Aquatic oligochaetes (Annelida: Clitellata) in reservoirs in São Paulo State: list of occurrence and ecological observations on the species

This work sought the survey of species and information about the distribution of the Class Oligochaeta in reservoirs sampled in the Sediment Quality Monitoring Network of CETESB (Environmental Company of the State of São Paulo). As such, this study aimed to inventory the limnic oligochaetes fauna to expand knowledge of the ecology and distribution of this group in reservoirs in the state of São Paulo. Ninety replicates were performed in 12 reservoirs in the state of São Paulo between 2014 and 2016, using van Veen or Ponar samplers in the sublittoral region, and Ekman-Birge in the deep region. Twenty-eight taxa were inventoried, belonging to the families Naididae and Opistocystidae. The species Dero righii and Pristina longisoma were recorded for the first time in São Paulo State, Nais magnaseta and Spirosperma velutina were first recorded in Brazil. The results presented here make this inventory extremely important for understanding the distribution of aquatic oligochaetes throughout the Brazilian territory.


Introduction
Species surveying is essential for understanding the biota of a given environment, specifically in Brazilian aquatic ecosystems where species diversity is poorly known due to the small number of taxonomists (ROCHA, 2003;AGOSTINHO et al., 2005). Although oligochaetes are among the most abundant species in sediments of Neotropical lakes and reservoirs, there is relatively poor ecological information, especially in comparison to the knowledge generated in temperate-zone habitats where these species are used to monitor water quality (BRINKHURST; GELDER 1991, MARTIN et al., 2008, CHRISTOFFERSEN, 2010MARTIN 2015, RODRIGUES;ALVES 2018). The community composition and structure of the Class Oligochaeta provides important information for the assessment of water and sediment quality, and has therefore proved to be a great tool for aquatic biomonitoring (LAFONT, 1989;ROSSO, 1995;PRYGIEL et al., 2000;VIVIEN et al., 2014). Despite their representativeness in aquatic macroinvertebrate fauna, oligochaetes are poorly studied compared to other benthic groups (GORNI, 2007), however, several authors have been collecting information about the diversity and ecology of the Oligochaeta assemblage in São Paulo State (MARCUS DU BOIS- REYMOND MARCUS, 1949;RIGHI, 1984;CORBI et al., 2004;PAMPLIN et al., 2005;DORNFELD et al., 2006;GORNI, 2007;SURIANI et al., 2007;GORNI;GORNI;ALVES, 2008b;GORNI;GORNI, 2007;GIROLLI et al., 2018).
Given this, gathering information about the assemblages of oligochaetes is essential for knowledge of limnic biodiversity, assessment and water management. To provide information to environmental management bodies and facilitate decision-making on recovery and / or preservation of Brazilian aquatic ecosystems.
Thus, this article aims to inventory the diversity of Class Oligochaeta species in lentic environments of São Paulo State monitored by CETESB, as well as contribute to the knowledge of distribution and ecological observations in the State of São Paulo.

Area of study
The Oligochaeta fauna samples were granted for the purpose of this research by the Aquatic Communities Sector (ELHC) and are part of the Sediment Quality Monitoring Network of CETESB. Twelve reservoirs were studied in the state of São Paulo between 2014 and 2016, where a total of 90 replicates were collected. Reservoir identification is described in Table 1, and the location of the points is illustrated in Figure 1.

Physical and Chemical Variables
The physical and chemical variables were collected in two groups, water and sediment. The variables collected in the water were: total surface phosphorus (P), bottom dissolved oxygen (DO), bottom electrical conductivity (EC), chlorophyll a (C), and depth (Dep). The variables collected in the sediment were: sediment organic matter (OM), total organic carbon (TOC), total Kjeldahl nitrogen (NKj), total phosphorus (Ptot) and granulometry were performed and determined by CETESB. The bibliography and analytical methods used to collect and determine the variables are available in Annex E of the Relatório da Qualidade das Águas Interiores no Estado de São Paulo (CETESB, 2017). The values of the environmental variables measured were tested using multivariate variance analysis (MANOVA) to identify possible significant differences between the collected points.
The Trophic State Index (IET) was used to classify the water quality of the reservoirs for nutrient enrichment. The IET is composed of the indices of the Trophic State for phosphorus -IET (PT), and for  (3) where: PT = total phosphorus concentration measured at the water surface, expressed in μg/L; CL = chlorophyll concentration at total measured at the water surface, expressed in μg/L; and ln = natural logarithm.

