P. Felisberto, pfelis(at)ualg.pt
J.P. Silva, joaoparentessilva(at)gmail.com
A.J. Silva, asilva(at)ualg.pt
S.M. Jesus sjesus(at)ualg.pt
LARSys, University of Algarve, Campus de Gambelas, PT-8005-139 Faro, Portugal.
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
H. Quental-Ferreira hferreira(at)ipma.pt
P. Pousão-Ferreira pedro.pousao(at)ipma.pt
and
M.E. Cunha micunha(at)ipma.pt
IPMA - Instituto PortugueĚ‚s do Mar e da Atmosfera, EPPO, Av. 5 de Outubro, 8700-305 Olhão, Portugal
Comments: download pdf file (not available).
Ref.: MTS/IEEE Oceans, Aberdeen, June 2017.
Abstract
This paper describes two experiments conducted in a pond covered by the seagrass Cymodocea nodosa
at the Aquaculture Research Station of the Portuguese Institute for the Sea and Atmosphere in Olhão,
Portugal, aiming at developing acoustic methods to assess oxygen production of seagrasses. The first
experiment was carried out in July covering two days, when warm water and high photosynthetic rates
give a high probability of oxygen supersaturation in water. The second experiment was carried out
in late October, covering a period of 10 days, when seagrass productivity was expected to be lower
than in July given the low irradiance and photoperiod. In the July experiment the high attenuation
of low frequency pulses and broadband water pump noise (<20 kHz) in the afternoon is ascribed to
bubbles formation during oxygen supersaturation conditions. This hypothesis is coherent with the
significant increase of the backscattering level, as measured by an acoustic backscatter system
operating at 0.5, 1, 2, 4 MHz. Both, the attenuation of low frequency signals and backscattering
level are correlated with oxygen supersaturation in water as measured by an optode. In the October
experiment, when only water pump noise was acquired, the acoustic variability that can be related
to photosynthetic activity was much weaker, nevertheless the attenuation shows a diurnal pattern
correlated with the dissolved oxygen. The results suggest a significant release of oxygen as bubbles
during photosynthesis, and therefore the potential contribution of acoustic methods to assess oxygen
production of seagrass ecosystems.
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