ME1’KOI)S OF SAMPLING THE BENTHOS
179
“ Treatise on Marine Ncology and Paleoecology ” (Thorson, 1957s ;
Gunter, 1957), in which many of the pieces of equipment in use are
described. It is therefore proposed to deal here only with the general
principles of sampling, instruments being described only when they
illustrate a particular feature of design.
At this stage it may be convenient to remark on the differences in
the samples required by the marine biologist as contrasted with the
geologist. Dredges may of course be used for both biological and
geological sampling, but where more precision is required as to position
and type of sample an instrument lowered vertically from the ship is
usually to be preferred.
For investigation of the geology of the sea floor a coring tube of
some 5 cni bore is often employed, and usually it is desired that the
coring tube penetrate as far as possible. I n the deep sea the Albatross
expedition obtained cores over 20 m in length, but for work on the
continental shelf a core of a metre or less in length may be all that can
be achieved. If the sediment is very coarse even a heavily weighted
coring tube may fail to penetrate 0s retain a sample, and then the
geologist may have to resort to a grab or similar instrument normally
used by the biologist in which, however, vertical stratification tends
to be lost.
When collecting the macrofauna, however, a much larger surface
area must be sampled, the usual area being 0.1 or 0-2 m2 (about 1 or
2 ft2). Ideally this should be sampled to a depth of about 30 cm, the
cross-sectional area of the sample not changing with depth. It will be
appreciated that the relatively great width of the sample implies that
the methods used in geological core sampling are on the whole unsatisfactory, although the ideal sample, if i t could be taken, would be a
short, wide, core.
Another difference affecting the design of the instruments is that in
geological sampling a single good core a t each position is usually
sufficient; it does not matter if it takes a little time to re-set the gear
as this can be done while steaming to the next station. For benthos
sampling, however, two or more samples per station are often required,
so that it is essential that the sampler can be quickly and easily re-set
for the next sample. This is not only to save time, but to minimize
drift of the ship while on station. (Such considerations do not arise
in deep-sea work where the time to re-set the gear is short relative
to that for lowering and hoisting. Here reliability must be the main
concern. )
I n sampling the benthos the main problems are due to the varied
nature both of the sediment and the fauna which inhabits it. Sampling
179
“ Treatise on Marine Ncology and Paleoecology ” (Thorson, 1957s ;
Gunter, 1957), in which many of the pieces of equipment in use are
described. It is therefore proposed to deal here only with the general
principles of sampling, instruments being described only when they
illustrate a particular feature of design.
At this stage it may be convenient to remark on the differences in
the samples required by the marine biologist as contrasted with the
geologist. Dredges may of course be used for both biological and
geological sampling, but where more precision is required as to position
and type of sample an instrument lowered vertically from the ship is
usually to be preferred.
For investigation of the geology of the sea floor a coring tube of
some 5 cni bore is often employed, and usually it is desired that the
coring tube penetrate as far as possible. I n the deep sea the Albatross
expedition obtained cores over 20 m in length, but for work on the
continental shelf a core of a metre or less in length may be all that can
be achieved. If the sediment is very coarse even a heavily weighted
coring tube may fail to penetrate 0s retain a sample, and then the
geologist may have to resort to a grab or similar instrument normally
used by the biologist in which, however, vertical stratification tends
to be lost.
When collecting the macrofauna, however, a much larger surface
area must be sampled, the usual area being 0.1 or 0-2 m2 (about 1 or
2 ft2). Ideally this should be sampled to a depth of about 30 cm, the
cross-sectional area of the sample not changing with depth. It will be
appreciated that the relatively great width of the sample implies that
the methods used in geological core sampling are on the whole unsatisfactory, although the ideal sample, if i t could be taken, would be a
short, wide, core.
Another difference affecting the design of the instruments is that in
geological sampling a single good core a t each position is usually
sufficient; it does not matter if it takes a little time to re-set the gear
as this can be done while steaming to the next station. For benthos
sampling, however, two or more samples per station are often required,
so that it is essential that the sampler can be quickly and easily re-set
for the next sample. This is not only to save time, but to minimize
drift of the ship while on station. (Such considerations do not arise
in deep-sea work where the time to re-set the gear is short relative
to that for lowering and hoisting. Here reliability must be the main
concern. )
I n sampling the benthos the main problems are due to the varied
nature both of the sediment and the fauna which inhabits it. Sampling