Fish fauna of Pratagi River coastal microbasin , extreme north Atlantic Forest , Rio Grande do Norte State , northeastern Brazil

The purpose of this study was to inventory the ichthyofauna of the coastal Pratagi River basin, located on the east coast of the state, region with intense tourist activities. A total of 2,181 specimens were collected, from August 2011 to August 2013, using sieves, trawls, cast nets, traps and gillnets. Additionally, two species ( Centropomus sp. and Lutjanus alexandrei ) have only been recorded through underwater observations, summing 22 species and genera, 18 families and nine orders. Along the Pratagi drainage some human impacts were identified, mainly related to tourist activities, such as removal of riparian vegetation and sedimentation caused by the passage of vehicles on dunes. Species richness was lower near the most visited places and greater in the lower portion of the basin, due to the presence of estuarine and marine species. Apparently, a set of small waterfalls act as a barrier to some fish species, both upstream and downstream.


Introduction
The knowledge about the fish diversity of the northeastern Brazil coastal basins is partial, especially from the Mid-Northeastern Caatinga freshwater ecoregion (Rosa et al. 2003;Abell et al. 2008, Albert et al. 2011).This region includes the coastal watersheds between the rivers São Francisco and Parnaíba, covering the Alagoas, Pernambuco, Paraíba, Rio Grande do Norte, Ceará and Piauí States (Rosa et al. 2003) and is considered one of the main gaps in ichthyofaunal studies in the world (Lévêque et al. 2008).
Although the semiarid Caatinga biome is predominant in this region, the east coastal margin of Alagoas, Pernambuco, Paraíba and Rio Grande do Norte States are characterized by the Atlantic Forest (Langeani et al. 2009).Despite little knowledge about fish fauna of the Atlantic Forest, this is one of the richest Neotropical biomes, and features a high variety of habitats (Abilhoa et al. 2011).However, the rivers of this biome are characterized by having limited extent and environmental fragility (Serra et al. 2005), and are threatened by urban pressure in most of its length, leaving few unchanged forest areas (Menezes et al. 2007;Ribeiro et al. 2009).According to Langeani et al. (2009) urgent additional inventories shall be made on stretches of rivers that drain the northeastern Atlantic Forest, mostly impacted by urban sprawl and agricultural, industrial and aquaculture activities.
Besides presenting smaller areas, microbasins can exhibit high species richness of fish due to greater environmental heterogeneity, as those of the Atlantic Forest in the southern coast of Bahia, with high levels of richness and endemism (Menezes et al. 2007).Moreover, the estuarine portion of these basins regions Abstract: The purpose of this study was to inventory the ichthyofauna of the coastal Pratagi River basin, located on the east coast of the state, region with intense tourist activities.A total of 2,181 specimens were collected, from August 2011 to August 2013, using sieves, trawls, cast nets, traps and gillnets.Additionally, two species (Centropomus sp. and Lutjanus alexandrei) have only been recorded through underwater observations, summing 22 species and genera, 18 families and nine orders.Along the Pratagi drainage some human impacts were identified, mainly related to tourist activities, such as removal of riparian vegetation and sedimentation caused by the passage of vehicles on dunes.Species richness was lower near the most visited places and greater in the lower portion of the basin, due to the presence of estuarine and marine species.Apparently, a set of small waterfalls act as a barrier to some fish species, both upstream and downstream.
Samples were taken from August 2011 to August 2013 (Figure 1, Figure 2S1-2S5 and Table 1).Each location was sampled traversing a stretch of about 50 m.The collections of specimens were carried out using sieves, trawls, cast nets, traps and gillnets, according to environmental and hydrological conditions of each sampling site.Besides these fishing gears, snorkeling observations were also performed.Fish collections were made under ICMBio/ SISBIO (Instituto Chico Mendes de Conservação da Biodiversidade/Sistema de Autorização e Informação em Biodiversidade) permits #30532-1/2011.Collected specimens were anesthetized with eugenol (two drops per liter), fixed in 10% formalin, posteriorly preserved in 70% ethanol and deposited at Universidade Federal do Rio Grande do Norte (UFRN) fish collection (Table 2).Some specimens were photographed alive (Figure 3) to obtain registration of natural color pattern.
Species were identified to the lowest possible taxonomic level, using available specialized literature (Araújo et al. 2004;Britski et al. 1984Britski et al. , 2007;;Figueiredo andMenezes 1978, 1980;Kullander 1988;Menezes andFigueiredo 1980, 1985;Marceniuk 2005;Menezes et al. 2007;Ploeg 1991).The taxonomic classification followed Eschmeyer (2013).Species were assigned to each habitat according to the classification proposed by Froese and Pauly (2013).The popular names were directly accessed through questionnaires with photos of each species to the local population and vendors, while the main anthropic impacts were identified based on direct observations and photographic records.

