South Lake, I know what you did last summer

Loss of water challenges aquatic animal survival, and although it happens annually in seasonal wetlands, its effect on faunal dynamics is poorly understood. We studied these dynamics in detail in a single wetland, South Lake. The aims of these experiments and surveys were to observe faunal occupancy over different hydroperiods and invertebrate response. Although located in suburban Perth it is relatively undisturbed, drying to a pool before completely drying out during summer. We have sampled South Lake over multiple years and hydroperiods, including the dry phase. Temperature loggers were placed in and around South Lake, logging ambient air, water and sediment temperature throughout multiple hydroperiods, showing some extreme high temperatures in summer. During spring, invertebrate diversity was very high. As the water level declined, and then dried out, diversity declined and large invertebrate predators/scavengers fed on stranded invertebrates. Before surface water completely disappeared predatory insects pupated and flew away. Other invertebrates used resting stages to survive drying, hatching once South Lake reflooded. When ‘dry’ South Lake retains deep crevices in the sediment that are connected to the groundwater, providing a refuge for taxa such as amphipods and isopods that do not have resting stages and cannot leave the wetland. Thus, the decline and reassembly of the invertebrate community during drying and reflooding depends on three processes: flying insects with resilience traits that leave and return; taxa requiring at least perennial dampness that make micro-scale movements into sediment crevices; and taxa with resting stages that remain in the dry sediment