Detritus formation from eelgrass (Zostera marina L.): The relative effects of fragmentation, leaching, and decay

Abstract

In laboratory decomposition experiments dead eelgrass leaves lost a maximum of 35% of the original dry weight in 100 days at 20°C. Whole leaves lost 0.5% of their organic content per day whereas particles smaller than 1 mm lost 1% per day. Sterilization of leaves by dry heat or potassium cyanide showed that leaching accounted for 82% of the total loss of organic matter from predried material and 65% of the loss from undried material. Bacteria acting alone increased the nitrogen content of the detritus but only slowly degraded the leaf material. When protozoa were introduced, they grazed on the bacteria, maintained the bacterial population in an active metabolic state, and hastened the rate of decay. The C : N ratio of incubated detritus decreased from over 20 : 1 to as low as 11 : 1, indicating an increase in its potential food value. The overall slow rate of decomposition could enable the eelgrass detritus system to continue functioning during periodic short term fluctuations in eelgrass primary production by ensuring that a reservoir of slowly decomposing material is always present.