Vol. 53 - Alaska Resources Library and Information Services

A similar differential behavior of filter-feeding versus detrital feeding
bivalves was reported recently in an actual spill (Boehm et al. 1982b). In this study, the
authors found that the benthic-dwelling Macoma balthica was slower to initially acquire
oil than was the filter-feeder Mytilus edulis which resided in the phytal zone. After
beaching and erosional transport, and/or direct sedimentation of oil, the petroleum body
burden increased in Macoma and only slowly decreased as the sediment levels dropped.
Mytilus, on the other hand, exposed to a massive initial amount of water-borne oil,
depurated rapidly and almost completely over one year's time.
During the first two to three weeks after the spills, there was a notable lack
of significant biodegradation of oil in the water column and in the sediments. There is no
chemical evidence for the existence of biodegradation as a removal mechanism with the
short-term post-spill period (3 weeks) either in the water column or in the sediment. One
would have predicted higher rates of biodegradation in surface sediments, especially in
the surface floc, but none was observed through degradation of the "easily" degraded n-
alkanes. However, degradation of n-alkanes in the oil resulting in the classic loss of n-
alkane relative to isoprenoid and other highly branched alkanes is observed within Mya and
Serripes and to lesser extents in other benthic species. Rapid degradation of alkanes only
occurs in vivo. Whether or not this unique finding can be ascribed to microbiotal
populations within the organism itself, a likely mechanism, must be confirmed
independently. We suspect that given an unspecified amount of time, microbial
populations will begin to utilize the hydrocarbons as an energy source (i.e., biodegradation
will become more significant).
The use of a variety of biological monitors or sentinel organisms in the BIOS
study has served to delineate oil transport paths and changing environmental compartment
levels with time during the immediate post-spill (0-3 weeks) period. Furthermore, this
study has shown that although similarly behaving animals (e.g., Mya/Serripes;
Macoma/Strongylocentrotus) may on a gross level appear to act in concert, the details of
in vivo modifications and retentions of individual petroleum components are quite
different and may be intimately associated with long-term biological effects on the
individual benthic species.
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