Freshwater mollusks and environmental assessment of Guandu River , Rio de Janeiro , Brazil

The Guandu River Basin is extremely important to state of Rio de Janeiro, as a water supplier of several municipalities. However, the malacological knowledge and environmental status is not well known to this basin. The aim of this paper is to present an inventory of freshwater mollusks, as well as an environmental assessment through a Rapid Assessment Protocol, of ten sampling sites at Guandu River basin in six municipalities (Piraí, Paracambi, Japeri, Seropédica, Queimados and Nova Iguaçu). Thirteen species of molusks were found, eight native (Pomacea maculata, Biomphalaria tenagophila, Gundlachia ticaga, Gundlachia radiata, Omalonyx matheroni, Diplodon ellipticus, Anodontites trapesialis and Eupera bahiensis) and five exotics (Melanoides tuberculata, Ferrissia fragilis, Physa acuta, Corbicula fluminea and Corbicula largillierti). The environmental analysis ranked most sites as “modified”. The expansion of exotic species with their associated negative effects, as well the gap in knowledge of native species calls attention to the need of future studies of biology and ecology of the species found.


Introduction
Few molluscan studies were conducted in Guandu River Basin.Tubbs-Filho & Vettorazzi (2012) recorded the occurrence of the exotic bivalve Corbicula fluminea (Müller, 1774) in the tributaries of Ribeirão das Lajes which is an affluent of Guandu River.Lacerda et al. (2013) reported the first occurrence of Gundlachia radiata (Guilding, 1828) from southeast Brazil in this area.Thiengo et al. (2001) reported sixteen species of limnic gastropods in the municipalities of Itaguaí, Seropédica, Queimados, Japeri, Paracambi and Nova Iguaçu, but without the information of the water body surveyed.
The concern with the conservation of natural resources is growing due to constant alteration of habitats, overuse of natural resources and introduction of exotic species, which causes loss or reduction of the diversity at all scales (Lydeard et al. 2004, Amaral et al. 2008, Santos et al. 2012, Miyahira et al. 2012).An important step for conservation is making the information of occurrence and distribution of different taxa available (Metzger & Casatti 2006).Therefore it is necessary to inventory native flora and fauna, in order to support conservation plans (Moulton et al. 2000).Molluscan fauna were not considered in most surveys, although it is the most diverse group after arthropods, occurring in different freshwater habitats such as streams, rivers, lakes, wetlands, swamps, dams, ponds and drainage ditches, with different degrees of eutrophication.Moreover, freshwater molluscs are among the most threatened faunal group in the world (Lydeard et al. 2004, Bogan 2008, Strong et al. 2008, Pereira et al. 2014).
Thus, the goals of this work were to: 1) study the freshwater mollusks diversity and distribution at the Guandu River Basin and, 2) evaluate the degree of preservation of the studied area through the application of a Rapid Assessment Protocol (RAP).

Study area and sampling
The Guandu River is formed mainly by the Ribeirão das Lajes River and the waters transposed of the Paraiba do Sul River (Tubbs-Filho & Vettorazzi 2012, Costa et al. 2013).The total length of the Guandu River is 108.5 km (Costa et al. 2013), flowing through the municipalities of Piraí, Paracambi, Japeri, Seropédica, Queimados, Nova Iguaçu and Rio de Janeiro, all in the state of Rio de Janeiro.In Guandu River Basin there are crops, pastures, sand extraction areas, cities, industries, hydroelectric plants and a reservoir at the responsibility of CEDAE (Companhia Estadual de Águas e Esgotos), that provide water to approximately eight million people in the metropolitan area of Rio de Janeiro (Tubbs-Filho & Vettorazzi 2012).

