Ceratium furcoides (Levander) Langhans: first record in Nova Avanhandava reservoir, Southeast Brazil 1

e742019. http://dx.doi.org/10.1590/2236-8906-74/2019 ABSTRACT – ( Ceratium furcoides (Levander) Langhans: first record in Nova Avanhandava reservoir, Southeast Brazil). This is the first record of Ceratium furcoides in the Nova Avanhandava reservoir, São Paulo, whose samples were collected in three stations (S1, S2, S3) in March and October of the years 2015 and 2016. Physico-chemical analyzes of the water were performed. The reservoir was classified, according to the TSI, as mesotrophic. The first record of the species occurred in October 2015 at S3 and, the following year, the dispersion for the other stations was verified. The highest density of the species (28 org mL -1 ) was recorded in October 2016. Similar values were documented in Furnas (MG) and Ilha Solteira (SP). The low density values of C. furcoides and the presence of phytoplankton groups with higher densities (Cyanobacteria and Cryptophyceae) suggest that the colonization of the species is at an early stage. Thus, studies about dispersion, dynamics, and interaction of C. furcoides with phytoplankton and the potential impacts on aquatic communities are essential to understand the responses of this species to


Introduction
Reservoirs are habitats prone to bioinvasion, especially for ease of dispersion through the flow of water. The invasion of microscopic alien species in these environments is still poorly understood, and it is not possible to accurately estimate what impacts such species would promote to communities, including phytoplankton (Kastovsky et al. 2010, Silva et al. 2012). However, based on studies of invasion of alien species in other environments, it is possible to predict that the establishment of an invasive species may result in changes in species composition, diversity, and dominance, and in primary production (Elbrächter 1999, Ricciardi & Kipp 2008, Souza et al. 2009, Vitule & Prodocimo 2012.
Species of the genus Ceratium are considered invasive in continental aquatic environments of South America (Silva et al. 2012, Pereira et al. 2013, Cavalcante et al. 2016, Crossetti et al. 2019. The species Ceratium furcoides (Levander) Langhans demonstrates easy adaptation to different temperatures, trophies and physical and chemical conditions of the water thus presenting rapid dispersal and establishment in tropical reservoirs, including Brazilian ones, whose records of the species have been frequent (Santos-Wisniewski et al. 2007, Matsumura-Tundisi et al. 2010, Oliveira et al. 2011, Cavalcante et al. 2013, Jati et al. 2014, Nishimura et al. 2015, Oliveira et al. 2016, Rosini et al. 2016, Campanelli et al. 2017, Silva et al. 2018, Roriz et al. 2019.
The increase in the density of C. furcoides and the formation of blooms in tropical reservoirs is mainly associated with the availability of nutrients (Matsumura-Tundisi et al. 2010, Silva et al. 2012. In this way, reservoirs that receive external loads of nutrients or where intensive activities are carried out, such as the creation of fish in net cages, become environments conducive to the mass development of the species in question. In this context, the aim of this work was to document the first occurrence of Ceratium furcoides in the Nova Avanhandava reservoir, one of the three main centers of the fish farm in State of São Paulo.

Materials and Methods
Ceratium furcoides (Levander) Langhans was identified from phytoplankton sampling carried out during the development of a doctorate degree project in which three reservoirs from the State of São Paulo with fish farms were sampled: Chavantes, Nova Avanhandava, and Ilha Solteira. In this study, we documented the first record of the species in Nova Avanhandava Reservoir.
Study area -The reservoir of the Nova Avanhandava Hydroelectric Plant (21°07'01" S and 50°12'06" W) is located in Buritama city and is in Baixo Tietê Basin (figure 1). It presents an area of 210 km 2 , a maximum depth of 30 m and residence time of 46 days. Nova Avanhandava is the penultimate reservoir of a system of consecutive lakes, with the reservoirs of Promissão upstream of it and Três Irmãos downstream.
Samplings were carried out in the subsurface of the water column in March and October of 2015 and of 2016 in three sampling stations (S1, S2 and S3) corresponding to the three different fish farms (f) of creation and their respective upstream areas (u) and downstream (d) (n = 28). S2 is located upstream of S3 and, consequently, only upstream and downstream were sampled for the two stations.
For the phytoplankton taxonomic study, the samples were obtained with 20 µm mesh plankton net and fixed in situ with formaldehyde in the final concentration of 4 to 5%. The phytoplankton community was identified using an optical microscope with a capture camera, specialized bibliography and measurements were obtained with the aid of the Axio Vision 4.8 program. The identification of the Ceratium furcoides species (n= 25) was performed according to Santos-Wieniewski et al. (2007) and Cavalcante et al. (2013).
Samples referring to the first records of C. furcoides in the Nova Avanhandava reservoir are deposited in the collection of Herbário Maria Eneyda P. Kauffmann Fidalgo of the Institute de Botânica of São Paulo State.
Samples for quantitative analysis were collected with a Van Dorn bottle and fixed in situ with 1% Lugol solution. The count of the phytoplanktonic community and consequently of the populations of Ceratium furcoides was carried out by the method of Utermölh (1958). The results of the densities were expressed in org mL -1 and the biomass was estimated by calculating the biovolume based on the work of Hillebrand et al. (1999) and Fonseca et al. (2014).
Descriptive statistics were performed: mean and standard deviation of limnological variables and nutrients.

