PARENT SESSION
OOS 4: Organisms as Ecosystem Engineers: Conceptual Progress, Limits and Challenges.
Organized by: JP Wright and CG Jones
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room E 146.

Impacts of bioturbation by spawning salmon on the seasonal dynamics of Alaskan streams.

Moore, Jonathan ^*,1, Schindler, Daniel¹, ¹ University of Washington, Seattle, WA, USA

ABSTRACT- Ecosystem processes and community dynamics are often controlled by a few dominant species. For example, it is now widely recognized that migrations of Pacific salmon provide a critical pulse of marine-derived nutrients and energy to coastal freshwater ecosystems. However, less understood is the role that salmon play as modifiers of the physical habitat. While Pacific salmon often spawn at high densities and dig large nests, the impacts of this disturbance on benthic community dynamics and stream ecosystem processes are largely unknown. We investigated the role of this temporally predictable disturbance in controlling the seasonal dynamics of stream ecosystems in the Bristol Bay region of southwestern Alaska. We collected data every two weeks for three summers on a suite of abiotic and biotic variables in six streams that span a gradient of salmon densities. In streams and years with high densities of salmon, disturbance from spawning salmon had striking and widespread impacts on both abiotic and biotic aspects of stream ecology. Disturbance by salmon led to the stream-wide export of enormous quantities of silt and nutrients, as demonstrated by large increases in the total phosphorus, total nitrogen, and particulate loads in the outflow of creeks during peak salmon spawning. In addition, there was a pronounced decline in benthic invertebrate abundance and periphyton biomass associated with disturbance from salmon nest-digging. Thus, salmon redd-digging can be an important component of aquatic disturbance regimes, affecting a variety of biota as well as modifying the physical characteristics and ecosystem processes of coastal aquatic systems. Removing populations of strong interactors like salmon, or other ecosystem engineers, modifies disturbance regimes and could lead to unforeseen ecosystem consequences.

Key words: disturbance, succession, Oncorhynchus, benthic