PARENT SESSION
Oral Session #12: Aquatic Ecology: Marine.
Presiding: R. Lewison
Monday, August 5. 8:00 AM to 11:30 AM. Mesquite Room, Radisson.
Influence of hypoxia on trophic interactions between the ctenophore Mnemiopsis leidyi and Chesapeake Bay ichthyoplankton.
Kolesar, Sarah*,1, Breitburg, Denise2, Rose, Kenneth3, Adamack, Aaron3, 1 University of Maryland Center for Environmental Research-Chesapeake Biological Laboratory, Solomons, MD2 Academy of Natural Sciences Estuarine Research Center, St. Leonard, MD3 Louisiana State University-Coastal Fisheries Institute, Baton Rouge, LA
ABSTRACT- Low dissolved oxygen (DO) in aquatic ecosystems limits the habitat available to organisms, altering encounter rates and subsequent predator/prey interactions. We investigated the influences of hypoxia on trophic interactions between lobate ctenophores, Mnemiopsis leidyi, and Chesapeake Bay ichthyoplankton. Hypoxic conditions may favor ctenophores over fish because of their greater tolerance to low DO. Field surveys show that the vertical overlap between predator and prey varies with bottom DO, with the highest overlap at bottom DO equal to or greater than 4 mg/L, and lowest at bottom DO between 1 and 2 mg/L. Laboratory experiments indicate that predation rates by ctenophores on Gobiosoma bosc larvae and Anchoa mitchilli eggs and yolk sac larvae were unaffected by hypoxia, but swimming speeds and behavior could change, potentially affecting encounter rates. The age and size of ichthyoplankton prey may also contribute to the outcome of a predation interaction. However, while initial small-scale video observations of ctenophore/larva interactions at different DO concentrations and larval ages yielded significant differences in ctenophore ingestion success due to DO, age was not a significant factor. An individual-based model using these field and laboratory results predicts how hypoxia influences predator/prey dynamics. Overall larval survival was sometimes higher when the bottom layer was hypoxic than when DO was high throughout the water column. Hypoxia shifts the vertical distribution of ctenophores and ichthyoplankton according to bottom DO and depth, altering predation rates. I will expand this model to incorporate food web dynamics within the system, including intraguild predation between ctenophores and fish larvae to examine if predation by ctenophores has less impact on fish populations than does competition, and whether environmental conditions, such as seasonality or hypoxia, shift the relative importance of interactions between these species, allowing persistence of food web structure.
KEY WORDS: hypoxia, mnemiopsis leidyi, ichthyoplankton, predation