Atlantic Westerly Winds Biome
179
occupies the whole shelf area that is then significantly greener than the deep water beyond.
I suggest that this permanent chlorophyll hot spot may represent benthic macroalgal
meadows in the very shallow water surrounding the archipelago that lies 20–30 km
offshore. Other coastal regions with higher-than-background chlorophyll accumulation
lie along the Nile delta, in the NW Adriatic Sea off the Po delta, on the French coast
off the Rhone delta, and in the inner Aegean Sea. The entire shelf off Israel lies within
the photic zone and chlorophyll profiles show near-bottom maxima; in such areas, as
has been shown in the northern Adriatic (Ott, 1992), the high biomass of suspensionfeeding macrobenthos appear to control pelagic biomass. Such benthic organisms have
a very high weight-specific metabolic rate. This process may be interrupted by summer
stratification, in which case a DCM forms some distance above the bottom.
Major upwelling events occur in the Sicilian Channel that appear to be wind induced;
they occur mostly with a lag of 3 days after a westerly gale (often originating in a Provençal
mistral event) passes through the area. They are usually based on the southwestern tip
of Sicily (near Cape Granitola), although they often involve the entire southern coast
of the island. They may also extend across the entire Sicilian Channel to the African
coast (Piccioni et al., 1988). In the eastern Mediterranean, important surface enrichment
was induced by the annual Nile discharge prior to the closure of the Aswan High Dam
and the control of the annual flood. This feature is now very restricted, and in the
Levant Basin, offshore water is now of clarity equal to that of the central oceanic gyres.
The pelagic fisheries of the region are much diminished. On the Israeli shelf, there is a
subsurface algal bloom in bottom water over the narrow shelf, and here, the chlorophyll
profile consistently shows a maximum value just above the bottom deposits (Townsend
et al., 1988). Whether this is induced by the episodic upwelling of nutrients across the
shelf break, or whether it is due to regeneration of nutrients within sediments, and their
subsequent release, is not clear.
There are also persistent surface chlorophyll features in the Alboran Sea related to
upwelling, both along the east coast of Spain and around the Alboran eddies. A jet of
Atlantic water along the Spanish coast induces geostrophic upwelling and a very shallow
chlorophyll maximum. Upwelling is forced around the anticyclonic gyre that occupies the
western Alboran Sea (Minas et al., 1991). Farther east, a divergent front between Spain
and the Balearics between southward coastal and northward offshore flow is associated
with upwelling and chlorophyll enhancement (Estrada and Margalef, 1988). Cyclonic
eddies generated at the coast within the Algerian Current are not wind induced but
nevertheless force upwelling over sufficient spatial and temporal scales to induce algal
growth and surface enhancement of the chlorophyll field (Millot, 1987). But they are not
prominent in the chlorophyll images.
The copepods of the Mediterranean basin resemble those of the subtropical Atlantic,
and since the sill depth excludes all abyssal biota that do not perform vertical migrations,
the vertical ranges of many species extend much deeper here. Diel vertical migrations
are unusually extensive: Pyrosoma atlanticum, Clio pyramidata, and Cymbulia peroni rise
from 600–800 m to around 45–50 m at night in the western basin, for example.
The copepods of mass occurrence in the photic zone are typically Oithona spp., Clausocalanus spp., Neocalanus gracilis, and Centropages typicus, whereas C. helgolandicus is
restricted almost completely to much greater depths. Several studies of species distributions in the Adriatic show that the northern shallow region is dominated by coastal
species (high numbers, low diversity), and the southern, deep-water region by oceanic
species (low numbers, high diversity).
Black Sea Any account of the ecology of the Black Sea must start with the extraordinary
fact that below some depth between 80 and 200 m, shoaler in mid-gyre but deeper near
the coast, oxygen is absent and hydrogen sulfide concentrations increase progressively
179
occupies the whole shelf area that is then significantly greener than the deep water beyond.
I suggest that this permanent chlorophyll hot spot may represent benthic macroalgal
meadows in the very shallow water surrounding the archipelago that lies 20–30 km
offshore. Other coastal regions with higher-than-background chlorophyll accumulation
lie along the Nile delta, in the NW Adriatic Sea off the Po delta, on the French coast
off the Rhone delta, and in the inner Aegean Sea. The entire shelf off Israel lies within
the photic zone and chlorophyll profiles show near-bottom maxima; in such areas, as
has been shown in the northern Adriatic (Ott, 1992), the high biomass of suspensionfeeding macrobenthos appear to control pelagic biomass. Such benthic organisms have
a very high weight-specific metabolic rate. This process may be interrupted by summer
stratification, in which case a DCM forms some distance above the bottom.
Major upwelling events occur in the Sicilian Channel that appear to be wind induced;
they occur mostly with a lag of 3 days after a westerly gale (often originating in a Provençal
mistral event) passes through the area. They are usually based on the southwestern tip
of Sicily (near Cape Granitola), although they often involve the entire southern coast
of the island. They may also extend across the entire Sicilian Channel to the African
coast (Piccioni et al., 1988). In the eastern Mediterranean, important surface enrichment
was induced by the annual Nile discharge prior to the closure of the Aswan High Dam
and the control of the annual flood. This feature is now very restricted, and in the
Levant Basin, offshore water is now of clarity equal to that of the central oceanic gyres.
The pelagic fisheries of the region are much diminished. On the Israeli shelf, there is a
subsurface algal bloom in bottom water over the narrow shelf, and here, the chlorophyll
profile consistently shows a maximum value just above the bottom deposits (Townsend
et al., 1988). Whether this is induced by the episodic upwelling of nutrients across the
shelf break, or whether it is due to regeneration of nutrients within sediments, and their
subsequent release, is not clear.
There are also persistent surface chlorophyll features in the Alboran Sea related to
upwelling, both along the east coast of Spain and around the Alboran eddies. A jet of
Atlantic water along the Spanish coast induces geostrophic upwelling and a very shallow
chlorophyll maximum. Upwelling is forced around the anticyclonic gyre that occupies the
western Alboran Sea (Minas et al., 1991). Farther east, a divergent front between Spain
and the Balearics between southward coastal and northward offshore flow is associated
with upwelling and chlorophyll enhancement (Estrada and Margalef, 1988). Cyclonic
eddies generated at the coast within the Algerian Current are not wind induced but
nevertheless force upwelling over sufficient spatial and temporal scales to induce algal
growth and surface enhancement of the chlorophyll field (Millot, 1987). But they are not
prominent in the chlorophyll images.
The copepods of the Mediterranean basin resemble those of the subtropical Atlantic,
and since the sill depth excludes all abyssal biota that do not perform vertical migrations,
the vertical ranges of many species extend much deeper here. Diel vertical migrations
are unusually extensive: Pyrosoma atlanticum, Clio pyramidata, and Cymbulia peroni rise
from 600–800 m to around 45–50 m at night in the western basin, for example.
The copepods of mass occurrence in the photic zone are typically Oithona spp., Clausocalanus spp., Neocalanus gracilis, and Centropages typicus, whereas C. helgolandicus is
restricted almost completely to much greater depths. Several studies of species distributions in the Adriatic show that the northern shallow region is dominated by coastal
species (high numbers, low diversity), and the southern, deep-water region by oceanic
species (low numbers, high diversity).
Black Sea Any account of the ecology of the Black Sea must start with the extraordinary
fact that below some depth between 80 and 200 m, shoaler in mid-gyre but deeper near
the coast, oxygen is absent and hydrogen sulfide concentrations increase progressively