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Chapter 9: The Atlantic Ocean
Thorson reviewed the characteristic macrobenthic species associations that are specific to
mud, muddy sand, and sand deposits in these seas. He recorded that these communities
had been identified on the coasts of North Africa and Israel, in the Adriatic, on the west
coast of Italy, and on the shelf of the western Black Sea. So, on sandy deposits down
to 50 m, we would have expected to find a Venus community and in shoaler water, or
where the sand was very compact, a Tellina community. In muddy sediments from 10
to 100 m, the boreo-mediterranean Amphiura community occurred. Closer inshore, or
where organic content of muddy sediments was very high, a Syndosmya association was
usually found. Off the Danube delta, extensive midshelf and highly organic deposits have
been described as “Mytilus-mud” from the abundance there of that bivalve.
The northern shelves of the Black Sea have a very gentle slope so that water as shallow
as 30 m extends out to midshelf. Meadows of the red alga Phyllophora reach this depth
and, at least until the 1950’s, covered much of the shelf between the Crimean peninsula
and the Danube delta. Shoreward, Zostera meadows are very extensive. It is possible
that these macrophytes may be the origin of some of the high chlorophyll patches to be
observed in satellite images in the northwestern Black Sea and the Sea of Azov.
In the shallow northern Adriatic the suspension-feeding activity of the bivalve mollusks of the benthic communities is sufficiently active to control phytoplankton biomass
during periods when mixing extends to the bottom. In spring, after shallow stratification
is established within the winter mixed layer, this balance is interrupted and if algal blooms
extend into this period of the year, massive sedimentation events of dead cells may occur.
Such events provide organic material to the sediments at a faster rate than deposit-feeding
organisms can process it. Consequently, local anoxia and mass mortality of the benthic
fauna may occur. The relationship between production of phytoplankton in the water column and the nature of the subjacent benthos has been investigated in front of the Danube
delta. An inner zone, characterized by large sinking rates of organic particulate material,
is dominated by deposit-feeding benthic infauna. A zone lying to the north, below a
permanent anticyclonic gyre, is characterized by low sedimentation rates and is inhabited
by a macrobenthos dominated by suspension feeding organisms: here, benthic remineralization rates are high. Finally, to the south of the delta, sedimentation rates are also low,
as are rates of benthic remineralization, and here also the macrobenthos is dominated by
suspension-feeding bivalves. Off the Nile delta, the rim current carries organic particles
in the river effluent principally eastward and, consequently, biomass and productivity
of benthic communities is almost twice as high to the east of the delta than to the west.
In these two basins it is difficult to recover the ecology of the fish populations in
their pristine state. Invasions, introductions, and largely uncontrolled fisheries that have
devastated the benthic habitat all make such a task very difficult. Taxonomically, of
course, this province is a meeting place for Atlantic subtropical fish that we shall meet
again on the NW African coast, and some elements of the boreal Atlantic fauna. To these
are now added a Red Sea element of Lessepsian migrants, of which some have become
abundant in the eastern Mediterranean to the point of supporting new fisheries.
Synopsis
Case 3—Winter-spring production with nutrient limitation—(MEDI only). Although Z m
undergoes a large boreal winter excursion (10 m June–July, 100 m February–March), the
thermocline is illuminated from April to November. Rate increase in P is initiated in
December and is sustained until annual maximum occurs in March–April (Fig. 9.12);
the rate begins to decrease in May–June when Z m is very shoal, and declining rates are
sustained until November. Chlorophyll accumulation begins much earlier and reaches
maximal values between December and March, from which a decline is initiated even
though the P rate continues to increase. Annual minimum values of integrated chlorophyll
Chapter 9: The Atlantic Ocean
Thorson reviewed the characteristic macrobenthic species associations that are specific to
mud, muddy sand, and sand deposits in these seas. He recorded that these communities
had been identified on the coasts of North Africa and Israel, in the Adriatic, on the west
coast of Italy, and on the shelf of the western Black Sea. So, on sandy deposits down
to 50 m, we would have expected to find a Venus community and in shoaler water, or
where the sand was very compact, a Tellina community. In muddy sediments from 10
to 100 m, the boreo-mediterranean Amphiura community occurred. Closer inshore, or
where organic content of muddy sediments was very high, a Syndosmya association was
usually found. Off the Danube delta, extensive midshelf and highly organic deposits have
been described as “Mytilus-mud” from the abundance there of that bivalve.
The northern shelves of the Black Sea have a very gentle slope so that water as shallow
as 30 m extends out to midshelf. Meadows of the red alga Phyllophora reach this depth
and, at least until the 1950’s, covered much of the shelf between the Crimean peninsula
and the Danube delta. Shoreward, Zostera meadows are very extensive. It is possible
that these macrophytes may be the origin of some of the high chlorophyll patches to be
observed in satellite images in the northwestern Black Sea and the Sea of Azov.
In the shallow northern Adriatic the suspension-feeding activity of the bivalve mollusks of the benthic communities is sufficiently active to control phytoplankton biomass
during periods when mixing extends to the bottom. In spring, after shallow stratification
is established within the winter mixed layer, this balance is interrupted and if algal blooms
extend into this period of the year, massive sedimentation events of dead cells may occur.
Such events provide organic material to the sediments at a faster rate than deposit-feeding
organisms can process it. Consequently, local anoxia and mass mortality of the benthic
fauna may occur. The relationship between production of phytoplankton in the water column and the nature of the subjacent benthos has been investigated in front of the Danube
delta. An inner zone, characterized by large sinking rates of organic particulate material,
is dominated by deposit-feeding benthic infauna. A zone lying to the north, below a
permanent anticyclonic gyre, is characterized by low sedimentation rates and is inhabited
by a macrobenthos dominated by suspension feeding organisms: here, benthic remineralization rates are high. Finally, to the south of the delta, sedimentation rates are also low,
as are rates of benthic remineralization, and here also the macrobenthos is dominated by
suspension-feeding bivalves. Off the Nile delta, the rim current carries organic particles
in the river effluent principally eastward and, consequently, biomass and productivity
of benthic communities is almost twice as high to the east of the delta than to the west.
In these two basins it is difficult to recover the ecology of the fish populations in
their pristine state. Invasions, introductions, and largely uncontrolled fisheries that have
devastated the benthic habitat all make such a task very difficult. Taxonomically, of
course, this province is a meeting place for Atlantic subtropical fish that we shall meet
again on the NW African coast, and some elements of the boreal Atlantic fauna. To these
are now added a Red Sea element of Lessepsian migrants, of which some have become
abundant in the eastern Mediterranean to the point of supporting new fisheries.
Synopsis
Case 3—Winter-spring production with nutrient limitation—(MEDI only). Although Z m
undergoes a large boreal winter excursion (10 m June–July, 100 m February–March), the
thermocline is illuminated from April to November. Rate increase in P is initiated in
December and is sustained until annual maximum occurs in March–April (Fig. 9.12);
the rate begins to decrease in May–June when Z m is very shoal, and declining rates are
sustained until November. Chlorophyll accumulation begins much earlier and reaches
maximal values between December and March, from which a decline is initiated even
though the P rate continues to increase. Annual minimum values of integrated chlorophyll