The physiological ecology of black-ribbed mussels, Septifer virgatus (Wiegmann) (Bivalvia : Mytilidae) on a sub-tropical wave-exposed shore in Hong Kong

Oxygen consumption and ammonium excretion by Septifer virgatus were measured in situ on an exposed rocky shore monthly from January to December 1999. Condition index and reproductive cycle were determined simultaneously. Spawning was diphasic, the first phase being recorded in spring (March to April). The second spawning was more prolonged (July to October), but less intense than the first. Oxygen consumption was temperature-dependent and demonstrated a seasonal pattern with a peak being recorded from summer to early autumn and with lowest values in winter. Seasonal variation in excretion rate was small with a major peak in summer, possibly associated with post-reproductive stress and high temperatures. O:N ratio reflected energy metabolism and utilization with a peak in spring and early summer (>30) when growth and gametogenesis were resumed. In late summer, spawning was initiated and temperatures rose high and became lethal, O:N decreased to minimum values.