Occurrence of Oligochaeta species (Annelida: Clitellata) in Rivers in the State of São Paulo (Brazil)

: The knowledge about the diversity and fauna distribution in tropical freshwater ecosystems is of extreme ecological importance, however studies on this theme are still scarce. Organisms belonging to the Oligochaeta Class are considered important bioindicators for environmental quality analysis, but detailed knowledge about these organisms is still insufficient. This study aims to investigate the occurrence of oligochaeta species in eight rivers of the State of São Paulo (Brazil), to expand the species catalogue and identify their relationship with the trophic state of sampled environments. The samples were collected by the Environmental Company of the State of São Paulo (CETESB) from 2014 to 2016 and include areas with different land uses,


Introduction
The knowledge about the diversity and fauna distribution in tropical freshwater ecosystems still presents gaps, despite the importance of these groups in processes of biomonitoring of environmental quality (HARPER, 1992). One of the most common and abundant groups in the benthic community is oligochaetes, which generally has a wide geographic distribution and can reach numerous populations (WETZEL, 1992;JAMIESON, 1971). In addition, oligochaetes are recognized as bioindicators of water and sediment quality, because they are sensitive to chemical pollution and eutrophication (MASSON et al. 2010).
Currently, environmental monitoring programs such as the Environmental Company of the State of São Paulo (CETESB), use the calculation of the Trophic State Index (TSI; LAMPARELLI, 2004) to evaluate the water quality in relation to nutrient enrichment. Thus, considering the degree of trophy, water bodies can be classified as: oligotrophic, mesotrophic, eutrophic and hypertrophic (CETESB, 2019).
In Brazil, we still know little about the actual number of species of the Oligochaeta Class in the continental systems. This scarcity of information occurs due to some factors, such as the large number of River basins not yet inventoried; the lack of researchers and adequate infrastructure to carry out the samplings; the loss of information that is often not available and the need for a taxonomic review for various oligochaete groups (AGOSTINHO; THOMAZ; GOMES, 2005).
Studies concerning taxonomy and faunal survey present important information about the biodiversity of each group, as well increase the knowledge about their distribution and habitat preference. Ecological information is used in the development of environmental monitoring and biodiversity conservation programs (AGOSTINHO; THOMAZ;GOMES, 2005). In the case of the Oligochaeta assemblages, the studies are still insufficient . Despite efforts of a few experts (MARCUS, 1942;RIGHI, 1984;MARCHESE, 1989;MARCHESE, 2005), it is necessary to carry out new research and update information on oligochaetes in Brazil. In this context, it is necessary to emphasize the importance of bioindicator organisms, such as those belonging to the Oligochaeta Class, which can indicate the impacts resulting from industrial urban development .
This information can aid as a basis for environmental management and for decision making on the preservation and / or recovery of Brazilian aquatic ecosystems (GIROLLI, 2019). Studies on the ecology and taxonomy of these organisms should be advanced, in order to obtain knowledge of the diversity of freshwater species in Brazil (SURIANI et al., 2007).

Objective
This study aims to investigate the occurrence of Oligochaeta species in eight rivers of the State of São Paulo (Brazil), and to expand the species catalogue, identifying the as relationship with the trophic state of sampled environments.

Fonte: Elaborado pelos autores
The sediment samples were collected in triplicate, with Van Veen or Ponar grab samplers in the depositional riverbanks, according to the CETESB L5.309 (Technical Standard). Aiming to complement the analysis of the sampled points, the Trophic State Index (TSI) were calculated (LAMPARELLI, 2004). This index aims to classify water bodies in different degrees of trophy, evaluating the quality of the water in terms of nutrient enrichment.
Faunal identification was made using the taxonomic criteria (BRINKHURST; JAMIESON, 1971;RIGHI, 1984;MARCHESE, 1989;TIMM, 2009). After identification, the organisms were deposited in the collection of the Water Communities Sector of CETESB. In order to evaluate the coverage of the sample design, the Bootstrap species richness estimator was used. For calculations we use the Vegan package (OKSANEN et al., 2019), software "R" version 3.1.1 (R CORE TEAM, 2017).

Results and discussion
The oligochaete fauna found in the eight sampled rivers in the State of São Paulo is distributed within three families (Alluroididae, Naididae, Opistocystidae) and 25 species, totalizing 7,398 individuals sampled ( Table 2). The result obtained by the Bootstrap richness estimator (29.9 ± 1.9), indicates that the sample design adopted in this study was satisfactory, considering that the recorded species richness is very close to the estimated range.  (Marcus, 1944 (Marcus, 1943) 0 + + + 0 0 0 0 Nais communis (Piguet, 1906) + + + + 0 0 + + Nais variabilis (Piguet, 1906) 0 (Marcus, 1942)  The Naididae family was considered the most representative of this assemblage of Oligochaetas, presenting 92.3% of the taxa found, being divided into four subfamilies: Naidinae, Pristininae, Rhyacodrilinae and Tubificinae. See Table 2 for more details on species occurrence in the analyzed sites.
The Alluroididae was represented by only one individual identified at the family level and the Opistocystidae was represented by the species Opistocysta funiculus. Studies suggest that the O. funiculus is able to inhabit environments with low oxygen availability and a higher concentration of organic matter, characteristics generally associated with low environmental quality (PAMPLIN; ALMEIDA; ROCHA, 2006;SANCHES, 2016;GIROLLI, 2019). Thus, our results corroborate previous studies, since O. funiculus was registered in the Tietê River, which is inserted in an area with predominantly industrial activity and was classified as hypereutrophic according to the TSI.
The most frequent species registered in this study, present in seven of the eight rivers sampled was Bothrioneurum sp. According to Brinkhurst and Marchese (1989), this species has a wide geographical distribution. However, in the studies by the authors Alves and Lucca (2000), MARTINS and ALVES (2008), BEHREND et al. (2012), SANCHES (2016) and GIROLLI (2019), Bothrioneurum sp. demonstrated ability to tolerate polluted environments, organically enriched and with high levels of electrical conductivity. In this study, Bothrioneurum sp. was recorded in the Moji Guaçu River, which corroborates the results found by the authors mentioned above, since it is a river inserted in an area with predominantly industrial activity, located in the Municipality of Cubatão (microregion of Santos, State coast) and was classified as mesotrophic.
The second most frequent species recorded was Pristina synclites present in six of the eight rivers sampled. According to Davis (1982), this species can inhabit several habitats, from clean waters to degraded waters with industrial discharges. Similarly, authors Lin and Yo (2008) also reported that P. synclites is able to tolerate polluted habitats. In this research it was found in the Aguapeí River, located in the Municipality of Lins (Midwest region), which has predominantly farming and was classified as hypereutrophic according to the TSI.

Conclusion
In general, this study points out the importance of biomonitoring using Oligochaeta organisms, since it is possible to correlate certain species with characteristics of the environmental quality of water bodies. Additionally, these results are of great importance for the knowledge of the taxonomic distribution of aquatic oligochaetes in Brazilian lotic systems, assisting in water quality monitoring programs in Brazil.