Abstract
This study describes the occurrence, importance and seasonal patterns of picoplankton in two wetlands (TDNP and La Safor), and compares them to a system of fifteen interconnected lakes (Ruidera). In TDNP we performed a six‐year monthly study in three sites of the wetland. Bacterial abundance increased throughout time and the autotrophic picoplankton (APP) range was wide (up to 33 × 10^6^ cells/ml). The annual averaged APP contribution to total picoplankton and phytoplankton biovolumes was 0.5–22% and 0.03–6% respectively. There were large differences among sites in terms of APP absolute and relative abundance and seasonal patterns. In La Safor, the APP relative contribution to picoplankton and phytoplankton biovolumes was 0–25% and 0–40%, respectively, while in the Ruidera lakes was 0–47% and 0–5%, respectively. In the three systems there was a significant correlation between bacterial abundance and chlorophyll a but the slopes of the linear regressions were different. No significant relationships were found of APP abundance and trophic status in the wetlands, but were noted in the lake system. There was no clear relationship of APP contribution to total phytoplankton biomass to the trophic gradient in wetlands. In the lakes, the higher contribution of APP was found in those with higher trophic levels.