Seagrass-Watch Magazine Issue 47 - March 2013 | Page 29

the mechanical impact
of otter doors causes
continuous furrows in
seagrass meadows,
where 93% of Posidonia shoots
in the healthiest
seagrass meadows
are uprooted6

The damage caused by trawling is linked
to the lead weights fixed to the lower part
of the net's opening, which keep it in
contact with the seabed, and to the heavy
'otter boards' fixed to the net, in a way that
widens the opening of the trawl. Trawling
opens up furrows in the P. oceanica
meadow, uproots 100,000 to 360,000
shoots per hour(4), severely reduces the
seagrass cover and induces resuspension

of the sediment. In addition, trawling
constitutes a vector of dissemination of
invasive species (e.g. Caulerpa taxifolia
and C. cylindracea).
Otter trawling has also resulted in major
changes in the structure of demersal
communities with differences in fish
assemblages inhabiting healthy and
disturbed Posidonia meadows(5,6).

The effects of trawling on the
megabenthos in Posidonia meadows has
resulted in the reduction or elimination of
species typical of hard bottoms and their
replacement by ubiquitous species and
others typical of sandy/muddy bottoms, as
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