Results
Nova Avanhandava presented at the sampling stations, high conductivity, neutral pH and temperature ranging between 23°C and 29 °C. As for the trophic level, the seasons were classified as mesotrophic in all samples (mean TSI: 59). The mean values of the physical, chemical and nutrient variables recorded at the sampling stations are presented in Table 1 and 2.
Comments -Some specimens presented morphological variation characterized by the third horn, which makes them similar to C. hirundinella, however, Bourrelly (1970) points out that variations in the number and size of horns are linked to environmental changes such as temperature. Thus, the confirmation of the C. furcoides populations was carried out observing that the fourth apical plate (4') does not reach the apex of the epitheca. The first occurrence of populations of C. furcoides in the Nova Avanhandava reservoir occurred in October 2015 (S2u) and remained in the other samples: March 2016 (S1u) e October 2016 (S1u, S2f1, S3f2). The density and biovolume of C. furcoides were low in comparison to the other organisms of the phytoplankton community recorded together, being the highest values (density: 28 org mL -1 ; biovolume: 0,442 mm³ L -1 ) for the species registered upstream of S1 (u), in October 2016 ( figure 3 a-b).
The records of C. furcoides in such distinct aquatic environments demonstrate the great ecophysiological plasticity of the species. In addition, Ceratium presents important adaptive strategies for the development and establishment in tropical reservoirs such as encystment (resistance to sedimentation, dispersion capacity, population survival), mobility and low predation by zooplankton (Hickel 1988, Pollingher 1988, Xie et al. 1998, Cavalcante et al. 2016.
We do not have results that indicate concretely how the species was introduced into the reservoir in question, but we considered a passive dispersion of cysts or specimens from Barra Bonita reservoir, whose species had previously been recorded by Pires et al. (2012), carried by the water flow of the central body of the reservoir where the endorheic river Tietê flows. However, other forms of dispersal should also be considered: transport of specimens or their form of resistance attached to birds and aquatic insects moving between reservoirs or by anthropic intervention, as mentioned by Kristiansen (1996) and Meichtry et al. (2014) or consider Ceratium propagules already existing in the sediment, but which only now did they become available for invasion (Reynolds 1996, Rengefors et al. 2004, Padisàk 2010. The literature indicates that some limnological variables are essential in the establishment of populations of C. furcoides. Thus, it has been observed the dominance of dinoflagellates, including the Ceratium genus in mesotrophic conditions (Periotto et al. 2007, Santos-Wisniewskis et al. 2007, Silva et al. 2018 and development of C. furcoides between 10° e 25°C (Cassol et al. 2014, Cavalcante et al. 2016) and recurrence of the species in environments with high transparency associated with lower stability of the water column and also at high concentrations of ammonia and nitrite.
New Avanhandava is one of the three largest fish farming centers of São Paulo and as well as all economic activity fish farming is likely to cause pollution in the environment. In this case, the continuous and pronounced nutrient discharge from fish feeds and metabolism effectively alter the phytoplankton community, favoring the development of certain groups over the decrease of others, as well as favoring the establishment of invasive species (Mack et al. 2000, Degefu et al. 2011. In this study, the maximum value of density and biovolume of C. furcoides was, respectively, 28 org mL -1 and 0,442 mm 3 L -1 recorded in S1(Oct/16). Density values are extremely low compared to densities in other São Paulo reservoirs recorded by Matsumura-Tundisi et al. (2010) (535 ind.mL -1 ) on the Taquacetuba arm at the Billings dam or by Hackbart et al. (2015) on Jaguari dam (131.954,0 ind.mL -1 ) and low biomass compared to the records of Nishimura et al. (2015) on Billings dam (5,7 mm 3 L -1 ) and on Guarapiranga (2,6 mm 3 L -1 ), of Rosini et al. (2016) on Ilha Solteira (15,698 mm 3 L -1 ) and of Crossetti et al. (2019) on Lago das Garças (12,3 µg L -1 ).
Based on the limnological and phytoplankton community results obtained and based on reports in the literature of limnological conditions of the others Brazilian environments in which C. furcoides has been registered, it can be said that Nova Avanhandava has environmental conditions favorable to the adaptive success of the species since both the maximum density and the peaks above 15 org mL -1 of C. furcoides recorded in Oct/15 (u and f1 of S1) and Oct/16 (u S1 and f2 S3) were associated with high values of electrical conductivity and at temperatures of 24° C and high dissolved inorganic nitrogen values, principally in the fish farm areas. However, the low density and biovolume values, as well as the absence of C. furcoides in other sampled compartments, suggest that the colonization of the species is at an early stage.
At first, were not observed changes of phytoplankton due to the presence of C. furcoides on this aquatic environment, it was found that other phytoplankton groups (Cyanobacteria and Cryptophyceae) showed high densities / biovolumes compared to C. furcoides, which corroborates the hypothesis that the species is in the process of colonization of the reservoir, establishing competition with the other species for nutrients due to its migration capacity vertical in the water column (Stephaniak et al. 2007, Cassol et al. 2014, Moreira et al. 2015, Almanza et al. 2016. Punctual records in different environments and some possible equivocal identifications of Ceratium species may be underestismating the invasion of the species in the Brazilian territory since the species demonstrate a great capacity of dispersion and adaptation to different conditions. Thus, a greater number of studies in aquatic environments with similar limnological conditions and consequently their sediments (to verify the presence of cysts) could indicate if C. furcoides is already dispersed but not yet registered. From our results, we can suggest more specific studies in the Nova Avanhandava reservoir that establish the dispersion forms of Ceratium furcoides as well as studies that identify the closest aquatic environments that are favorable to the bioinvasion of the species and later studies to understand the relationships with the other groups of phytoplanktonic algae in addition to evaluating the consequences of establishing the species for the ecosystem.

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