284
Paul A. TYLER
turbidites (4.95±8.5 S.E. individuals cm
−2 ). Woods and
Tietjen (1985) related these differences to the increased
organic-carbon concentration in the hemipelagic site.
The meiofauna was dominated by nematodes followed
by harpacticoid copepods, both groups being commonest in the top 2 cm of the sediment.
The biomass and density of the macrofauna was
significantly different among the stations (Richardson
et al., 1985). In hemipelagic sediments, numbers of
individuals varied from 376 to 1004 m
−2 , between 148
and 364 m
−2 in the pelagic sediments and between 124
and 428 m
−2 in the turbidites. At all three stations
polychaetes dominated numerically, with reasonable
numbers of tanaids and isopods, particularly in the
hemipelagic sediments (Richardson et al., 1985). At
all stations a wide variety of fauna was found, but
often in very low numbers. Biomass reflected the
density at each station, the hemipelagic site having
values between 287 and 392 mg wet weight m
−2 , the
pelagic sediments 22 to 127 mg wet weight m
−2 and
the turbidite 41 to 261 mg wet weight m
−2 . Biomass
was dominated by polychaetes at the turbidite and
hemipelagic sites, but the biomass of this group was
low at the pelagic site. Mollusca and echinoderms
were sub dominant at the turbidite and hemipelagic
sites, whilst the sipunculids generally dominated at
the pelagic-ooze site. As with the meiofauna the
higher biomass at the hemipelagic site is related
to increases in organic matter, as a result of both
the input of terrigenous sediment and the flux from
surface production. The data have been summarized by
Richardson et al. (1985) and Richardson and Young
(1987).
Both density and biomass of macrofauna decreased
with depth into the sediment, numbers being highest
in the top 4 cm but extending down to 12 cm depth
at the hemipelagic site. Biomass was concentrated in
the top 8 cm of the pelagic and turbidite sediments,
but was still relatively high at a depth of 12 cm at the
hemipelagic site (Richardson et al., 1985).
The megafauna also showed variation in both
density and biomass between stations (Richardson
and Young, 1987). Density of megafauna was highest at the pelagic-sediment site, although biomass,
particularly that of sponges, was significantly higher
at the hemipelagic site. Apart from sponges, the
megafauna was dominated by anthozoans, holothurians
and decapods. There was no significant difference in
megafaunal densities between the three sites. Briggs
(1985) has examined the feeding potential of two
species of seastar and two species of holothurian
from the three different sedimentary provinces in the
Venezuela Basin. On the pelagic and hemipelagic
sediments, the sediment composition within the gut
of the echinoderms was similar to that of the top
5 mm of sediment, suggesting unselective depositfeeding. On the turbidite, the gut contents suggested
that the echinoderms fed on recently-settled faecal
pellets from midwater or surface production, which
indicates selective feeding. Wolff (1976, 1979) has
analysed the fauna associated with plant debris in the
deep Caribbean. Isopods were the commonest group,
but there were significant numbers of gastropods,
polychaetes and other taxa. Some species were using
the plant material as food, whilst others were using it
as a substratum or shelter (Wolff, 1976).
Anderson et al. (1985) described the entire fish fauna
collected from below 2000 m in the Caribbean. These
authors reported 35 species of demersal fish, dominated
by Ophidiiformes (17 species) and the alepocephalids
(7 species), and recognized the fish fauna of the
Caribbean as being a depauperate component of the
world’s abyssal fish fauna.
Gulf of Mexico
With the exception of the cold-seep communities found
along the Mediterranean Ridge, all the deep water
communities of the peripheral seas considered so far
have relied on input from surface production for
their energy source. As a result these communities
are considered allochthonous. By contrast, the Gulf
of Mexico has both allochthonous and autochthonous
communities. The autochthonous communities are at
cold seeps on the Louisiana Slope and at the base of
the Florida Escarpment, and their energy is derived
from chemosynthesis driven by hydrogen sulphide and
methane in sediments (see Chapter 4). The species of
the two community types are quite distinct, although
there are some species overlaps. The Gulf of Mexico
has received much general attention, particularly in the
late 19th century, when the US steamship Albatross
sampled extensively. These cruises resulted in a series
of monographic treatments of the samples and the
reader is referred to Menzies et al. (1973) for a list of
publications.
