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Ref.: Conf. on the Effects of Aquatic Noise, Den Haag (The Netherlands), July 2019.
In coastal zones, snaps, clicks, pops and crackles produced by benthic fauna can be quite representative in the soundscape (Butler et al., 2017). These sounds can be caused simply by the movement of these organisms on the substrate, by the stridulation/friction of the hard parts of their bodies or water circulation (Simmonds and MacLennan, 2008.) Thus, when many individuals are active in an environment, the sounds merge into a timed sound, producing a Rocky Shore Bioacoustic Signature (RSBS). The Cabo Frio region is recognized as one of the main points of occurrence of upwelling phenomenon on the Brazilian coast. This phenomenon is characterized by the outcropping of deep, cold (lower than 20°C) and nutrient-rich waters to the surface and increasing of the primary productivity (Valentin and Coutinho, 1990), especially during spring and summer. This one along with other hydrodynamic features makes the site a unique biological environment (Ferreira, 2003).
This work aims to characterize the RSBS and its upwelling regime relationship. A structure with 4 hydrophones was installed near the Cabo Frio Island, in Arraial do Cabo, RJ, Brazil. Temperature data were collected and analyzed together with acoustic data. In addition, was utilized a sound propagation model to evaluate the transmission loss from sources distributed along the rocky shore (simulating RSBS). This simulation was performed for two scenarios, with and without upwelling characteristics.
The results showed the usual daily pattern, which present an increase in biological noise during twilight periods. In addition, the RSBS is modulated by the water temperature (decreases in cold waters). This occurs due to both high transmission loss and low source level caused by upwelling and probably decrease in benthic metabolic rate, respectively. This relationship between temperature and Rocky Shore Bioacoustic Signature can contribute to the understanding of the organisms behavior in relation to the upwelling and to the development of new biotechnological applications.