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4.3.7 Deep-sea basins
The ocean occupies c .71% of the Earth's surface with a mean depth of 3700 m. Deep-sea
regions of 2000 m depth cover c .60% of the Earth's surface and can be affected by climate
change, with major implications and consequences on a global scale. Using a decadal data
set (from 1989 to 1998), Danovaro et al . ( 2001 ; 2004 ) provided evidence that deep-sea nem-
atode diversity can be strongly and rapidly affected by temperature shifts. An abrupt tem-
perature shift (of about 0.4 °C) in the deep eastern Mediterranean Sea caused a signific-
ant change in nematode biodiversity. This temperature decrease also resulted in decreased
functional diversity and species evenness, and an increase in the similarity of Mediterranean
nematode assemblages to colder deep-Atlantic fauna. This evidence suggests that deep-sea
fauna is highly vulnerable to environmental alteration, and that deep-sea biodiversity is also
significantly affected by very small temperature changes. In the north-east Pacific, changes
in megafaunal abundance appeared to be related to long-term, climate-driven variations in
POC flux, and hence to productivity in the overlying surface waters (Ruhl and Smith, 2004 ) .
An increase in abundance was associated with a decrease in mean body size, suggesting the
occurrence ofrecruitment events, while sharp declines in abundance were related to compet-
itivefaunalinteractions andsurvivorship(Ruhl, 2007 ).Inthenorth-eastAtlantic, large-scale
changes in the abundance of megafauna occurred in 1996 in which some species, that had
been rare components of the fauna for many years, became very abundant. One of these, the
holothurian Amperima rosea , increased in abundance (over three orders of magnitude) and
became the dominant megafaunal species (Billett et al., 2001 ) . Large-scale changes in the
flux of organic matter to the abyssal seafloor have been noted in the time series, particularly
in 2001, and may be related to the sudden mass occurrence of A. rosea the following year
(Billet et al., 2010 ).IntheArctic,theHausgartenStationnearSvalbardhasprovidedthefirst
long-term time series of the benthos in the region. Work by the Alfred Wegener Institute has
demonstrated a small but important temperature increase between 2000 and 2008 at 2500
m depth, in the Fram Strait between Svalbard and Greenland (Barange et al., 2011 ) . Within
the MarBEF project DEEPSETS, a five-year (2000−2004) time-series study of nematodes
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