An Introduced Polychaete in South America – Ecologic Affinities of Manayunkia speciosa (Polychaeta, Sabellidae) and the Oligochaetes of Uruguay River, Argentina

The ecosystems present a great diversity worldwide and use various functionalities according to ecologic regions. In this new context of variability and climatic changes, these ecosystems undergo notable modifications amplified by domestic uses of which it was subjected to. Indeed the ecosystems render diverse services to humanity from their composition and structure but the tolerable levels are unknown. The preservation of these ecosystemic services needs a clear understanding of their complexity. The role of research is not only to characterise the ecosystems but also to clearly define the tolerable usage levels. Their characterisation proves to be important not only for the local populations that use it but also for the conservation of biodiversity. Hence, the measurement, management and protection of ecosystems need innovative and diverse methods. For all these reasons, the aim of this book is to bring out a general view on the function of ecosystems, modelling, sampling strategies, invading species, the response of organisms to modifications, the carbon dynamics, the mathematical models and theories that can be applied in diverse conditions.


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algae and detritus) to the superior consumers (aquatic vertebrates and birds). As they have evolved in an unpredictable environment, many of them have developed opportunistic ways of life and generalistic diets. Their communities often show a great plasticity with respect to their vital features and reproductive strategies which they optimize according to the environmental characteristics (Barbour et al., 1999;Rodrigues Capítulo et al., 2009).
The community of organisms living at the bottom of a water body constitutes the benthos. The characteristics of the physical habitat, the water quality and the availability and quality of the food determine, to a great extent, the presence and abundance of benthic organisms.
In fluvial environments the current and type of substratum also determine the benthic structure. The current produces a homogenizing effect of the environment, diminishing diversity, removing particles and favoring the gaseous exchange. The type of substratum can be formed by sediments of different granulometry, such as gravel, sand, silt and clay, and by riparian vegetation. Spatial and temporal variations of the fluvial systems determine that the communities of organisms inhabiting the upstreams usually differ from those inhabiting the middle and downstreams. Besides, it is possible to distinguish a littoral benthos, with habitat heterogeneity, greater diversity, and coarse particulate organic matter, and a profoundal benthos with less available habitats, moderate diversity and thin particulate organic matter (Margalef, 1983).

The introduced species
The introduction of species is one of the processes which produce major alterations in the biodiversity of ecosystems. Even though it is not a problem caused only by human activity, the number of species involved and the frequency of their relocation has grown enormously as a result of the expansion of transportation and trade (Glasby & Timm, 2008;Penchaszadeh, 2005). The continental aquatic environments are highly susceptible to the accidental or deliberate introduction of exotic species. Besides, the natural connection of the basins and the dispersion capacity of the aquatic organisms together with the human activity determine the possibility of invasion of new species (Ciutti & Cappelletti, 2009). In these aquatic environments, the transfer of exotic species occurs through a wide variety of ways and means, for example, in maritime transportation, in the ballast water of ships (El Hadad et al., 2007).
In South America, most of the coastal ecosystems between the Río de la Plata Estuary and central Patagonia have been modified due to the introduction of exotic organisms. From 31 identified cases, 6 have caused a considerable ecological impact (Orensanz et al., 2002). In this region, the introduction of crustaceans such as Balanus glandula Darwin, 1854 and www.intechopen.com  (Valenciennes, 1846), and polychaetes such as Ficopomatus enigmaticus (Fauvel, 1923) have been recorded in the last 40 years (Penchaszadeh, 2005). Recently, the presence of Manayunkia speciosa Leidy, 1858 has been registered in Uruguay River.
M. speciosa is a small polychaete strictly from freshwater, first recorded in Schuylkill River (USA) in 1858. Some decades later its distribution extended through the whole Nearctic Region, being recorded in the eastern and western lotic systems of North America (Brehm, 1978;Hazel, 1966;Holmquist, 1967;Krecker, 1939;Leidy, 1883;Mackie & Qadri, 1971;Meehean, 1929;Spencer, 1976). A hundred and fifty years after its first record, it is found for the first time in the Neotropical Region, enlarging its limit distribution from the United States of America to Argentina. Although it could not be determined whether its introduction had been recently, it can be assumed that M. speciosa arrived at the Uruguay River through the ballast water of commercial ships .
In recent years, the studies on M. speciosa have been focused in some aspects of its population dynamics and in its role as intermediate host of Myxozoa parasites of Salmonidae (Bartholomew et al., 1997;Bartholomew et al., 2006;Stocking & Bartholomew, 2007). Due to the lack of information on the ecological requirements of M. speciosa together with the scarce knowledge on the annelid fauna of the Lower Uruguay River, we propose, in this chapter, to analyze the main ecological variables which could have determined the establishment of M. speciosa with the oligochaete annelids, forming the benthic assemblage of the Lower Uruguay River.

