156
Lisa A. LEVIN and Andrew J. GOODAY
and Duncan, 1985, 1987a,b). Overall, the dominant
deep-sea families are the Alepocephalidae (slickheads),
Macrouridae (grenadiers) and Ophidiidae (cusk eels).
The macrourids are particularly well represented at all
depths from the upper slope to the abyss, and the
ophidiids are unusual because the number of species
increases with bathymetric depth, both absolutely and
relative to the total number of fish species (Haedrich
and Merrett, 1988; Merrett and Haedrich, 1997). The
505 species belonging to 72 families recorded from
areas beyond the 200 m contour in the North Atlantic
represent 39% of all deep-sea species (Merrett, 1994).
Taxonomically, the North Atlantic fauna is most similar
to the Indian Ocean fauna (40% of genera in common)
and least similar to the Northeast Pacific fauna (14%
of genera in common) (Merrett and Haedrich, 1997).
As in the case of many invertebrate taxa, fish diversity
is greatest on the middle and lower parts of the slope.
In the North Atlantic, the species/family ratio, a useful
measure of diversity, is lowest in the depth ranges
200–399 m (species/family ratio = 2.5) and >4000 m
(species/family ratio = 2.9) and highest between 400
and 1999 m (species/family ratio = 6.0) (Merrett and
Haedrich, 1997, table 2.1 therein). However, it is useful
to be reminded (Merrett and Haedrich, 1997) that deepsea fish are not a particularly diverse group compared
with the small invertebrates on which perceptions of
high deep-sea diversity are based.
Haedrich and Merrett (1988) have summarized the
distribution of species in different bathymetric zones
at a series of localities around the North Atlantic continental margin (slope and rise), the region where most
demersal fish species occur. Their compilation indicates
that two species, the synaphobranchiid eel Synaphobranchus kaupi and the grenadier Coryphaenoides
armatus, are particularly widespread. On the other
hand, many other species have restricted geographical
ranges, leading Haedrich and Merrett (1988, 1990)
to conclude that it is impossible to recognize real
demersal fish communities in the deep North Atlantic.
Like some invertebrate megafauna (e.g., Billett, 1991),
fish species have well-defined bathymetric ranges on
North Atlantic continental margins. However, these
ranges are often different in different parts of the
North Atlantic, and the impression they convey of
vertically zoned communities are merely artifacts of
species replacement patterns (Haedrich, 1997; Merrett
and Haedrich, 1997). Most demersal species probably
do not interact ecologically with each other to any great
extent.
Truly oceanic abyssal demersal fish faunas (4000–
6000 m) are less well documented than those from
the continental margin. Nevertheless, the faunas of
the Northeast Atlantic basins are reasonably well
sampled, and their characteristics can be related to the
structure of the overlying water column and patterns
of primary production. Merrett (1987) recognized a
northern assemblage (Porcupine Abyssal Plain, 49ºN)
dominated by three grenadier species (two in the
subgenus Coryphaenoides (Chalinura) and one in the
subgenus C. (Nematonurus)) and the synaphobranchiid
Histiobranchus bathybius, and a southern assemblage
(Madeira Abyssal Plain, 30ºN) dominated by ipnopids
(Bathymicrops regis and Bathypterois longipes) and the
rattail Echinomacrurus mollis. The northern species are
large benthopelagic fish with functional swim bladders
and robust musculature, which imply considerable
mobility and hence the ability to catch relatively large
prey. Limited data suggest that fecundity is high. The
southern species are small, microphagous fish which
are either negatively buoyant, or able to maintain
neutral buoyancy only by reducing ossification and
musculature and therefore mobility. Limited data suggest that fecundity is low. Merrett (1987) advanced the
hypothesis that these characteristics reflect the switch
from the seasonal deposition of phytodetritus at the
Porcupine Abyssal Plain site to the more oligotrophic,
non-seasonal system which prevails on the Madeira
Abyssal Plain. Subsequent sampling has modified
this picture somewhat, with the recognition of two
assemblages between 31–38ºN and another southern
assemblage off the Northwest African margin around
20–22ºN (Merrett, 1992; Merrett and Haedrich, 1997).
The latter appears to be related to high productivity
associated with the main upwelling zone off Cap Blanc,
referred to above (p. 139). Merrett and Haedrich (1997)
suggested that, in abyssal open-ocean settings, trophic
inputs derived from primary production in the overlying
photic zone usually exert a strong influence on the
distribution of demersal species. On the other hand,
along continental margins, vertical water-column fluxes
are obscured by food inputs derived from upwelling,
terrigenous sources, currents, shelf production, and
interactions between horizontally distributed pelagic organisms and the continental slope. In such areas, these
factors have the most decisive effect on distribution
patterns.
