltovskoy, Demetrio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Sylvester, Francisco. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Instituto para el Estudio de la Biodiversidad de Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

While invasion success is usually associated with the biological fitness of the invader and environmental similarity between the area of origin and the invaded range, some of the most notorious aquatic invasions involve species with traits that for millions of years were a burden, rather than an advantage, for their survival. These odd characteristics became major assets after man started reshaping the surface of the earth, facilitating their spread. Invasion risk-assessment models, chiefly based on environmental match parameters, are unlikely to predict the dispersion of these (and probably many other) species, whose invasive nature involves subtle and intricate mechanisms that operate at levels normally ignored by (and often unknown to) the models. Much of the literature on introduced species is focused on demonstrating their negative impacts on the ecosystems invaded. While the fact that invasive organisms can, and very often do, have enormous negative impacts, is beyond doubt, and all efforts possible for keeping biological invasions at bay should be made, once the introduction happens and the eradication of the invader is unfeasible, research efforts should be centered on objective analyses of how the invader interacts with the new ecosystem, untainted by efforts to forcibly demonstrate its negative impact.

Fil: Sandoval, Maria I.. Universidad de Costa Rica; Costa Rica. Universite de Lausanne; Suiza

Analysis of 307 species of Radiolaria Polycystina in a worldwide dataset of 4774 plankton, sediment trap, and surface sediment samples allows recognizing six major biogeographic Domains. Five of them are circumglobal (Polar North, Polar South, Bi-Subpolar, Transitional and Tropical-Subtropical), and one is restricted to the Eastern Equatorial Pacific. Each Domain is characterized by a particular suite of species, all of which, however, occur widely, albeit sparsely, in one or more other Domains. Of the eight environmental variables evaluated, temperature correlates best with the partitions established. Species distributions in the water column and in the sediments are generally in agreement, but in the sediments cold water forms extend farther towards the equator than do warm water radiolarians towards the poles. In the Recent sedimentary record of planktonic Foraminifera the same phenomenon is magnified by the higher dissolution rates of warm water species, as compared with the cold water ones. Of the three major oceans, the Pacific was the most speciose, but estimates based on data corrected for sample-size show much smaller inter-oceanic differences, with ∼10 radiolarians probably being absent from either basin. The radiolarian biogeographic pattern is generally similar to those based on other planktonic and nektonic open-ocean organisms, but the degree of uniqueness of the Domains, as well as the position of the intervening boundaries, are variable, which reflects methodological differences, as well as taxon-specific traits. Partitions of the World Ocean defined on the basis of species ranges resemble the major divisions (presumably functionally homogeneous units) established on the basis of physical traits and chlorophyll fields, but secondary divisions nested within the latter are not reflected by any of the biogeographic schemes based on species distribution ranges. This conflict raises questions about the importance of several physical mechanisms for structuring pelagic communities, and/or on the coupling of structure and function in the pelagic realm. Fil: Boltovskoy, Demetrio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Correa, Nancy Myriam. Ministerio de Defensa. Armada Argentina. Servicio de Hidrografía Naval; Argentina

Climatic and oceanographic processes in the Pacific Ocean have global implications. Reliable sedimentary proxies in this region are thus necessary to understand the magnitude of past climate variability. Radiolarian assemblages are of particular relevance in some regions of the Pacific Ocean where other proxies are either poorly preserved or are biased towards a specific season. Previously published radiolarian-based transfer functions in the Pacific Ocean did not cover some regions, such as the Western Pacific marginal seas or high-latitude Southwestern Pacific. Filling these gaps in sample distribution and using a thorough methodology for finding the most important variable for radiolarian assemblages in surface sediment are both essential steps in quantitative studies. In this study, we use published radiolarian census counts from 801 core-tops distributed across the Pacific Ocean, to investigate which environmental factors drive the assemblages. We harmonized taxonomically the modern microfossil dataset, and using multivariate statistical analyses, we determined that sea surface temperature at 10 m (SST10) is the most important variable influencing the changes observed in the radiolarian assemblages. The calibration method weighted-mean modern analogue technique with five analogs (WMAT-K5) corrected for autocorrelation using a cut-off distance of 500 km, showed a performance of R2cv = 0.83; RMSEP = 3.8 °C. This calibration method was then applied to taxonomically harmonized radiolarian census counts from 31 cores located in the Bering Sea, Western Pacific marginal seas, and Southwest and Eastern Equatorial Pacific, with some of these records covering at least the last 165 ka. We assessed the analogue quality and significance of the downcore SST10 reconstructions in all of them. We found that temperatures at 10 and 200 m were the most significant variables for the fossil assemblages. Finally, we compare the temperature reconstructions to previously published radiolarian-based SST estimates for the same cores, or to other SST records based on other methodologies. We find some differences between our new temperature estimates compared to existing ones, in particular in the Eastern Equatorial Pacific. Comparison to other methods in the Japan and Bering Sea and Sea of Okhotsk show that radiolarian-based reconstructions provide robust temperature estimates compared to biogeochemical methods, which showed SST overestimation during glacial periods.

