The bioturbulence generated by the fish can help to mix and distribute nutrients in coastal waters

Vigo, April 7, 2022.- A new study, published this Thursday, April 7 by 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 that make up the oceans, but the contribution could not be demonstrated. of swimming organisms to this phenomenon. Thus, the results of this research, which are also collected in an informative pill available in English and in Galician , constitute the first evidence obtained from in situ measurements of a biologically driven oceanic mixture.

In this study, an international team composed of several research institutions, including the Institute of Marine Research (IIM-CSIC) , the University of Vigo, the Spanish Institute of Oceanography (IEO, CSIC), The University of Southampton and the Swiss Federal Institute of Aquatic Science and Technology have been monitoring water turbulence in the Pontevedra estuary for fifteen days, specifically in the Bueu cove, aboard the BIO Ramón Margalef in the summer of 2018.

These observations arose in a “totally fortuitous way”, explains Beatriz Mouriño, principal investigator of the Remedios project (http://proyectoremedios.com/inicio/), in which this study is framed, since the oceanographic campaign aimed to study how it affects turbulence to 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 how during those two weeks of the campaign every night the turbulence in the water increased. 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 which can generate a storm. on the surface of the ocean, without us seeing any storm on the horizon “, 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 shoals that were concentrated at night in the area. In fact, the nets were full of anchovies or European anchovies, 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 estuaries are highly stratified: temperature and other properties change significantly 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, there are “previous studies that have suggested 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, we have shown that closer to the earth, where changes occur in a much smaller depth range, anchovies are able to generate mixture. ”Thus, this study reveals that although biological mixing may not be very important in 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 stocks 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 cability of living organisms to influence and reshape the physical environment in which they live.

Authorship

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 Centro Oceanográfico de Vigo  (IEO, CSIC); Miguel Gil Coto, from the Oceanic Processes in Global Chang group at the Institute of Marine Research (IIM-CSIC); Damien Bouffard of the Swiss Federal Institute of Aquatic Science and Technology and Alberto C. Naveira of the University of Southampton.

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1-The DOI number for your paper will be 10.1038 / s41561-022-00916-3. Once your paper has been published online, it will be available at the following URL: https://www.nature.com/articles/s41561-022-00916-3