Evaluation of coastal areas quality by sponges: state of the art

The term "bio-indicator" may denote those aquatic organisms which accumulat e contaminants in their tissues to high concentration. Ideal bioindicators should meet further selection criteria. They should be sedentary, abundant at the sites of interest, easy to identify, and easy to sample. They should be strong accumulators and should not regulate the contaminants. Nowadays, the use of multiple species which represent different trophic levels or fe eding guilds has been accepted as necessary for a more accurate evaluation of pollution impacts. In order to obtain a total picture of contaminant bio -availabilities in marine environments, it is necessary to use several bioi ndicators, including : (1) macroalgae or seagrasses, responding to dissolve d sources of contaminant -(2) suspension feeders, taking particles of a pec uliar size range and responding to sources in both dissolved and suspended phases -(3) detritivores, feeding on newly deposited superficial sediments. With the aim of taking part in the creation of a system for evaluating the littoral water quality, this paper shows that sponges fulfil all the condi tions of good bioindicators. Sponges are one of the major phyla found in th e marine hard substrate benthos. Sponges are sessile filter feeders and are able to ingest particles between 0.2 and 50 mu m as well as dissolved orga nic material due to a large amount of symbiotic bacteria. Several examples show all their potential by presenting their relationships with micro-organ isms and different contaminants. For example, sponges are able to accumulat e hydrocarbons, PCB, DDT and heavy metals. It has been demonstrated that th e process was not a simple saturation kinetics. The simple organisation of sponge tissues constitutes also an advantage for researching biological ans wers to stresses. For example, the function of Heat Shock Proteins (HSP) in sponges has been determined. As in vertebrate cells, HSP protect sponge ce lls against environmental stresses. It was found that sponges react to temp erature stress by induction of HSP70. Moreover, reactions of sponges accord ing to different contaminants were also tested. Prospective studies showed that cadmium, zinc and PCB's act as inductors of HSP70. The examples presen ted in this paper show that sponges are good candidates in marine biomonito ring even if this potential is not exploited in official biomonitoring prog rammes. Currently, a field application, concerning the aquatic environment contamination by heavy metals and detergents, is beginning with analysis of their accumulation in sponges and research for biological responses.