Interannual flow variability in a large subtropical-temperate floodplain: a challenge for fish reproduction

Fluctuations of temperature and water levels are the two main drivers of aquatic life in river floodplain ecosystems. The large Middle Parana River floodplain exhibits marked seasons and important interannual hydrological changes. Using a three-factor-based approach (fish reproductive traits, hydroclimatic conditions, and floodplain recruitment patterns), we analyzed how fish life history evolves within this fluctuating environment. We observed that hydroclimatic conditions can be considered through three main interannual variations that prompt the most abundant Parana species to adopt four different main reproductive strategies: (i) typical periodic strategists are dependent on large spring-summer floods and juveniles strongly predominate in the floodplain when such a condition occurs, (ii) periodic-opportunistic strategists are associated with floods, regardless of their timing, (iii) periodic-equilibrium strategists take advantage of spring-summer floods whatever the intensity and duration, and (iv) equilibrium strategists have low flood dependence and higher stability in temporal fish recruitment. This work brings forth a first synthesis of fish life history in the Middle Parana River and evidences how important both hydrological and temperature fluctuations are to interpret its complexity.