In the last decades, thousands of investigations confirmed the detrimental effects of species translocated by man outside of their native ranges (non-indigenous species, or NIS). However, results concluding that many NIS have null, neutral, or positive impacts on the biota and on human interests are as common in the scientific literature as those that point at baneful impacts. Recently, several scholars confronted the stand that origin per se is not a reliable indicator of negative effects, suggesting that such conclusions are the expression of scientific denialism, often led by spurious purposes, and that their numbers are increasing. When assessed in the context of the growing interest in introduced species, the proportion of academic publications claiming that NIS pose no threats to the environment and to social and economic interests is extremely low, and has not increased since 1990. The widely prevailing notion that many NIS are effectively or potentially harmful does not conflict with the fact that most have mixed (negative, neutral, and positive) impacts. When based on solid grounds, reports of positive or neutral impacts should not be labeled as manipulative or misleading unless proven otherwise, even if they may hamper interest in- and funding of research and control bioinvasion programs. Fil: Boltovskoy, Demetrio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Paolucci, Esteban Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Sylvester, Francisco. Universidad Nacional de Salta; Argentina

We describe here the life and career of geologists who beyond their nationality (Russian, Ukrainian, Tatar, German, etc.), were born on the territory of the Russian Empire, the Soviet Union or the Russian Federation and their descendants that became geologists, all of whom lived and worked in Latin-American countries (where Spanish and Portuguese languages prevail). We include also geologists from USSR who worked temporary in some countries of Latin America and left contributions to geology in form of publications., Se describe la vida y trayectoria de geólogos que más allá de su nacionalidad (rusa, ucraniana, tártara, alemana, etc.), nacieron en territorios que pertenecieron al Imperio Ruso, la Unión Soviética o la Federación Rusa, y de sus descendientes graduados en geología, todos los cuales vivieron y trabajaron en países de Latinoamérica (en los cuales las lenguas que prevalecen son el español y el portugués). También se incluyen geólogos de la URSS que trabajaron temporariamente en algunos países de Latinoamérica y que con sus publicaciones contribuyeron a la Geología., Descreve a vida e a trajetória de geólogos que, além de sua nacionalidade (russos, ucranianos, tártaros, alemães, etc.), nasceram em territórios pertencentes ao Império Russo, à União Soviética ou à Federação Russa, e seus descendentes se formaram em geologia, todos os quais viveram e trabalharam em países latinoamericanos (nos quais as línguas dominantes são o espanhol e o português). Também estão incluídos geólogos da URSS que trabalharam temporariamente em alguns países da América Latina e que contribuíram para a Geologia com suas publicações., Facultad de Ciencias Naturales y Museo

Since its introduction into South America around 1990, the freshwater bivalve Limnoperna fortunei (the golden mussel) has spread rapidly and is now a dominant component of the benthic and periphytic fauna in many rivers, lakes, and reservoirs. Sizable impacts of this nonindigenous species on nutrient recycling, plankton abundance and composition, and trophic relationships with fishes have been reported, but its effects on the sediments have received little attention. In this work, we use eighteen 20-L flow-through experimental units with and without mussels where changes in the mass and characteristics of the sediments accumulated throughout a yearly cycle in monthly, biannual, and annual intervals are analyzed. Experimental units with mussels yielded almost 2 times more sediments than units without mussels and contained significantly higher loads of organic matter and total N. Total P was not affected by the presence of mussels. Sediments accumulated in the biannual and annual experimental units agreed well with the yields of the monthly units, but the vertical stratification of organic matter, N, and P was unpatterned. Seasonal changes in the volume of total sediments, biodeposits, and their organic matter and N contents were positively associated with ambient water temperature and with intermediate (~150–250 NTU, nephelometric turbidity units) turbidity. Our results suggest that ecosystem-wide modifications in the living conditions of the benthic epifaunal and infaunal organisms in waterbodies invaded by the mussel are likely significant, although variable locally, regionally, and across taxa. Fil: Tokumon, Romina Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Boltovskoy, Demetrio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Cataldo, Daniel Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina

Larval fish development depends largely on their ability to capture and ingest food items, and on food availability. In this context, invasive species, eutrophication and river impoundments have complex impacts on fish larvae. Using samples collected in 2005–2009 in the Salto Grande reservoir (Argentina–Uruguay), periodically affected by cyanobacterial blooms, we studied the impact of the larvae of the exotic bivalve Limnoperna fortunei (Dunker, 1857) (Bivalvia) on larval fish diets. Compared with other nearby waterbodies, the abundance of fish larvae was scarcer in the reservoir, especially during algal bloom periods. Only 20% of the larval fish with gut contents fed on L. fortunei veligers. Seven fish taxa (of a total of 12) consumed veligers of L. fortunei, but only two showed a preference for this prey. Taxonomic changes in the larval fish assemblages due to the river's impoundment, and temporal uncoupling between veliger densities (affected by the toxigenic effects of Microcystis spp.) and ichthyoplankton could account for the comparatively low trophic importance of the invasive bivalve's veligers. These results reflect the complexity of interactions brought about when the same invasive species invades different environments, underscoring that the impacts involved depend as much on the invader, as on the regional and ecological settings of the area invaded. Fil: Paolucci, Esteban Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina Fil: Leites, Valentín. Comisión Técnica Mixta Embalse; Argentina Fil: Cataldo, Daniel Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentina Fil: Boltovskoy, Demetrio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina

