280
Paul A. TYLER
have invaded by larval dispersal (Young et al.,
1996).
The existence of a true abyssal fauna in the western
Mediterranean has been questioned (P´ er` es, 1985). If
one assumes that the abyssal zone begins at 3000 m
(see Chapter 2), the maximum depth in the western
Mediterranean is 3500 m in the Tyrrhenian Basin.
Originally a true abyssal fauna was believed not
to occur, but this has been challenged by Reyss
(1971, 1972), Laubier (1972) and Chardy et al.
(1973). Typical of abyssal species are the protobranch
Nuculoma tenuis and the cumaceans Diastylis jonesi,
Leptostylis bacescoi and Procampylaspis bascescoi.
Amongst the polychaetes, the species are either found
at bathyal and abyssal depths in both the Atlantic
and the Mediterranean, or they are endemic to the
Mediterranean at bathyal and abyssal depths. Truly
abyssal Mediterranean polychaetes are species of the
genus Aricidea and Macellicephala. Of remark is
a species of Macellicephaloides, previously found
only in trenches. P´ er` es (1985) concluded that a truly
abyssal fauna occurs in the Mediterranean, particularly
in the Matapan Deep (4690 m). Fredj and Laubier
(1985) recorded the polychaete Lacydonia laureci as
being the species occurring at greatest depths in the
Mediterranean. At other depths there is a predominance
of eurybathic species. Compared to similar depths
in the Atlantic, the Mediterranean abyssal fauna is
species-poor. Fredj and Laubier listed the endemic
Mediterranean species found below 2000 m and listed
their Atlantic congeners.
Certain taxa are noteworthy by their absence in
the deep Mediterranean, although found at similar
depths in the Atlantic. Typical of these are elasipod
holothurians, stalked crinoids, and the crab genus
Munidopsis; in the Mediterranean, ophiuroids rarely
occur below 700 m, although they are found at all
depths in the Atlantic. Fredj and Laubier concluded
that the species found in the deep Mediterranean
are representative of the older groups within their
respective phyla, whereas the ‘advanced’ forms, such
as Anamathia, Geryon and Munidopsis are much less
common.
As a result of programmes funded by the European
Union more data have recently become available,
although in many cases such observations are localized.
Of particular significance have been the studies along
the slope of the Golfe du Lion and the Catalan Sea.
De Bov´ ee et al. (1990) quantified the microbiota and
meiofauna at 29 stations in five canyons at depths
between 672 and 2367 m in the Golfe du Lion. Microbial numbers varied from 9×10
−3 to 3×10
−5 colony
forming units ml
−1 , the latter being in deep water.
Meiofauna was dominated by nematodes with a density
range from 3.6 to 100.5 individuals cm
−2 . Meiofaunal
abundance increased rapidly with depth – in fact, more
rapidly than in other oceans (see Chapters 5 and 6).
Such low abundance was attributed to the low organic
content of the sediment (2.7 mg C g
−1 ) resulting from
high degradation rates at the temperature of 13ºC near
the deep-sea bed. Stora et al. (1999) have determined
the abundance of macrobenthos in the Toulon Canyon
and the adjacent slope (south of Toulon in the Golfe
du Lion) at depths from 250 to 2000 m (Table 9.3). At
the stations examined there was a strong decrease in
species richness with depth particularly between 250
and 1000 m, below which there was stabilization of
species numbers. Biomass also decreased with depth
(except between 1500 and 2000 m) from 2.14 g m
−2
at 250 m to 0.05 g m
−2 at 2000 m (Stora et al.,
1999). At most of the stations surface deposit feeders
dominated, followed by subsurface deposit feeders.
Carnivores were well represented at the upper stations
but decreased with depth. Stora et al. (1999) divided the
slope into a series of groups (Table 9.3) and identified
species characteristic of bathyal deep mud or abyssal
assemblages. The megabenthos of the deep western
Mediterranean has been described by Sard` a et al.
(1994). Decapod crustacean biomass was higher in
submarine canyons than outside, whilst fish abundance
was highest on the lower slope.
In the Catalan Sea an active slope programme has
been conducted by workers at the Institut de Ci` encies
del Mar in Barcelona. These studies have concentrated
on the distribution and diet of benthic and pelagic
crustaceans, and also on the local fish assemblages
and their diet. Cartes and Sard` a (1992, 1993) trawled
at a variety of depths between 552 and 2261 m on
the Catalan slope; multivariate analysis of their data
showed zonal boundaries between 1200 and 1300 m,
and between 1900 and 2000 m, based on the decapod
fauna. Total abundance, biomass and species richness
all declined with depth. The deepest community
was dominated by Acanthephyra eximia (pelagic),
Nematocarcinus exilis and Stereomastis sculpta. Cartes
and Sard` a (1993) concluded that decapod zonation
was determined by trophic factors, the middle slope,
with highest diversity, being influenced by resuspension
of particles associated with local submarine canyons.
