Long-term dynamics of the zooplankton community during large salinity fluctuations in a coastal lagoon

Aquatic coastal systems are affected by high fluctuations in salinity and the zooplankton may rely on dispersal or dormancy to recolonise these environments. Here, we analysed the long-term dynamics of the zooplankton community over 6 years during large salinity fluctuations in a coastal lagoon (Garças Lagoon, Brazil) and the effect of salinity on the hatching patterns of the resting egg bank. We hypothesised that salinity is the main driving factor of the zooplankton community structure, and that increases in salinity reduce the species richness and the abundance of hatchlings. Multiple regression analysis showed that salinity was associated negatively with species richness in the open water, whereas total phosphorus and chlorophyll-a concentrations were negatively and positively related to abundance respectively. Redundancy analysis demonstrated that temporally structured environmental variables (total phosphorus and salinity) were important for zooplankton composition. Periods of low salinity allowed the presence of freshwater organisms, changing the zooplankton composition over the years. However, our hatchling experiment showed a depauperate resting egg bank. Overall, our results showed a strong influence of salinity on the structure and dynamics of the zooplankton at Garças Lagoon, and that the resting egg bank likely plays a minor role in the zooplankton colonisation during low-salinity periods.