Radiolarian flux rates, their intermittency, and changes in their species compositions are assessed using data from 73 time-series sediment trap deployments (1357 samples) covering 7-12 calendar months. Results are analyzed as a function of trap depth, latitude, and seasonal and geographic variations in sea surface temperature and primary production. Radiolarian flux rates are highest in the tropics and subtropics, decreasing towards the high latitudes. Low and highly intermittent primary production (PP) regimes are reflected in more pulsating radiolarian flux rates, but in moderate to high PP areas, radiolarian fluxes are not associated with phytoplanktonic growth cycles. At sites where simultaneous trap deployments at different depths were performed, shallower traps yield lower and more pulsating radiolarian flux values than deeper ones. Enhanced dissolution of biogenic silica in the shallower traps is probably responsible for these differences. Intermittency in radiolarian flux is highest in the seasonally ice-covered Southern Ocean waters, but much lower in the also seasonally ice-covered northern hemisphere sites investigated, suggesting differences in the mechanisms that govern the production and recycling of organic matter in the upper ocean and at mid depths. Radiolarian flux rates and their species richness do not seem to be coupled, neither temporally nor geographically. Temporal stability in the composition of the radiolarian taxocoenoses is generally high, and positively associated with absolute flux values and trap depth. The bulk of the assemblages are little affected by environmental seasonality, and only a few species, albeit often numerically dominant, seem to reflect these changes. Fil: Boltovskoy, Demetrio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina

Previous work has shown that the invasive bivalve Limnoperna fortunei has had a measurable impact on local food webs, but knowledge of the trophic interactions involved is still very limited. On the basis of samples collected along the lower Paraguay-middle Parana´ rivers, we studied the feeding behavior and selectivity of larval fish, with emphasis on veligers of the introduced bivalve L. fortunei. Among feeding larvae (i.e., without a yolk sac), 16.5% had only Limnoperna veligers in their guts, while 15.6% had veligers and some other prey. Half of the fish taxa recorded (8 out of a total of 16) consumed Limnoperna veligers. The Paraguay and Parana´ rivers differed strongly in the proportions of fish larvae that consumed veligers: 14 and 68%, respectively. This difference paralleled the availability of veligers in the water column, which was significantly lower in the Paraguay (0.8 ± 0.5 ind. l-1 ) than in the Parana´ River (5.5 ± 2.3 ind. l-1 ). Conversely, cladocerans, originally the staple food of fish larvae, were more abundant in the Paraguay (consumed by 48% of the individuals) than in the Parana´ River (26%). These results indicate that, when widely available, Limnoperna veligers largely replace the original prey of fish larvae, especially in their younger stages (protolarvae). Fil: Paolucci, Esteban Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Almada, Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina. Ministerio de Seguridad. Prefectura Naval Argentina; Argentina Fil: Cataldo, Daniel Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Boltovskoy, Demetrio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina

We summarize current knowledge on the effects of the invasive Asian bivalve Limnoperna fortunei (introduced in South America around 1990) on local biota. Limnoperna modifies nutrient concentrations and decreases concentrations of particulate organic matter in the water column (including phytoplankton and zooplankton), thus enhancing light penetration and stimulating growth of periphyton and macrophytes. Selective grazing and modification of the N:P ratio are responsible for strong enhancements of toxic cyanobacterial blooms. Limnoperna beds significantly enhance the numbers, biomass, and diversity of practically all accompanying invertebrates. The mussel’s planktonic larvae represent an important food item for the larvae of 18 fish species, while juveniles and adults are consumed by at least 50 fish species. Limnoperna is the first and only abundant benthic filter-feeding animal in South American continental waters. The fact that it intercepts and retains in the freshwater lotic domain particulate organic matter that would otherwise be swept into the sea must represent an important energetic subsidy, but the ecosystem-wide consequences of this trophic shift have not yet been addressed. Comparison with the impacts of the zebra mussel in Europe and North America suggests important differences.

In contrast to the classical notion of an increasing biodiversity from the poles to the equator, a number of studies concluded that the diversity of marine species is highest at the middle latitudes, and decreases at the equator. Using a worldwide database critically compiled from 72 surveys (307 species, 4,807 water column and surface sediment samples), we analyzed the latitudinal gradients in species richness (LGSR) of a highly diversified group of marine holoplanktonic protists, the polycystine Radiolaria. Species richness values were corrected for uneven sample coverage and sample size, and contrasted with gradients in 11 environmental variables. Radiolarian species richness decreases from the equator to the poles both in the water column and in the surface sediments and is tightly coupled with temperature throughout the entire thermal range of marine waters. In the tropical Pacific Ocean, a conspicuous east-west gradient in diversity is also associated with temperature. Globally, diversity is negatively correlated with mean annual concentrations of nutrients (N, P, Si) and chlorophyll a. Disagreements with results reported for many other oceanic plankton may stem from the reduction of 3D distributional patterns onto 2D or 1D spaces, to the intermittent mixing of Subtropical and Subpolar species at the middle latitudes, and to a Mid-Domain Effect. The fact that radiolarian LGSR do not show this drop at the equator is partly due to methodological and database-related differences, and probably also in part a reflection of taxon-specific traits.

