Chapter Two - Disturbance and successional processes from spawning salmon and floods in Wolf Point Creek, Glacier Bay, Alaska

Abstract

Redd construction by spawning salmon disturbs patches of unconsolidated benthic substrate; their cumulative impact can decimate the benthos. Juvenile salmon residing in the water column and incubating eggs buried in the streambed, may be eliminated by floods. Based on summertime surveys, these contrasting impacts were used to build knowledge of the dynamics of disturbance-recovery and long-term succession in Wolf Point Creek, Glacier Bay (WPC).Pink salmon (Onchorynchus gorbuscha) first colonized WPC in 1989, with populations gradually increasing to 15,000 fish in 2005. Although redd disturbance decimated benthic macroinvertebrates, recovery was rapid (<1 year) and demonstrated remarkable assemblage fidelity. In contrast, the impact of a November flood appeared less extreme, yet changes in community structure endured for several years. Wash-out of eggs reduced the salmon count to 500 individuals in 2007, however, populations recovered within a generation.Exacerbated by prior redd disturbance (presenting a streambed of loosely packed substrate) this unexpectedly destructive flood transformed the habitat template at the sampling site to recast macroinvertebrate succession. An alteration in source-sink dynamics contributed to species turnover. Meanwhile, at the catchment-scale, the rebound of salmon populations indicated benthic conditions remained largely unchanged.Combined with the long-term study, these data portray succession as a spatio-temporal process of ecological differentiation where intrinsic and extrinsic community disturbance promotes development of an expanding spectrum of habitats within a dynamically integrated system. This emphasizes the importance of habitat heterogeneity and connectivity in underpinning ecological resilience against global change and highlights the potential catalytic role of salmon for ecosystem restoration.