Simoni Maria Loverde-Oliveira

Hydrology-Driven Regime Shifts in a Shallow Tropical Lake

Shifts between alternative stable states have become a focus of research in temperate shallow lakes. Here we show that sharp transitions between a clear, macrophyte-dominated state and a turbid state without submerged plants can also occur in tropical floodplain lakes, albeit driven by a largely different set of mechanisms. We show how a shallow lake in the Pantanal becomes covered by an exploding population of the submerged macrophyte Egeria najas Planchon as the water level rises during the annual high-water period. Water clarity increases spectacularly in this period due to flushing with river water that has lost most of its suspended matter during its slow flow over the flooded vegetated plains. A few months later when the water level drops again, the submerged plant beds die and decompose rapidly, triggering a phase of increasing turbidity. During this period an increase in dissolved organic matter, suspended matter, and phytoplankton biomass results in a sharp deterioration in water clarity. The concomitant water level decrease largely counteracts the effects on the underwater light climate, so that the amount of light at the bottom may not differ in comparison with the high-water period. Therefore, changes in light climate seem unlikely to be the sole driver of the vegetation shifts, and other mechanisms may prevent recovery of the submerged vegetation until the next high-water episode. Also, contrary to what is found in temperate lakes, there is no evidence for top-down control of phytoplankton biomass associated with the macrophyte-dominated state in our tropical lake.

Checklist of green algae (Chlorophyta) for the state of Mato Grosso, Central Brazil

A checklist of Chlorophyta species was made from a bibliographic database in order to contribute to the knowledge of the biodiversity of algae in the state of Mato Grosso. The list records 563 species of the phylum Chlorophyta distributed in 105 genera, 38 families, 21 orders and seven classes. The class Zygnematophyceae has 386 species (16% of families), followed by Chlorophyceae with 154 species (55% of families). The other classes together contributed with 23 species (29% of families). The contributions of Desmidiaceae (52%), Closteriaceae (9%), Scenedesmaceae (9%) and Oocystaceae (5%) were noteworthy; the others were composed of no more than thirty species (25%). The genera with the highest number of species were Cosmarium (82 species), Staurastrum (55 species) and Closterium (53 species). This checklist of Chlorophyta corroborates the studies that highlight the high degree of richness of this phylum in the aquatic systems of Brazil.

Fish from urban tributaries to the Vermelho River, upper Paraguay River Basin, Mato Grosso, Brazil

The fish fauna of urban streams is still poorly known, it difficult to assess the effects of urbanization expansion on fish species composition, for this reason the aim of this study was to provide a checklist of species that compose the ichthyofauna of six urban streams, tributaries to the Vermelho River, upper Paraguay River Basin, Rondonopolis, Mato Grosso State, Brazil. The samples were performed with seine nets on a spatial gradient of 75 m, and with sieves for a period of 15 minutes in each site. A total of 56 species belonging to five orders, Characiformes, Siluriformes, Gymnotiformes, Cyprinodontiformes, and Perciformes, 21 families and 44 genera were sampled. The most common species were Astyanax asuncionensis Gery, 1972, Astyanax abramis (Jenyns, 1842), Odontostilbe pequira (Steindachner, 1882), Odontostilbe paraguayensis Eigenmann & Kennedy, 1903 , Characidium zebra Eigenmann, 1909 and Hypostomus sp. This checklist brings additional knowledge on fish that inhabit tributaries to the major rivers of northern Pantanal.

The structuring role of free-floating plants on the fish community in a tropical shallow lake: an experimental approach with natural and artificial plants

Abstract Free-floating plants are important components of aquatic ecosystems in tropical climates, playing a key role in the structure and spatial distribution of fish communities. This study aims at elucidating the potential effects of free-floating vegetation on fish community structure in a tropical floodplain lake, using an experimental approach based on natural and artificial devices (Eichhornia crassipes), in high and low (LT) turbidity waters. A total of 32 fish species were found, richness, abundance, biomass, mean fresh body weight, and standard length were all significantly higher in the LT regions. Although no significant differences of community traits were found between artificial and natural substrates, regardless of water turbidity, fish composition differences between devices were observed in clear waters. Benthivorous fishes were the most widespread trophic group, with higher abundance and biomass in LT, while no differences were found among plant types. The results confirmed the structural role played by free-floating plants in the fish community by offering a refuge to smaller bodied fish species and younger specimens of larger species, independently of turbidity conditions. However, the effect was stronger in clear waters. The evidence also supported the hypothesis that the fish community forages within the plant beds. Turbidity spatial gradients or turbid regimes in tropical shallow lakes, as well as important floating macrophyte coverage could have strong impacts on the fish community structure.