The Asian mytiloid Limnoperna fortunei (Dunker, 1857) was first recorded in South America along the coast of the Rio de la Plata estuary in 1991 (Pastorino et al., 1993). Since then the mussel has expanded its range, colonizing most of the Rio de la Plata basin, as well as several minor watersheds. Because of its wide distribution, high densities and significant ecosystem engineering capabilities, L. fortunei has had sizeable impacts on the waterbodies colonized, including modification of nutrient concentrations and ratios, enhancement of water transparency, macrophyte growth and effects on cyanobacterial blooms, the abundance and diversity of benthic invertebrates, sedimentation rates and food availability for fishes (Sylvester, Boltovskoy & Cataldo, 2007; Boltovskoy et al., 2009, 2013; Cataldo et al., 2012a, b; Boltovskoy & Correa, 2015; Paolucci & Thuesen, 2015). Impacts on human activities have been especially marked: L. fortunei larvae enter raw water conduits of open cooling systems and develop large beds in pipes and other components, clogging them and causing pressure loss, overheating and corrosion (Boltovskoy, Xu & Nakano, 2015). Northward expansion of L. fortunei is expected to continue beyond South America and into Central and North America (Karatayev et al., 2015). Available data indicate that potentially colonizable areas include all continents except Antarctica (Kluza & McNyset, 2005; Karatayev et al., 2015), but the fact that water bodies lacking mussels exist in watersheds where L. fortunei has been present for decades suggests that some environmental conditions may limit the expansion of this invader (Darrigran et al., 2011). Among these, the concentration of suspended solids is of particular interest. Suspended matter can affect respiration, growth, parasite infestation and reproduction of the organisms (Robinson, Wehling & Morse, 1984; Alexander, Thorp & Fell, 1994; Rosewarne et al., 2013), thereby restricting their geographic spread, but this constraint has not been explicitly addressed in models of the potential distribution of L. fortunei (Kluza & McNyset, 2005;Oliveira, Hamilton & Jacobi, 2010). In order to estimate the tolerance of L. fortunei of inorganic suspended solids, thus providing data for analysis of its potential distribution worldwide, we assessed the species’ capability of filtering water and retaining phytoplankton at different clay concentrations. Individuals of L. fortunei were collected from Buenos Aires (348320S; 588250W) and stored in aerated aquaria filled with dechlorinated tap water at 23–25 8C. They were fed ad libitum on cultured algae (.95% Scenedesmus spp., mean biovolume 1300–1600 mm) known to be actively consumed by the mussel (Cataldo et al., 2012a). Individuals 15–20 mm (mean 17.3 mm) in shell length were isolated from the clumps and placed in flat trays in order to verify their vitality. Actively filtering individuals were transferred from the trays to acclimation vessels at 27 8C for 48 h. All individuals were starved for 24 h and then stocked in cylindrical plastic netting cages (10 cm high, 6 cm in diameter) placed at mid-depth in the experimental 2-l containers (Fig. 1). In the latter, an air hose was attached laterally to a tube located vertically on the bottom, thereby suctioning settling sediment particles and returning them to the water column (Fig. 1). Algal concentrations in the experimental containers ranged from 30 to 60 (mean 43.5+6.3 SE) mg Chl a l, mimicking usual values for eutrophic water bodies (Jones & Lee, 1982). Bentonite clay with a mean particle diameter of 9.45 mm, within the range of .90% of the inorganic suspended solids in the South American water bodies colonized by L. fortunei (Carignan, 1999; Sarubbi, Pittau & Menendez, 2004), was used at different concentrations: 0 g l (controls), 0.1, 0.5, 1, 2, 4, 6, and 8 g l. All experiments were performed at 27 8C (typical of the lower Parana River and Rio de la Plata estuary during the summer) in a controlled temperature chamber. For each sediment concentration, three replicates without (controls) and three with 60 individuals of L. fortunei were used. Upon termination of each experiment (120 min) all individuals were measured to the nearest 0.01 mm with digital calipers, and their tissues extracted and dried at 60 8C to constant weight (DTW). Immediately before start and after termination, each experimental container was sampled (40–150 ml) to estimate chlorophyll a concentrations. Samples were filtered through fibreglass filters (Whatman GF/F) and pigment extraction was performed with hot (60–70 8C) ethanol in darkness two or three times in order to avoid underestimations due to chlorophyll adsorption upon sediment particles (Koyama, Shimomura & Yanagi, 1968). The extracts were clarified by centrifugation, their volume adjusted and the absorbance at 665 and 750 nm measured with a spectrophotometer before and after acidification with HCl (1 N). Pigment concentrations were calculated according to Marker et al. (1980).

In order to evaluate the effects of the golden mussel Limnoperna fortunei on phytoplankton density and composition and nutrient recycling we conducted a 24 h filtration experiment in Rio Tercero Reservoir (Argentina) using four 400 L mesocosms, two of them stocked with 1700-1800 adult mussels each, and two controls (without mussels). Nutrient concentrations and phytoplankton composition and density were evaluated at 0, 3, 6, 12, and 24 h. Estimated filtration rates were 1.48-3.14 mL mg DW -1 h -1 . Grazing pressure by the mussel was not associated with algal taxonomy or cell size. After 24 h, L. fortunei removed 84% of the particulate nitrogen, and 49% of the particulate phosphorus. Nutrient regeneration was very significant as well: ammonium was produced at a rate of 3 μM NH3g DW -1 h -1 , whereas production of phosphates was 0.42 μM PO4g DW -1 h -1 . It is concluded that the impact of L. fortunei on phytoplankton and nutrient cycling can be as significant as that reported for another invasive bivalve - the zebra mussel Dreissena polymorpha in Europe and North America, but the overall effect of this impact on the biota may differ strongly under different environmental settings.

Limnoperna fortunei is an Asian mussel introduced to South America around 1990. One of the most important impacts of this invader is probably its grazing on the plankton. In this study we evaluate the vulnerability of several planktonic microcrustaceans from the Paraná River floodplain to predation by adult L. fortunei. We conducted 2-h laboratory feeding experiments where the bivalves were offered microcrustaceans differing in overall body shape, size, and locomotive abilities. Ingestion and clearance rates for each taxon were estimated. Results suggest that, in addition to detritus and phytoplankton, microcrustaceans may be a very important food item for this invasive mollusc. Limnoperna fortunei can prey on larger organisms (up to 1100 μm) than Dreissena polymorpha, the European and North American invasive mussel. Fil: Rojas Molina, Florencia Mercedes. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina Fil: Jose, Susana Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina Fil: Boltovskoy, Demetrio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina

