A multivariate data analysis of the clam Ruditapes decussatus as sentinel organism of the Bizerta lagoon (Tunisia)

From May 1998 to May 1999, the clams Ruditapes decussatus were collected each month at three stations of the Bizerta lagoon. This paper represents a synthesis between the results already published of catalase (CAT) activity, of glutathione S-transferase (GST) activity and acetylcholinesterase (AChE) activity measured in the clams. Hydrological parameters (temperature, salinity, dissolved oxygen, pH) were determined. Microbial loads (total aerobic bacteria, faecal bacteria and Vibrionaceae) were analyzed in the clams and the sediments. A global Principal Component Analysis was performed including all parameters. On the first principal axis, the temperature, salinity and bacterial loads as well as CAT activities were important factors always opposed to dissolved oxygen, whereas, on the second axis, AChE activity was opposed to pH. Principal Component Analyses were also carried out for results at each station with all parameters. CAT activities were generally high in summer from July to October. AChE activities were low during the months of January, February and March at one station whereas these low activities were shifted to the months of May, June and July at the two other stations. Among the biochemical biomarkers studied, the variations in CAT activities appeared to be the most significant factor of the multivariate analysis. The variations in AChE activity were also significant whereas those in GST activity appeared to be less significant.