Colonization and development of an Alaskan stream community over 28 years

Abstract

The application of general successional theory to stream ecosystems has not been widely addressed due to a lack of long-term studies on stream channels at sufficiently large spatial scales. Wolf Point Creek in Glacier Bay, Alaska, a lake-fed stream that began to emerge from under glacial ice in the mid-1940s, offers an opportunity to address this imbalance. We examine the stream's development from 1977 to 2005, with reference to concepts of succession and community assembly. Dispersal constraints have influenced the succession, as non-insect taxa required at least 20 years to colonize. We suggest that tolerance is a major mechanism of macroinvertebrate community assembly. Most taxa, with the exception of the cold-tolerant first colonizers, have persisted within the community following colonization, although relative abundance has changed markedly with time. However, biotic processes do influence colonization and succession. Redd (nest) digging by spawning salmon creates disturbed patches that facilitate the persistence of some early colonizers, and riparian vegetation facilitates colonization by caddisflies and chironomids. We further suggest that both deterministic and stochastic elements influence succession and community assembly in streams. Our study highlights the importance of reestablishing riparian vegetation during stream restoration programs and of increased in-stream habitat complexity from inputs of coarse woody debris to improve nutrient retention, particularly of salmon carcasses.