Oxygen consumption by a coral reef sponge

Oxygen consumption of the Red Sea coral reef sponge Negombata magnifica was measured using both incubation and steady-state methods. The latter method was found to be the more reliable because sponge activity remained stable over time. Oxygen consumption rate was measured during three levels of sponge activity: full activity, reduced activity and basal activity (starved). It was found that the active oxygen consumption rate of N. magnifica averaged 37.3±4.6 nmol O₂ min^-1 g^-1 wet mass, which is within the upper range reported for other tropical marine sponges. Fully active N. magnifica individuals consumed an average of 41.8±3.2 nmol O₂ min^-1 g^-1 wet mass. The mean basal respiration rate was 20.2±1.2 nmol O₂ min^-1 g^-1 wet mass, which is 51.6±2.5% of the active respiration rate. Therefore, the oxygen used for water pumping was calculated to be at most 10.6±1.8 nmol O ₂ min^-1 g^-1 wet mass, which is 25.1±3.6% of the total respiration. Combined oxygen used for maintenance and water pumping activity was calculated to be 30.8 nmol O₂ min^-1 g^-1 wet mass, which is approximately 74% of the sponge's total oxygen requirement. The remaining oxygen is directed to other physiological activities, mainly the energy requirement of growth. These findings suggest that only a relatively minor amount of energy is potentially available for growth, and thus might be a factor in controlling the growth rate of N. magnifica in oligotrophic coral reefs.