Listening to posidonia seagrasses
Using acoustic monitoring to detect oxygen gasThe optodes system is therefore one of the most robust methods for measuring oxygen in an ecosystem. The data this method has gathered has contributed to the establishment of a new method of measuring oxygen, resulting from the meeting of several research groups at the STARESO station. Due to the fact that they could compare their results to those of such a reliable system that Portuguese researchers were able to conclude their research. This time it was not optics that were involved but acoustics. And this method, even though it is not yet calibrated, could be used in unison with optodes yielding complementary observations in a multidisciplinary context. A method that is still at the embryonic stageThe synergy created during the meeting at Calvi made it possible to compare the acoustic data and the data obtained by the optodes and to notice a correlation between the variations in the two phenomena studied. This synergy made it possible to demonstrate that the production of the ecosystem is more important than was initially imagined. But the added-value of the acoustic system still presents many limitations. In particular, it allows to observe the relatively high or lower presence of oxygen bubbles but not to calculate the volumetric quantity from a qualitative point of view, whereas optodes are quite precise when it comes to measuring the level of dissolved oxygen. It must also be noted that the system is difficult to put in place because it requires the permanent presence of several physicists and divers to put the microphones in place and record the data which presents a lot of constraints with regard to the independence of the optodes. In conclusion, the method encountered several difficulties linked to the presence of many parasitic noises which needed to be factored into the analysis of the recordings. These sounds were linked to currents or were of biological origin. Several noises from fish were recorded for example. The relatively noisy environment therefore did not help the identification of the evolution of the sound emitted and to establish the contribution made by the oxygen bubbles to this variation to. Nonetheless, the acoustic apparatus, though still at the embryonic stage, is providing complementary information on the photosynthetic activity of the posidonia meadows. “At the moment, conclude the researchers, “this technology cannot be applied as routinely as that of the optodes. It would be necessary to avoid the problems linked to its autonomy and the necessity to quantify the observed phenomena. But it does enable us to listen to the posidonia and therefore come up with new approaches”. |
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