In order to assess the effects of the introduced bivalve Limnoperna fortunei on water-column properties of Salto Grande reservoir, experiments were conducted using six 400 L mesocosms: 2 with 100 mussels, 2 with 300 mussels, and 2 controls (without mussels). At 0, 1, 2, 3, 7, 14, 21, 28, and 35 days we measured nutrient and chlorophyll a concentrations, counted and identified the phytoplankton, and estimated the density, size, and number of cells of the colonies of Microcystis spp. Cumulative periphyton growth and total accumulated sediments were assessed in all enclosures at the end of the experiment. Throughout the experiment, in the controls ammonia and phosphates dropped to near zero, whereas in the mesocosms with L. fortunei they increased two- to tenfold. Nitrates decreased in all mesocosms. In the presence of the mussel, chlorophyll a and algal cells dropped until day 3 increasing thereafter, whereas in the controls they increased from day 0. Periphyton growth and sediment accumulation were significantly higher in the mesocosms with mussels that in the controls. Cell density, proportion of colonial cells and colony size of Microcystis spp. increased in all enclosures, but these increases were dramatically (and very significantly) higher in enclosures with 100 and, especially, with 300 mussels, than in the controls. Our results indicate that L. fortunei modifies nutrient concentrations and proportions, and promotes aggregation of solitary Microcystis spp. cells into colonies; both these effects can favor blooms of this often noxious cyanobacteria.

Between July 2007 and December 2008 we surveyed 194 commercial vessels for compliance with ballast water (BW) regulations at five Argentine ports (four of them along the Patagonian coast). Our survey included the inspection of the BW reporting forms and collection of BW samples for salinity and biological (plankton) analyses from 261 BW tanks. Most (77%) ships had some type of BW form on board, but the information in these forms was often unclear, incomplete or inconsistent and did not allow tracking the origin of the BW. Salinity of the BW was often in conflict with the reported geographic location of BW exchange, and the reported volumes of BW discharged in the ports surveyed appeared to be fictitious. Most (80%) BW tanks contained identifiable organisms, usually in very good state of preservation, totaling 408 plant and animal taxa, but only three of these had not been previously recorded in Argentina (two diatoms and one copepod). In spite of the fact that compliance with national and international regulations and guidelines on BW management is poor in the area, the number of recorded marine aquatic nonindigenous species (ANS) in Argentina is comparatively low (ca. 40). Several factors seem to buffer the Argentine coastline from ANS: (1) the low activity of most Patagonian ports; (2) the fact that most (61%) incoming ship traffic originates from domestic ports or areas unlikely to supply ANS; (3) the harsh environmental conditions (cold and turbulent, with few sheltered areas); and (4) the scarcity of hard substrates. In order to maintain its waters relatively free of ANS, Argentina needs to significantly increase its efforts at enforcing existing international and national legislation, and to revise and update its standards on BW management. We anticipate that the problems encountered are also characteristic of many other developing countries, both in South America and elsewhere, where compliance with IMO's BW guidelines is still seldom tested or enforced.

In this study, for the first time, using similar methods, we compared the population density and distribution across different substrate types of Limnoperna fortunei and Dreissena polymorpha, as well as their impacts on the composition of benthic communities. Data on L. fortunei were obtained in Rio Tercero Reservoir, Argentina, whereas studies on D. polymorpha were conducted in North America and Europe. We found that, similar to the zebra mussel, L. fortunei creates high densities on hard substrates in the littoral zone, and avoids soft substrates in the profundal zone; however, the overall population density of L. fortunei in a water body seems to be higher than that of zebra mussels. Additional studies on Limnoperna are needed to confirm this hypothesis. The effect of L. fortunei on macrobenthos is very similar to the effect of D. polymorpha and is associated with an increase in the overall diversity, density, and biomass of native macroinvertebrates in druses compared with bare sediments. The...

SUMMARY 1. Larvae of 'sabalo', Prochilodus lineatus, whose adults represent over 60% of overall fish biomass in the Ro ´o de la Plata Catchment, have been observed to feed intensively on veligers of the exotic bivalve Limnoperna fortunei. 2. To assess the effects of this dietary shift on the growth of P. lineatus, 28-day laboratory experiments were carried out feeding newly hatched P. lineatus larvae with three diets: zooplankton artificially enriched with L. fortunei veligers; natural zooplankton; and zooplankton artificially enriched with cladocerans and copepods. The average length, weight and gut contents of the fish larvae were assessed weekly and metabolic rates of fish larvae were measured. 3. Proportions of veligers in gut contents were always higher than those in the experimental diet: 100, 76 and 21% for veliger-enriched, natural and low-veliger diets, respectively. Larvae fed a veliger-enriched diet grew to a significantly larger size than larvae fed the other two diets. In energetic balance comparisons using metabolic rates and prey energy content, all three diets were sufficient to support metabolism and growth. The greatest values of excess energy at the end of each week were in the veliger-enriched experiments. 4. Feeding on veligers of L. fortunei significantly enhances the growth of P. lineatus larvae and supports the idea that this new and abundant resource is selectively preyed upon by P. lineatus during its larval stage. Higher growth rates may stem from the higher energy contents of veligers compared to crustaceans and ⁄ or from the lower energy costs of capturing slower prey.