More recently, Maynou et al. (1996) have shown that
Paul A. TYLER
have invaded by larval dispersal (Young et al.,
1996).
The existence of a true abyssal fauna in the western
Mediterranean has been questioned (P´ er` es, 1985). If
one assumes that the abyssal zone begins at 3000 m
(see Chapter 2), the maximum depth in the western
Mediterranean is 3500 m in the Tyrrhenian Basin.
Originally a true abyssal fauna was believed not
to occur, but this has been challenged by Reyss
(1971, 1972), Laubier (1972) and Chardy et al.
(1973). Typical of abyssal species are the protobranch
Nuculoma tenuis and the cumaceans Diastylis jonesi,
Leptostylis bacescoi and Procampylaspis bascescoi.
Amongst the polychaetes, the species are either found
at bathyal and abyssal depths in both the Atlantic
and the Mediterranean, or they are endemic to the
Mediterranean at bathyal and abyssal depths. Truly
abyssal Mediterranean polychaetes are species of the
genus Aricidea and Macellicephala. Of remark is
a species of Macellicephaloides, previously found
only in trenches. P´ er` es (1985) concluded that a truly
abyssal fauna occurs in the Mediterranean, particularly
in the Matapan Deep (4690 m). Fredj and Laubier
(1985) recorded the polychaete Lacydonia laureci as
being the species occurring at greatest depths in the
Mediterranean. At other depths there is a predominance
of eurybathic species. Compared to similar depths
in the Atlantic, the Mediterranean abyssal fauna is
species-poor. Fredj and Laubier listed the endemic
Mediterranean species found below 2000 m and listed
their Atlantic congeners.
Certain taxa are noteworthy by their absence in
the deep Mediterranean, although found at similar
depths in the Atlantic. Typical of these are elasipod
holothurians, stalked crinoids, and the crab genus
Munidopsis; in the Mediterranean, ophiuroids rarely
occur below 700 m, although they are found at all
depths in the Atlantic. Fredj and Laubier concluded
that the species found in the deep Mediterranean
are representative of the older groups within their
respective phyla, whereas the ‘advanced’ forms, such
as Anamathia, Geryon and Munidopsis are much less
common.
As a result of programmes funded by the European
Union more data have recently become available,
although in many cases such observations are localized.
Of particular significance have been the studies along
the slope of the Golfe du Lion and the Catalan Sea.
De Bov´ ee et al. (1990) quantified the microbiota and
meiofauna at 29 stations in five canyons at depths
between 672 and 2367 m in the Golfe du Lion. Microbial numbers varied from 9×10
−3 to 3×10
−5 colony
forming units ml
−1 , the latter being in deep water.
Meiofauna was dominated by nematodes with a density
range from 3.6 to 100.5 individuals cm
−2 . Meiofaunal
abundance increased rapidly with depth – in fact, more
rapidly than in other oceans (see Chapters 5 and 6).
Such low abundance was attributed to the low organic
content of the sediment (2.7 mg C g
−1 ) resulting from
high degradation rates at the temperature of 13ºC near
the deep-sea bed. Stora et al. (1999) have determined
the abundance of macrobenthos in the Toulon Canyon
and the adjacent slope (south of Toulon in the Golfe
du Lion) at depths from 250 to 2000 m (Table 9.3). At
the stations examined there was a strong decrease in
species richness with depth particularly between 250
and 1000 m, below which there was stabilization of
species numbers. Biomass also decreased with depth
(except between 1500 and 2000 m) from 2.14 g m
−2
at 250 m to 0.05 g m
−2 at 2000 m (Stora et al.,
1999). At most of the stations surface deposit feeders
dominated, followed by subsurface deposit feeders.
Carnivores were well represented at the upper stations
but decreased with depth. Stora et al. (1999) divided the
slope into a series of groups (Table 9.3) and identified
species characteristic of bathyal deep mud or abyssal
assemblages. The megabenthos of the deep western
Mediterranean has been described by Sard` a et al.
(1994). Decapod crustacean biomass was higher in
submarine canyons than outside, whilst fish abundance
was highest on the lower slope.
In the Catalan Sea an active slope programme has
been conducted by workers at the Institut de Ci` encies
del Mar in Barcelona. These studies have concentrated
on the distribution and diet of benthic and pelagic
crustaceans, and also on the local fish assemblages
and their diet. Cartes and Sard` a (1992, 1993) trawled
at a variety of depths between 552 and 2261 m on
the Catalan slope; multivariate analysis of their data
showed zonal boundaries between 1200 and 1300 m,
and between 1900 and 2000 m, based on the decapod
fauna. Total abundance, biomass and species richness
all declined with depth. The deepest community
was dominated by Acanthephyra eximia (pelagic),
Nematocarcinus exilis and Stereomastis sculpta. Cartes
and Sard` a (1993) concluded that decapod zonation
was determined by trophic factors, the middle slope,
with highest diversity, being influenced by resuspension
of particles associated with local submarine canyons.
More recently, Maynou et al. (1996) have shown that