Certain benthic species of molluscs, crustaceans, large polychaete worms, 

 and spinculid worms, referred to as the macrofauna, may play a role in hydro- 

 carbon degradation in the sediments. As noted above, microbes are most effec- 

 tive in hydrocarbon degradation when working at the water-sediment interface. 

 Many of the benthic animals rework the sediment so that hydrocarbons adsorbed 

 to this sediment would be more exposed to microbial action. Tidal flow causes 

 resuspension of fine sediments, with their associated hydrocarbons. These 

 resuspended sediments can be taken in by benthic filter feeders, such as 

 clams, mussels, and oysters. The clam Macoma feeds directly on organic matter 

 in the sediment. The work of Farrington and Quinn (1973) has shown the impor- 

 tance of bivalves in the uptake of hydrocarbons from sediments. There is 

 no evidence of hydrocarbon metabolism by these bivalve molluscs, but the dis- 

 charge of hydrocarbon in the feces and pseudofeces would allow attack by 

 microfauna and meiofauna. 



Oil uptake from the sediment has been shown for the brown shrimp Cvangon 

 orangon (Blackman 1972), and benthic decapods are able to metabolize petroleum 

 hydrocarbons quickly, with subsequent excretion of hydrocarbon metabolites 

 (Corner et al. 1973, Lee et al . 1976). 



Many of the large polychaetes ingest sediment during their feeding. 

 Recent work has shown that polychaetes are able to metabolize petroleum hydro- 

 carbons (Rossi and Anderson 1977, Lee et al . 1977b). When benz(a)anthracene 

 was incorporated into sediment containing Nereis suoainea and N. virens , 

 the major metabolite produced by the worms was 5, 6-dihydro-5, 6-dihydroxybenz- 

 (a)anthracene (Figure 2). The hydroxylated and conjugated products of these 

 oxidation reactions are subsequently excreted by the worms. 



CONCLUSIONS 



As noted earlier, the fate of oil spills at sea depends on the compo- 

 sition of the oil, as well as such external factors as light and temperature. 

 The extent of degradation also depends on the type of coastal area in which 

 the spill occurs. In open, exposed coastline areas, with good circulation 

 of water, most fractions of spilled oil are soon degraded (Rashid 1974). 

 In protected shallow areas with less circulation, spilled oil is incorporated 

 into sediments and much of it remains unaltered for many years (Blumer and 

 Sass 1972). Photo-oxidation, dissolution, emulsif ication, adsorption to 

 particles, biodegradation, and uptake by marine animals are not processes 

 that act independently, but the interactions of all of these determine the 

 fate of oil in water. The various filter feeders, grazers, and deposit feeders 

 of the meiofauna and macrofauna utilize the organic matter of the sediment. 

 In this process, they may expose deeper sediments to the water sediment inter- 

 face where there is more microbial activity. The involvement of both microbes 

 and animals in hydrocarbon degradation in marine sediments may be similar 

 to their symbiotic association in recycling organic material in terrestrial 

 sediments. 



49 



