Kasandra

Fluctuation of Rotifera of a tropical lake in Amazonia (Acre River floodplain, Brazil)

Fluctuación de rotíferos de un lago tropical en la Amazonia (Río Acre llanura de inundación, Brasil)

Erlei Cassiano Keppeler*, Alzenira Jacob Serra, Lisandro Juno Soares Vieira, Jardely Pereira de Souza, Maralina Torres da Silva, Maria José Alencar dos Santos and Antônio Sergio Ferraudo

*Post Graduate in Marine Sciences & Limnology, Universid Nacional Autónoma de México. Edifício UMF. Universidad Nacional Autónoma de México, Av. de lo Barrios, n.o 1, Los Reyes, Tlalnepantla, Campus Iztacala, Distrito Federal, México. 54090, University Federal of Acre, Cruzeiro do Sul, Water Analyses and Limnology Laboratorie, Multidisciplinar Center, Glebas Formoso, Canela Fina, 69980-000 and University Federal of Acre, Rio Branco, Post Graduate Program in Ecology and Natural Resource Management, Distrito Industrial, 69915-900.

*Author for correspondence: erleikeppeler@gmail.com

ABSTRACT

The tropics are centers of biodiversity of Rotifera that are highly variable and abundant, that play a key role since they are link in the interaction network with members of other communities. In this work, we consider four season periods: rainy, very rainy, dry and very dry based in rainfall. Between 2008 and 2009 Rotifera were sampled monthly with plankton net in qualitative and quantitative sampling, and seven limnological variables were recorded at three sampling stations along the lake. We found 23.6% from of a total of Rotifera listed for Amazonia. The high Menhinick index revealed a high species dominance, except in the rainy season. The Shannon index not showed a greater distribution of organisms independent of the layer, and time season. In general, the equitability index showed that all species were equally abundant in all the seasonal seasons, with higher values in surface and middle of the water column. Significative differences for the Rotifera were found between the rainy and dry seasons, but only in the bottom. The limnological variables also showed differences between all the seasons in at least a layer of the water column. The fluctuations in the communities of Rotifera of Amapá lake was influenced by the season periods, that determined a different pattern of distribution of species over time.

Keywords: abundance; oxbow lake; seasonal; zooplankton. 

RESUMÉN

Los trópicos son centros de biodiversidad de rotíferos que son muy variables y abundante, que juegan un papel clave,  ya que son los eslabones de la red de interacción con los miembros de otras comunidades. En este trabajo, consideramos cuatro períodos estacionales: lluviosa, muy lluvioso, seco y muy seco basado en la precipitación. Entre 2008 y 2009 rotíferos fueron muestreados mensualmente con red de plancton en el muestreo cualitativa como cuantitativa, y siete variables limnológicas se registraron a tres estaciones de muestreo a lo largo del lago. Encontramos un 23,6% de un total de rotíferos enumerado para la Amazonía. El alto índice de Menhinick reveló una alta dominancia de las especies, excepto en la época de lluvias. El índice de Shannon no mostró una mayor distribución de los organismos independientes de la capa, y la temporada de tiempo. En general, el índice de equidad mostró que todas las especies fueron igualmente abundante en todos los períodos estaciones, con valores más altos en la superficie y media de la columna de agua. No se encontraron diferencias significativas para el Rotifera entre las estaciones lluviosas y secas, pero sólo en la parte inferior. Las variables limnológicas también mostraron diferencias entre todas las estaciones en al menos una capa de la columna de agua. Las fluctuaciones en las comunidades de rotíferos de lago Amapá  fue influenciado por los períodos estacionales, que determinaron un patrón diferente de distribución de las especies a través del tiempo.

Palabras clave: abundancia; estacional;; meandro abandonado;; zooplancton

INTRODUCTION

In almost all kinds of aquatic habitat we can find communities of the open water and the zooplankton, which include the Rotifera, and are those animals close to neutral buoyancy, suspended relatively passively in the water, living in aquatic habitats, such as lakes that are rain-fed (Mann, 2004). The zooplankton é considered to be some of the most important organisms on earth, due to the food supply they provide to most aquatic life (Wetzel & Likens, 2007).

