Scale of H. perlevis introduction in Elkhorn Slough. A. A large aggregation in South Marsh; B. A large individual exposed at low tide; C. Map of Elkhorn Slough, CA with monthly monitoring sites marked with stars and long-term monitoring sites marked with dots. APN: Azevedo Pond; KP: Kirby Park; NM: North Marsh; WSL: Whistlestop Lagoon; RSM: South Marsh – WSL; RBR: South Marsh Bridge; VM: Vierra Mouth; BSE: Bennett Slough; MLN: Moss Landing Road; JR: Jetty Road S1 and S2 mark the NERR sondes which collected water quality parameter data; D. Sponge cover was measured using 1 × 1 meter photoquadrats. Map: Created in ArcGIS Pro; service layer credit Esri, FAO, NOAA, USGS, California State Parks, Esri, HERE, Garmin, SafeGraph, METI/NASA, USGS, Bureau of Land Management, EPA, NPS, USDA.