This seems obvious, but from a scientific perspective it is not so clear. Researchers of the Group of Marine Ecology and Paleoceanography, which belongs to the Marine Observatory of Asturias of the University of Oviedo, have confirmed this hypothesis using data collected in the Aviles Canyon. Technically, this is a quite simple idea, which implies that small animals would be placed in lower trophic levels, closer to the base of the trophic pyramid-- herbivores--, while the bigger predators would be on the top.

The researchers in charge of this work, published in the journal Ecology, highlight that, despite this hypothesis is consolidated and scientifically accepted as one of the characteristic features of the structure of ecosystems, it does not rely on a consolidated set of data up to date. The traditional way to estimate the trophic level of an organism is through the analysis of its digestive content, or in situ observation of its prey selection behavior. These approaches are highly laborious, and hinder the measurement of the trophic level in a representative group of animals in an ecosystem.

The study of the University of Oviedo, published in the journal ‘Ecology', states that in the Asturian submarine valley, predators weigh between 1.000 and 4.000 times more than their preys.

The new study, directed by José Luis Acuña, Professor of the Department of Organisms and Systems Biology, and led by PhD student Sonia Romero Romero, as author of the work, is based on the analysis of 15N, a stable nitrogen isotope. 15N is less common than the normal isotope -14N-, and it is located in the tissues in every transfer between predator and prey. That is, the higher the15 N ratio in an animal´s body, the higher position in the trophic level. Using this technique, researchers could estimate simultaneously the body mass and trophic level of 897 individuals of different animal species collected in the Avilés Canyon. The analysis includes from tiny crustaceans that are fed on microalgae to giant squids and cetacean mammals characteristic of this ecosystem, and also fish, birds, echinoderms and other taxa which live in the depths of the sea and the water column. Research proves that in the great submarine valley in the Asturian coast predators weigh between 1000 and 4000 times more than their preys.

This work has been led by Sonia Romero, PhD student, with the collaboration of Juan Höfer y Axayacatl Molina Ramírez and directed by José Luis Acuña, all of them belonging to the Marine Observatory of Asturias of the University of Oviedo, an initiative framed in the Campus of International Excellence. It was funded by the Ministry of Economy and Competitiveness through the projects BIOCANT/DOSMARES (ref. CTM2012- 2180- CO3- 02) and SCAPA (ref. CTM2013- 45089), also joined by the Center for Fishing Experimentation of the Principality of Asturias, the Department of Stratigraphy, Paleontology and Marine Sciences of the University of Barcelona, the Institute of Marine Sciences of CSIC in Barcelona, and the Spanish Institute for Oceanography of Gijón. SEO/BIRDLIFE provided samples of tissues of marine birds and Luis Laria, of the CEPESMA, granted access to the tissue samples of cetacean mammals and giant squids.

Reference:

• Body size-based trophic structure of a deep marine ecosystem. Ecology. Volume 97, Issue 1. January 2016. Pages 171–181.
• Sonia Romero-Romero, Axayacatl Molina-Ramírez, Juan Höfer, José Luis Acuña.

Imagen de portada: Neolithodes grimaldii / Axayacatl Molina-Ramírez

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