Study area
The study was carried out in the Lower Uruguay River (Figure 1). Eight sampling sites were selected between 33º 05´ S 58º 12´W, 33º 5.94´ S 58º 25´ W. Sites S1 to S5 were established on the main river basin, site S6 at the centre of Bellaco Bay, site S7 inside Ñandubaysal Bay, and site S8 in Inés Lagoon. Sites S1 to S3 were located upstream of a pulp mill industry on the Uruguayan coast. Site S4 is an area of sediment accumulation, located downstream of the mentioned industry. Site S5 is located at the centre of the main riverbed. It is characterized by a high current velocity and a pronounced erosion effect. Hence, it constitutes a clean water zone with a limited offer of refuge and food for the benthic fauna. Site S6, located in a zone with calm waters, with bulrush (Schoenoplectus californicus (C. A. Mey) Palla) and riverside vegetation is influenced by Gualeguaychú River and Gualeguaychú city. Site S7 is also located in a zone with a low current velocity, Ñandubaysal Bay, with low waters and abundant littoral vegetation. Depending on the seasonal hydrological regime of the river, this site is connected with site S8 that shows lentic characteristics.
The sediments of the study area were formed by plastic silty clay with small proportions of scarcely sorted quartz sand (Iriondo & Kröhling, 2004).

Sampling of the annelid assemblage
The work methodology included the taking of samples with a van Veen dredge (470 cm 2 ) from a boat ( Figure 2). Seasonal samples, from November 2007 through March 2009, were extracted in the 8 mentioned sites, distinguishing, when possible, the main riverbed and the bulrushes from the coast (Fig. 1). Site S8 was not sampled during autumn and winter due to the scarce depth of the river and the abundant aquatic vegetation which made navigation impossible. Six replicates in each site and season were collected. The samples were fixed in situ with formaldehyde 5%. The following physicochemical variables were measured: Temperature in ºC and pH (Hanna HI 8633), dissolved oxygen in mg/l (Ysi 52), conductivity in µS/cm (Lutron CD-4303) and turbidity in UTN (Turbidity meter 800-ESD). Due to difficulties with the equipment, depth could only be measured in spring, summer and autumn. In March 2009, water samples for the analysis of nutrients (nitrates, NO 3 -; nitrites, NO 2 -; ammonium, NH 4 + ; and soluble reactive phosphorus PO 4 3-) were also taken. In the laboratory, the samples were washed with a 500 µm mesh sieve, dyed with erythrosine B, and the organisms were separated manually from the sediment under stereoscopic microscope. Annelids were identified under optical microscope according to keys and specific bibliography (Brinkhurst & Marchese, 1992;Glasby & Timm, 2008;Opinion 2167, ICZN, 2007Pettibone, 1953;Struck & Purschke, 2005). Final preservation of the organisms was made in alcohol 70%.
Indirect measurements of the content of organic matter (OM) in sediment of the collected samples were measured using the loss organic ignition method (LOI: loss organic ignition) at 500°C during 4 h, with a previous drying of 48 h at 60°C (APHA, 1998).