The effect of the hydrological regime has been reported as one of the causes that determine community structure and biodiversity over time (Magalhães et al., 2009; Costa et al., 2013). However, it is important to learn more about the influence of rainfall on community structure, considering that many works consider only two seasons: rainy and dry.

Temporal changes in the community structure of the Rotifera assemblage is related to hydrologic phases and seasonal cycle (Frutos, 1998), species habitat preference (Azevedo & Bonecker, 2003) in lakes in the tropics, which are centers of biodiversity (Lewis Jr., 2000).

The seasonal variations of water levels favor the occupation of different lowland habitats, that remain isolated or in connectivity, according to the season of the year, thereby providing an exchange of species between the river and the lake. The floodplains promote the relocation of organisms to new habitats within a period that can vary from days to weeks (Arrington & Winemiller, 2006). Changes in species richness can lead to losses of zooplankton in large quantities and impacts on succession.

The zooplankton make extensive vertical excursions through the water column (Mann, 2004) and are subject to the influence of several factors such as rainfall, temperature, water oxygen availability, pH, electrical conductivity who act together or separately, which may cause fluctuations in communities, where according to Bodin and Norberg (2007), individuals within the compartments can if benefit from the neighboring stratum resources (Bodin & Norberg, 2007).

Approximately 40% of tropical lakes originate from rivers (Lewis Jr., 1996). Tropical lakes thus form part of floodplains, and are specific ecosystems with many interactions between the land and the water (Junk, 1999; Arringt & Winemiller, 2006). Floodplain lakes are considered dynamic systems, influenced by rainfall, which change with the effects of fluctuations in the water level or pulses throughout the year, where they are mainly seasonal.

Oxbow lakes, typical environments of the floodplain (Junk & Welcome, 1990), are major components of Amazon watersheds, which are subject to seasonal changes and become more pronounced when considering biotic factors, such as the movement of individuals, species multiplication, and predation.

In this study we focus on testing the hypothesis that the seasonal changes in alpha diversity and abundance (standing-stocks) of Rotifera, considering also limnological variables, would be mainly related to rainfall patterns. We consider still as yours the folding in this paper that: 1) There are diversity of Rotifera in Amapá Lake in different layer of water column; 2) The community structure is affected by precipitation due to changes in water level; 3) Species are dominant in all the seasonal periods.

MATERIAL AND METHODS

Study area Amapá Lake is located at the coordinates 10°2'36 "S and 67º50' ^[a]24" within the municipality of Rio Branco, Acre State, in South-western Amazonia. The lake is about 6km in length, and is surrounded by dense tropical forest and disturbed areas by deforestation (40%), and therefore, there is an input of organic matter from the forest to the lake (Keppeler & Hardy, 2004a).

Fluctuations in the water level are characteristic of Amapá Lake, changing the hydrometric levels by the influence of hydrological periods (Figure 2).

Figure 1. Location of Amapá Lake and sampling stations: S1, S2 and S3. Lake located in Rio Branco municipality, Acre State, Amazonia, Brazil.

Figure 2. Daily variation in river level (solid line) and oscillation in the water level of the Amapá lake (dashed line), Rio Branco, between October 2008 and september 2009. Font: Silva et al. (2013) modified.

This oxbow lake is located at the floodplain of the Acre River, characterized as white and turbid water (Philips et al., 2008), originating in Peru at approximately 300 m.a.s.l. The river has a length of 1190 km and flows to 100 m on the right bank of the Purus River in the city of Boca Acre, Amazonas State.

The sub-basin of the Acre River is located in the depression of Acre River, and has sedimentary rocks of lacustrine and fluvial origin predominate, making soils extremely poor (Fittkau et al., 1975), and their geologic positioning indicate that the region emerged during the Pliocene to Pleistocene (Araújo et al., 2005).

With respect to fishes in Amapá Lake, between 2008 and 2009 were identified a total of 2131individuals of fishes were collected, including 53 species, 18 families, and five orders (Silva et al., 2013). According to Pereira et al. (2011) and Silva et al. (2013), the lake has a large predominance of small species such as Hypoptopoma gulare (Siluriformes) and medium-size species such as Triportheus curteus during the dry season.

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