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Movers and shakers: nutrient subsidies and benthic disturbance predict biofilm biomass and stable isotope signatures in coastal streams
Author(s) -
Harding Jennifer N.,
Harding Joel M. S.,
Reynolds John D.
Publication year - 2014
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/fwb.12351
Subject(s) - benthic zone , oncorhynchus , environmental science , nutrient , biomass (ecology) , abiotic component , ecology , streams , food web , fishery , spawn (biology) , isotope analysis , biology , predation , fish <actinopterygii> , computer network , computer science
Summary Nutrient subsidies and physical disturbance from migrating species can have strong impacts on primary producers. In the north Pacific, adult salmon ( O ncorhynchus spp.) transport marine‐derived nutrients back to freshwater streams and can also significantly disrupt the substratum during spawning events. We tested for effects of spawning pink ( O . gorbuscha ) and chum ( O . keta ) salmon on stream biofilm. Biofilm is a mix of algae, fungi and bacteria that provides food and habitat and forms the base of these aquatic food webs. We collected rock biofilm samples to compare stable isotopes and biomass prior to and following peak salmon spawning in 16 catchments on the central coast of B ritish C olumbia, C anada. We conducted two separate analyses. The first was a within‐stream comparison, which focused on 5 catchments that had a barrier to pink and chum salmon migration. The second was an among‐stream analysis that included all 16 catchments and explicitly considered biotic and abiotic factors, in addition to salmon density, known to influence biofilm growth and isotope ratios. Salmon density proved to be the best predictor of biofilm δ 15 N. Biofilm δ 13 C was best predicted by salmon density and catchment size. While spring chlorophyll a increased with mean salmon density, it was on average lower during spawning in the autumn, probably due to physical disturbance from spawning salmon. These results show that of the several variables considered to affect biofilm isotopes and biomass, salmon density and catchment size are among the most influential in coastal streams where salmon spawn.