Vol. 53 - Alaska Resources Library and Information Services

of time in the neuston layer.
If their occurrence at the surface
is part of a diurnal migration, then most megalopae could be expected
to be exposed to surface films of oil.
Further, since megalopae
are the last larval stage before metamorphosis, they represent the
survivors of larval development during which natural mortality has
substantially reduced populations from initial densities of SI
zoeae hatched.
Extensive mortality of the megalops stage could
exacerbate natural mortality rates and threaten recruitment to the
benthos.
3. Year. Somerton (1981) shows that C. opilio in the area of the St.
George Basin have successfully recruited juveniles to benthic populations
only three times in 10-11 years.
If a major oil disaster
occurs in what is otherwise an auspicious year for C. opilio larvae,
then extensive mortality could imperil an infrequent, yet crucial
year-class for this species' reproductive effort in the area
of the St. George Basin.
Because of the widespread distribution of Tanner crab over the
southeastern shelf, a major oil spill would be required to significantly
affect a larval year-class.
However, because megalopae may aggregate
near the surface, a widespread spill of shallow depth could affect larvae
over a very large area.
Since adults of these species are primarily
in water deeper than 70 m, direct impacts on adult crabs are unlikely.
The results of work reported by Incze (1983) indicate that events affecting
the larval stage may be responsible for much of the sporadic nature
of recruitment in this species.
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