Results
A total of 2,181 specimens belonging to 20 species and genera, 16 families and nine orders (Table 2) were collected.Besides these, two species (Centropomus sp. and Lutjanus alexandrei) have only been recorded visually through snorkeling in the stretch downstream Cachoeirinha de Pitangui waterfall (S5).Specimens of Centropomus sp.(10-20 cm standard length, SL) were observed in August 2012 and of Lutjanus alexandrei (5-30 cm SL) in July, August and October 2012.None of the species recorded in this study is rare, endangered, exotic or allochthonous.
Of the 22 species recorded, 13 are freshwater, three estuarine and six marine (Figure 3, Table 2).The species Cichlasoma orientale, Crenicichla menezesi, Hemigrammus marginatus, Hoplias malabaricus and Poecilia vivipara were collected in all sampling sites, including the lower portion of the basin under tidal influence (approximately 0.5 km from the sea), indicating that these may have tolerance to salinity or were   1) and some anthropogenic impacts (I1-I3) in Pratagi River microbasin, Rio Grande do Norte State, Brazil.I1, carciniculture tank and removal of riparian vegetation adjacent to middle Pratagi River; I2, dune erosion and sedimentation mainly due to buggy traffic at Lavacu; and I3, uncontrolled tourism at Cachoeira de Pitangui.2) suggests that this set of small waterfalls (maximum height 1.9 m) can act as a physical barrier.
The sampling sites with lowest species richness were S3 and S4, with six and eight species, precisely the river patches that receive most tourist visitation, adjacent to the Lavacu and Cachoeirinha de Pitangui, respectively.The highest species richness was found in the lower stretch S5 with 19 species recorded, most of them estuarine or marine species, with eight of these restricted to this locality (Genidens barbus, Mugil curema, Atherinella brasiliensis, Microphis lineatus, Centropomus sp., Lutjanus alexandrei, Eucinostomus argenteus and Dormitator maculatus) (Table 2).
Among the freshwater species, five are used as sources of protein for human consumption according to the local population: Cichlasoma orientale, Hoplias malabaricus, Trachelyopterus galeatus, Megalechis thoracata and Synbranchus marmoratus, which are the larger freshwater species found in Pratagi River.Among the marine species, Centropomus sp., Eucinostomus argenteus, Genidens barbus and Lutjanus alexandrei are also important for subsistence feeding, but feature as small importance in local commercial fisheries.
Along the basin some human impacts were identified, primarily related to tourist activities.In many stretches occurred suppression of riparian vegetation (Figure 2 S1 and S2), with implementation of agricultural, cattle raising and carciniculture (Figure 2 I1) immediately adjacent to Pratagi River main course.During field visits, a large number of visitors was observed, mainly in Lavacu and Cachoeirinha de Pitangui (Figure 2 I2 and 2 I3).In Lavacu the intense traffic of off-road vehicles in the dunes that border the river may have intensified the erosion process (Celliers et al. 2004;Davenport and Davenport 2006;Thompson and Schlacher 2008) and sedimentation of the river, that could have resulted in a widest river, with laminar flow, formation of sandbanks and diversion from the main channel (Figure 2 I2), only observed in this stretch of the basin.In Cachoeirinha de Pitangui an area were opened for vehicles parking and installation of food stalls, that serve drinks and food to visitors at tables in the riverbed (Figure 2 I3), contributing to the increase of solid waste that falls in the water, and accumulates mainly in the river mouth.

