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Type: Journal article
Title: Land-to-sea connectivity: Linking human-derived terrestrial subsidies to subtidal habitat change on open rocky coasts
Author: Gorman, D.
Russell, B.
Connell, S.
Citation: Ecological Applications, 2009; 19(5):1114-1126
Publisher: Ecological Soc Amer
Issue Date: 2009
ISSN: 1051-0761
Statement of
Daniel Gorman, Bayden D. Russell and Sean D. Connell
Abstract: Spatial subsidies are considered strong where differences in resource availability between donor and recipient systems are greatest. We tested whether human activities on land can increase subsidies of terrigenous nitrogen to open rocky coasts and whether these differences can predict apparent deforestation of kelp forests. We first identified landscape-scale variation in the human-mediated transfer of dissolved inorganic nitrogen (DIN) from natural, agricultural, and urban catchments to temperate coasts after episodes of rainfall. Compared to natural catchments, subsidies of DIN were on average 8–407 times greater in urban catchments, and 1–63 times greater in agricultural catchments. Urban derived nitrogen was attributed to the release of sewage effluent, as delineated by δ15N isotopic values of transplanted algae. Having made this link, we then assessed whether this catchment-scale variation may account for variation in structure of subtidal habitats, particularly as related to theory of nutrient-driven shifts of habitat from perennial (i.e., canopy-forming algae) to opportunistic species (i.e., turf-forming algae). We not only detected patterns consistent with this theory, but also established that the size and total proportion of patches of turf-forming algae were greater where the ratio of donor : recipient nitrogen loads was greater (i.e., size of subsidy). An important realization was that deforestation may be more strongly related to variation in the size of subsidy rather than size of human populations, particularly among urban catchments. These data directly link the type of human activity within catchments to the modification of land-to-sea subsidies and indirectly support theory that predicts terrestrial inputs to have greater ecological effects where the disparity in resource availability between donor and recipient is exacerbated. Our evidence has been used by coastal managers to reconsider their management of coastal systems and has subsequently contributed to new water-recycling policy and initiatives.
Keywords: canopy-forming algae
coastal development
habitat loss
regime shift
South Australia
spatial subsidy
terrestrial runoff
turf-forming algae
Ulva australis
Description: Copyright 2009 Ecological Society of America. All rights reserved.
DOI: 10.1890/08-0831.1
Grant ID: ARC
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