POTENTIAL CARBON-SOURCES FOR THE HEAD-DOWN DEPOSIT-FEEDING POLYCHAETEHETEROMASTUS-FILIFORMIS

In this study we investigated potential carbon sources for the capitel lid polychaete, Heteromastus filiformis. It is a head-down deposit fee der ingesting sediment from at least 15 cm below the sediment-water in terface. This orientation appears to minimize the worm's ability to ac quire food and oxygen and maximize its exposure to sulfide. The food s ources we examined were metabolically active bacteria, benthic algae, detritus and chemoautotrophic bacteria. Carbon retention efficiencies from metabolically active bacteria, benthic algae and detritus by H. f iliformis were 26%, 8% and 4% respectively. These values are relativel y low compared to other deposit feeding species suggesting that H. fil iformis does not possess unique digestive capabilities. Rubisco (Ribul ose bisphosphate carboxylase) assays were negative, which indicates an absence of symbiotic chemoautotrophic bacteria in tissue or absorbed carbon. Average delta C-13 were - 12.83 for worms and - 20.70 for 15 c m sediment, which indicates that external gardening of chemoautotrophs is not a major carbon source for H. filiformis. Nevertheless, several experiments showed that this capitellid worm had an unusually high gr oss heterotrophic CO2 uptake. We suggest that H. filiformis utilizes b oth dissolved and particulate carbon sources stored within anoxic and sulfidic sediments that are not utilized by other deposit feeding orga nisms.