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. 2019 Aug 8;9(1):11495.
doi: 10.1038/s41598-019-47793-2.

Human pressures on two estuaries of the Iberian Peninsula are reflected in food web structure

I Donázar-Aramendía  1 , J E Sánchez-Moyano  2 , I García-Asencio  2 , J M Miró  3 , C Megina  4 , J C García-Gómez  3
Affiliations

Human pressures on two estuaries of the Iberian Peninsula are reflected in food web structure

I Donázar-Aramendía et al. Sci Rep. .

Abstract

As a result of the increased urban and agricultural development in coastal environments, estuaries are among the most modified and threatened aquatic ecosystems. This study used stable isotopes to examine the effects of human impacts by contrasting the food web structures of two Iberian estuaries exposed to different degrees of human pressure. More complex feeding pathways were found in the more altered estuary (Guadalquivir). Greater spread among species along the carbon axis suggests that the primary consumers exploit organic matter with various origins, whereas different nitrogen signals of the secondary consumers suggest that they feed on different suites of prey. In contrast, the similar isotopic signals of secondary consumers in the relatively little influenced estuary (Guadiana) suggests similarity in diet composition and feeding on the same organic matter sources. Understanding trophic interactions in estuaries is vital for defining proper management and conservation, and the preliminary data provided here are one step in this direction.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Sampling locations in the oligohaline zone of the Guadiana estuary (left) and Guadalquivir estuary (right). The salinity gradient of the estuaries is provided in grey scale from the euhaline zone (black) to the oligohaline zone (hatched area). The maximum turbidity zone is within the oligohaline zone.
Figure 2
Figure 2
δ13C and δ15N (mean ± standard deviation) of the primary producers, invertebrates and fishes collected in the Guadalquivir (left) and Guadiana (right) estuaries in summer 2017. Horizontal bars below the x-axis represent the δ13C ranges of primary producers extracted from the literature (Supplementary Table S1). POM: particulate organic matter, SOM: sedimentary organic matter, MPB: microphytobenthos (upper limit of MPB range, −14‰, is out of the axis limit). Figures of the different organisms are provided for a better understanding of the species. Colours indicated trophic position: Secondary consumers: red. Primary and/or secondary consumers: yellow. Primary consumers: blue. Producers: green.
Figure 3
Figure 3
Trophic niche width according to the convex hull area (dotted lines) and standard ellipse areas corrected for a small sample size (SEAc) for the Guadalquivir (black lines) and Guadiana estuaries (blue lines). Triangles represent individuals of all the species measured in the Guadalquivir estuary, and circles represent species found in the Guadiana estuary.
Figure 4
Figure 4
Bayesian results for the estuarine community-wide metrics that provide information on trophic diversity: carbon range (CR), nitrogen range (NR), mean distance to the centroid (CD) and trophic redundancy measured as the mean nearest neighbour distance (M-NND) and its standard deviation (SD-NND). Black dots are the modes, and boxes indicate the 50%, 75% and 95% credible intervals. The numbers above the red crosses represent the values of the crosses, which are the true population values.
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