Limnoperna fortunei (Dunker, 1857) (Bivalvia) invaded Argentina through the Rio de la Plata estuary around 1990 and is presently established throughout five South American countries as a dominant component of the benthic fauna and a major nuisance for industry and power plants. Between 1997 and 2006 we monitored the reproductive activity of L. fortunei through weekly measurements of planktonic larvae in six South American water bodies: Rio de la Plata estuary, Parana and Carapachay rivers, Salto Grande, Itaipu and Embalse de Rio Tercero reservoirs. Mean larval densities varied between 4000 and 7000 individuals m⁻³; except in the reservoirs of Itaipu (450 ind. m⁻³) and Salto Grande (869 ind. m⁻³), where the mussel was first recorded shortly before our surveys, and upstream dispersal is limited (Salto Grande). In all cases, reproductive output decreases during the winter. At four of the six sites surveyed larval densities were comparatively high for 8.8-10.2 months per year. A lower food supply is possibly responsible for the shorter reproductive period of 5.9 months at Embalse. At Salto Grande, there is a well-defined mid-summer drop in larval numbers, coinciding with blooms of cyanobacteria. We propose that, in addition to temperature, two major factors may regulate the reproductive activity of L. fortunei: (i) the availability of food; and (ii) blooms of toxic cyanobacteria, significantly shortening the otherwise very long reproductive period. This information is important for the design of antifouling programmes involving the use of molluscicides, and has potential for reduced biocide use. These results provide supporting evidence for some fundamental ecological theories of invasions discussed here.

Since its introduction in South America around 1990, the freshwater Asian mussel Limnoperna fortunei has been shown to strongly interact with several components of the local biota. However, investigation of its ecosystem-wide effects was hindered by (1) difficulties associated with evaluation of its densities over large spatial scales and (2) scarcity of pre-invasion environmental data. The present survey overcomes these shortcomings and addresses the question whether Limnoperna’s impact on the ecosystem-wide scale is measurable and significant. On the basis of diver-collected bottom samples, we estimated the overall density of this mussel in a reservoir (Embalse de Rio Tercero, Argentina), where Limnoperna is present since 1998 and analyzed changes in several water-column properties before and after the invasion. The 47 km2 reservoir hosts around 45 billion mussels; at these densities, a volume equivalent to that of this water body can potentially be filtered by the bivalves every 2–3 days. Data collected regularly since 1996 indicate that after the invasion water transparency increased, and suspended matter, chlorophyll a, and primary production decreased significantly, with strong changes occurring in the area with highest mussel densities. Our results indicate that the ecosystem-wide impacts of Limnoperna are generally comparable to those described in Europe and North America for another invasive mussel—Dreissena polymorpha. However, given Limnoperna’s wider tolerance limits, its influence on newly invaded water bodies, potentially including Europe and North America, will probably be stronger.

We conducted a field experiment to assess the influence of conspecific adults on recruitment success of the golden mussel Limnoperna fortunei. Tiles of 225 cm2 in surface were used as artificial substrates in four treatments: control (blank tiles), low (800 mussels m-2), medium (4000 mussels m-2) and high (12 000 mussels m-2) density treatments. Results obtained indicate that recruitment is strongly affected by the presence and density of conspecifics: after one and three months of exposure numbers of recruits were significantly higher on tiles with conspecific adults than on blank tiles, and there was a positive and significant relationship between the number of recruits and the number of adults in the three treatments assayed. Also, after three months of exposure recruits in all treatments with adults present were larger than recruits in the control treatment. Our results suggest that conspecific adults have a positive effect on recruitment success and growth of the newly settled juveniles through factors that enhance larval settling and/or that contribute to the survival of settlers in areas colonized by adult conspecifics. Fil: Sardiña, Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina Fil: Cataldo, Daniel Hugo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina Fil: Boltovskoy, Demetrio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina

We studied experimentally the feeding selectivity of larvae of Prochilodus lineatus (Pisces), with particular emphasis on the role of veligers of the exotic bivalve Limnoperna fortunei. Three concen- trations of veligers were offered to three develop- mental stages of P. lineatus. Veliger concentrations were: (1) higher than in the field (''enriched'', 0.09 ind. ml -1 ), (2) unmodified from field conditions (''normal'', 0.06 ind. ml -1 ), and (3) lower than in the field (''low'', 0.02 ind. ml -1 ). Fish developmental stages were protolarvae (approx. 10 days old), me- solarvae (17 days), and metalarvae (25 days). Pro- portions (in terms of numbers and biomass) and selectivity values were calculated for each prey item evaluated: veligers, small cladocerans ? nauplii, medium-sized cladocerans, copepodits, and large cladocerans ? copepods. Protolarvae and mesolarvae consumed veligers almost exclusively (88-90%, both in numbers and in biomass) when offered prey enriched in veligers, whereas for metalarvae veligers represented only 16.0% of the food consumed. At lower veliger concentrations, only protolarvae pre- ferred Limnoperna veligers, whereas older fishes switched gradually to crustacean plankton. We con- clude that veligers are preferred by the early fish developmental stages, and we speculate that this may be because their slower swimming makes them easier to capture than planktonic crustaceans. However, as fish larvae grow larger, veligers become too small a prey for their energetic needs, and they switch to larger items like cladocerans and copepods. We anticipate that this new and abundant food resource has an important impact on the survival and growth of P. lineatus.

We examined the importance of the introduced Asian golden mussel (Limnoperna fortunei) in structuring invertebrate communities in South American rresnwaters. An experiment using artificial substrata (i.e., concrete tiles with either a layer of living mussels, a layer of intact empty shells that mimicked living mussels, or blank tiles) showed that, when considered in bulk, invertebrates (density and biomass) are enhanced significantly in the presence of live mussels (as compared with shells only and blank tiles). On a taxon-by-taxon basis, however, significantly higher densities and biomass on live mussel tiles than on blank and/or shells-only tiles were found only for Oligochaeta, which would especially benefit from the feces and pseudofeces produced by the living mussel beds. At the end of the experiment, the amount of accumulated sediment on the tiles differed greatly among treatments, with values up to three times higher on shells-only tiles than on live-mussel and blank tiles. Dead mussels act as a sediment trap, whereas the activity of live mussels helps keep the tiles less clogged with sediments. On the other hand, proportions of organic matter were two times higher in the presence of live mussels than in the other two treatments. Although the physical structure created by mussel shells plays a significant role, we conclude that the activity of living mussels is of major importance for controlling invertebrate numbers, biomass and diversity.

