The influence of flood pulse on fish communities of floodplain canals in the Middle Solimões River, Brazil

Abstract

The functioning of large river systems with adjacent floodplains is strongly influenced by the flood pulse. This phenomenon is the main structuring force for the biota, including fish communities that use floodplain environments for spawning, feeding, nursery and refuge. In floodplains and in the entire basin, the volume of water controls internal flows. During rising water, the high discharge of the river acts as a natural barrier to the canals that connect floodplain lakes and the Solimões River, because the water flows from river to lake. During the dry period, there is a reduction of discharge and the water flow is reversed or stationary. These canals are environments with distinct ecological characteristics such as differentiated limnology and water level variation intensely affected by the hydrological cycle. Therefore, we surveyed the influence of the flood pulse on fish communities that inhabit two canals that connect floodplain lakes to the Middle Solimões River. Particularly, we evaluated the hypothesis that the Solimões River flow direction is not perfectly parallel to its banks, which creates peripheral flows that direct water from the rivers to the floodplain lake canals. Our analysis indicated that the seasonal pattern is stronger than the spatial. Beside this, we observed that the positions of the canals in relation to the main river flow somehow affect the fish assemblages. Finally, we conclude that the flood pulse is the main structuring force acting on these fish communities.A dinâmica dos sistemas de grandes rios com áreas inundadas adjacentes é fortemente influenciada pelo pulso de inundação, sendo este fenômeno o principal agente estruturador da biota, inclusive dos peixes, que utilizam este ambiente para a desova, alimentação, berçário e refúgio. Nesta região e em toda a bacia, a intensidade da vazão controla os fluxos internos. Na época da cheia, a forte vazão atua como uma barreira natural nos canais de ligação entre os lagos de várzea e o rio Solimões, com um fluxo no sentido rio-lago. Enquanto na seca, com a redução da intensidade da vazão, o fluxo se inverte. Estes canais são ambientes com características ecológicas especiais, profundamente afetadas pelo ciclo hidrológico. Neste trabalho, estudamos a influência do pulso de inundação sobre as comunidades de peixes existentes nos canais entre dois lagos de várzea e o Médio rio Solimões, avaliando a hipótese de que a direção do fluxo do rio Solimões não é perfeitamente paralelo às margens criando, desta forma, fluxos preferenciais que direcionam o sentido da correnteza para os canais dos lagos de várzea. Nossas análises indicaram que padrões sazonais predominam sobre padrões espaciais. Além disso, observamos que a posição do canal em relação ao fluxo da corrente do rio principal afeta de alguma maneira as assembléias de peixes. Finalmente, concluímos que o pulso de inundação é a principal força responsável pela estruturação destas comunidades de peixes.

Spatio-temporal distribution of fish larvae in relation to ontogeny and water quality in the oligohaline zone of a North Brazilian estuary

“…On the contrary, the greater water transparency during the dry season favours primary production and therefore larval survival through an increase of aliments availability (Cushing 1990, Mertz & Myers 1994. Besides food availability, floodplains that form with rising water level are crucial to the survival of many species that use these temporary environments as nursery grounds (Sousa & Freitas 2008, Sarpedonti et al 2008, Barletta-Bergan et al 2002b.…”

Possible impacts of climate change on wetlands and its biota in the Brazilian Amazon

“…This connection is transient, influenced by changes in the hydrological cycle and is characterized by a strong unidirectional flow from rivers towards the lakes during seasonal flooding (Freitas and Garcez, 2004;Sousa and Freitas, 2008). One immediate effect of increased rainfall will be an increase in the velocity of water flow, accompanied by a large movement of sediments that might cause the displacement and death of many fish (Pujolar et al, 2011).…”

Condition factor variations over time and trophic position among four species of Characidae from Amazonian floodplain lakes: effects of an anomalous drought

“…These environments are highly dynamic, with an annual hydrologic cycle known as the flood pulse (Junk et al, 1989). The flood pulse is the main driving force structuring the aquatic biota of the floodplain ecosystem along the Amazon River (Junk et al, 1989;Sousa and Freitas, 2008;Hurd et al, 2016). In general, the seasonal flood reaches its peak in June and July, and its lowest point in October and November (Bittencourt and Amadio, 2007).…”