Stable isotope‐based community metrics as a tool to identify patterns in food web structure in east African estuaries

Abstract

Summary1. 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. 2. Here, stable isotope-based Bayesian community-wide metrics are used to investigate patterns in trophic structure in five estuaries that differ in size, sediment yield and catchment vegetation cover (C3/C4): the Zambezi in Mozambique, the Tana in Kenya and the Rianila, the Betsiboka and Pangalanes Canal (sampled at Ambila) in Madagascar. 3. 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 d 15 N, varied between 3Á6 (Ambila) and 4Á7 levels (Zambezi) and did not vary seasonally for any estuary. Trophic structure differed the most at Ambila, where trophic diversity and trophic redundancy were lower than at the other estuaries. Among the four open estuaries, the Betsiboka and Tana (C4-dominated) had lower trophic diversity than the Zambezi and Rianila (C3-dominated), probably due to the high loads of suspended sediment, which limited the availability of aquatic sources. 4. There was seasonality in trophic structure at Ambila and Betsiboka, as trophic diversity increased and trophic redundancy decreased from the prewet to the postwet season. For Ambila, this probably resulted from the higher variability and availability of sources after the wet season, which allowed diets to diversify. For the Betsiboka, where aquatic productivity is low, this was likely due to a greater input of terrestrial material during the wet season.5. 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.

Heterogeneity in food-web interactions of fish in the Mwanza Gulf, Lake Victoria: a quantitative stable isotope study

“…In our study, seasonal environmental factors such as wind, rainfall and temperature correlated with trophic diversity and niche size. In estuaries, seasons also influence trophic diversity of food-web structures where higher variabilities of carbon sources due to primary production and terrestrial inputs result in increased trophic diversities after rainy periods (Abrantes et al, 2014).…”

“…This approach has been used to compare foodweb structures between ecosystems, seasons and habitats (Carlier et al, 2009;Jackson et al, 2012;Doi et al, 2013;Abrantes et al, 2014), and to study the effects of invasive species on trophic interactions of populations (Jackson et al, 2012).…”

Initial response of fish trophic niche to hydrological alteration in the upstream of Three Gorges Dam

“…By contrast, Layman et al (2007) showed that compared to pre-restored period, CR did not change because similar basal resources were present (Layman et al 2005). Abrantes et al (2014) also found trophic diversity in an African estuary increased as greater input of terrestrial organic matter during the wet period.…”

“…This approach is considered as a more in-depth utility of stable isotope data for the analysis of consumer's trophic niche. Jackson et al (2011) proposed a Bayesian framework to standardize the calculation of these trophic niche metrics, which has been applied to several studies of terrestrial (Perkins et al 2014) and aquatic trophic niches (Jackson et al 2011;Abrantes et al 2014).…”

Diet composition and foraging ecology of U.S. Pacific Coast groundfishes with applications for fisheries management

“…An alternative method of prey evaluation therefore was required. Biological metrics and indices have been commonly and reliably employed to evaluate ecological data for research (Washington 1984;Krebs 1999;Abrantes et al 2014) and fishery management (Cury et al 2005;Jennings 2005;Samhouri et al 2009;Kaplan and Levin 2009). Therefore, the creation and application of an index was used as the basis for the determination of major prey in this study.…”