Importance of terrestrial subsidies for estuarine food webs in contrasting east African catchments

Abrantes, Katya G., Barnett, Adam, Marwick, Trent R. and Bouillon, Steven 2013, Importance of terrestrial subsidies for estuarine food webs in contrasting east African catchments, Ecosphere, vol. 4, no. 1, pp. 1-33, doi: 10.1890/ES12-00322.1.

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Title Importance of terrestrial subsidies for estuarine food webs in contrasting east African catchments
Author(s) Abrantes, Katya G.
Barnett, Adam
Marwick, Trent R.
Bouillon, Steven
Journal name Ecosphere
Volume number 4
Issue number 1
Start page 1
End page 33
Total pages 33
Publisher Ecological Society of America
Place of publication Washington, D.C.
Publication date 2013
ISSN 2150-8925
Keyword(s) Africa
Bayesian mixing models
stable isotopes
terrestrial subsidies
Summary Little is known on the degree to which terrestrial organic matter delivered to tropical estuaries contributes to estuarine consumers. Here, stable isotope analysis is used to constrain this contribution for contrasting east African estuaries whose catchments differ in relative C3/C4 vegetation cover. As these two types of vegetation differ strongly in δ13C, we anticipated that terrestrial subsidies would be reflected in a gradient in estuarine consumer δ13C values, following the relative importance of C3 (characterised by low δ13C) vs. C4 (characterised by high δ13C) cover. Five estuaries were sampled for aquatic biogeochemical parameters, primary producers and consumers of different trophic ecologies: the Zambezi (catchment with a C3/C4 cover of 61/39%) in Mozambique, the Tana in Kenya (36/64%) and the Betsiboka (42/58%), Rianila (85/15%) and Canal des Pangalanes (C3-dominated) in Madagascar. Sampling was done before and after the 2010/2011 wet season. There were positive relationships between the proportion of C4 cover in the catchment and turbidity, δ13CDIC, δ13CDOC, δ13CPOC and δ15NPN. There were also significant positive relationships between δ13CPOC and consumer δ13C and between δ15NPN and consumer δ15N for all consumer trophic guilds, confirming the incorporation of organic material transported from the catchments by estuarine consumers, and implying that this material is transported up to high trophic level fish. Bayesian mixing models confirmed that C4 material was the most important source for the highly turbid, C4-dominated estuaries, contributing up to 61–91% (95% CI) to phytodetritivorous fish in the Betsiboka, whereas for the less turbid C3-dominated estuaries terrestrial subsidies were not as important and consumers relied on a combination of terrestrial and aquatic sources. This shows that the ecology of the overall catchment affects the estuaries at the most basic, energetic level, and activities that alter the turbidity and productivity of rivers and estuaries can affect food webs well beyond the area of impact.
Language eng
DOI 10.1890/ES12-00322.1
Field of Research 060202 Community Ecology (excl Invasive Species Ecology)
060205 Marine and Estuarine Ecology (incl Marine Ichthyology)
050102 Ecosystem Function
Socio Economic Objective 960503 Ecosystem Assessment and Management of Coastal and Estuarine Environments
HERDC Research category C1 Refereed article in a scholarly journal
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