Spatial and Temporal Variability of Macroinvertebrates in Spawning and Non-Spawning Habitats during a Salmon Run in Southeast Alaska

Emily Y Campbell,M Eric Benbow,Richard W Merritt,Kenneth W Cummins

doi:10.1371/journal.pone.0039254

Emily Y Campbell, M Eric Benbow + Show 2 more

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https://doi.org/10.1371/journal.pone.0039254

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Abstract

Spawning salmon create patches of disturbance through redd digging which can reduce macroinvertebrate abundance and biomass in spawning habitat. We asked whether displaced invertebrates use non-spawning habitats as refugia in streams. Our study explored how the spatial and temporal distribution of macroinvertebrates changed during a pink salmon (Oncorhynchus gorbuscha) spawning run and compared macroinvertebrates in spawning (riffle) and non-spawning (refugia) habitats in an Alaskan stream. Potential refugia included: pools, stream margins and the hyporheic zone, and we also sampled invertebrate drift. We predicted that macroinvertebrates would decline in riffles and increase in drift and refugia habitats during salmon spawning. We observed a reduction in the density, biomass and taxonomic richness of macroinvertebrates in riffles during spawning. There was no change in pool and margin invertebrate communities, except insect biomass declined in pools during the spawning period. Macroinvertebrate density was greater in the hyporheic zone and macroinvertebrate density and richness increased in the drift during spawning. We observed significant invertebrate declines within spawning habitat; however in non-spawning habitat, there were less pronounced changes in invertebrate density and richness. The results observed may be due to spawning-related disturbances, insect phenology, or other variables. We propose that certain in-stream habitats could be important for the persistence of macroinvertebrates during salmon spawning in a Southeast Alaskan stream.

Highlights

The idea of the refuge is critically important and some argue that it should be considered an integrating concept in ecology and evolution [1]
Chlorophyll a was not statistically tested, but we observed a decline in pools and an increase in riffles and margins during the salmon run (Table 1)
Macroinvertebrates in Riffles Macroinvertebrate assemblages in riffles significantly changed during salmon spawning

Summary

Introduction

The idea of the refuge is critically important and some argue that it should be considered an integrating concept in ecology and evolution [1]. Salmon resource subsidies have been documented to positively influence benthic macroinvertebrates [5,8], perhaps by the provision of nutrients and carbon that have been shown to increase during salmon runs [9]. Stream environmental factors such as sediment size and large wood recruitment [9,10,11] along with spawning disturbance intensity [5,12] can alter the degree of marine-derived nutrient transfer available to benthic communities

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