Ontogenetic and temperature-dependent changes in tolerance to hypoxia and hydrogen sulfide during the early life stages of the Manila clam Ruditapes philippinarum.

Wind-induced upwelling of hypoxic waters containing hydrogen sulfide (HS) sometimes causes mass mortalities of aquatic organisms inhabiting coastal areas, including the hypoxia-tolerant Manila clam Ruditapes philippinarum. We examined the tolerance of Manila clam to HS under controlled laboratory conditions. Larvae and juveniles obtained by artificial fertilization or from a wild population were exposed to normoxic or to hypoxic water with or without un-ionized HS (concentrations, 0.2-52.2 mg/L). Twenty-four-hour exposure experiments revealed ontogenetic changes in the clam's tolerance to HS exposure: tolerance was enhanced from the larval stages to juveniles just after settlement but was attenuated as juveniles grew. Tolerance of larvae and juveniles to HS exposure weakened as the water temperature rose from 20 to 28 °C. Prolonged 48-h exposure to HS attenuated the tolerance of juveniles to HS. Temporary suspension of HS exposure by 24-h reoxygenation improved the ability of juveniles to withstand repeated HS exposure.