To assess the trophic impact of the planktonic larvae of the invasive Asian bivalve Limnoperna fortunei, introduced in South America around 1990, we investigated the gut contents of fish larvae collected at monthly intervals between October 2000 and March 2001 at three locations along a 600 km stretch of the Parana River, and during November 2004 in two areas of marginal lagoons connected to the river near the city of San Nicolas, Argentina. Zooplankton was also collected in the lagoons in 2004. In total, 11,956 fish larvae were retrieved, of which 1,511 were used for detailed analyses. Of the 15 fish taxa collected, 11 had veligers of L. fortunei in their gut. Fish larvae with empty guts represented 60% (San Nicolas) to 72% (Parana River) of the total number of fish. Proportions of feeding fish larvae with L. fortunei veligers in their guts varied between 20% (San Nicolas) and 56% (Parana River); in 15% of the guts analyzed, L. fortunei was the only food item recorded. For those specimens that had consumed L. fortunei larvae and any other food item, L. fortunei was the most important item in 55% (Parana River) to 71% (San Nicolas) of the animals in terms of biomass. No major temporal or spatial changes in the diet were observed along the Parana River, but the relative biomass contribution of L. fortunei larvae differed strongly in fishes of different developmental stage. In protolarvae and mesolarvae, veligers accounted for 30–35% of the gut contents. In metalarvae, veligers accounted for only 3%, indicating enhanced food supply for the earliest fish life stages. Comparison of the relative proportions of the three main zooplankton types (L. fortunei veligers, cladocerans, and copepods) in the water and in larval fish guts indicates that L. fortunei is always selected positively over the other two prey types. While our results strongly suggest that the expansion of L. fortunei results in an enhanced food supply for local fish populations, they do not necessarily imply that the overall effect on the ecosystem in general, and on the fish fauna in particular is beneficial.

We assessed the effects of the introduced bivalve L. fortunei on the abundance and biomass of associated benthic invertebrates in South American large floodplain rivers. The survey was based on comparisons of L. fortunei-covered and L. fortunei-barren areas in five artificial cages from where large predators were excluded, exposed to colonization by the mussel for a total of 17 months in the lower Parana river delta. Accompanying invertebrates were dominated by Oligochaeta, Nematoda, Rotifera, Copepoda, Gastropoda, Hirudinea, Chironomidae and nauplii. Also present in minor numbers were Tardigrada, Turbellaria, Cladocera, Ostracoda, Insecta, Hydracarina and Decapoda. Dominant invertebrates were 27–100% more numerous (and hosted 43–100% more biomass) in areas with L. fortunei than in areas barren of the mussel. In areas with L. fortunei, total invertebrate biomass (excluding the bivalve) was positively correlated with mussel biomass, and increased with time of exposure under water. No such trend was observed in areas barren of L. fortunei. It is suggested that higher invertebrate growth is associated with enhanced substrate complexity and, probably, the transfer of organic matter from the plankton to the sediments due to the mussels’ feces and pseudofeces. Some of the adverse ecosystem-wide effects of filter-feeding invasive mussels observed in European and North American water bodies may be offset in the Parana by the extremely high loads of organic matter in these turbid waters.

Comparison of Limnoperna fortunei numbers and biomass in screened (5, 15 and 40 mm) and unscreened cages deployed for 18 months in the lower Parana delta indicates that predators harvest 26-79% (numbers), or 20-85% (biomass) of the mussel population. Predation impact decreases with mussel size. On average, 6 kg of whole live mussel ¥ m -2 ¥ year -1 (0.36 g of dry mussel tissue ¥ m -2 ¥ day -1 ) were eliminated from the unscreened cages. Cages with 15 and 40 mm screens lost between 1 and 2 kg ¥ m -2 ¥ year -1 . Aquatic mammals, birds, and especially fish, are probably the main consumers of large mussels. Small L. fortunei are most probably eaten by fish and also by several invertebrates, including crustaceans, leeches and gastropods. It is suggested that L. fortunei intercepts a significant fraction of the organic carbon that the Parana-Uruguay rivers flush into the ocean, locally boosting numbers of benthophagous animals, deposit feeders and, indirectly, higher level predators. Our results indicate that only 15 years after its first introduction in South America this invasive species is very actively consumed by local predators, but predatory suppression of the mussel seems very unlikely. Comparisons with the effects reported for the zebra mussel (Dreissena polymorpha) in Europe and North America suggest that L. fortunei is consumed more actively and that its negative impact on the local fauna is more restricted. These differences are attributed to the fact that while D. polymorpha feeds chiefly on plankton, a limited resource, L. fortunei feeds on detrital particulate organic matter, whose supply in these large South American rivers largely exceeds consumption.

