Uptake and loss of Cd, Hg and Pb by transplanted sponges, along Eastern Mediterranean coasts (Lebanon); a comparative study betweenHippospongia communis
and DGT (Diffusive Gradients in Thin films).

• K. Nakhlé^*, G. Khalaf^* and D. Cossa^*
• ^* National Council for Scientific Research-National Centre of Marine Sciences; Batroun-Lebanon.
  E-mail: bihar@cnrs.edu.lb
• ^** Institut Français de recherche pour l’Exploitation durable de la Mer (IFREMER); Nantes-France.
  E-mail: dcossa@ifremer.fr

Abstract

The life habits of sponges in particular feeding, could make them excellent bioindicators for evaluating the health of marine environment. In case of absence of classical bioindicators like bivalves (mussels, oysters…) found mainly on rocky shores the use of a substitute organism becomes vital. Sponges' transplants could also be used in order to evaluate the long term impact of a contamination source (industrial or municipal sewages).

The goals of the present work were to develop a suitable technique for sponge culture, to test their practical value as bioindicators of trace elements contamination like Hg, Cd and Pb, and to compare results with concentrations found in water and in DGT devices (Diffusive Gradients in Thin films).

A practical and relatively easy method was developed for the transplantation and transport of sponges. Mortality rate was brought to less than 20%. Heavy metals accumulation capacity was tested on Hippospongia communis, species of the Mediterranean hard-substratum communities. Sponge transplants were transported from a polluted area to a clean one and vice versa in order to study the speed and rate of bioaccumulation and depuration. These transplants experiences were accompanied by direct analysis of trace elements in water. DGT devices were fixed in parallel with sponge cuttings in order to evaluate the difference between labile and bioavailable forms in seawater.

The response of sponges to the change of heavy metals concentrations were found to be slow compared to DGT response. Nevertheless, we managed to observe changes in these concentrations after 14 days of submerging. Trace metals rate in sponges tissue increased when transported from a clean to a contaminated area and vice versa.

Key words: Contamination - Sponges - Transplants - Hippospongia communis - Bioindicator- Trace metals - DGT - Mercury - Cadmium - Lead