Atlantic Westerly Winds Biome
181
15 mg chl m
−3 in winter (January) and, during the summer period (June), only from
0.25 to 25 mg chl m
−3 . Obviously, this situation differs significantly from the pristine
condition of the sea, prior to the massive eutrophication of recent decades and the catastrophic decline of herbivores. As late as 1980, the eddy field along the Anatolian coast
carried strong filaments of high chlorophyll, observable in the CZCS images and quite
distinct from offshore blue water. In fact, during early part of the period 1978–1986,
many CZCS images revealed a response of the chlorophyll field to the dynamic instabilities of meanders within the Rim Current (Saur et al., 1994). I am unable to observe this
response in the SeaWiFS or MODIS images for 1998–2005.
Consensus appears to have developed concerning the forcing of these changes and,
once again, diverse human interventions are the cause. The Black Sea has been massively fertilized by nutrients from agricultural and domestic runoff in recent decades and
concurrently phytoplankton biomass has increased by an order of magnitude over the
western shelves and by a factor of 3–4 over deep water, and has become taxonomically less
diverse. Exotic ballast-water species (Noctiluca, Pleurobrachia, Aurelia, and Mnemiopsis)
now dominate the zooplankton biomass to more than 90% by weight, having largely
eliminated the omnivorous and herbivorous copepods and cladocerans whose consumption formerly balanced algal growth. It is suggested that prior to 1990, and the massive
upgrowth of Mnemiopsis, the intense winter blooms that now characterize the plankton
calendar were unknown. The continuous algal blooms of today’s Black Sea are very different from the healthy state that existed until the 1960s, when algal biomass stood at
much lower levels and apparently varied more strongly with the seasons. The present situation is extremely complex and dynamic: the newly arrived ctenophore Beroe ovata now
feeds largely on the longer-established zooplanktivore Mnemiopsis leidyi. This predation
appears, at least in the northern Black Sea, to have reduced the impact of Mnemiopsis on
the indigenous zooplankton herbivores (Finenko et al., 2003). How the dynamics of this
new situation will work out is anybody’s guess.
Discharge of nutrients from rivers, especially of the Danube and Dniester, is associated
with massive local blooms of the newly arrived coccolith Emiliania huxleyi. These blooms
are observable in satellite imagery as a dominant feature of the western part of the Black
Sea, especially between May and July. In this region, the contributing organisms and
the magnitude of blooms have progressively changed in recent years toward blooms
dominated by nanoplankton, including coccoliths (Mihnea, 1997). More generally, the
northwest shelf is a major source of nutrients for the southern Anatolian coast and for the
open western basin. When transport around the rim current is interrupted, chlorophyll
biomass on the southern coast diminishes rapidly. So far as it can now be discerned, the
pristine phytoplankton calendar began in early winter with algal growth near the base
of the euphotic zone that by November encompassed the entire euphotic water column,
to be terminated in January or February by nutrient depletion and consumption by
mesozooplankton.
There have been other major perturbations in the ecological balance of the pelagial in
the Black Sea in recent decades. The stocks of pelagic clupeid fish have almost completely
collapsed, and declared landings of Engraulis dropped by an order of magnitude between
1979 and 1990. To what extent this was due to overfishing in the classical sense, or to
the concomitant collapse in zooplankton food organisms, has not been established.
Regional Benthic and Demersal Ecology
Because the coastal regions were well investigated by the early benthic naturalists from
Monaco, Naples, Split, and other marine stations, we know that the pristine benthic
macrofauna of the shelves of the Mediterranean was in no way singular. That of the Black
Sea followed the usual pattern, though with a somewhat attenuated cast of characters.
181
15 mg chl m
−3 in winter (January) and, during the summer period (June), only from
0.25 to 25 mg chl m
−3 . Obviously, this situation differs significantly from the pristine
condition of the sea, prior to the massive eutrophication of recent decades and the catastrophic decline of herbivores. As late as 1980, the eddy field along the Anatolian coast
carried strong filaments of high chlorophyll, observable in the CZCS images and quite
distinct from offshore blue water. In fact, during early part of the period 1978–1986,
many CZCS images revealed a response of the chlorophyll field to the dynamic instabilities of meanders within the Rim Current (Saur et al., 1994). I am unable to observe this
response in the SeaWiFS or MODIS images for 1998–2005.
Consensus appears to have developed concerning the forcing of these changes and,
once again, diverse human interventions are the cause. The Black Sea has been massively fertilized by nutrients from agricultural and domestic runoff in recent decades and
concurrently phytoplankton biomass has increased by an order of magnitude over the
western shelves and by a factor of 3–4 over deep water, and has become taxonomically less
diverse. Exotic ballast-water species (Noctiluca, Pleurobrachia, Aurelia, and Mnemiopsis)
now dominate the zooplankton biomass to more than 90% by weight, having largely
eliminated the omnivorous and herbivorous copepods and cladocerans whose consumption formerly balanced algal growth. It is suggested that prior to 1990, and the massive
upgrowth of Mnemiopsis, the intense winter blooms that now characterize the plankton
calendar were unknown. The continuous algal blooms of today’s Black Sea are very different from the healthy state that existed until the 1960s, when algal biomass stood at
much lower levels and apparently varied more strongly with the seasons. The present situation is extremely complex and dynamic: the newly arrived ctenophore Beroe ovata now
feeds largely on the longer-established zooplanktivore Mnemiopsis leidyi. This predation
appears, at least in the northern Black Sea, to have reduced the impact of Mnemiopsis on
the indigenous zooplankton herbivores (Finenko et al., 2003). How the dynamics of this
new situation will work out is anybody’s guess.
Discharge of nutrients from rivers, especially of the Danube and Dniester, is associated
with massive local blooms of the newly arrived coccolith Emiliania huxleyi. These blooms
are observable in satellite imagery as a dominant feature of the western part of the Black
Sea, especially between May and July. In this region, the contributing organisms and
the magnitude of blooms have progressively changed in recent years toward blooms
dominated by nanoplankton, including coccoliths (Mihnea, 1997). More generally, the
northwest shelf is a major source of nutrients for the southern Anatolian coast and for the
open western basin. When transport around the rim current is interrupted, chlorophyll
biomass on the southern coast diminishes rapidly. So far as it can now be discerned, the
pristine phytoplankton calendar began in early winter with algal growth near the base
of the euphotic zone that by November encompassed the entire euphotic water column,
to be terminated in January or February by nutrient depletion and consumption by
mesozooplankton.
There have been other major perturbations in the ecological balance of the pelagial in
the Black Sea in recent decades. The stocks of pelagic clupeid fish have almost completely
collapsed, and declared landings of Engraulis dropped by an order of magnitude between
1979 and 1990. To what extent this was due to overfishing in the classical sense, or to
the concomitant collapse in zooplankton food organisms, has not been established.
Regional Benthic and Demersal Ecology
Because the coastal regions were well investigated by the early benthic naturalists from
Monaco, Naples, Split, and other marine stations, we know that the pristine benthic
macrofauna of the shelves of the Mediterranean was in no way singular. That of the Black
Sea followed the usual pattern, though with a somewhat attenuated cast of characters.