Keys of jellyfish evolutionary success revealed

This research, financed by the Ministry of Science and Innovation by means of the projects CONSOLIDER Malaspina 2010: Expedición de Circunnavegación, Cambio Global and Exploración de la Biodiversidad del Océano Global, reports how the jellyfish has evolved with an increase in the amount of water in its tissue; this process has allowed the jellyfish to become bigger and more gelatinous and also to be an exceptionally efficient hunter.

José Luis Acuña, lecturer of the University of Oviedo, Ángel López-Urrutia, researcher of the Oceanographic Centre of Gijón (Spanish Institute of Oceanography), and Sean Colin, lecturer of the Roger Williams University (USA), are the authors of this study that provides the first approach based on experimental data. The research is aimed to explain the evolutionary strategy of jellyfishes in the fragile balance that connects them with fishes, with which they compete in spite of being blind, slow and old organisms.

"While fishes have developed an extraordinary visual acuity to detect their preys, the jellyfish relies on a primitive system based on the direct contact with its prey. Its success can be explained by an increase in size, which has allowed this type of organism to move a bigger amount of water and draw more preys towards its tentacles," states José Luis Acuña. "It is an effective strategy as long as the swimming speed of the jellyfish is slow enough," points out Ángel López-Urrutia.

This research, supported by the Campus of International Excellence of the University of Oviedo and the Aquarium of Gijón (providing study materials), confirms that the overexploitation on fishing stocks can result in a change of the marine ecosystem that promotes the expansion of jellyfishes against fishes. As a predator, the jellyfish can be as efficient as any fish, so "these organisms are threatened by the same dangers that fishes regarding overfishing or any other issue," according to the researchers of the study.

Aiming to value the feeding efficiency, this study takes into account the different body density of the organic material of jellyfishes and fishes and they observed that, when organisms with the same amount of organic material are compared, the predation rate is the same one in fishes and jellyfishes. "The allometric techniques we have used consider size and water temperature; this allows us to analyse the energetic waste and the feeding capacity of different organisms with a high level of accuracy," stated Ángel López-Urrutia.

In order to reach these conclusions, Acuña and López-Urrutia relied on the collaboration of Sean Colin, of Roger Williams University (USA), who is an expert in jellyfish feeding and swimming. Researchers gathered data on the feeding, the breathing and the swimming process of jellyfishes, fishes and their preys; this information was combined with biomechanical equations to produce a synthesis that brings together experimentation and theoretical grounds.