Oligochaeta Collection and Identification
The sediment samples for analysis of Oligochaeta assemblage were collected by CETESB with van Veen or Ponar sewers in the sublittoral region and Ekman-Birge in the deep region. The fixation and sample preparation followed the CETESB Technical Standard L5.309 (CETESB, 2003). For the identification of the organisms the taxonomic criteria adopted by Brinkhurst and Jamieson (1971), Righi (1984), Brinkhurst and Marchese (1989) and Timm (2009) were used.
To evaluate the efficiency of the samples collected in the reservoirs, species richness estimators (Jackknife 1 and 2, Bootstrap) and randomized species accumulation curves (collector curve) were used. Species accumulation curves were constructed using 100 curves generated by the random addition of the samples, using the software "R" version 3.1.1 (R CORE TEAM, 2017).
We applied a Boxplot chart and selected the most abundant species (upper quartile) to perform a descriptive analysis of the reservoirs in which these species were found.

Results and Discussion
The means of environmental variables (depth, sand, silt, clay, organic matter, dissolved oxygen, total surface phosphorus, total sediment phosphorus, electrical conductivity, chlorophyll a, total organic carbon, total Kjeldahl nitrogen, and trophic state index), as well as the standard deviation, are exposed in Table 2. The same variables were submitted to a Multivariate Variance Analysis (MANOVA), in which a significant difference was identified between the points (p<0.05), which means that the reservoirs are statistically different from the environmental variables presented above.
As for the Trophic State Index, the highest values were recorded in two regions of the Billings reservoir. The first was in the central body (72.9) and in the Taquacetuba arm (70.8), they were classified as Hypereutrophic, followed by the Rio Grande (65.6) and PEBA (63.4) reservoirs, which were classified as Supereutrophic. However, all other reservoirs showed a degree of nutrient enrichment, since the lowest IET class recorded was Mesotrophic. None of the reservoirs were classified as Ultraoligotrophic or Oligotrophic.
The highest values of the variables OM (20.2%), EC (204), P (0.15 mg / L), Ptot (5,573 mg / Kg) and C (93.56 μg / L) and the lowest value of DO (3.1 mg / L) were recorded in the central body of the Billings reservoir. Other reservoirs, such as SANT and JURU, had opposite values for the same variables.
The assemblage of oligochaetes inventoried in this study was composed of two families (Naididae and Opistocystidae) distributed in 28 species. The sample design adopted in the present study can be considered adequate for species survey, since the accumulation curve stabilized in 70 samples. Figure 2 illustrates the species accumulation curve and richness estimators.
The Naididae family presented 96% of the found taxa (n=27), being represented by the subfamilies Naidinae, Pristininae, Rhyacodrilinae Opistocysta and Tubificinae. Among the Naidids, the subfamily Naidinae, which represented 59% of the species (n=16), was composed by the genera Aulophorus, Chaetogaster, Dero, Nais, Slavina and Stephensoniana. The subfamily Pristininae presented 22% of species (n=6), represented by its only genus (Pristina). The subfamily Rhyacodrilinae was represented by the taxa, Bothrioneurum sp. and Branchiura sowerbyi, corresponding to 7% of the identified species. Finally, the subfamily Tubificinae was represented by the genera Aulodrilus, Limnodrilus and Spirosperma making up 11% of the identified species (n=3). The Opistocystidae family was represented by only one species, Opistocysta funiculus, corresponding to 4% of the identified species. Among the 28 species identified in this study, Dero righii and Pristina longisoma had not been registered in the state of São Paulo, occurring only in the states of Mato Grosso do Sul, Minas Gerais and Paraná, and Mato Grosso do Sul and Paraná, respectively. Two other species had not been recorded in Brazil, Nais magnaseta whose knowledge of their distribution was restricted to Texas, USA (Harman, 1973); and Spirosperma velutina, whose distribution was registered in Venezuela and Europe (CHRISTOFFERSEN, 2007).
The species identified in this study, as well as the record of their ecological observations in the State of São Paulo, are presented below distributed in family, genus and species, following alphabetical order. The synonym list was based on the catalog proposed by Christoffersen (2007).
Other authors such as Prygiel et al., (2000), Ragonha et al. (2013) and Sales et al. (2014), corroborate that A. pigueti reaches high densities in environments with great intake of organic matter.
The Bothrioneurum sp. it is a Tubificinae commonly found in impacted waters, presenting high numerical density, often occurring together with Limnodrilus hoffmeisteri, in organically enriched places, with high conductivity and low oxygenation Lucca, 2000). Its tolerance to eutrophication and organic pollution has already been stated by Timm (2009) and Dumnicka (2007). Timm (1997) goes so far as to report that a high level of organic pollution is a limiting factor for the occurrence of the genus. Similarly, L. hoffmeisteri is commonly known as an indicator of eutrophic environments, which explains its frequency in places more intensely influenced by this condition.
Aulodrilus pigueti, which was the most abundant species in this study, is a cosmopolitan organism found in greater density in environments with high conductivity, low to moderate current speed and mud and clay sediments with abundant organic matter. The authors Schenková et al. (2010) collected the species on the bottom substrate of a fish pond and in the submerged coastal vegetation. In addition, Aulodrilus pigueti has the habit of digging the sediment and forming tubes from detritus (Timm;Veldhijzen Van Zanten, 2002). Although the species occurs in lentic or lotic freshwater environments (Finogenova;Arkhipova, 1994;Schloesser et al., 1995;Šporka, 1996), but it demonstrates having preference for environments in which the quality of the water and the substrate present characteristics of oligo to mesotrophic trophic level (Šporka, 2003), and is able to tolerate smaller amounts of dissolved oxygen and acidification (Orciari;Hummon, 1975). These characteristics reinforce the expressive occurrence of the species in intensely eutrophic reservoirs, showing its possible preference for lentic waters, rich in nutrients and with high conductivity.
The high trophic level can provide a series of microhabitats for Oligochaeta, such as surface macrophytes and sediments with abundant availability of organic matter. Notably, for Naidinae, microorganisms associated with macrophytes, such as epiphytic algae, bacteria and protozoa, are important sources of food Jamieson, 1971;Gorni, 2007;Timm;Martin, 2015). On the other hand, tubificinae reach high abundances in the superficial layers of the sediment with a high concentration of total organic carbon, nitrogen and organic matter Jamieson, 1971). Lin and Yo (2008), studying the effect of organic pollution on the distribution of Oligochaeta found the highest values for species richness, abundance and diversity in the sites with the greatest organic enrichment. Several other authors point out that high numbers of the total of Oligochaeta occur when the environment is highly polluted (Chapman et al., 1980;Rosenberg;Resh, 1993;Suriani et al., 2007).
The enriched reservoirs showed high metabolic potentials, where the organic load present in the sediment favored diversity of species and abundance of the Oligochaeta. However, they have low ecological quality, as they do not present the expressive occurrence of sensitive species. In general, sensitive species occurred in a low percentage in all reservoirs. However, it should be noted that the list of sensitive species was based on Lafont et al. (2012) for temperate environments, with the need for a functional survey for neotropical taxa, aiming at the biomonitoring of water and sediment quality.