We contrast ecological and life history traits of the well studied freshwater invader, the zebra mussel (Dreissena polymorpha), with the lesser known invasive golden mussel (Limnoperna fortunei) to compare salient biological traits and environmental limits, and to predict the potential spread and ecosystem impacts of L. fortunei in areas where it is introduced. Both species are sessile, byssate bivalves with a planktonic larval stage and extremely high reproductive capacity. For both species adults attain much higher biomass in waterbodies they invade than all of the native invertebrates combined, and they create substrate complexity otherwise not found in freshwater systems. Both are very active suspension feeders, greatly enhance benthic- pelagic coupling, and act as effective ecosystem engineers. Although taxonomically unrelated, their ecosystem impacts are surprisingly similar and follow from the novel ecological niche they share, rather than being species specific. The golden mussel has broader environmental tolerances and therefore may be a much more successful invader than D. polymorpha in regions dominated by acidic, soft and contaminated waters. In the near future L. fortunei may colonize the southern and central parts of North America, much farther north than has been previously predicted. Although to date the zebra mussel is considered the most aggressive freshwater invader, soon many waterbodies may receive another, even more aggressive invader.

The ability of the freshwater bivalve Limnoperna fortunei to voluntarily detach from the substratum, crawl and reattachas a function of illumination, temperature, substratum orientation, and mussel size was investigated. Thirty-two per centof the 879 experimental animals detached and reattached elsewhere at least once during five- to eight-day experiments.The proportions of mobile mussels were significantly higher in permanent darkness than under permanent illumination.Displacement distances were also higher in darkness, but statistical differences with illuminated individuals wereinconclusive. No evidence of circadian rhythms was detected. Mobile mussels were often significantly smaller thannon-mobile individuals. It was not possible to detect the effect of water temperature (22°C and 31°C), or substratumorientation (topside and underside) on mussel mobility, but because the power of the statistical tests was low, futureexperiments are needed to confirm this result. The ability of mussels to voluntarily detach and reattach elsewhere hasimportant implications for biofouling control. Fil: Duchini, Daniela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Boltovskoy, Demetrio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Sylvester, Francisco. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Instituto para el Estudio de la Biodiversidad de Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Latitudinal changes in the species richness of planktonic diatoms in Southwestern Atlantic and Antarctic waters (29-76 S) were analyzed from local to regional scale in three spring and one summer seasons. A total of 220 diatom species (16-87 per station) were recorded. Despite the noticeable interannual variability, species richness showed a maximum in the northern sector of the Brazil-Malvinas Confluence Zone and a highly significant decrease with latitude. Fil: Olguin Salinas, Hector. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Alder, Viviana Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Puig, Alba. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina Fil: Boltovskoy, Demetrio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina

Young Limnoperna fortunei mature sexually from 5–6 to ~15 mm. The species is generally dioecious, with approximately equal numbers of males and females and very small (< 0.6 %) proportions of hermaphrodites. The gametogenic cycle has been described for both Asian and South American populations, recognizing between four and five reproductive phases. Gonadal cycles based on histological sections yielded somewhat dissimilar results for different areas. In Hong Kong, two yearly peaks in reproductive output were detected. In South America, mature sperm and ova have been recorded year round and several irregularly spaced spawning events have been observed, as well as more or less continuous breeding punctuated by peaks in spring and at the end of the summer. Reproductive studies based on changes in the abundance of larvae in the water column have been carried out in South America and in Japan. In tropical and subtropical South America, larval output is more or less continuous for 6–10 months of the year, often with a major peak in spring–early summer, and a smaller one in the late summer–autumn. In Japan, at considerably lower water temperatures, larval production is limited to 1–2 months centered around summer. Apparent disagreements between results based on histological data and on larval counts stem from the fact that while the latter integrate the reproductive output of extensive mussel beds dispersed over large areas, histological evidence pinpoints with high precision the ripening and spawning of isolated mussel clusters. Aside from water temperature, several other factors (pH, salinity, dissolved oxygen, suspended solids, chlorophyll a, flood–drought cycles) have been proposed as reproductive triggers, but actual associations have not been demonstrated. Peak larval densities can exceed 20,000 ind./m3, but, normally, values range around 6000 ind./m3, showing major fluctuations within short periods, as well as changes as a function of time elapsed post colonization, and availability of substrata suitable for adult occupation. Microcystin-producing cyanobacterial blooms can kill L. fortunei larvae., Facultad de Ciencias Naturales y Museo

This is the first study on diatom spatial patterns in relation to major oceanographic features along a megascale transect in the Southwestern Atlantic Ocean and provides a comparison with diatom distribution in surface sediments. Absolute abundances of diatoms, silicoflagellates and dinoflagellates (>10-μm fraction) were assessed in 80 bottle samples from 5 to 50 m, retrieved in November 1993 at 20 stations (30-61°S) along 53°W. Siliceous phytoplankton were scarce in the northern half of the transect and in the south of 57°S (100-150 cells L-1), with a strong peak in the vicinity of the Polar Front (∼200 000 cells L-1), whereas dinoflagellates were more abundant at the northern stations (up to 24 000 cells L-1). In the south of 50°S phytoplanktonic cell densities were loosely (but significantly, r = 0.54, P 0.1). In total, 191 diatoms and 4 silicoflagellates were recorded. Changes in diatom assemblage compositions along the transect allowed identification of five discrete areas: Subtropical (29°S), Northern Transitional (34-41°S), Southern Transitional (43-48°S), Subantarctic (49-54°S) and Antarctic (55-59°S), each characterized by a set of typical species. Diversity changed little with latitude, but numbers of species were higher in the north of 40°S. Comparison of diatom assemblage makeup in the plankton and in the surface sediments shows very strong disagreements, whereby cold water species are very significantly over-represented in the sedimentary record, suggesting enhanced preservation and strong subsurface equatorward advection of the cold water taxa. © The Author 2006. Published by Oxford University Press. All rights reserved.