Diapositive 1 - de l'Université libre de Bruxelles

Chapitre IIIroom). Salinity was increased by evaporation and was decreased by adding MilliQ water(Millipore). Once the required conditions were reached (at the end of January 2007),starfish arm length was measured monthly, and food was provided freely using ninedifferent batches of mussels from Knokke. Salinity and pH were measured daily andevery two days, respectively, in each aquarium using a WTW Multi 340i multi-meterequipped with a conductivity cell and a pH electrode. Temperature was measured dailyusing the same multi-meter and at intervals of 6 hours using Stow Away Tidbit TempLoggers (ONSET Corporation) as a control. Salinity was adjusted by addition of Milli-Qwater to compensate for evaporation and pH was maintained by adding NaHCO 3 (Sodiumbicarbonate 99.5%, for analysis, Acros Organics). Temperature and salinity conditions ofthe entire experiment are summarized in Table 10. Nitrites, nitrates, KH and calcium werechecked regularly using Tetra tests. Ten percent of the seawater of each aquarium werechanged twice a month using Wimereux seawater diluted with MilliQ water or salted withhw-Sea Salt professional (Wiegandt). Death rate was low except in the aquarium at 18°Cand 35 psu (75%).Table 10: Temperature (°C) and salinity (psu) recorded throughout the aquarium experiment (S.D. =Standard deviation, Min. = Minimum, Max. = Maximum).Temperature (°C)Salinity (psu)Aquarium Mean S.D. Min. Max. Mean S.D. Min. Max.A 11.2 0.1 10.9 11.6 32.0 0.1 31.8 32.3B 11.2 0.1 11.0 11.7 35.0 0.1 34.8 35.3C 10.9 0.2 10.6 11.4 25.0 0.1 24.8 25.4D 10.7 0.1 10.5 11.0 28.0 0.1 27.9 28.3E 18.3 0.2 18.0 19.0 32.0 0.1 31.7 32.3F 18.0 0.1 17.8 18.4 35.1 0.1 34.7 35.2G 17.8 0.2 17.6 18.4 25.1 0.1 24.7 25.5H 17.6 0.1 17.3 18.0 28.0 0.1 27.8 28.2The newly formed parts of juvenile arms, after 4 months of growth under controlledconditions (June 2007), were determined using the monthly size measurements and theresults from a separate calcein labelling experiment (data not shown). The distal newlygrown parts of the starfish arms were dissected in starfish that reached at least 41 mm(maximum size reached was 66 mm) and were stored at -20°C. At the end of theexperiment, water samples were taken in triplicates from the different systems and storedat -20°C until analysis. Ca consumed by the starfish for biomineralization was less than1% of the initial Ca present in the aquarium seawater. Therefore, Ca, Mg and Srconcentrations in the seawater could be considered as constant throughout the experiment.64