title: Unintended consequences of management actions in salt pond restoration: cascading effects in trophic interactions.
abstract: Salt evaporation ponds have played an important role as habitat for migratory waterbirds across the world, however, efforts to restore and manage these habitats to maximize their conservation value has proven to be challenging. For example, salinity reduction has been a goal for restoring and managing former salt evaporation ponds to support waterbirds in the South Bay Salt Pond Restoration Project in San Francisco Bay, California, USA. Here, we describe a case study of unexpected consequences of a low-dissolved oxygen (DO) event on trophic interactions in a salt pond system following management actions to reduce salinity concentrations. We document the ramifications of an anoxic event in water quality including salinity, DO, and temperature, and in the response of the biota including prey fish biomass, numerical response by California Gulls (Larus californicus), and chick survival of Forster's Tern (Sterna forsteri). Management actions intended to protect receiving waters resulted in decreased DO concentrations that collapsed to zero for ≥ 4 consecutive days, resulting in an extensive fish kill. DO depletion likely resulted from an algal bloom that arose following transition of the pond system from high to low salinity as respiration and decomposition outpaced photosynthetic production. We measured a ≥ 6-fold increase in biomass of fish dropped on the levee by foraging avian predators compared with weeks prior to and following the low-DO event. California Gulls rapidly responded to the availability of aerobically-stressed and vulnerable fish and increased in abundance by two orders of magnitude. Mark-recapture analysis of 254 Forster's Tern chicks indicated that their survival declined substantially following the increase in gull abundance. Thus, management actions to reduce salinity concentrations resulted in cascading effects in trophic interactions that serves as a cautionary tale illustrating the importance of understanding the interaction of water quality and trophic structure when managing restoration of salt ponds.
authors.affiliation: U.S. Geological Survey, Western Ecological Research Center, San Francisco Bay Estuary Field Station, 505 Azuar Drive, Vallejo, CA 94592, United States of America.
authors.forename: John Y
authors.initials: JY
authors.lastname: Takekawa
authors.affiliation: U.S. Geological Survey, Western Ecological Research Center, Dixon Field Station, 800 Business Park Drive, Suite D, Dixon, CA 95620, United States of America.
authors.forename: Joshua T
authors.initials: JT
authors.lastname: Ackerman
authors.affiliation: U.S. Geological Survey, Western Ecological Research Center, San Francisco Bay Estuary Field Station, 505 Azuar Drive, Vallejo, CA 94592, United States of America.
authors.forename: L Arriana
authors.initials: LA
authors.lastname: Brand
authors.affiliation: U.S. Geological Survey, Western Ecological Research Center, San Francisco Bay Estuary Field Station, 505 Azuar Drive, Vallejo, CA 94592, United States of America.
authors.forename: Tanya R
authors.initials: TR
authors.lastname: Graham
authors.affiliation: U.S. Geological Survey, Forest and Rangeland Ecosystem Science Center, 3200 SW Jefferson Way, Corvallis, OR, 97331, United States of America.
authors.forename: Collin A
authors.initials: CA
authors.lastname: Eagles-Smith
authors.affiliation: U.S. Geological Survey, Western Ecological Research Center, Dixon Field Station, 800 Business Park Drive, Suite D, Dixon, CA 95620, United States of America.
authors.forename: Mark P
authors.initials: MP
authors.lastname: Herzog
authors.affiliation: U.S. Geological Survey, National Research Program, 345 Middlefield Road, Mail Stop 466, Menlo Park, CA 94025, United States of America.
authors.forename: Brent R
authors.initials: BR
authors.lastname: Topping
authors.affiliation: U.S. Geological Survey, California Water Science Center, Placer Hall, 6000 J Street, Sacramento, CA 95819, United States of America.
authors.forename: Gregory G
authors.initials: GG
authors.lastname: Shellenbarger
authors.affiliation: U.S. Geological Survey, National Research Program, 345 Middlefield Road, Mail Stop 466, Menlo Park, CA 94025, United States of America.
authors.forename: James S
authors.initials: JS
authors.lastname: Kuwabara
authors.affiliation: Don Edwards San Francisco Bay National Wildlife Refuge, U.S. Fish and Wildlife Service, Newark, CA 94560, United States of America.
authors.forename: Eric
authors.initials: E
authors.lastname: Mruz
authors.affiliation: U.S. Geological Survey, Western Ecological Research Center, San Francisco Bay Estuary Field Station, 505 Azuar Drive, Vallejo, CA 94592, United States of America.
authors.forename: Sara L
authors.initials: SL
authors.lastname: Piotter
authors.affiliation: U.S. Geological Survey, Western Ecological Research Center, San Francisco Bay Estuary Field Station, 505 Azuar Drive, Vallejo, CA 94592, United States of America.
authors.forename: Nicole D
authors.initials: ND
authors.lastname: Athearn
mesh_terms: D000818:Animals; D002140:California; D046091:Charadriiformes; D017753:Ecosystem; D004784:Environmental Monitoring / Q000379:methods*; D061005:Ponds / Q000737:chemistry* / Q000382:microbiology; D054712:Salinity; D012495:San Francisco; D012965:Sodium Chloride / Q000032:analysis
chemical_list: D012965:Sodium Chloride