Abstract
Determining the significance of biotic and abiotic factors in the structuring of fish assemblages in freshwater environments is an important question in ecology, particularly in view of environmental changes caused by man. In this paper we sought to identify the factors responsible for the composition and abundance of fish species collected with gill nets in six locations near ports in forest clearance areas opened up for oil and natural gas exploration (Petrobras Pedro Moura Base) in the Urucu River, during drought and flood cycles. In all, 923 individuals from 23 families and 82 species were collected, totalling a biomass of 182,244 g. The most abundant species during the flood season were Bryconops alburnoides (Kner, 1858) and Dianema urostriatum (Miranda Ribeiro, 1912); in the drought season, the predominant species were Osteoglossum bicirrhosum (Cuvier, 1829) and Serrasalmus rhombeus (Linnaeus, 1766). The species with the greatest biomass during the flood season were Pellona castelnaeana (Valenciennes, 1847), S. rhombeus and Pellona flavipinis (Valenciennes, 1847). During the drought season, the predominant species was O. bicirrhosum. When both periods were analysed together, electrical conductivity, water transparency and dissolved oxygen were the most important factors. The species Hemisorubim platyrhynchos (Valenciennes, 1840), O. bicirrhosum, Chaetobranchus flavenscens Heckel, 1840, Geophagus proximus (Castelnau, 1855) were strongly related to high values of conductivity, pH and water current velocity during the drought season, as well as Serrasalmus altispinis Merckx, Jegu & Santos, 2000, Triportheus albus Cope, 1872, Triportheus angulatus (Spix & Agassiz, 1829) and Brycon melanopterus (Cope, 1872) that were associated with less depth and width in the drought season whereas P. castelnaeana, D. urostriatum, Rhytiodus argenteofuscus Kner, 1858 and Sorubim lima (Bloch & Schneider, 1801) were mainly associated with high transparency and dissolved oxygen during the flood season.
Highlights
Elucidation of the processes that determine the composition and structure of natural communities and the prevalence of abiotic or biotic factors in these processes remains an important challenge in ecology (CHESSON & HUNTLY 1997, JACKSON et al 2001)
This study evaluated the influence of environmental variables on the structure of fish assemblages in a stretch of the Urucu River during the drought and flood seasons and could constitute a baseline to identify changes due environmental pressures mediated by the oil and gas exploration plant
Several studies have shown that the composition, structure and diversity of fish assemblages in flooded areas are correlated with abiotic factors such as dissolved oxygen (SAINT-PAUL & SOARES 1987), temperature, pH, conductivity and habitat complexity; geomorphological features such as depth (STEWART et al 2002, FREITAS et al 2013), transparency (RODRÍGUES & LEWIS 1997, SÚAREZ et al 2001), lake area (SÚAREZ et al 2001), connectivity and distance between water bodies (FREITAS & GARCEZ 2004); and biotic factors such as predation and competition (SAINTPAUL et al 2000)
Summary
Elucidation of the processes that determine the composition and structure of natural communities and the prevalence of abiotic or biotic factors in these processes remains an important challenge in ecology (CHESSON & HUNTLY 1997, JACKSON et al 2001). Aquatic ecosystems throughout the world are facing continuous threats from human activities The resulting changes they suffer exert a detrimental influence on aquatic communities (DUDGEON et al 2006) and may be responsible for the extinction of numerous species. Taking into account the scarce information about fish fauna in the upper stretches of tributaries of the Amazonas River, and the complete inexistence of data from the Amazonian fish assemblages inhabiting the water bodies surrounding the oil and natural gas plant, we tested the hypothesis that the structure of fish assemblages differ among the studied periods due to the change of limnological variables from port activities over a stretch of that watershed. This study evaluated the influence of environmental variables on the structure of fish assemblages in a stretch of the Urucu River during the drought and flood seasons and could constitute a baseline to identify changes due environmental pressures mediated by the oil and gas exploration plant
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