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Background noise in areas covered by marine plants in the Ria Formosa lagoon during the summer

P. Felisberto(1), J.P. Silva(1), J. Silva(2), R. Santos(2) and S.M. Jesus(1)
(1) LARSyS, University of Algarve, 8005-139 Faro, Portugal
(2) Marine Plant Ecology research group, Center of Marine Sciences of University of Algarve, Faro, Portugal.

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Ref.: OCEANS MTS/IEEE, Kobe (Japan), May 2018

Abstract: This paper analysis the ambient noise recorded at two sites in the Ria Formosa lagoon, South Portugal aiming at developing passive acoustic methods for monitoring marine ecosystems status. The sites are closely located, only 125 m distant, but covered by different marine plants: the seagrass Cymodocea nodosa and the seaweed Caulerpa. Both sites are very shallow water (∼1 m in low tide) and subject to large tidal forcing (peak to peak amplitude of order 3 m). Small motor boats and yachting have a large contribution for the ambient noise of the area, over a broad spectrum. Using a simple non-linear filtering technique, their contribution was removed from the background noise. The results show that the variability of the noise in both sites is complex, but the overall characteristics did not change significantly among sites, and the observed differences can not be ascribed to the different bottom coverage. The variability pattern of background noise in low frequency band (<2.5 kHz) suggests its correlation with human activity. In the frequencies above, the variability patterns are similar to those observed in other littoral environments due to marine taxa, like fish and crustaceans. The variability of the dissolved O2 is also similar among sites, and no correlation with the variability of noise power was found. These preliminary results suggest that longer lasting experiments are needed to support the development of acoustic passive methods to monitor the health of coastal ecosystems.

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