Lisa A. LEVIN and Andrew J. GOODAY
and Duncan, 1985, 1987a,b). Overall, the dominant
deep-sea families are the Alepocephalidae (slickheads),
Macrouridae (grenadiers) and Ophidiidae (cusk eels).
The macrourids are particularly well represented at all
depths from the upper slope to the abyss, and the
ophidiids are unusual because the number of species
increases with bathymetric depth, both absolutely and
relative to the total number of fish species (Haedrich
and Merrett, 1988; Merrett and Haedrich, 1997). The
505 species belonging to 72 families recorded from
areas beyond the 200 m contour in the North Atlantic
represent 39% of all deep-sea species (Merrett, 1994).
Taxonomically, the North Atlantic fauna is most similar
to the Indian Ocean fauna (40% of genera in common)
and least similar to the Northeast Pacific fauna (14%
of genera in common) (Merrett and Haedrich, 1997).
As in the case of many invertebrate taxa, fish diversity
is greatest on the middle and lower parts of the slope.
In the North Atlantic, the species/family ratio, a useful
measure of diversity, is lowest in the depth ranges
200–399 m (species/family ratio = 2.5) and >4000 m
(species/family ratio = 2.9) and highest between 400
and 1999 m (species/family ratio = 6.0) (Merrett and
Haedrich, 1997, table 2.1 therein). However, it is useful
to be reminded (Merrett and Haedrich, 1997) that deepsea fish are not a particularly diverse group compared
with the small invertebrates on which perceptions of
high deep-sea diversity are based.
Haedrich and Merrett (1988) have summarized the
distribution of species in different bathymetric zones
at a series of localities around the North Atlantic continental margin (slope and rise), the region where most
demersal fish species occur. Their compilation indicates
that two species, the synaphobranchiid eel Synaphobranchus kaupi and the grenadier Coryphaenoides
armatus, are particularly widespread. On the other
hand, many other species have restricted geographical
ranges, leading Haedrich and Merrett (1988, 1990)
to conclude that it is impossible to recognize real
demersal fish communities in the deep North Atlantic.
Like some invertebrate megafauna (e.g., Billett, 1991),
fish species have well-defined bathymetric ranges on
North Atlantic continental margins. However, these
ranges are often different in different parts of the
North Atlantic, and the impression they convey of
vertically zoned communities are merely artifacts of
species replacement patterns (Haedrich, 1997; Merrett
and Haedrich, 1997). Most demersal species probably
do not interact ecologically with each other to any great
extent.
Truly oceanic abyssal demersal fish faunas (4000–
6000 m) are less well documented than those from
the continental margin. Nevertheless, the faunas of
the Northeast Atlantic basins are reasonably well
sampled, and their characteristics can be related to the
structure of the overlying water column and patterns
of primary production. Merrett (1987) recognized a
northern assemblage (Porcupine Abyssal Plain, 49ºN)
dominated by three grenadier species (two in the
subgenus Coryphaenoides (Chalinura) and one in the
subgenus C. (Nematonurus)) and the synaphobranchiid
Histiobranchus bathybius, and a southern assemblage
(Madeira Abyssal Plain, 30ºN) dominated by ipnopids
(Bathymicrops regis and Bathypterois longipes) and the
rattail Echinomacrurus mollis. The northern species are
large benthopelagic fish with functional swim bladders
and robust musculature, which imply considerable
mobility and hence the ability to catch relatively large
prey. Limited data suggest that fecundity is high. The
southern species are small, microphagous fish which
are either negatively buoyant, or able to maintain
neutral buoyancy only by reducing ossification and
musculature and therefore mobility. Limited data suggest that fecundity is low. Merrett (1987) advanced the
hypothesis that these characteristics reflect the switch
from the seasonal deposition of phytodetritus at the
Porcupine Abyssal Plain site to the more oligotrophic,
non-seasonal system which prevails on the Madeira
Abyssal Plain. Subsequent sampling has modified
this picture somewhat, with the recognition of two
assemblages between 31–38ºN and another southern
assemblage off the Northwest African margin around
20–22ºN (Merrett, 1992; Merrett and Haedrich, 1997).
The latter appears to be related to high productivity
associated with the main upwelling zone off Cap Blanc,
referred to above (p. 139). Merrett and Haedrich (1997)
suggested that, in abyssal open-ocean settings, trophic
inputs derived from primary production in the overlying
photic zone usually exert a strong influence on the
distribution of demersal species. On the other hand,
along continental margins, vertical water-column fluxes
are obscured by food inputs derived from upwelling,
terrigenous sources, currents, shelf production, and
interactions between horizontally distributed pelagic organisms and the continental slope. In such areas, these
factors have the most decisive effect on distribution
patterns.