PARENT SESSION
Contributed Oral Session 147: Aquatic Communities, Disturbance, and Dispersal
Friday, August 12, 8:00 AM - 11:30 AM, Meeting Room 511a, Level 5, Palais des congrès de Montréal
Strong impacts of invasive crayfish on a littoral lake community: Roles of ecosystem engineering and size.
Usio, Nisikawa*,1, Kamiyama, Rui2, Saji, Azumi1, Takamura, Noriko 1, 1 National Institute for Environmental Studies, Tukuba-si 305-8506, Japan2 Institute of Low Temperature Science, Sapporo-si 060-8589, Japan
ABSTRACT- Some long-lived aquatic invertebrates such as crayfish undergo dramatic size change according to their ontogenetic stages. When such invertebrates are ecosystem engineers, significance in ecosystem functioning may change according to their life stages. During 60 days in summer, we examined impacts of simple and combined effects of crayfish size classes on a littoral lake community using 20 enclosures (3 m × 2 m × 2 m high) constructed along a shoreline of a northern Japanese lake. We used signal crayfish (Pacifastacus leniusculus), originally introduced from Oregon, as test organisms; their grazing impacts are believed to be one the major mechanisms of dramatic decline in macrophytes richness and abundance in northern Japanese lakes in the past few decades. We tested the following questions. Do different-sized crayfish have 1) proportional impacts to their biomass or 2) differential roles as ecosystem engineers? In addition, 3) do they have combined consequences when both size classes are present? By 18 days from the start of crayfish introduction, both large-sized and all-sized crayfish (small+large crayfish) had eliminated macrophytes in the enclosures. In the small-sized crayfish treatments, macrophytes had been greatly reduced by day 38. Consequently, invertebrate biomass, abundance and taxa richness as well as periphyton abundance associated with macrophytes declined in the presence of crayfish regardless of crayfish size. Overall, large crayfish played a key role as ecosystem engineers. Although small crayfish were less influential as ecosystem engineers compared with large crayfish, their impacts were nevertheless dramatic for macrophytes and associated biota. Finally, we will also discuss consequences of engineering activities by small and/or large crayfish when colonisation availability for other biota remained constant (i.e. sediment biota).
Key words: crayfish, submersed macrophytes, grazing, ontogenetic stage