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. 2014 Jul 30;9(7):e103132.
doi: 10.1371/journal.pone.0103132. eCollection 2014.

Longer and less overlapping food webs in anthropogenically disturbed marine ecosystems: confirmations from the past

Fabiana Saporiti  1 , Stuart Bearhop  2 , Laura Silva  3 , Damián G Vales  3 , Lisette Zenteno  1 , Enrique A Crespo  3 , Alex Aguilar  1 , Luis Cardona  1
Affiliations

Longer and less overlapping food webs in anthropogenically disturbed marine ecosystems: confirmations from the past

Fabiana Saporiti et al. PLoS One. .

Abstract

The human exploitation of marine resources is characterised by the preferential removal of the largest species. Although this is expected to modify the structure of food webs, we have a relatively poor understanding of the potential consequences of such alteration. Here, we take advantage of a collection of ancient consumer tissues, using stable isotope analysis and SIBER to assess changes in the structure of coastal marine food webs in the South-western Atlantic through the second half of the Holocene as a result of the sequential exploitation of marine resources by hunter-gatherers, western sealers and modern fishermen. Samples were collected from shell middens and museums. Shells of both modern and archaeological intertidal herbivorous molluscs were used to reconstruct changes in the stable isotopic baseline, while modern and archaeological bones of the South American sea lion Otaria flavescens, South American fur seal Arctocephalus australis and Magellanic penguin Spheniscus magellanicus were used to analyse changes in the structure of the community of top predators. We found that ancient food webs were shorter, more redundant and more overlapping than current ones, both in northern-central Patagonia and southern Patagonia. These surprising results may be best explained by the huge impact of western sealing on pinnipeds during the fur trade period, rather than the impact of fishing on fish populations. As a consequence, the populations of pinnipeds at the end of the sealing period were likely well below the ecosystem's carrying capacity, which resulted in a release of intraspecific competition and a shift towards larger and higher trophic level prey. This in turn led to longer and less overlapping food webs.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Study areas (central-northern Patagonia and southern Patagonia) and sampling approximate zones. Empty dots represent archaeological sites.
Figure 2
Figure 2. Isotopic niches/resource use areas of the species/functional groups described in the text and calculated with the standard ellipse areas corrected for small sample size (SEAC) over time in the two geographical areas.
a) Central-northern Patagonia and b) Southern Patagonia. Herbivores = mussels and limpets; Aa = South American fur seals; Of = South American sea lions; Sm = Magellanic penguins.
Figure 3
Figure 3. Probability values of Layman's metrics over the time in the central-northern Patagonia.
Metrics that present differences over the time are indicated by an asterisk and superscripts. Pre = pre-contact period; Mod =  modern period.
Figure 4
Figure 4. Probability values of Layman's metrics over the time in the southern Patagonia.
Metrics that present differences over the time are indicated by an asterisk ad superscripts. Groups sharing the same superscript number (1, 2) are not significantly different. EAP = early aboriginal period; LAP = late aboriginal period; Mod = modern period.
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Publication types

Grants and funding

Fundación BBVA funded this research as part of the project “Efectos de la explotación humana sobre depredadores apicales y la estructura de la red trófica del Mar Argentino durante los útimos 6000 años” (BIOCON08-194/09 2009-2011). Agencia Nacional de Promoción Científica y Tecnológica (Argentina) provided additional funding through the project “Análisis del uso de los recursos tróficos y su relación con cambios en la abundancia en tres predadores tope del Mar Argentino”. FS has been supported by an FPU Fellowship granted by the Spanish Ministerio de Educación, Cultura y Deporte (AP 2009- 4573). Half of the cost of the publication of this article has been funded by the University of Barcelona. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.