FATTY-ACIDS AS SENSITIVE TRACERS OF SEWAGE-SLUDGE CARBON IN A DEEP-SEA ECOSYSTEM

Dumping into the open ocean is considered a viable political option to cope with the rapidly increasing global production of municipal sewag e sludge. However, before such an option can be justified, the impact of mega-scale dumping upon the marine environment must be fully addres sed scientifically. Here we present a methodology whereby the impact o f sewage dumping upon deep-sea invertebrates can be tracked. We examin ed the relative abundances and carbon isotopic compositions of membran e fatty acids of the sea urchin Echinus affinus from one deep-sea site heavily affected by municipal sewage sludge dumping (Sludge Max; Dump site DWD 106) and one marginally affected (station 13; 18 km SSE of DW D 106). Such analyses reveal marked differences linked to the relative importance of sewage sludge in diet. 18:2(n-6) is much more abundant in Sludge Max urchins with similar, highly C-13-depleted isotopic comp ositions in all samples (delta(13)C = -25.8 to -27.8 parts per thousan d). Conversely, 20:5(n-3), is most abundant in station 13 individuals and has less negative delta(13)C values at both sites (delta(13)C = -2 0.7 to -22.6 parts per thousand). We propose that the relative abundan ce and stable isotopic composition of 18:2(n-6) and 20:5(n-3) can be u sed to indicate the importance of sewage sludge in the diet of E. affi nus.