Statistical analysis
The annelid assemblage was evaluated through the application of ecological indexes: diversity (H') (Shannon-Wiener, in log e ), evenness (E') and specific richness (R: number of species or taxa). The frequency of occurrence of each species was calculated as FO (%) = 100 m i /M, where m i : is the number of samples containing species i, and M: the total number of samples. According to this, the species were classified in: Constant (C): with a FO ≥ 75 %; Frequent (F): with 75% < FO ≤ 50%; Accesorial (A): 50% < FO ≤ 25%; and Incidental (I): FO < 25%.
A Pearson correlation was performed in order to analyze the relationship between: 1) percentage of the organic matter sediment vs. individual abundance (N) of M. speciosa and 2) percentage of the organic matter sediment vs. total abundance of oligochaetes.
The relationship between the sampled sites and the environmental variables recorded was explored by a Principal Components Analysis (PCA). A Detrended Correspondence Analysis (DCA) was applied to the biotic data in order to determine if the species responded linearly to gradients or passed through some environmental optimum. Due to the fact that the maximum length of gradients in standard deviation units in this analysis was 3.328, a model of unimodal response for the species has been assumed. It was decided to apply a Canonical Correspondence Analysis (CCA) (Ter Braak & Smilauer, 2002) to explore the relationships between the annelid abundance and the environmental variables recorded in the sampling sites. The abundances of the species were log e (x+1) transformed, and all the species presenting a frequency of occurrence higher than 3 % were included (Table 1). The physicochemical variables were standardized. Their inflation factors were smaller than 3. Depth was excluded from the analysis due to the lack of records corresponding to winter 2008. Significance of all canonical axes was evaluated through the Monte Carlo test (499 permutations under the reduced model, P < 0.05). The two first axes of the ordination were selected for the graphical representation.

The annelid assemblage and its ecological affinities
The annelid assemblage studied in the Uruguay River during the period comprised a total richness R=40 taxa, most of which belonged to the oligochaete Naididae, being significant the quantity of species of Naidinae and Pristininae (Table 1). According to their frequency of occurrence and taking into account all the sampling sites, no species was constant. Only two taxa, Aulodrilus pigueti and Megadrili, were frequent; 11 taxa, among them Limnodrilus hoffmeisteri, Bothrioneurum americanum, Nais variabilis, Pristina longidentata, Enchytraeidae, Narapa bonetoi, and Manayunkia speciosa were accessories, while the rest of the taxa were incidental. Nevertheless, considering sites S3 and S7, M. speciosa was constant during the studied period. Annelid density (N) varied between 66 (S5, spring) and 3985 ind./m 2 (S8, summer) ( Figure  4). M. speciosa was present in sites S3 and S7 in all the seasons, while it was never recorded in site S8; in the rest of the sampling sites its presence was variable during the year. Its density varied between 4 (S6, spring) and 517 ind./m 2 (S3, autumn). Two egg-bearing females were found in March 2009. According to the PCA results, the first two axes explained 57.4 % of the cumulative variance of the data set (  Axis 1 (33.7 % cumulative variance) Axis 2 (23.7 % cumulative variance) Fig. 6. Ordination (PCA) diagram of the first two axes showing the variation in the sampling sites (dots) among habitat related variables (arrows). S1-S8: sampling sites; su: summer; a: autumn; w: winter; s: spring.
All the sampling sites corresponding to autumn and winter were grouped in the right (top and bottom) quadrants of the biplot, while the sampling sites corresponding to spring and summer were grouped in the left quadrants.
The first two axes of CCA explained 60.7 % of the cumulative variance from the data set (axis 1, eigenvalue: 0.592; axis 2, eigenvalue: 0.340) (Figure 7). The variables that best correlated with axis 1 were pH (r= 0.613) and conductivity (r= 0.533), while turbidity (r= 0.525) and temperature (r= 0.409) were the variables that best correlated with axis 2. The annelid species were distributed along a gradient associated to turbidity, for example Dero digitata, Stephensoniana trivandrana, Trieminentia corderoi, and Slavina appendiculata, among others. Bratislavia unidentata, Limnodrilus hoffmeisteri, Branchiura sowerbyi, and Pristina osborni were associated to organic matter. Stylaria fossularis markedly separated from the rest of the species and presented a strong association with conductivity and pH. Otherwise, M. speciosa, did not show any particular association with the physicochemical variables and grouped together with other species as Narapa bonettoi, Limnodrilus udekemianus, Aulodrilus pigueti, Pristina jenkinae and the Enchytraeidae, close to the intersection of the axes.  Table 1.

