Changes in Aliphatic Hydrocarbon Tracer Composition during the Digestive Process of the Marine Worm Nereis

In the laboratory, marine worms were fed with a mixture of algae and several aliphatic hydrocarbons for 15 days. By comparing hydrocarbons in food and in faeces, it appeared that the worm's digestive process led to changes in the distribution of the n-alkanes mixture. These changes were different from those only due to physical processes in the experimental conditions, indicating that marine worm feeding could substantially affect the fate of hydrocarbons in the sedimentary marine ecosystem. In the sediments, a number of biologically mediated processes could affect the cycling of hydrocarbons1,2. Among these processes, bioturbation, which can be defined as the stirring or movement of sediments by the activity of benthic organisms, and more particularly worms, plays an important role in the vertical redistribution of hydrocarbons in the sedimentary column3,4. Moreover, by modifying the chemical and microbial hydrocarbon environment, bioturbation may enhance the subsequent degradation of hydrocarbons compared to non-bioturbated sediments5-8 and extend it throughout the whole depth of bioturbated sediment depth9. However, if hydrocarbon redistribution is principally the result of particle transport induced by macrofauna during various activities (e.g. tube and burrow construction), it may also be realized through the faeces production process1. In areas of intensive reworking, where surface sediments are ingested several times a year10, passage through the gut exposes sorbed hydrocarbons to a harsh chemical and active microbiological environment11. If the metabolization of polycyclic aromatic hydrocarbons7,12-14 by worms has been demonstrated, little information is available on the uptake of aliphatic hydrocarbons3 by worms and their fate through the digestion process. A laboratory experiment has been carried out in order to investigate the fate of a mixture of aliphatic hydrocarbons ingested by the marine worm Nereis virens which is widely distributed in estuarine ecosystems. In this paper, we present the preliminary results obtained.