Sponge 'sentinel' of heavy metals

The possibility of monitoring siliceous sponges as an ideal bioindicator of 17 trace metals and halogens was investigated. Of the two species of Demosponge from the Indian coastal waters receiving stable and radioactive nuclides (54Mn, 63Ni, 65Zn, 60Co, 75Se, 113Sn, 90Sr, 131I, 137Cs), Spirastrella cuspidifera was found to accumulate Cd, Cr, and Sn in the range of 15-2000 micrograms g-1 dry tissue, some 5-7 orders of magnitude higher than in the ambient waters. Prostylyssa foetida, from the same microecological niche, was found to be totally free of these three metal ions. The bioaccumulation of Ni was also significantly higher in S. cuspidifera (400-2250 micrograms g-1) than in P. foetida (7-15 micrograms g-1). The former species was also found to be an ideal sentinel for detecting levels of Co, Zn, and Ti; levels of Cu, Mn, Pb Fe and Sr were higher in P. foetida, but those of the halogens I and Br were practically identical in both species. Furthermore, bioaccumulation of metal ions was found to be a function of sponge tissue itself, rather than that of either obligate or facultative symbiont microflora. In view of the high degree of species specificity which sponges exhibit while accumulating many trace metal ions, a 'sponge watch programme' is proposed on a global scale for monitoring the health of coastal ecosystems against a variety of potentially toxic pollutants.