Collection and analysis
The mollusks were searched in all suitable habitats, including marginal and floating vegetation, using a handled metallic scoop as described by Fernandez et al. (2008).Large freshwater mussels (Unionida) were searched in sand and muddy substrates using bare hands and feet.The search was made by three collectors during 20 minutes, totalizing one hour per sampling site.The abundance values presented are the sum of the specimens obtained in each site.The field work was done at May/2013 and January/2014.
After field work the gastropods were submitted to a parasitological test, light/dark cycle exposures test (Fernandez et al. 2008).The cercariae were identified following Schell (1970) and preserved in AFA.Thereafter, the mollusks were anesthetized with menthol (C 10 H 20 O), sacrificed in hot water (only gastropods), soft parts were preserved in 70% ethanol and shells were preserved dry.
We used the RAP developed by Callisto et al. (2002) to evaluate the conservation status in each sampling site at the Guandu River Basin.This protocol evaluates 22 characteristics of the water body, margins and surroundings.The final score reflects the conservation level of the site:  zero to 40 points is "impacted", 41 to 60 points is "modified" and above 61 points is "natural".

Species diversity, distribution and parasitological test
Thirteen species of freshwater mollusks were found: eight gastropods and five bivalves (Table 1, Figure 3 2).
Gundlachia ticaga is found at upstream-intermediate sites (PR1, PA1 and ITA); F. fragilis is found at intermediate sites (ITA and SE2); and G. radiata, D. ellipticus, A. trapesialis and E. bahiensis at intermediate-downstream sites (SE2, NI1 and NI2).The other species not presented a distribution limited to any specific section of the basin.
The most abundant species at Guandu River Basin was C. fluminea (431 specimens), and the less abundant was F. fragilis (3 specimens) and O. matheroni (5 specimens) (Table 2).Gundlachia radiata, D. ellipticus and E. bahiensis were restricted to few sampling sites; however these species were abundant locally.
The parasitological survey revealed only the interaction of G. ticaga with Longifurcate pharyngeate monostome cercaria (Vivax cercaria) (Trematoda: Digenea) in PR1.The exposition of the other gastropods to light/dark cycles returned negative results.

Habitat and environmental evaluation
All bivalves were found buried in soft sediment with some organic matter, except by E. bahiensis found attached to the roots of Eichornia sp.Ferrissia fragilis, G. radiata, G. ticaga and P. acuta were found attached to aquatic plants, decayed debris and on artificial substrates such as plastic bottles.Melanoides tuberculata and P. maculata were found over soft and hard substrates.Omalonyx matheroni was found on plants at interface water-air.
Only PR1 and PR2 were considered as "natural" on RAP; NI1 was characterized as "impacted" and the remaining sites as "modified" (Table 2).The downstream stations received the lowest scores on the RAP.