Discussion
Few ichthyological surveys have been made in the coastal basins under the influence of the Atlantic Forest north of the São Francisco river, and these are practically restricted to Paraíba and Pernambuco States.Ramos et al. (2005) in an inventory of the fish fauna of Curimataú drainage (about 120 km extent) found 22 species from 17 genera and eleven families of freshwater fish, although this study excluded the area of the basin under marine influence.Torelli et al. (1997) and Gomes-Filho and Rosa (2001) conducted surveys in Gramame coastal basin (54 km long), and recorded 22 species and genera and 15 families, and 32 species of which 23 were freshwater, respectively.Rosa and Groth (2004) in studies on fish fauna of the northeastern upland forest (brejos de altitude) of Paraíba and Pernambuco States, which consist in wet forests remnants of Atlantic Forest in Caatinga areas at the Borborema plateau, recorded 27 species belonging to 23 genera of 12 families.
Compared to these fish surveys of largest coastal basins, the fish fauna of the Pratagi drainage present a similar species richness (22 species), however, the number of freshwater species was relatively low, with only 13 species recorded, nine of these are considered primary freshwater fishes.This species richness is relatively high considering the reduced size of the basin (about 10 km extent), and could be explained by the high diversity of habitats usually present in microbasins (Súarez 2008).
Once it is a coastal microbasin, with small extension and therefore greater marine influence, the Perciformes order showed higher species richness in Pratagi River, with presence of estuarine and marine species.In most basins of the Neotropical region, the predominant groups are Characiformes and Siluriformes (Reis et al. 2003;Buckup et al. 2007).Of the 13 freshwater species, one is peripheral (Awaous tajasica) and three are secondary (Cichlasoma orientale, Crenicichla menezesi and Poecilia vivipara (Albert and Reis, 2011).
One of the major differences between the freshwater fish fauna of the Pratagi River and the largest adjacent basins (e.g., Ceará-Mirim and Potengi) is related to the absence of larger species (e.g., Hypostomus pusarum (Starks, 1913)) or species that perform small migrations (e.g., Leporinus piau Fowler, 1941 and Prochilodus brevis Steindachner, 1875).These species may not occur in this microbasin because the size and other characteristics of the basin can not meet the ecological requirements of these species, or because they may have been extirpated during marine transgressive events, above the current sea level that occurred during the late Quaternary (Suguio 1999;Bezerra et al. 2002), due to its low elevation (Table 1).In this case, only salt resistant species or freshwater species that recently recolonized the basin would be present in Pratagi River.
Although the Pratagi River basin present relative ecological integrity, with patches of Restinga and Atlantic Forest and without introduced fish species, some human impacts were identified along the river, such as removal of riparian vegetation, carciniculture, inordinate tourism, accumulation of solid waste and sedimentation caused by the passage of vehicles on the dunes that border the river (Figure 2 I1-I3).This later is in an advanced stage and may soon jeopardize the basin downstream of Lavacu, including the regular water flow to the Cachoeirinha Pitangui.Once dunes are considered highly sensitive to direct human disturbance, including the erosion of the foredunes caused by vehicles traffic, active mitigation and conservation measures are recommended to reconcile human recreational demands with sustainable use of coastal assets (Thompson and Schlacher 2008).
Moreover, in coastal plain of the Pratagi River will be built a large real estate development, whose environmental impacts assessment study (EIA) indicates the occurrence of only six fish species in the basin (ECOPLAM 2006), which represent 27% of the species herein listed.Thus, this survey will contribute to the monitoring of environmental changes resulting from the rapid urbanization and unregulated tourism development in Pratagi microbasin, which may reduce habitat quality and biodiversity (Dudgeon et al. 2006).

Figure 1 .
Figure 1.Location of Pratagi River microbasin, Rio Grande do Norte State, Brazil, showing sampling sites.Natal city indicated by open dot.

Table 1 .
Geographic coordinates, elevation and locality of five sampling sites in Pratagi River microbasin, Rio Grande do Norte State, Brazil.

TABLE 2 .
List of fish species of Pratagi River microbasin, Rio Grande do Norte State, Brazil, based on records by site.Abbreviations are F, Freshwater, E, Estuarine, M, Marine.* Visual records.