Discussion and conclusions 
Macroinvertebrates are good indicators of the ecological quality of rivers; they integrate the changes occurring over time in the environmental conditions. The species respond to the environmental variables through the gradients and the communities of specific assemblages can be used as entities in order to describe the biological state of rivers under certain environmental conditions. Ordination techniques are used to describe the species-environment associations and to identify the factors which could influence the www.intechopen.com An Introduced Polychaete in South America: Ecologic Affinities of Manayunkia speciosa (Polychaeta, Sabellidae) and the Oligochaetes of Uruguay River, Argentina 87 habitat preference of each taxon. It is a way of understanding the range of tolerance of a particular species to certain environmental variables (Adriaensses et al., 2007). In this study, ordination techniques were used in order to understand the environmental preferences of each species. Nevertheless, as the ordination only analyzes the correlations between environmental variables and species distribution, and does not reveal causal relationships, it cannot be used as a tool to determine the real factors within the many variables which could be affecting the species distribution (Lin & Yo, 2008). The Principal Components Analysis (PCA) showed that the tendency in the habitat distribution between the sampling sites was affected, to a great extent, by seasonality. The principal environmental variables acting in the ordination of the sites were temperature, conductivity and dissolved oxygen. The Canonical Correspondence Analysis (CCA) evaluated the relationship between the species populational abundance and the environmental variables. The length of the arrows representing certain variables, such as turbidity, pH and conductivity shows the impact they have had on the annelid assemblage. Some species showed a strong association with turbidity (e.g. Dero digitata and Stephensoniana trivandrana), others to organic matter (e.g. Bratislavia unidentata and Limnodrilus hoffmeisteri), while others, like Manayunkia speciosa, Aulodrilus pigueti, Narapa bonettoi did not show a particular association with the physicochemical variables and grouped together close to the intersection of the axes. L. hoffmeisteri is a species frequently associated to eutrophic environments (Dumnicka, 2002;Krodkiewska & Michalik-Kucharz, 2009;Särkkä, 1987) and together with A. pigueti dominates in the alluvial plain environments of Paraná River (Ezcurra de Drago et al., 2007). N. bonettoi is a species commonly associated to coarse sediment and sand, generally found in the main riverbed of Paraná and Paraguay rivers, where it can reach high densities (Ezcurra de Drago et al., 2007;Marchese et al., 2005;Takeda et al., 2001). Nevertheless, we found it mainly in shallow zones (bays) with abundant aquatic vegetation.


