The marine biology dredge is used to sample
organisms living on a rocky bottom or burrowing
within the smooth muddy floor of the ocean
(benthic) species).The dredge is pulled by
a boat and operates at any depth on a cable
or line, generally with a hydraulic winch.
The dredge digs into the ocean floor and bring
the animals to the surface where they are
caught in a net that either follows behind
or is a part of the digging apparatus.
Early dredging samplers did not have a closing
device, and many organisms were washed out.
This led to a mistaken impression that the
deep-sea bed lacked species diversity, as
theorised by Forbes in his Azoic hypothesis.
Later samplers devised by Howard L. Sanders
and the Epibenthic sled designed by Robert
Hessler showed that deep-sea bottoms are sometimes
rich in soft-bottom benthic species.
== History ==
The first marine biology dredge was designed
by Otto Friedrich Müller and in 1830 the
results of two dredging expeditions undertaken
by Henri Milne-Edwards and his friend Jean
Victoire Audouin during 1826 and 1828 in the
neighbourhood of Granville were published.
This was remarkable for clearly distinguishing
the marine fauna of that portion of the French
coast into four zones.
Müller's design was modified by the Dublin
naturalist Robert Ball in 1838 and at the
Birmingham meeting of the British Association
for the Advancement of Science in 1839 a committee
was appointed for dredging research with a
view to the investigation of the marine zoology
of Great Britain, the illustration of the
geographical distribution of marine animals,
and the more accurate determination of the
fossils of the Pliocene period.
The committee was led by Edward Forbes.
Later annual reports of the British Association
contained communications from the English,
Scottish and Irish branches of the committee,
and in 1850 Forbes submitted its first general
report on British marine zoology.
Ball's dredge was still in use in 1910.
In the 20th century the 'anchor-dredge' was
developed to sample deep burrowing animals.
It is not towed but digs in, and is released,
in the manner of an anchor.
The wide variety of dredges and other benthic
sampling equipment makes site comparison difficult.
== Gallery ==
== See also ==
Fishing dredge
