Seasonal dynamics of the fish assemblage in a floodplain lake at the confluence of the Negro and Amazon Rivers

Abstract

The temporal effect of discharge and limnology on fish composition and species diversity in a floodplain lake at the confluence of the Amazon and Negro Rivers was evaluated. Species richness, abundance and assemblage composition were strongly influenced by seasonal discharge of the Amazon and Negro Rivers, which affects lateral connectivity, water conductivity and temperature. As a consequence, temporal β-diversity was high in the lake and the assemblage was dominated by seasonally transient species. Relatively large species known to feed on resources within the floodplain were captured almost exclusively during the flood period. During the dry season, the assemblage was dominated by fishes adapted to harsh conditions of high temperature and low dissolved oxygen concentrations. An open system with high spatial and temporal heterogeneity created by the meeting of two large rivers with different water chemistry, Lago Catalão has a dynamic fish assemblage. Given its high temporal β-diversity and abundance of fishes, many of great importance in local fisheries, Lago Catalão and other floodplain lakes in this region merit special attention for conservation.

Simultaneous abrupt shifts in hydrology and fish assemblage structure in a floodplain lake in the central Amazon

“…The environmental perturbation caused by the extreme drought of 2005, which dried out about 70% of aquatic habitats in the Amazon floodplains34, is the most plausible trigger for the abrupt change in assemblage structure. Several mechanisms probably account for synchronicity of changes in assemblage structural components, including 1) migration restriction and 2) increased mortality due to harsh abiotic conditions and predation, owing to higher per-unit-area fish densities within smaller, less-connected aquatic habitats during the dry season3536. However, not every functional change was synchronous, which suggests a significant influence from intrinsic biological factors, or additional environmental drivers that were not analyzed here.…”

“…The decline in abundance of PS strategists after 2008 probably was influenced by reduced lateral connectivity during dry seasons. Several of these species migrate seasonally between floodplain lakes and the river channel for feeding and reproduction (e.g., Hemiodus sp., Curimatella alburna, Triportheus angulatus ), and would be especially affected by reduced habitat connectivity during longer dry seasons35. Mean abundance of PL strategists declined gradually until 2008, after which abundance was stable at a lower level.…”

“…Fishes were sampled using sets of 10 gillnets with multiple mesh sizes (details appear in ref. 35 and supplementary Material and Methods). In the laboratory, each specimen was identified, measured for standard length (SL, mm), weighed (g) and examined to determine sex and reproductive status according to criteria described in ref.…”

Spatio-temporal variation of fish taxonomic composition in a South-East Asian flood-pulse system

“…Consequently, the patterns highlighted in temperate lakes may not hold in tropical ones. Studying community composition, how they vary spatially and temporally and what are the determinants of these variations is therefore an important step toward a better understanding of the functionning of tropical ecosystems [15]. This is of utmost importance if we are to better manage these ecosystems which sustain important biodiversity and fisheries.…”

The density and biomass of mesozooplankton and ichthyoplankton in the Negro and the Amazon Rivers during the rainy season: the ecological importance of the confluence boundary

“…The black water of the Negro River is derived from the high concentration of humic substances, while the white water of the Amazon River is derived from highly suspended inorganic materials (Sioli, 1984; Furch & Junk, 1997; Junk et al, 2015). The water properties of the white and black waters are different in terms of many parameters such as flow speed, conductivity, turbidity, pH, water temperature, nutrient concentrations, and dissolved and particulate organic matter concentrations (Laraque et al, 1999; Moreira-Turcq et al, 2003; Leite, Silva & Freitas, 2006; Filizola et al, 2009; Laraque, Guyot & Filizola, 2009; Franzinelli, 2011; Röpke et al, 2016). Due to these differences, the black and white water rivers are not completely mixed until over 100 km beyond the confluence (Laraque, Guyot & Filizola, 2009).…”