The Effect of Organic Nitrogen Supplement on the Utilization of Different Sources of Detritus

A particulate organic nitrogen supplement was added to two detrital materials (red macroalga Gracilaria foliifera and marsh grass Spartina alterniflora) and its effect on their utilization by the polychaete Capitella capitata was investigated with isotope tracer techniques. With the decay-resistant Spartina, added nitrogen had no effect on the oxidation or the net incorporation of Spartina carbon by the worms. With easily decomposable Gracilaria detritus there was an exponential increase in bot oxidation and net incorporation with increasing nitrogen. Added organic nitrogen had no effect on the microbial biomass associated with Spartina detritus but resulted in an increase with Gracilaria detritus. Nitrogen enrichment by microbial activity is not the only regulator of nutritional value of detritus to macroconsumers. The extent to which the substrate can be broken down and utilized by associated microbes and macrodetritivores also influences the nutritional quality of detritus to macroconsumers.