Finals considerations
The results presented above make this inventory extremely important for the knowledge of the distribution of aquatic oligochaetes, not only for the State of São Paulo, but throughout the Brazilian territory. Moreover, using the methodology of species accumulation curves and richness estimators, it was found that the sample number of this research was sufficient to obtain a reliable result, since the number of identified species corroborated the richness estimators.
The number of taxa identified (total of 28) in this research was higher than other studies performed in lentic environments in Brazil, such as Suriani et al. (2007) who identified 17 species in São Paulo; in Paraná, Behrend et al. (2012) identified 25 species; Gomes et al. (2017) identified 12 species in Rondônia; and Gorni et al. (2018) who identified 22 species in Mato Grosso. In addition, the identified species represented 36.4% of the 77 previously recorded species in the State of São Paulo GIROLLI et al., 2018;GIROLLI et al., 2020).
In relation to South America, Christoffersen (2010) claims that the cataloged Oligochaeta represent only a fraction of their true diversity, which emphasizes the need for more studies that contemplate the species inventory in the Neotropical regions. However, it is noteworthy that over the past few years the number of surveys with freshwater Oligochaeta has been growing, especially in Brazil, and there are more than 2,300 surveys between the years 1985 and 2015 Alves, 2018).
In this research, the three most abundant species were found in organically enriched reservoirs with low dissolved oxygen levels. This factor favors the development of dominant species, such as Aulodrilus pigueti (55.4%), Limnodrilus hoffmeisteri (16.4%) and Bothrioneurum sp. (7.9%). Generally, these species are found in sediments with abundant organic matter (Marchese, 1987;Montanholi-Martins;Takeda, 1999;Behrend et al., 2009;Lafont et al., 2012). Other studies (Rosenberg; In this context, inventories of oligochaete fauna and ecological relationships between species and the environment are very important for the formulation of biodiversity conservation policies, especially in tropical environments (Christoffersen, 2010;Alves, 2018). Studies of oligochaete assemblage patterns can be useful to predict changes along environmental gradients, as well for standardized methods for testing organisms in ecotoxicological studies (Castro et al., 2020;Suriani et al., 2007;Behrend et al., 2012). However, oligochaete species surveryed and systematics studies still are scarce in Brazilian environments, probably due to the lack of specialists in the taxonomic identification of these worms.
Finally, further research using the Oligochaeta class is necessary due to its importance as bioindicators of water quality and sediment associated with the unique characteristics of Brazilian continental ecosystems.