At the end of each respiratory trial, the chamber closed cycle was extended to 20 min, during which time
_ MO2was simultaneously recorded
and used to determine the O:N ratio. A 50-mL sample of seawater was
thendrawnfromeachchamber,sealedin10%HClacid-washedglass
vials with a drop of 10% chloroform added to prevent bacterial accumulationandstoredat−20 °C prior to analysis. The ammonia-N concentration in these samples was determined using a salicylate-hypochlorite
method following the procedure ofBower and Holm-Hansen (1980)
and expressed in mg NH4-N g DM−1h−1after the subtraction of
ammonia-N concentration in control vials.