A high concentration of jellyfish could lead to "devastating effects" on zooplankton and fish larvae populations in the Canarian oceanic perimeter, which in turn could affect traditional fisheries, according to a thesis from the University of Las Palmas de Gran Canaria (ULPGC).
Under the title 'Jellyfish as predator and prey. Study of their respiratory metabolism and biochemical composition', the thesis, which was presented on April 22 by its author, Daniel R. Bondyale Juez, obtained outstanding cum laude and "can be considered as the most complete study to date in Spain on the respiratory metabolism of certain specific species of jellyfish, a complex organism to study due to its fragility, the cumbersome nature of its morphology and the stinging characteristics of some of its species", according to the ULPGC.
One of the conclusions of this thesis, directed by May Gómez Cabrera and Theodore T. Packard from the EOMAR group of the University Institute of Research in Sustainable Aquaculture and Marine Ecosystems (IU-ECOAQUA) of the ULPGC, indicates that a high concentration of one of the species studied, Pelagia noctiluca, could lead to "devastating effects" for its potential prey, zooplankton and fish larvae, in the Canarian oceanic perimeter.
As an example, the research by Daniel R. Bondyale Juez estimates, based on the demand associated with metabolism, although there is no data on recent arrivals, that a 'bloom' (large arrivals) of Pelagia noctiluca of 20 grams per cubic meter would have "serious consequences" on the populations of zooplankton and fish larvae in the waters surrounding the island of Gran Canaria. A circumstance that could take place in 'blooms' such as those that occurred in 2012, when 10 tons of jellyfish were collected only from Las Canteras Beach, and that could affect traditional fisheries to some extent by reducing the amount of fish and available food.
On the other hand, the results on the composition also show a high concentration of lipids in the initial stages of life of the aforementioned Pelagia noctiluca and Aurelia aurita. A fact that is stated could contain implications of great scientific interest on the metamorphosis of these species. In fact, it is pointed out that a high lipid content throughout the first days of life could lead to "these jellyfish being able to withstand quite a long time without feeding and, however, become a very attractive prey for their predators".
Jellyfish, which are usually known by common names such as jellyfish or Portuguese man-of-war, are predators, but "in turn they are food for other species despite their high water content". Thus, it is pointed out that studying their composition can help to understand this mystery, such as, for example, the high lipid concentration in larval phases.
To carry out the study, Bondyale Juez worked with two scyphozoans, the so-called true jellyfish - Aurelia aurita and the aforementioned Pelagia noctiluca - and with two hydrozoans, a siphonophore and a colonial hydromedusa - Physalia physalis and Velella velella -.
The study measured the respiratory rate of jellyfish as a way to achieve approximate estimates of their nutritional needs and the energy transformations of the organism, content that was also determined to better understand their contribution when they serve as prey to other predators from the measurement of their basic composition in proteins, lipids and carbohydrates.
The research used both a traditional method of measuring oxygen consumption and a method based on enzymes for analyzing the electron transport system that allowed a more detailed study of respiratory metabolism. "The enzymatic methodology also offers an alternative for respiratory measurements that do not require sampling and keeping the jellyfish alive. As a result of the results achieved in the respiratory rate, it is possible to calculate the demand for carbon and, therefore, for prey that are necessary to satisfy this respiration", it is detailed.
Bondyale Juez's thesis manages to make "original contributions" in the field of research into its composition and respiratory metabolism, since in this work are some of the first results on respiration and composition in Physalia physalis and Velella velella, which "despite being very common floating members in the Canarian waters, have been very little studied throughout the history of marine biology".
In fact, the results of the study could reveal the motivations behind the predation of these hydrozoans, since "they may be very different from their close relatives, the scyphozoans or true jellyfish". "Their content is significantly lower in water, a finding that indicates that a jellyfish and a hydrozoan of the same mass will have a very divergent composition in proteins, lipids and carbohydrates. In this sense, the jellyfish, having a higher content in water and less in those substances, could be less attractive than its relatives for predators", it is explained.
The study also sheds light on their floating nature, in which they are carried away by the wind, which seems to imply a lower respiratory rate and therefore a capacity to remain sailing without food, limiting their metabolism until the moment of capture. However, "jellyfish do not lag behind, and have demonstrated to be able to survive up to 8 weeks without food by resorting to decreasing their size and reducing their respiratory metabolism to below 15% of the original", it is pointed out.
The thesis was presented before a court formed by José Luís Acuña, professor of Ecology at the University of Oviedo (president), by José Juan Castro Hernández of the BIOCON group, IU-ECOAQUA (secretary) and by Natalia Osma Prado, of the Millennium Institute in Oceanography of Chile (member) and received the qualification of outstanding (Cum laude).
Bondyale Juez has received several academic awards such as the Extraordinary End of Degree Award for the Degree Studies in Marine Sciences together with the Honorable Mention of the Branch of Sciences or the Extraordinary End of Degree Award for the Master's Studies in Oceanography. He has been a speaker at numerous international conferences such as the Ocean Science Meeting, the Jellyfish Bloom International Symposium or the International Symposium of Marine Science. He has given talks at prestigious research centers such as the University of Washington (USA), MBARI (California, USA) or CICESE (Ensenada, Mexico). In addition, he has been the main author of one article and co-author in five others in high-impact journals in the field of marine sciences.
