Longitudinal patterns of fish assemblages in a large tropical river in southeastern Brazil: evaluating environmental influences and some concepts in river ecology

Abstract

This study aimed to evaluate environmental influences on fish distribution and to assess the extent to which concepts in river ecology accommodate levels of spatio-temporal heterogeneity of fish assemblages in a 1,080-km long tropical river. A total of 25 sites were sampled between November 2002 and March 2003 in two seasons (summer/wet versus winter/ dry). A thermal gradient separating the upper reaches from the lower reaches was detected. The middle-upper reaches showed higher conductivity and lower dissolved oxygen and pH levels compared with the other reaches. Although some significant associations were found between some fish abundance and environmental variables, the most abundant species (Tilapia rendalli, Geophagus brasiliensis, and Oligosarcus hepsetus) occurred in most sites and under most environmental conditions. Fish community structure varied more in space (longitudinal) than through time (seasonal). The community in the lower reach species was more diverse in comparison with the other reaches. Differences in the fish assemblage structure among the longitudinal river sections appear to have been influenced by the effects of damming, and seem to be partially consistent with the Serial Discontinuity Concept, which views dams as discontinuities within the river continuum. Only the lower river reach showed seasonal differences in the fish community structure, attributable to the influence of flooding. Management plans and biodiversity conservation will benefit by considering the effects of dam disruption and flood increased connectivity to the lotic systems.

Fish assemblage structure in the Chishui River, a protected tributary of the Yangtze River

“…In contrast, Culter mongolicus and Squalidus argentatus were abundant in the lower reaches, these lentic species commonly appear in lakes, ponds, pools and backwaters of large rivers in China (Chen, 1998). In addition, conductivity and dissolved oxygen survived in the forward selection procedure and acted as surrogates for axis 2, these two factors were also observed and influenced the fish communities in a tropical river (Araujo et al, 2009). However, other expected factors such as substratum types and the meteorological factors were not significant in CCA, the former were due to their redundancy with altitude and were excluded by the variable selection procedure; the latter may be because the study area was relatively small that annual rainfall and sunlight exhibited no significant difference among the three reaches.…”

Influence of limnological zones on the spatial distribution of fish assemblages in three Brazilian reservoirs

“…Damming establishes physical barriers that limit fish movement (upstream and downstream), contributing to population isolation and extirpation ( Hughes et al, 2005;Araújo et al, 2008;Pompeu et al, 2012). Thus, loss of connectivity is another relevant issue related to river damming, and it is associated with degraded fish assemblage condition (Musil et al, 2012).…”

Factors affecting the distribution of fish during receding flood in lower Irtysh: effects of water level and diurnal cycle

“…Finally, relative contribution of spatial and temporal factors may change during the flood cycle (Scarabotti et al, 2011). Highly variable environments should strongly favour generalist species (Poff and Allan, 1995) which would be relatively tolerant to spatial and temporal (including seasonal) effects, so that their abundance would not respond much to these environmental changes (Arau´jo et al, 2009). Most fish in our study were represented by generalist cyprinids.…”

“…However, such effects are not always straightforward. For example, while spatial factors may sometimes be more important than seasonal (e.g., Ostrand and Wilde, 2002;Arau´jo et al, 2009), relative role of spatial and non-spatial effects may differ in different locations (e.g., Idaho versus Ohio; Kautza and Sullivan, 2012). Furthermore, in relatively high latitude temperate rivers (e.g., Sveden; Lepori et al, 2005), local environmental heterogeneity may not significantly structure fish assemblages.…”