Influences of ENSO and PDO phenomena on the local climate variability can drive extreme temperature and depth conditions in a Pampean shallow lake affecting fish communities

The aim of this study was to characterize occurrence of extreme temperature and depth conditions affecting fish community in a shallow lake as result of local climate variability, in turn influenced by the ENSO and PDO phenomena. Extreme depth and water temperature events (modeled from local weather conditions) were characterized from 1966 to 2012 to estimate changes in Chascomús lake fish communities. The ENSO and PDO influences on the occurrence probability of these ecosystem changes were investigated. Four significant changes in Chascomús Lake fish assemblage were identified during period assessed, as response to extreme temperature and depth events. Extreme high depth conditions would have changed fish community during 1987 and 2002, leading to a configuration characterized by the absence of the most emblematic fish species in Chascomús Lake, the pejerrey (Odontesthes bonariensis). On the other hand, extreme low water temperatures would have promoted a fish community characterized by the dominance of this last species during 1966–1986, 1997–2001 and 2008–2013 periods. Furthermore, extreme shortening in pejerrey spawning season was significantly related with decrease of its relative abundance. The occurrence probability of the extreme physical conditions modifying Chascomús Lake fish communities was significantly explained by ENSO (by depth influences) and by PDO (by water temperature influences). Thus, this study showed strong correlations between the ENSO and PDO influences and the occurrence probability of the extreme physical conditions changing fish community in Chascomús Lake.