To be interpreted and for the potential trends to be identified, environmental changes must be recorded, which requires the establishment of an integrated long-term observing system.
Chosen for this programme was the HOBO® Water Temp Pro v2 Logger with an autonomy of 42 000 measurements that makes a six-year autonomy for one measurement per hour. It is installed in a protective PVC box attached to a threaded rod sealed in the substratum. Precision of sensors as specified by the manufacturer is ±0.2 °C, which is adequate in waters where temperature varies by
several degrees a year. The logger is equipped with an optic USB interface for rapid data readout. Drift is estimated to be at 0.1 °C.yr-1.

Equipment used for measurement and recording of temperature (click on the link)
video temperature probe
* HOBO Optic USB Base Station
* tutorial software

Temperature logger installed at Ile Suhm (15 m depth).
In order to facilitate the relocation of the logger, a white golf
ball is fixed on the bolt to which the thermo-recorder in its
protective boot is attached.

Summary table of the operatinal data loggers
S : Sector:
1- Passe Royale, 2- Baie du Morbihan, 3- Choiseul, 4- Baleiniers, 5- Audierne
St : Site of obsevation: CHA: Ilot Channer, SUH: Ile Suhm, HAU: Ile Haute, LON: Ile Longue, PXR: Port Christmas, I3B: Ilot des Trois Bergers, PNO: Fjord des Portes Noires, MON: Iles du Prince de Monaco
z : depth: 5m & 15m