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each cruise, one multiple-corer sample was collected for the study of
meiofauna and three box-corer samples were gathered for investigating the
abundance of macrofauna. Reference samples were collected 2 nautical
miles up current from the DEA.
This sampling design appeared to be appropriate at the beginning of
DISCOL, but initial species and abundance data demonstrated that the
number of samples was too low. Additionally, throughout the study it was
difficult to recognize disturbed samples when the degree of disturbance
was not particularly heavy. Mounting cameras to the corers and imaging
the seafloor just before bottom contact became a helpful method, but this
was still a blind search for disturbed areas. Adding video control to the
sampling systems during the last post-impact study allowed us to search
and sample the disturbed areas successfully. Thus, the limitations
introduced by the radial and non-continuous heavy disturbance created
difficulties in unequivocal sampling of disturbed areas.
The macrofauna was defined to be larger than 500 microns during
the first cruise, but we realized that this would not be sufficient for
evaluation of this faunal component. During later cruises, sieves with 250-
µm meshes were employed, limiting overall data comparability. Such errors
could have been avoided with a separate pre-impact cruise into this specific
area.
1.4. Sampling sequence
During the preparation phase for DISCOL, no information or prior
experience was available on which we could base a suitable time sequence
for revisiting and resampling the DEA. It is known that processes in the
deep sea are slow, while recolonisation in shallow waters may be a matter
of months. Small-scale experiments with defaunated sediments in the deep
sea 17 have demonstrated the existence of opportunistic species and their
fast colonisation potential in those small (less than 1 m²) experimental
sediment patches, but reestablishment of a community with natural
successional changes appears to be a process extending over several
years. Experimental and commercial large-scale disturbances will certainly
last more than a decade.
Early in the planning process, we decided to return to the DEA after
several months, and again after several years. The sampling schedule
achieved was determined not only by scientific considerations, but also by
ship-time availability (table 1).
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