Atlantic Coastal Biome
267
zone of the Brazil Current has a sparse but very diverse mesozooplankton of typical
warm-water species—Clausocalanus furcatus, C. pavo, Mecynocera clausii, and the rest.
Over the Abrolhos Bank and the other wide shelf regions to the north of Cape Frio, a
much more oligotrophic regime is represented by mesozooplankton of low biomass and
high diversity with very minor intrusions of the upwelling fauna from the southwest.
The low-trophic level pelagic fish of the region are dominated by the presence of
Sardinella brasiliensis and Engraulis anchoa that are both especially associated with the
Cape Frio region; the sardine population off Brazil comprises a larger number of yearclasses (six to seven) under normal circumstances than does S. anchovia that occurs
farther north off the Venezuelan coast and comprises only two to three year-classes. In
both species, spawning peaks correspond with upwelling seasons off Cape Frio and in
the Carioco Basin, respectively. Anchovy schools appear to occur preferentially over the
slope rather than the shelf.
Regional Benthic and Demersal Ecology
Benthic studies in this region rather commonly emphasize the process of carbonate sedimentation on the substrates, principally due to the presence of foraminiferans; north
of Cape Frio, the presence of Halimeda, of bryozoans, and of coralline algae is emphasized. South of Cape Frio, the carbonate-rich sediments are restricted to the outer
shelf where coralline algae and foraminiferan masses contribute largely to carbonate
formation. Inshore, a “mud line” is described, within which foraminifera are not abundant.
The very unusual abundance at such latitudes of rhynchnonelliform brachiopods (two
groups: Terbratulina + Argyrotheca and Bouchardia + Platidia) occurs on the outer shelf
of the South Brazilian Bight, always on carbonate sediments to which they themselves
contribute. The former group especially favors sediments with high (70–95%) CaCO 3
content, and both groups occur over depth ranges of 100–200 m, at very high abundance
(terebratulids alone may occur at densities of >100 ind m
−2 ), preferentially in areas that
lie under the influence of shelf-edge upwelling. These assemblages appear to be unusual
relics of ecological conditions that were dominant in Paleozoic seas.
The ecology of the demersal fish here, as elsewhere, responds directly to water mass
and deposit characteristics; as in the eastern Atlantic, the superficial subtropical water
mass is occupied by species associations in which Sciaenidae dominate: a tropical sciaenid community penetrates southward inshore of a subtropical sciaenid community
and is characterized by species of Ctenosciaena, Cynoscion, and Paralonchurus. Offshore,
on sandy and shelly deposits, and in cooler water, yet another version of the subtropical sparid fauna occurs, including Pagrus pagrus and Cheilodactylus bergi. There is, of
course, a high diversity of demersal fish on the Abrolhos and Royal Charlotte Banks
associated with the hermatypic coral formations and other rocky grounds; these will
include a very much greater range of genera and a higher diversity than elsewhere in the
province.
Synopsis
Case 2—Nutrient-limited spring production but modified by shallow-water processes. This
province has an overall production cycle closely resembling that of NECS, but shifted by 6
months with maximum accumulation of chlorophyll biomass in early austral summer and
a shoulder on the descending limb of the biomass cycle in fall. The mixed layer defined
by the pycnocline Z m has moderate seasonality, deepening to 40 m in austral winter
from summer depths of about 10 m. Z eu lies at about 30–50 m so that the thermocline is
illuminated in all months (Fig. 9.29).
267
zone of the Brazil Current has a sparse but very diverse mesozooplankton of typical
warm-water species—Clausocalanus furcatus, C. pavo, Mecynocera clausii, and the rest.
Over the Abrolhos Bank and the other wide shelf regions to the north of Cape Frio, a
much more oligotrophic regime is represented by mesozooplankton of low biomass and
high diversity with very minor intrusions of the upwelling fauna from the southwest.
The low-trophic level pelagic fish of the region are dominated by the presence of
Sardinella brasiliensis and Engraulis anchoa that are both especially associated with the
Cape Frio region; the sardine population off Brazil comprises a larger number of yearclasses (six to seven) under normal circumstances than does S. anchovia that occurs
farther north off the Venezuelan coast and comprises only two to three year-classes. In
both species, spawning peaks correspond with upwelling seasons off Cape Frio and in
the Carioco Basin, respectively. Anchovy schools appear to occur preferentially over the
slope rather than the shelf.
Regional Benthic and Demersal Ecology
Benthic studies in this region rather commonly emphasize the process of carbonate sedimentation on the substrates, principally due to the presence of foraminiferans; north
of Cape Frio, the presence of Halimeda, of bryozoans, and of coralline algae is emphasized. South of Cape Frio, the carbonate-rich sediments are restricted to the outer
shelf where coralline algae and foraminiferan masses contribute largely to carbonate
formation. Inshore, a “mud line” is described, within which foraminifera are not abundant.
The very unusual abundance at such latitudes of rhynchnonelliform brachiopods (two
groups: Terbratulina + Argyrotheca and Bouchardia + Platidia) occurs on the outer shelf
of the South Brazilian Bight, always on carbonate sediments to which they themselves
contribute. The former group especially favors sediments with high (70–95%) CaCO 3
content, and both groups occur over depth ranges of 100–200 m, at very high abundance
(terebratulids alone may occur at densities of >100 ind m
−2 ), preferentially in areas that
lie under the influence of shelf-edge upwelling. These assemblages appear to be unusual
relics of ecological conditions that were dominant in Paleozoic seas.
The ecology of the demersal fish here, as elsewhere, responds directly to water mass
and deposit characteristics; as in the eastern Atlantic, the superficial subtropical water
mass is occupied by species associations in which Sciaenidae dominate: a tropical sciaenid community penetrates southward inshore of a subtropical sciaenid community
and is characterized by species of Ctenosciaena, Cynoscion, and Paralonchurus. Offshore,
on sandy and shelly deposits, and in cooler water, yet another version of the subtropical sparid fauna occurs, including Pagrus pagrus and Cheilodactylus bergi. There is, of
course, a high diversity of demersal fish on the Abrolhos and Royal Charlotte Banks
associated with the hermatypic coral formations and other rocky grounds; these will
include a very much greater range of genera and a higher diversity than elsewhere in the
province.
Synopsis
Case 2—Nutrient-limited spring production but modified by shallow-water processes. This
province has an overall production cycle closely resembling that of NECS, but shifted by 6
months with maximum accumulation of chlorophyll biomass in early austral summer and
a shoulder on the descending limb of the biomass cycle in fall. The mixed layer defined
by the pycnocline Z m has moderate seasonality, deepening to 40 m in austral winter
from summer depths of about 10 m. Z eu lies at about 30–50 m so that the thermocline is
illuminated in all months (Fig. 9.29).