CIM-UVigo scientific staff participates in this research on the effect of fish schools movement. The data from the study were obtained offshore Bueu as part of the Remedios project
A new study, published Thursday in the journal Nature Geoscience, shows that fish contribute to the production of turbulence and ocean mixture in coastal regions, so the role they play in the distribution of heat, nutrients and oxygen is more important than previously thought. The relevance of this article lies in the fact that until now, the scientific community had shown that it was the winds and tides that supplied most of the energy that drives the mixture of the different layers of the oceans, but the contribution of swimming organisms to this phenomenon could not be proved. Thus, the results of this research, which are also presented as an informative pill available in English and Galician, constitute the first evidence obtained from in situ measurements of a biologically driven ocean mixture. It is known as bioturbulence, a phenomenon that has fascinated the scientific community for decades.
In this study, an international team composed of several research institutions, including the Marine Research Center of the University of Vigo, the IIM-CSIC Marine Research Institute, the Spanish Institute of Oceanography (IEO, CSIC), the University of Southampton and The Swiss Federal Institute of Aquatic Science and Technology, monitored water turbulence in the Pontevedra ria for fifteen days, specifically in the Bueu cove, aboard the BIO Ramón Margalef in the summer of 2018. These observations arose “completely by chance”, explains. Beatriz Mouriño, principal investigator of the Remedios project in which this study is framed, as the oceanographic cruise aimed to study how turbulence affects marine life, but “we have just shown that marine life can influence ocean turbulence, which in turn influences marine life! ” This research started when the scientific team observed that during the two weeks of the campaign, the turbulence in the water increased every night. Using a microstructure profiler, they found that “from dusk to dawn, the measurements indicated that, under our feet, from a depth of about 10 to 30 meters, there was a very intense turbulence, comparable to that generated by a storm on the surface of the ocean ”, explains Beatriz Mouriño.
Using acoustic information from the echo sounder mounted on the hull of the ship and the samples collected with nets, the research team was able to attribute this turbulence to the presence of fish schools that concentrated at night in the area. In fact, the nets were full of European anchovy or anchovy eggs, Engraulis encrascicolus, which shows that the signal corresponds to spawning aggregations of this fish that, with its frantic behavior, generates bioturbulence.
The stratification of estuaries, the key
“We believe that the biological mixture was intense in our observations because the rias are very stratified: temperature and other properties undergo very important changes at different depths,” said Dr. Bieito Fernandez Castro, a researcher at the University of Southampton and first author of the article. In fact, according to the scientist, “previous studies suggest that biological turbulence causes little mixing because the circular motion of water generated by fish while swimming is too small. This is true in the open ocean, where temperature changes occur in tens of meters. However, our data show that closer to the ground, where the changes occur in a much smaller depth range, the anchovies are able to generate mixture”.
Thus, this study reveals that while biological mixing may not be very important in the open ocean, it may be significant in coastal ecosystems, where high biological production coexists with rapid vertical changes in ocean properties. The vertical mix created by fish schools could affect the redistribution of temperature, nutrients and dissolved gases, such as oxygen, which play a key role in the functioning of the ecosystem on which the fish themselves depend. Therefore, the findings highlight the ability of living organisms to influence and reshape the physical environment in which they live.
The article is signed by Bieito Fernández Castro, of the University of Southampton, as the first author, together with researchers from the CIM-UVigo Biological Oceanography Group Beatriz Mouriño, Esperanza Broullón and Antonio Comesaña; Marian Peña, from the Balearic Oceanographic Center (IEO, CSIC); Enrique Nogueira, from the Vigo Oceanographic Center (IEO, CSIC); Miguel Gil Coto, from the Oceanography Department of the Marine Research Institute (IIM-CSIC); Damien Bouffard of the Swiss Federal Institute of Aquatic Science and Technology and Alberto C. Naveira of the University of Southampton.
Source: DUVI
