Researchers from the University of Oviedo and the Oceanographic Centre of Gijón (Spanish Institute of Oceanography) in collaboration with Roger Williams University have shown the evolutionary keys of jellyfishes in a research which has been published on Science magazine. This project, funded by the Ministry of Science and Innovation through the Malaspina CONSOLIDER 2010 project: Expedition, Circumnavigation, Global Change and Exploration of Global Ocean's Biodiversity, has shown how jellyfishes have evolved increasing water content in their tissues, which has made them bigger and gelatinous as well as exceptionally effective hunters.

José Luis Acuña, teacher of Ecology, researcher and manager of the Erasmus Mundus master's degree in Marine Biodiversity and preservation of the University of Oviedo; Ángel López-Urrutia, researcher from the Oceanographic Centre of Gijón- IEO; and Sean Colin, teacher from the Roger Williams University in the USA, are the authors of this study, which means the first theory, bases on experimental data, which explains the evolutionary strategy followed by jellyfishes and the careful balance which links them to fishes, with which they compete on equal terms in spite of being blind, slow and very old.

"While fishes have developed a great visual acuity in order to find their preys, jellyfishes depend on a primitive system based on direct contact with the prey. The key of their success is that, when increasing their bodies' size, they move a higher quantity of water and they draw more preys to their tentacles" as José Luis Acuña, first signer of the article, explains. "This is a very effective strategy as long as the jellyfish's swimming speed is slow enough", Ángel López- Urrutia points out.

This research, supported by the Campus of International Excellence from the University of Oviedo and with the collaboration of the Aquarium of Gijón in providing the necessary materials for the study, confirms that the overexploitation of fishing stocks can lead to a change in the marine ecosystem which favours the spreading of jellyfishes instead of fishes. Jellyfishes are as effective predators as fishes so "they are ready to fill the fishes' role when facing overexploitation or any other damage that they can suffer", they explained.

In order to assess the efficiency in obtaining food, researchers have taken into account the diverse corporal density between jellyfishes and fishes and they observed that, when creatures with same quantity of organic matter are compared, the predation rate is the same in jellyfishes and fishes. "Allometric techniques as the ones we have already explained, where size and the water temperature in which they live are taken into consideration, allow us to analyze the energetic waste and the ability to gain food of different bodies, with a great level of accuracy", as Ángel López-Urrutia affirms.

Acuña and López- Urrutia were helped by Sean Colin, from the Roger Williams Universiyt, located in the USA, who a swimming and jellyfishes feeding specialist. Researchers collected jellyfishes, fishes and their preys' feeding, breathing and swimming, which were also combined with biomechanical equations so as to produce a synthesis which join experimentation and theoretical reflection.