Project Deliverable D50 Report on Best Practices Workshop - Ifremer

Hydrothermal ecosystems from video imagery and temperature time-series
Authors: J. Sarrazin, P-M. Sarradin, O. Gauthier (IFREMER) and M. Grégoire (Telecom
Bretagne)
Abstract: Located on oceanic ridges, hydrothermal ecosystems are characterized by strong
physico-chemical gradients and the presence of a unique fauna, sustained by microbial
chemosynthesis. Several studies have shown that the spatial distribution and composition of
vent faunal assemblages were strongly correlated to geological, physical and chemical
processes at different spatial and temporal scales but almost no data are available on the
temporal dynamics of these ecosystems. The major objective of this research project is to
develop a video processing platform to analyze the temporal dynamics of hydrothermal
ecosystems. This data along with abiotic data measured within the environment (temperature,
iron and oxygen concentrations) will be analyzed and compared using multivariate statistics
including PCNM and cluster analyses. Finally, all the data will be fed within a GIS that will
allow for a graphical representation of all the observed temporal variations. More specifically,
we are looking to answer the following questions: (i) What biological and geological data can
be automatically extracted from video imagery to feed the temporal data base, (ii) what are
the different scales of variations of environmental conditions (e.g. temperature) and (iii) what
are the links between environmental changes and faunal dynamics in hydrothermal
ecosystems ?
Methane bubbles analysis in the framework of MARMARA demonstration mission
Author: I. Leblond (IFREMER)
Slides in Annex F5
Abstract: Observations of fluid plumes in the water column, bubbles of methane for
example, show an increasing interest since several years. The study of the long-term
variability of the emitted quantities could be linked to varied works: we can cite prevention of
natural risks (earthquakes, tsunamis, etc), impact of the methane discharge to climate change,
etc. So, a bubbles detector demonstrator, with acoustic sensor, has been deployed in 2009 in
the Marmara sea. The principle of the engine is as follow: the module, named BOB (Bubbles
OBservatory Module) is put on the seafloor. It’s an autonomous module, and we can expect a
continuous recording during about one month. At the top of the instrument, we find the
acoustic sensor (a 120 kHz split-beam echo-sounder, as used in fisheries acoustics), placed on
a pan & tilt system. With this system, the position of the sounder (geographical sectors for
example) can be easily changed. The principle of acquisition data is as follow: an acoustic
signal is emitted by the echo-sounder, in an horizontally position according to previously
chosen sectors, and the backscattering signal is recorded.
Post-processing is realised a posteriori, after the recovery of the module. It consists at first to
compute the volume backscattering vs time (echo-integration principle, used in fisheries
acoustics).
A particular attention is made to guaranty quantitative measures and a certain interoperability:
o Data are recorded in an international format “Hac” (Description of the ICES HAC
standard data exchange format – ICES Cooperative Research <strong>Report</strong>. 278,
December 2005).
o Data are calibrated, which allow quantitative measures and comparisons with other
acoustic sensors.
o Data are georeferenced, which allow comparisons with several sensors (acoustic or
others) or with other surveys.
<strong>Deliverable</strong> #50 - update October 2010 24