Lotti, Alessia

Pazzi, Veronica

English

Florence Research

Geophysical Research AbstractsVol. 19, EGU2017-14259, 2017EGU General Assembly 2017© Author(s) 2017. CC Attribution 3.0 License.Ambient seismic noise as an interesting indirect cue for the Cerithideadecollata migrationsVeronica Pazzi and Alessia LottiDepartment of Earth Sciences, University of Firenze, Firenze, Italy (veronica.pazzi@unifi.it)Presence or absence of water, food availability, capability of avoiding predation, and body temperature are con-stantly changing according to the tidal excursion. In fact, more than the diurnal light-dark variation, tide is shapingthe whole intertidal animal life. Therefore, physiological and behavioural systems exist to reduce the stress that theintertidal fauna may face during the unsuitable tidal phase. Cerithidea decollata is a common western Indian Oceanmangrove gastropod. It feeds on the ground at low tide, and climbs the trees two/three hours before the water arrivalto avoid submersion. In spite of the irregular East African tidal pattern, it also regularly settles on trunks roughly 40cm above the maximum level of the incoming tide. Migrations usually take place about twice a day unless at NeapTide, when snails may remain on the dry ground. Past experiments showed that a biological clock cannot accountfor water level foreseeing, nor direct visual cues or chemical information from the water itself or from previousmigrations have been detected. On the other hand, tidal gravity variations can be felt by the snails. Moreover, otherindirect cues could be hypothesize related to a) the oceanic waves reaching the coast and the barrier reef (seismicnoise), or b) the changes in ground resistivity (self potential) caused by the sea water moving close. To verify thesehypotheses, an integrated geophysical survey (single-station seismic noise and self potential survey) was carriedout at Mida Creek (Kenya) to characterize the local seismic wavefield in terms of its amplitude and to measure thetemporal variations of the electric potential field. Final goal was to verify whether a correlation exists between thetime evolution of these phenomena and the snail movements. Here we present the first results of the seismic noisemeasurements. Data were acquired by means of a single station all-in-one 3-directional 24-bit digital tromometerequipped with 4.5 Hz geophones. The acquisition run for 11 days (29th June, 2013 - 9th July, 2013). We assumedthat the tide transgressions/regressions generate pressure fluctuations on the ground, that are locally transformedinto microseismic waves at seafloor propagating inland. Therefore, we evaluated a possible correlation, in termsof decision to climb up or not, between the seismic signals amplitude fluctuations and the snails’ movements. Todo so we performed: a) the analysis of the trend of the LF (0.1-2 Hz) and HF (2-60 Hz) seismic noise amplitudes,and b) the comparison of the seismic signals with the height of tide, the number of animals that climbed to thesafety level, and the height that they reached during each tide cycle. The study showed an interesting similaritybetween the time evolution (mean value) of the LF amplitude trend and the animals’ movements. Even thoughtadditional data should be collected to improve the results, it is the first time that a consistent physical cue otherthan the obvious but discarded ones (visual and chemical), has been identified that could potentially be detected bythe snails as well as by other intertidal organisms.

Ambient seismic noise as an interesting indirect cue for the Cerithidea decollata migrations

https://flore.unifi.it/bitstream/2158/1094411/1/2017%20Pazzi%20%26%20Lotti%20-%20EGU.pdf

Ambient seismic noise as an interesting indirect cue for the Cerithidea decollata migrations

Abstract

Similar works

Full text

Available Versions

Florence Research