Deep-water allochthonous communities
Rowe and Menzel (1971) and Rowe et al. (1974)
determined the biomass of macrofauna at a series of
Paul A. TYLER
turbidites (4.95±8.5 S.E. individuals cm
−2 ). Woods and
Tietjen (1985) related these differences to the increased
organic-carbon concentration in the hemipelagic site.
The meiofauna was dominated by nematodes followed
by harpacticoid copepods, both groups being commonest in the top 2 cm of the sediment.
The biomass and density of the macrofauna was
significantly different among the stations (Richardson
et al., 1985). In hemipelagic sediments, numbers of
individuals varied from 376 to 1004 m
−2 , between 148
and 364 m
−2 in the pelagic sediments and between 124
and 428 m
−2 in the turbidites. At all three stations
polychaetes dominated numerically, with reasonable
numbers of tanaids and isopods, particularly in the
hemipelagic sediments (Richardson et al., 1985). At
all stations a wide variety of fauna was found, but
often in very low numbers. Biomass reflected the
density at each station, the hemipelagic site having
values between 287 and 392 mg wet weight m
−2 , the
pelagic sediments 22 to 127 mg wet weight m
−2 and
the turbidite 41 to 261 mg wet weight m
−2 . Biomass
was dominated by polychaetes at the turbidite and
hemipelagic sites, but the biomass of this group was
low at the pelagic site. Mollusca and echinoderms
were sub dominant at the turbidite and hemipelagic
sites, whilst the sipunculids generally dominated at
the pelagic-ooze site. As with the meiofauna the
higher biomass at the hemipelagic site is related
to increases in organic matter, as a result of both
the input of terrigenous sediment and the flux from
surface production. The data have been summarized by
Richardson et al. (1985) and Richardson and Young
(1987).
Both density and biomass of macrofauna decreased
with depth into the sediment, numbers being highest
in the top 4 cm but extending down to 12 cm depth
at the hemipelagic site. Biomass was concentrated in
the top 8 cm of the pelagic and turbidite sediments,
but was still relatively high at a depth of 12 cm at the
hemipelagic site (Richardson et al., 1985).
The megafauna also showed variation in both
density and biomass between stations (Richardson
and Young, 1987). Density of megafauna was highest at the pelagic-sediment site, although biomass,
particularly that of sponges, was significantly higher
at the hemipelagic site. Apart from sponges, the
megafauna was dominated by anthozoans, holothurians
and decapods. There was no significant difference in
megafaunal densities between the three sites. Briggs
(1985) has examined the feeding potential of two
species of seastar and two species of holothurian
from the three different sedimentary provinces in the
Venezuela Basin. On the pelagic and hemipelagic
sediments, the sediment composition within the gut
of the echinoderms was similar to that of the top
5 mm of sediment, suggesting unselective depositfeeding. On the turbidite, the gut contents suggested
that the echinoderms fed on recently-settled faecal
pellets from midwater or surface production, which
indicates selective feeding. Wolff (1976, 1979) has
analysed the fauna associated with plant debris in the
deep Caribbean. Isopods were the commonest group,
but there were significant numbers of gastropods,
polychaetes and other taxa. Some species were using
the plant material as food, whilst others were using it
as a substratum or shelter (Wolff, 1976).
Anderson et al. (1985) described the entire fish fauna
collected from below 2000 m in the Caribbean. These
authors reported 35 species of demersal fish, dominated
by Ophidiiformes (17 species) and the alepocephalids
(7 species), and recognized the fish fauna of the
Caribbean as being a depauperate component of the
world’s abyssal fish fauna.
Gulf of Mexico
With the exception of the cold-seep communities found
along the Mediterranean Ridge, all the deep water
communities of the peripheral seas considered so far
have relied on input from surface production for
their energy source. As a result these communities
are considered allochthonous. By contrast, the Gulf
of Mexico has both allochthonous and autochthonous
communities. The autochthonous communities are at
cold seeps on the Louisiana Slope and at the base of
the Florida Escarpment, and their energy is derived
from chemosynthesis driven by hydrogen sulphide and
methane in sediments (see Chapter 4). The species of
the two community types are quite distinct, although
there are some species overlaps. The Gulf of Mexico
has received much general attention, particularly in the
late 19th century, when the US steamship Albatross
sampled extensively. These cruises resulted in a series
of monographic treatments of the samples and the
reader is referred to Menzies et al. (1973) for a list of
publications.
Deep-water allochthonous communities
Rowe and Menzel (1971) and Rowe et al. (1974)
determined the biomass of macrofauna at a series of