Discussion
Five exotic species were found: three freshwater snails (M.tuberculata, P. acuta and F. fragilis) and two freshwater bivalves (C.fluminea and C. largillierti); except by F. fragilis, a cryptic species that were recently reported to Brazil (Lacerda et al. 2015), the other species can also be considered as invasive.Among these species, the most widespread and harmful are C. fluminea and M. tuberculata.Both species can cause modification of community (Santos et al. 2012).Melanoides tuberculata is widespread in Brazil (Fernandez et al. 2003, Thiengo et al. 2007, Santos et al. 2012), reaching high population densities that affect native species (Freitas et al. 1987, Giovanelli et al. 2003, Braga et al. 2014).Furthermore, it is the first host of different parasites that causes human diseases (Vaz et al. 1986, Guimarães et al. 2001, Pinto & Melo, 2010).However, no parasitological interaction was found for this species in Guandu River Basin.
Corbicula fluminea is a widespread species in Brazil compared to C. largillierti, that has a restrict distribution (Santos et al. 2012).These  3L) Corbicula largillierti (Philippi, 1844) (Figure 3M) observations are consistent with the situation that we found in the Guandu River Basin, where C. largillierti had a restricted distribution whereas C. fluminea was found everywhere.Previous record of C. fluminea on Guandu River Basin stated only tributaries of Ribeirão das Lajes River (Tubbs-Filho & Vettorazzi 2012), but it is clear that is widespread at the basin.This last species also has caused serious economic damage to industries and power plants, due to obstruction of water pipes and competition with native bivalves (like D. ellipticus and A. trapesialis that occurs at Guandu River Basin), reducing their populations (Mansur et al. 2004, Santos et al. 2012).Corbicula fluminea is also the most abundant species at Guandu River Basin, as already observed by other authors in other sites (e.g., Mansur et al. 2004, Santos et al. 2012, Pereira et al. 2014, Meyer et al. 2017).
The Unionida species needs a minimum amount of nutrients in the water to survive and usually occurs in lower sections of the rivers, where there is large amount of nutrients (Pereira et. al. 2011(Pereira et. al. , 2014)), as observed for D. ellipticus and A. trapesialis at Guandu River Basin.Gundlachia radiata also prefer the large section of the river, at least at Guandu River Basin (Table 2), and it is possible that have higher nutrients requirements compared to other ancylids species.The first record of this species was in this section of the river, also occurring downstream of Guandu Reservoir (Lacerda et al. 2011).It is not possible to found a reason to the restricted distributions of G. ticaga and F. fragilis based in our data.
Eupera bahiensis is recorded for the first time to the state of Rio de Janeiro and it is also the southernmost record of this species.Until now, it was found in the states of Bahia (Mansur & Meier-Brook 2000), Pernambuco (Haas 1939), Ceará (Haas 1939), Pará (Haas 1949 a,b;Haas 1952) and Amazonas (Haas 1949b).
All other species were previously recorded to state of Rio de Janeiro.However some of them, like A. trapesialis was rarely reported.This species was recorded only one time to state of Rio de Janeiro at Juturnaíba Reservoir, municipality of Silva Jardim (Alvarenga et al. 1979).Diplodon ellipticus is only mentioned to Paraíba do Sul River in the state of Rio de Janeiro (Morretes, 1949).These new records evidence the gaps on the distribution of freshwater mollusks species as a result of the low sampling effort.
We noticed some new municipalities occurrences compared to Thiengo et al (2001): F. fragilis to Seropédica; G. radiata to Seropédica and Nova Iguaçu; and M. tuberculata, O. matheroni and P. maculata to Paracambi and Nova Iguaçu.
We noticed only the presence of Longifurcate pharyngeate monostome cercaria (Vivax cercaria) in G. ticaga.Previous studies in the state of Rio de Janeiro have pointed out other cercaria types in this species: Gymnocephalous cercaria to the municipality of Angra dos Reis (Lopes et al. 2011), Echinostome cercaria to Itaguaí and Vassouras (Thiengo et al. 2001) and Nova Friburgo (Thiengo et al. 2002).The final host of longifurcate pharyngeate monostome cercaria are birds and mammals (Pinto & Melo 2013).
The RAP classification identified the most upstream collecting sites (PR1 and PR2) as natural environments.In PR1 were found more species than in PR2 (Table 2) due the greater environmental heterogeneity (more habitats available).In PR1 there are more macrophytes and some side pools, habitats for O. matheroni and G. ticaga.As the Guandu River flows across the cities of Paracambi, Itaguaí, Japeri, Seropédica and Nova Iguaçu, receives domestic and industrial sewage and margins are sharply modified.NI2 was the richest in freshwater molluscs species, and also one of the most clearly anthropized.However, it was on a small bay near the main channel of the river, thus with a good water renovation.In NI1, near to NI2, with same habitats available (soft and hard substrates, as also rooted and floating macrophytes) but with more organic input and less water circulation sustained fewer species (Table 2).
In a dense populated area, in the metropolitan area of Rio de Janeiro, we found new municipalities records, and even a new record to the state of Rio de Janeiro.The dominance and wide distribution of M. tuberculata and C. fluminea in almost all sampling sites, emphasizes the need for a continuous monitoring and control of the spread of exotic species.Also, biological and ecological aspects of native species must be studied to support conservation strategies and reduce the effects of exotic species.

Figure 1 .
Figure 1.Studied area and the ten sampling sites at Guandu River Basin in six municipalities of the state of Rio de Janeiro.

Table 1 .
Taxonomic list of freshwater molluscs found at Guandu River basin.