Floodplain-lake hydroperiod modulates the response of zooplankton and phytoplankton resting stages to extreme droughts

Abstract

Zooplankton and phytoplankton produce resting stages that enable populations to persist through adverse conditions. Between 2019 and 2022, the Paraná River in South America experienced historical drought leading to the desiccation of floodplain lakes. To evaluate the resilience of plankton communities under such conditions, we experimentally assessed the emergence of zooplankton and phytoplankton from resting stages in 13 temporary shallow lakes of the Lower Paraná floodplain varying in lake hydroperiod (i.e., water permanence). We determined species richness and composition and assessed the time to zooplankton first hatching. We compared the composition of emerged plankton with the corresponding active assemblages recorded in the lakes. The species richness in assemblages recruited from the sediments was lower than in the active communities and decreased with increasing lake water permanence. The dissimilarity between emerged and active assemblages increased with lake permanence. The time until the first zooplankton hatching lengthened with greater water permanence. Our results demonstrate a negative effect of extreme droughts on the recovery of plankton communities from resting stages and highlight the key role of lake hydroperiod as a modulator of resting bank responses to drought. This study provides insights into the consequences of more frequent and prolonged droughts for floodplain plankton communities.