HR: 0800h
AN: B41B-03    [Abstracts]
TI: Investigating the Impact of a Burrowing Shrimp on Biogeochemical Processes and Microbial Communities in a Shallow Lagoon, Catalina Harbor, California, U.S.A.
AU: * Bertics, V J
EM: bertics@usc.edu
AF: University of Southern California, Marine Environmental Biology, AHF 335, Los Angeles, CA 90089, United States
AU: Ziebis, W
EM: wziebis@usc.edu
AF: University of Southern California, Marine Environmental Biology, AHF 335, Los Angeles, CA 90089, United States
AB: Understanding the interactions between the activity of macrofauna organisms and the biogeochemistry and microbiology of marine sediments is crucial in evaluating marine ecosystem functioning and nutrient cycling. Burrows built by different organisms often vary in architecture, size, and permanence, making it difficult to extrapolate from one organism to another and from one location to another, the impact that bioturbation or bioirrigation has on the local biogeochemical processes. The overall goal of this study is to combine interdisciplinary approaches to assess the impact of the ghost shrimp Callianassa californiensis, on the biogeochemistry of a shallow lagoon located in Catalina Harbor, California, USA. Field investigations were performed in the lagoon along a transect from the shoreline out to 10 m. The area is bioturbated by Callianassa californiensis with a linear increase in burrows with distance from the shore (R² = 0.9481). Highest numbers were found at the 10 m distance with approximately 866 burrows m^-2. Oxygen penetration depths were determined using Clark-type amperometric microsensors. These measurements were accompanied by detailed analyses of sediment and pore water parameters (porosity, TOC, H₂S, NH₄⁺, NO₃^-, Fe (II)/Fe (III)) by taking sediment cores at 2 m intervals along the transect and slicing these cores in a vertical resolution of 1 cm. Microbial abundances with sediment depth and along the transect were determined by direct counts (AODC) and microbial diversity patterns were analyzed using the molecular finger printing method ARISA (Automated rRNA Intergenic Spacer Analysis). In addition to the field studies, we examined the effects of the shrimp burrows in more detail by using narrow aquaria (40 cm x 15 cm x 5 cm). Each aquarium was filled with sediment collected from the study site, populated by one or two shrimps, and placed in a flowing seawater system. The front walls of the aquaria were perforated with holes in a 1 cm grid that were filled with silicone, which allowed for sampling from the side, directly targeting specific burrow structures. We used three parallel setups, which was ideal for studying the burrow structure (average burrow depth was ~19.5 cm) and recording burrowing activity. Initially, detailed microsensor measurements were performed in vertical profiles in each aquarium but the aquaria also allowed for direct measurements from the side in and around deeper burrow compartments. Subsequently, the aquaria were subsampled in detail for geochemical and microbiological analyses by removing the front wall. The investigations clearly showed that the shrimp not only increased oxygen penetration into the sediment and thus altered the redox conditions throughout the sediment, but there was also a clear impact on microbial abundances and microbial community structures. Investigations are underway to estimate microbial activity increase associated with bioturbation activity (i.e. sulfate reduction, nitrogen fixation, ammonium oxidation).
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0465 Microbiology: ecology, physiology and genomics (4840)
DE: 0470 Nutrients and nutrient cycling (4845, 4850)
DE: 0471 Oxidation/reduction reactions (4851)
DE: 4804 Benthic processes, benthos (0408)
SC: Biogeosciences [B]
MN: 2007 Joint Assembly