The oligochaetes are important organisms in the aquatic systems due to their impact on the sediment structure and water-sediment exchanges. Their role in the trophic nets and as intermediate hosts for several myxozoan parasites of fishes of economic importance is significant, as well as their application in pollution monitoring programs and their potential use to reduce sludge volumes in sewage treatment systems (Martin et al., 2008). Current studies on the zoobenthos of Uruguay River only deal with the fauna of its middle and upper sections (Ezcurra de Drago & Bonetto, 1969;Amestoy et al., 1986;Di Persia & Olazarri, 1986;Pintos et al., 1992). The annelid fauna of the lower section has not received much attention so far. In our work, the freshwater polychaete Manayunkia speciosa was associated with the oligochaete assemblage formed by cosmopolitan organisms, like Naididae (mainly Tubificinae and Naidinae) and Enchytraeidae (Martin et al., 2008), and an endemic family of the Neotropical region, Narapidae (Ezcurra de Drago et al., 2007). Such assemblage showed certain similarities with the oligochaete fauna recorded in other large South American rivers as Paraguay and Paraná (Ezcurra de Drago et al., 2007;Marchese et al., 2005;Monthanoli & Takeda, 1999;, although a higher number of species have been recorded in our study in the Lower Uruguay River. Among the especies registered in all these rivers, A. pigueti, L. hoffmeisteri, L. udekemianus, Bothrioneurum americanum, Pristina americana, P. longidentata, Stephensoniana trivandrana, Trieminentia corderoi and Narapa bonettoi can be mentioned. Ezcurra de Drago et al., (2007) noticed that the benthos of large rivers (with sandy-mobile beds) has a high similarity world-wide, with high abundances, low biomass and low species richness. In the lateral dimension of the alluvial plain, these authors (Ezcurra de Drago, op. cit.) observed a gradient from the main channel to the temporary marginal wetlands, with an increase in the species richness, diversity and biomass, and a decrease in abundance. In the alluvial river-plain transect they found a higher occurrence of oligochaetes in channels and lakes. The spatial heterogeneity, habitat structure, temporal instability and high productivity determine the highest importance of the transversal dimension over the longitudinal in the large rivers with alluvial plain. Vertical dimension also plays an important role in these systems, as it offers refuge for the hatching of eggs and the eclosion of juveniles, providing a habitat for these first stages which represent a faunistic reserve of the system under adverse conditions. Many invertebrate species, the oligochaetes among them, can move to the sediments during the drought phases until favorable conditions are restored. In the Parana River system, the benthic assemblage exhibits more variation in an extended spatial scale, where geophysical processes occur, rather than in smaller scales.
We observed a similar complex as pointed out by Marchese et al., (2005), and Ezcurra de Drago et al., (2007) in Paraná River, in which the highest richness and diversity were recorded in the marginal habitats (or floodplain lakes), that represent the highest spatial and temporal heterogeneity of habitats. Likewise, these authors recorded the highest densities in the main riverbed with values much higher than the ones registered by us. In our study, the highest abundances of individuals have been found in sites with high values of richness and diversity (as bays and lagoon), but not in the main riverbed. In our case, the low values of abundance, diversity and richness observed in the main riverbed (S4), may be due to the influence of the pulp mill industry placed upstream. It is known that the benthic invertebrates are exposed to xenobiotic chemicals in several ways, like the direct contact with sediment through the tegument or the ingestion of contaminated sediment, as the pulp mill effluents and their sediments contain possibly bioavailable and toxic amounts of resin acids, β-sitosterol and chlorophenolics (Merilaïnen & Oikari, 2008).
In the large South American Rivers (e.g. Paraná and Paraguay), the composition of the benthic assemblage and the total density show changes determined by the annual pulse of floods and the degree of connectivity of the alluvial environments, and by the long term phenomena involving ecological successions. For the benthic communities, the low water periods represent a more significant stress factor than the floods (Ezcurra de Drago et al., 2004;2007;Montanholi & Takeda, 2001). Nowadays, the ENOS (El Niño/ Southern Oscillation) is one of the most widely studied weather phenomena. During the sampling period in the Lower Uruguay River, the ENOS (El Niño/La Niña) events underwent a cold phase or "La Niña" with transition to a neutral phase (information of the Departamento Climatológico, Servicio Meteorológico Nacional, Argentina, www.smn.gov.ar), related with periods of normal to low discharges (Pasquini & Depetris, 2007). Montaholi & Takeda (2001) recorded Aulodrilus pigueti in the Upper Paraná River during the low water phase, where it was dominant. In our study, this species appeared in every site and sampling occasion. Other studies associated A. pigueti with fine sediment and a high content of organic matter (Ezcurra de Drago et al., 2007;Lin & Yo, 2008). Montaholi & Takeda (op. cit.) considered that its highest abundances in the alluvial lagoons during the low water phase and its low density in lotic environments is an adaptation to lentic environments and muddy substrate with a high quantity of organic matter and low velocity of current. Besides, its asexual reproductive mode would be intensified during these low water periods.

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Many studies indicate that the anthropogenic pressure in natural ecosystems favors the invasion and persistence of non-native species when the habitat conditions are modified (Gabel et al., 2011). Polluted areas could accumulate a higher quantity of invasive species than the less impacted areas (Crooks et al., 2011). Freshwater ecosystems are particularly affected by biological invasions. The artificial navigation routes, when connecting the freshwater systems previously separated by natural biogeographic boundaries, constituted important ways of invasion for non-native species, especially with maritime ports as entrance gates from overseas. Freshwater species can be transported attached to the hulls of ships (in continental aquatic systems) or in their ballast water (Gabel et al., 2011). The anthropogenic alteration of the abiotic factors (pollution, physic disturbances, artificial navigation routes, etc.) facilitates biological invasions (Crooks et al., 2011;Gabel et al., 2011). Estuaries, coastal lagoons and inner waters generally present more species of introduced invertebrates than the marine environments (Zaiko et al., 2011). This can be due to the fact that they are more vulnerable environments (variety of habitats, salinity gradient, nutrient enrichment, etc.) and with a higher anthropogenic pressure -extensive shipping activities, proximity to invasive corridors, e.g. channels, artificial substrata, degradation of habitat, over-fishing-. Some authors even consider that these ecosystems should be treated as "hot spots" for the introduction of species (Zaiko et al., 2011) and therefore the management strategies and monitoring programs tending to prevent the invasion impacts should be focused on them. The efforts to improve the environmental conditions and to prevent the mechanisms which favor potential invaders should be encouraged.

