Listening to the ocean for more comprehensive study of the seas
The French Institut de recherche pour le développement (IRD) and the Instituto del Mar del Perú (IMARPE) have developed an innovative acoustic method to observe the evolution of oxygen minimum zones (OMZs) in the world's oceans. This new technique makes it possible to measure these oxygen-free (anoxic) zones, which are home to many marine organisms, in greater detail. The findings, published in the open-access journal Public Library of Science (PLoS) ONE, open up new perspectives for the study of the oceans as well as the management of fisheries resources. The researchers measured the vertical distribution of marine organisms, such as plankton, crustaceans and fish, in the water using routine underwater acoustic observation techniques along the Peruvian coast. The measurements, made with the help of echo sounders, allowed them to determine the oxycline, which delimits the top of the OMZ, with high precision. Combining the data obtained in this way with regular hydrological measurements, they managed to compile high-resolution maps that are 50,000 to 100,000 times more precise than common hydrological profiles. As well as shedding new light on the state and spread of OMZs, the scientists were also able to calculate precisely the size of the habitat available to the Peruvian anchovy, for instance, providing information that might be of interest for fisheries management. 'This method ... allows performing integrated studies since acoustic data provides information on most ecosystem components [...] to which we can add ancillary information (satellite data, vessel monitoring system, top predator tagging, etc.),' the paper reads. 'Such integrated approaches are crucial to implement the ecosystem approach to fisheries. 'Our methodology can also be applied to other ecosystems, e.g. oceanic dead zones, and opens new perspectives for comprehensive multiscale studies on the impact of physical forcing on organisms.' OMZs are a naturally occurring phenomenon, found at depths of about 100 to 1,000 metres. They are home to numerous organisms that are specially adapted to the low-oxygen environment, including not only anaerobic bacteria but also larger organisms such as vampire squid. Oxygen-loving organisms, however, cannot survive in these zones. OMZs currently cover about 10% of the planet's surface. But they have been spreading for the past 50 years due to global warming and humankind's impact on the seas through rising levels of chemical nutrients (eutrophication), for example.
Countries
France, Peru