Oxygen production-consumption of the pelagic Sargassum community in a flow-through system with arsenic additions

The metabolism of entire clumps of Sargassum collected from the Florida Straits in February was measured in a flow-through system with and without the addition of arsenic. Net production and respiration ranged from 0.14 to 0.76 mg C g⁻¹ h⁻¹ and 0.22 to 0.86 ml O₂ g⁻¹ h⁻¹, respectively. Net production of the community over 24 h exceeded respiration by 1.3 times. Respiration values varied with time of night; maximum respiration occurred shortly after sunset. Arsenic additions had no measurable effect upon the metabolism of the community, but when the ‘steadystate’ distribution of arsenic species was altered, there was a rapid response to re-establish the ambient As (III)/As (V) ratio.