282
Paul A. TYLER
A third shark species, Etmopterus spinax, has a diet
similar to that of C. coelolepis, and may compete
with the latter more than C. coelolepis does with
G. melastomus (Carrass´ on et al., 1992).
From the deep waters of the Tyrrhenian Sea, there is
evidence that the six-gilled shark (Hexanchus) and the
seven-gilled shark (Heptanchus) are bottom scavengers
feeding on sunken whale remains. There is evidence
for fin whales in this region, as well as the blue whale
(Balaenoptera musculus) passing through on migration. These mammals may form a significant organic
input when compared to phytodetrital sedimentation
(M.V. Angel, personal communication).
Benthic data for the eastern Mediterranean are more
limited, possibly as a result of the oligotrophic nature of
the area. Forbes (1844) suggested that life was absent
below a depth of 550 m in the Aegean. More recently
however, because of projects funded nationally and by
the European Union, there has been more interest in
this region. In a transect from the Gulf of Taranto
(Italy) to the coast of Egypt, Boetius et al. (1996) have
determined microbial biomass and activity in deepwater sediments. There was phytodetrital input to these
sediments, but the chloroplastic pigment equivalent
(CPE) in the Ionian and Levantine Seas declined from
<6 mg cm
−2 at a depth of 200 m to 0.1 mg cm
−2 at
3000 m. Surprisingly, at 4260 m in the Pliny Trench
south of Crete, and in the Hellenic Trough at 4620
and 3750 m the chloroplastic pigment equivalent rose
to 10 mg cm
−2 . Such high values of phytodetritus were
explained by lateral transport down the adjacent steep
slopes. Microbial production in the trenches exceeded
that of the abyssal plains by an order of magnitude, and
bacterial biomass was 0.1 mg C cm
−2 in the trenches
compared to 0.05 mg C cm
−2 on the abyssal plain.
Boetius et al. (1996) concluded that microbial activity
in deep-sea sediments is regulated by food supply.
Danovaro et al. (1993) maintained that, even in such
oligotrophic waters, deep-sea sediments are not totally
depleted of nutrient value.
Quantitative analyses of macrofauna in deep water
of this region are few. Tselepides and Eleftheriou
(1992) quantified the distribution of the macrofauna
from a depth of 200 m to 985 m in relation to
environmental variables. As elsewhere in the Mediterranean, biomass, abundance and diversity decreased
with depth, especially below 500 m. The dominant
macrofauna were polychaetes, with surface deposit
feeders and carnivores dominating at the shallowest and
deepest sites respectively.
Chemosynthetic-based communities are also rare in
the Mediterranean. Most of the known hydrothermal
sites are shallow rather than deep, being confined
to shelf depths. Such sites contain no vent-specific
fauna (Dando et al., 1999). Cold seeps appear to
occur along the Mediterranean Ridge at depths of
~1900 m, consisting of mud volcanoes (Corselli and
Basso, 1996). These mud volcanoes have a rich benthic
community dominated by lucinid and vesicomyid
bivalves. Detailed descriptions are not available at
present.
Synecology has formed part of the study of Mediterranean ecosystems and there have been a number
of significant taxonomic works published by Western
European and Russian scientists. Such monographs
include inter alia the stony corals (Zibrowius, 1980),
polychaetes (Laubier and Ramos, 1973), the amphipods
(Bellini-Santini, 1990) and the Tanaidacea (KudinovaPasternak, 1982). Results from Russian works are
reviewed by Vinogradova et al. (1982) and more
recently by Vinogradova (1997).
Finally, it is necessary to consider whether the Mediterranean has a true deep-sea fauna, or whether the
fauna represents pseudopopulations from the Atlantic.
Bouchet and Taviani (1992) rehearsed the current
arguments, and concluded that the larval characteristics
of the fauna rather than physical barriers such as
the Gibraltar Sill control the potential colonization.
The high temperatures of the deep Mediterranean are
believed to inhibit successful colonization of the Mediterranean deep water, and reproduction of those species
that do recruit is prevented by the high temperatures.
As a result the Mediterranean populations are sterile
pseudopopulations that are constantly recruited from
larval inflow from Atlantic populations. Bouchet and
Taviani (1992) applied the same argument to the Red
Sea.
