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Monitoring bubble production in a seagrass meadow using a source of opportunity

P. Felisberto, pfelis(at)ualg.pt
O.C. Rodriguez, orodrig(at)ualg.pt
J.P. Silva, joaoparentessilva(at)gmail.com
S.M. Jesus sjesus(at)ualg.pt
LARSys, University of Algarve, Campus de Gambelas, PT-8005-139 Faro, Portugal.
H. Quental-Ferreira hferreira(at)ipma.pt
P. Pousão-Ferreira pedro.pousao(at)ipma.pt
M.E. Cunha micunha(at)ipma.pt
IPMA - Instituto Português do Mar e da Atmosfera, EPPO, Av. 5 de Outubro, 8700-305 Olhão, Portugal
C.B. de los Santos cbsantos(at)ualg.pt
I. Olivé iosamarra(at)ualg.pt
R. Santos rosantos(at)ualg.pt
Marine Plant Ecology research group, Center of Marine Sciences of University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal

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Ref.: 173rd Meeting of the ASA, Boston, MA, USA, June 2017.

Under high irradiance, the photosynthetic activity of dense seagrass meadows saturates the water forming oxygen bubbles. The diel cycle of bubble production peaks at mid-day, following light intensity pattern. It is well known that bubbles strongly affect the acoustic propagation, increasing signal attenuation and decreasing the effective water sound speed, noticeable at low frequencies. Thus, the diurnal variability of bubbles may show an interference pattern in the spectrograms of low frequency acoustic signals. In an experiment conducted in July 2016 at the Aquaculture Research Station of the Portuguese Institute for the Sea and Atmosphere in Olhão, Portugal, the spectrograms of low frequency (<20kHz) broadband noise produced by water pumps in a pond of 0.48ha covered by the seagrass Cymodocea nodosa showed interference patterns that can be ascribed to the variability of the sound speed in the water. Preliminary analysis suggests that the daily cycle of bubble concentration can be inferred from these interference patterns.