ONTOGENIC TRENDS OF ELEMENTS (NA TO SR) IN PRISMATIC SHELL OF LIVING CRASSOSTREA-VIRGINICA (GMELIN) GROWN IN 3 ECOLOGICALLY DISSIMILAR HABITATS FOR 28 WEEKS - A PROTON PROBE STUDY

Distribution of 16 trace and minor chemical elements was examined onto genetically with PIXE in the calcitic-prismatic margin of the shell of genetically close individuals of Crassostrea virginica (Gmelin) growi ng in three different marine habitats. Concentration of elements was a lso related to that in ostreid soft tissues and in suspended sedimenta ry particles in the ambient seawater. Distribution of the elements (Na , Mg, Al, Si, S, Cl, K, Ca, Ti, Mn, Fe, Ni, Cu, Zn, Br and Sr) was ana lyzed every 4 weeks (from May to November) with a non-destructive prob e (PIXE) in newly deposited shell of the left valve, and in pigmented, non-pigmented and the right valve of 30 living C. virginica grown for 28 weeks in three dissimilar environments (10 oysters in each habitat ): closed laboratory mariculture (HI), closed laboratory mariculture p lus suspended sediment (HII) and natural flowing estuary (HIII). The s ame elements were analyzed weekly in suspended particles (on 0.4 mu m Millipore filters) in the culture seawater in HI and HII and in ambien t seawater in HIII; and at the end of the study in gills, adductor mus cles, gonads and tissues of whole oysters. Elements in suspended sedim ent were concentrated primarily on the particles; not in the seawater filtrate. Barite crystals were present in some of the plankton samples . Growth rate was slowest in HI oysters, that of HII and HIII was simi lar and greater than that of HI. Seasonal trends in concentration of e lements in valves in the different habitats varied. Ti remained relati vely constant in HI valves during culture, but tended to decrease in H II, and increased in HIII. Other elements in HI tended to remain const ant (Cu), or to increase (Fe); in HII some elements decreased conspicu ously; in HIII some increases were prominent (Mg, Zn). A temporal chan ge in level of many elements in shell paralleled that of the same elem ent in suspended particles (Fe in HI, ME, Cu, Zn in HIII); levels decr eased in HII (Al, Ti, Fe). Parallelism of elemental concentration in s hell and suspended particles was expressed as major peaks in both, mos tly in HIII the natural estuarine setting. For Ni, Cu, Zn and Br, espe cially in HII, peaks were out of phase. Comparison of concentration of elements in old (4th week of culture) and new (28th week) shell showe d some trends among the three habitats; consistent association was evi dent in 10 elements in HIII. Maximal concentration of most elements oc curred in the right valve. Pigmented shell contained slightly higher l evels of most elements, but differences were only suggestive. After 28 weeks of culture, soft tissues contained several times the concentrat ion of elements, and greater variability, than shell. Maximal concentr ation (biomagnification) of 13 elements took place in gills, gonads an d adductor muscles, but not in whole oysters. There were clear differe nces in concentration of many of the elements among gills, gonads and adductor muscles in HI, HII and HIII, decreasing or increasing increme ntally from HI to HII. Concentration of a few elements was associated in shell and tissues: in shell in HI, Fe, and in HIII, Zn increased du ring the 28 weeks and was also maximal in the three organs at the end of the study. All other elements (less Ca, Mn and Sr) were more concen trated in tissues than in shell, Zn, Cl and Br to a high degree.The re lationship between biomagnification in different organs and the differ ent microstructures of the shell is still unclear. The investigation f ocused on ecological aspects of biomineralization in living bivalves, an aspect little studied in the past. It was made possible by the use of the non-destructive PIXE probe and suggests a model from which to i nitiate further comparative studies.