Cytotoxicity from sulfide exposure in a sulfide-tolerant marine invertebrate

It is unknown whether sulfide-tolerant marine invertebrates suffer cytotoxicity from sulfide exposure in vivo at environmentally-relevant concentrations. We tested this with the mudflat polychaete Glycera dibranchiata. Exposure of live animals to sulfide up to 2.4 mmol l^− 1 for 24 h did not affect animal survival, and animal condition (gross appearance and activity) was unaffected at sulfide concentrations up to 0.25 mmol l^− 1. However, animal condition was decreased at higher sulfide concentrations (P < 0.0001, n = 33). Coelomic fluid obtained from the animals showed decreased erythrocyte count (P = 0.0035, n = 14), indicating cell loss, and increased propidium iodide and Hoechst 33324 staining (P < 0.0001 and P = 0.0003, respectively, n = 14), indicating loss of plasma membrane integrity, even at sulfide concentrations that produced no change in animal condition. When G. dibranchiata were allowed a 72 h recovery period following 24 h sulfide exposure, there was no overall improvement in condition (P ≥ 0.12, n = 7-8), and worms that had been exposed to 1 mmol l^−  1 sulfide still had an erythrocyte count that was less than half that of control animals (P = 0.028, n = 7). The inability to completely recover the cell count was at least partially due to impaired production of new erythrocytes, since analysis of BrdU incorporation indicated that erythrocyte proliferation was reduced from 2% per day in control animals to 0.12% per day in animals exposed to 1 mmol l^− 1 sulfide (P = 0.010, n = 21). Together, these findings indicate that at least some sulfide-tolerant marine invertebrates experience significant cellular injury and impaired tissue proliferation when exposed to environmentally relevant sulfide concentrations, even when the appearance and behavior of the animal appear unaffected.