The influence of freshwater inflow on spatial resilience (measured in recovery of spatial distribution and abundance) of juveniles of two economically-important fishery species was examined in a large and heavily-urbanized river estuary along the Gulf Coast of the United States. The Tampa Bay study area included shallow waters throughout the bay and lower portions of several adjacent rivers containing the majority of nursery habitat for two size classes (15–50 mm Standard Length and 51–100 mm SL) of red drum (Sciaenops ocellatus) and spotted seatrout (Cynoscion nebulosus). Juveniles were collected with a 21.3-m center-bag seine via a long-term annual monitoring program. During the 13-year study, freshwater inflow varied and several perturbations occurred, including an industrial acid spill in one of the rivers, drought, and a major harmful algal bloom.
Spatial distribution and population abundance was positively related to freshwater inflow in at least one juvenile life stage of the two species. For those life stages related to freshwater inflow, populations recovered within the next year following an industrial acid spill which occurred during a period of high inflow, while recovery took several years following a major harmful algal bloom during an extended drought. These results suggest that spatial resilience of these juvenile populations to environmental perturbations is dynamic, and appears to vary positively with freshwater inflow. Riverine sources of freshwater are becoming more important for an increasing human population as groundwater sources are reaching sustainable limits in the region. This study suggests that reduced freshwater inflow can limit population size of these vulnerable juvenile life stages, as well as diminish population resilience to other environmental perturbations. Water managers and fishery managers may need to work more closely as reduced freshwater into the rivers and estuary may ultimately limit the size of adult stocks available for fishery harvest.