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

Abstract

Wind-induced upwelling of hypoxic waters containing hydrogen sulfide (H₂S) 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 H₂S 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 H₂S (concentrations, 0.2-52.2 mg/L). Twenty-four-hour exposure experiments revealed ontogenetic changes in the clam's tolerance to H₂S 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 H₂S exposure weakened as the water temperature rose from 20 to 28 °C. Prolonged 48-h exposure to H₂S attenuated the tolerance of juveniles to H₂S. Temporary suspension of H₂S exposure by 24-h reoxygenation improved the ability of juveniles to withstand repeated H₂S exposure.

Keywords: Anoxia; Benthos; Bivalve; Body size; Coastal ecosystem; Early life history; Eutrophication; Hydrogen sulfide; Hypoxia; Water temperature.