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The biogeographic aspects of the genus Manayunkia arises certain interest because it includes species which have colonized freshwater environments (Rouse, 1996). Benthic and littoral organisms can present a high degree of endemism, being an example M. speciosa (Margalef, 1983). Its distribution has been restricted to North America, with a rather disperse and also intriguing distribution pattern. Nevertheless, and as with other polychaete species, it is supposed that its distribution has been widened due to human activities, both intentionally (aquiculture) and inadvertently (basins interconnection and maritime transportation activities) (Glasby & Timm, 2008). As early as in the first decades of the 20 th century, Meehean (1929) suggests its entrance in Lake Superior through the ballast water of maritime ships.
 Manayunkia speciosa is a tube-dwelling organism, with poorly developed parapods and therefore a limited swimming capacity (Croskery, 1978). It builds its tubes with fine particles clustered by mucus secretions (Leidy, 1883). Under certain conditions -when disturbed-it can leave the tube and roam freely in the sediment (Rouse, 1996;Stocking & Bartholomew, 2007). Like other freshwater polychaetes, it has modified its reproductive strategies for protecting their larvae from osmotic stress. Although the knowledge on its reproductive ecology is scarce, it reproduces sexually or asexually inside the tube, forming typically large and yolky eggs. The juveniles develop within the tubes and when they become young adults, they leave the refuge to build their own ones (Croskery, 1978;Glasby & Timm, 2008). Like other representatives of the Fabricinae subfamily, it is believed that they are suspension feeders, and in a facultative way they are surface deposit feeders, consuming fine organic detritus and microalgae. As they require great quantities of organic matter and in order to optimize their ingesta, these polychaetes are able to select the size of the particles. They either reject or use those bigger particles in the building of their tubes (Stocking & Bartholomew, 2007). Successful non-native invertebrates often present ecological characteristics which result beneficial in disturbed environments, e.g. short generation time, early sexual maturity, high fecundity, a wide food range, euryhalinity and tolerance to pollution and habitat degradation (Gabel et al., 2011). Some of these characteristics would have allowed M. speciosa the settlement in the Lower Uruguay River. As regards its ecological requirements, Brehm (1978) found this polychaete associated to silt-clay sediments, scarce sands, abundant organic matter, salinities up to 11 ‰, and temperatures between 7 to 31 ºC. Besides, Margalef (1983) mentioned M. speciosa as a resistant species to polluted water. In the Lower Uruguay River, we have found this species mainly in calm water sites with aquatic vegetation and abundant organic matter. Despite the very low abundance of ovigerous females collected in March 2009, we suggest that the population of M speciosa could be well established in the Lower Uruguay River. During biological invasion, "lag times" are frequently observed between the first introduction and the consequent spread of the species, and ussually extend from decades to centuries. Several species have been present for long periods without an apparent major impact before rapidly increasing their populations and becoming highly consequential (Simberloff, 2011). We hypothesize that a similar event might be occurring with M. speciosa. Furthermore, the only record of this polychaete on the South American Uruguay River highlights that it goes unnoticed due to its small size, infaunal lifestyle and low abundances. According to Brehm (1978), who reported that most records are based on a few individuals, we found ca. 500 ind./m 2 . Only Hiltunen (1965) recorded more than 45,000 ind./m 2 at the mouth of Detroit River (USA). Nevertheless, this does not imply that introduced species that now have scarce or no repercussion could eventually have a greater impact on the involved ecosystems in the future.

Acknowledgments
We would like to thank Jorge Donadelli from Laboratorio de Química, ILPLA for the analyses of nutrients of the water samples and Mrs. Mónica Caviglia for the translation of the manuscript. This is scientific contribution Nº 914 of Instituto de Limnología Dr Raúl A. Ringuelet (ILPLA).