Red Sea
The fauna of the deep parts of the Red Sea is
depauperate as a result of the physical nature of the
environment. Because a number of the deep basins
have a high content of hydrogen sulphide and poor
convective mixing, a situation analogous to that in
the Black Sea develops, and no fauna has yet been
isolated from those deeps with a strong hydrothermal
influence. Within the brine/seawater interface the
sulphate-reducing bacterium Desulphovibrio has been
isolated (Tr¨ uper, 1969). The fauna that survives in
Paul A. TYLER
A third shark species, Etmopterus spinax, has a diet
similar to that of C. coelolepis, and may compete
with the latter more than C. coelolepis does with
G. melastomus (Carrass´ on et al., 1992).
From the deep waters of the Tyrrhenian Sea, there is
evidence that the six-gilled shark (Hexanchus) and the
seven-gilled shark (Heptanchus) are bottom scavengers
feeding on sunken whale remains. There is evidence
for fin whales in this region, as well as the blue whale
(Balaenoptera musculus) passing through on migration. These mammals may form a significant organic
input when compared to phytodetrital sedimentation
(M.V. Angel, personal communication).
Benthic data for the eastern Mediterranean are more
limited, possibly as a result of the oligotrophic nature of
the area. Forbes (1844) suggested that life was absent
below a depth of 550 m in the Aegean. More recently
however, because of projects funded nationally and by
the European Union, there has been more interest in
this region. In a transect from the Gulf of Taranto
(Italy) to the coast of Egypt, Boetius et al. (1996) have
determined microbial biomass and activity in deepwater sediments. There was phytodetrital input to these
sediments, but the chloroplastic pigment equivalent
(CPE) in the Ionian and Levantine Seas declined from
<6 mg cm
−2 at a depth of 200 m to 0.1 mg cm
−2 at
3000 m. Surprisingly, at 4260 m in the Pliny Trench
south of Crete, and in the Hellenic Trough at 4620
and 3750 m the chloroplastic pigment equivalent rose
to 10 mg cm
−2 . Such high values of phytodetritus were
explained by lateral transport down the adjacent steep
slopes. Microbial production in the trenches exceeded
that of the abyssal plains by an order of magnitude, and
bacterial biomass was 0.1 mg C cm
−2 in the trenches
compared to 0.05 mg C cm
−2 on the abyssal plain.
Boetius et al. (1996) concluded that microbial activity
in deep-sea sediments is regulated by food supply.
Danovaro et al. (1993) maintained that, even in such
oligotrophic waters, deep-sea sediments are not totally
depleted of nutrient value.
Quantitative analyses of macrofauna in deep water
of this region are few. Tselepides and Eleftheriou
(1992) quantified the distribution of the macrofauna
from a depth of 200 m to 985 m in relation to
environmental variables. As elsewhere in the Mediterranean, biomass, abundance and diversity decreased
with depth, especially below 500 m. The dominant
macrofauna were polychaetes, with surface deposit
feeders and carnivores dominating at the shallowest and
deepest sites respectively.
Chemosynthetic-based communities are also rare in
the Mediterranean. Most of the known hydrothermal
sites are shallow rather than deep, being confined
to shelf depths. Such sites contain no vent-specific
fauna (Dando et al., 1999). Cold seeps appear to
occur along the Mediterranean Ridge at depths of
~1900 m, consisting of mud volcanoes (Corselli and
Basso, 1996). These mud volcanoes have a rich benthic
community dominated by lucinid and vesicomyid
bivalves. Detailed descriptions are not available at
present.
Synecology has formed part of the study of Mediterranean ecosystems and there have been a number
of significant taxonomic works published by Western
European and Russian scientists. Such monographs
include inter alia the stony corals (Zibrowius, 1980),
polychaetes (Laubier and Ramos, 1973), the amphipods
(Bellini-Santini, 1990) and the Tanaidacea (KudinovaPasternak, 1982). Results from Russian works are
reviewed by Vinogradova et al. (1982) and more
recently by Vinogradova (1997).
Finally, it is necessary to consider whether the Mediterranean has a true deep-sea fauna, or whether the
fauna represents pseudopopulations from the Atlantic.
Bouchet and Taviani (1992) rehearsed the current
arguments, and concluded that the larval characteristics
of the fauna rather than physical barriers such as
the Gibraltar Sill control the potential colonization.
The high temperatures of the deep Mediterranean are
believed to inhibit successful colonization of the Mediterranean deep water, and reproduction of those species
that do recruit is prevented by the high temperatures.
As a result the Mediterranean populations are sterile
pseudopopulations that are constantly recruited from
larval inflow from Atlantic populations. Bouchet and
Taviani (1992) applied the same argument to the Red
Sea.
Red Sea
The fauna of the deep parts of the Red Sea is
depauperate as a result of the physical nature of the
environment. Because a number of the deep basins
have a high content of hydrogen sulphide and poor
convective mixing, a situation analogous to that in
the Black Sea develops, and no fauna has yet been
isolated from those deeps with a strong hydrothermal
influence. Within the brine/seawater interface the
sulphate-reducing bacterium Desulphovibrio has been
isolated (Tr¨ uper, 1969). The fauna that survives in