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Stable isotope‐based community metrics as a tool to identify patterns in food web structure in east A frican estuaries
Author(s) -
Abrantes Kátya G.,
Barnett Adam,
Bouillon Steven
Publication year - 2014
Publication title -
functional ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.272
H-Index - 154
eISSN - 1365-2435
pISSN - 0269-8463
DOI - 10.1111/1365-2435.12155
Subject(s) - trophic level , estuary , food web , ecology , isotope analysis , biology , community structure , trophic state index , phytoplankton , nutrient
Summary Quantitative tools to describe biological communities are important for conservation and ecological management. The analysis of trophic structure can be used to quantitatively describe communities. Stable isotope analysis is useful to describe trophic organization, but statistical models that allow the identification of general patterns and comparisons between systems/sampling periods have only recently been developed. Here, stable isotope‐based B ayesian community‐wide metrics are used to investigate patterns in trophic structure in five estuaries that differ in size, sediment yield and catchment vegetation cover ( C 3/ C 4): the Z ambezi in M ozambique, the T ana in K enya and the R ianila, the B etsiboka and P angalanes C anal (sampled at A mbila) in M adagascar. Primary producers, invertebrates and fish of different trophic ecologies were sampled at each estuary before and after the 2010–2011 wet season. Trophic length, estimated based on δ 15 N , varied between 3·6 ( A mbila) and 4·7 levels ( Z ambezi) and did not vary seasonally for any estuary. Trophic structure differed the most at A mbila, where trophic diversity and trophic redundancy were lower than at the other estuaries. Among the four open estuaries, the B etsiboka and T ana ( C 4‐dominated) had lower trophic diversity than the Z ambezi and R ianila ( C 3‐dominated), probably due to the high loads of suspended sediment, which limited the availability of aquatic sources. There was seasonality in trophic structure at A mbila and B etsiboka, as trophic diversity increased and trophic redundancy decreased from the prewet to the postwet season. For A mbila, this probably resulted from the higher variability and availability of sources after the wet season, which allowed diets to diversify. For the B etsiboka, where aquatic productivity is low, this was likely due to a greater input of terrestrial material during the wet season. The comparative analysis of community‐wide metrics was useful to detect patterns in trophic structure and identify differences/similarities in trophic organization related to environmental conditions. However, more widespread application of these approaches across different faunal communities in contrasting ecosystems is required to allow identification of robust large‐scale patterns in trophic structure. The approach used here may also find application in comparing food web organization before and after impacts or monitoring ecological recovery after rehabilitation.