Conversion of Kelp Debris and Faecal Material from the Mussel Aulacomya ater by Marine Micro-Organisms

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Abstract
Freshly powdered kelp debris from Laminaria pallida is characterized by a high C/N ratio of .apprx. 8.0; material which has passed through the gut of the dominant kelp bed suspension-feeding bivalve A. ater has a reduced C content and a C/N ratio of 4.8. This suggests that A. ater may derive a substantial proportion, possibly amounting to as much as 40-50% of its C requirements by absorption of the more labile C components of its diet; the more refractory components are returned to the environment as feces. Both freshly-fragmented kelp debris and fecal material are colonized by bacteria which are subsequently replaced by flagellates and ciliates whose biomass commonly reaches .apprx. 10% of that of the bacterial prey density. Calculation of the conversion efficiency of C into the C equivalent of bacterial biomass suggests that an efficiency of 10-15% is achieved by the bacteria which colonize particulate debris, irrespective of the fact that the fecal material may be different in composition from that of freshly-fragmented kelp. Approximately 85-90% of the fragmented kelp which is not consumed by the filter-feeders and the processed fecal material in the water column is mineralized within 33 days at 10.degree. C. The residual 10-15% assimilated into bacteria could represent a potential food resource for the consumer community. Because of the relatively low conversion of particulate C into bacteria, it is suggested that their trophic significance as a C resource is likely to be small in coastal waters.