Atlantic Trade Wind Biome
193
effluents. The community structure of the benthic infauna has been little investigated
in this region, despite the great commercial importance of the macrobenthic epifauna,
dominated by Penaeus setiferus and P. aztecus and the swimming crabs Callinectes spp. As
noted earlier, the De Soto canyon isolates the muddy “shrimp ground” of the Mississippi
sedimentary regime from the west shelf of Florida, populated by a variety of hard-ground,
warm-water epibenthic species.
In tropical seas, the nature of the fish fauna is dominated both by deposit type and by
water mass. Because the tropical surface water extends so deep on the shelf here, there is
no equivalent in the Caribbean to the passage of a subtropical sparid fauna through the
tropical region, deep on the shelf and in cooler water, as occurs in the eastern Atlantic.
The turbid waters and muddy deposits of the coastal regions are populated especially by
catfish, threadfins, and small sciaenids and everywhere it is the nature of the deposits
that chiefly determines the characteristic species associations of fish: softer deposits are
inhabited by a fauna of large sciaenids (Micropogon, Cynoscion), grunts (Haemulon),
and threadfins (Polynemus), much more diverse than that of the eastern Atlantic. On
sandy deposits and stony bottoms species associations occur in which lutjanids, sparids,
and pomadaysids are important. On the Campeche Bank, for instance, three species
associations having different core species of these families have been found to occur in
different microhabitats that are distinguished by deposit type and relative depth.
Here, we first meet the mass occurrence of the phytophagous, filter-feeding clupeid
fishes that we shall find are typical of warm seas where strong blooms of large diatoms
occur. In the case of the CARB province, this niche is occupied by the Gulf menhaden
(Brevoortia patronus), especially typical of the northern coast of the Gulf, where local
diatom blooms associated with river discharges are rather widespread. Menhaden have
a very fine filter-basket formed by their gill rakers, and diatoms such as Coscinodiscus
dominate their diet. Rather extensive migrations are undertaken to maintain the fish
in regions of appropriate blooms and when these are not accessible, they resort to a
maintenance diet of microzooplankton. The stocks of B. tyrannus of the eastern coast
of North America enter the Gulf of Mexico to spawn. Unlike the ecologically similar
Ethmalosa of the eastern Atlantic, Brevoortia does not occupy the lowest latitudes. A very
large biomass is maintained and has supported major industrial fisheries.
Synopsis
Case 4—Small-amplitude response to trade wind seasonality—The density-dependent
mixed layer undergoes weak boreal winter excursion from <20 m in June–September to
35 m in February while Z eu remains 45–50 m in all months; the thermocline is therefore
permanently illuminated. Productivity follows the irradiance cycle with a shoulder (as
so frequently is observed elsewhere) on the descending limb of the curve. Seasonality
in chlorophyll accumulation is complex and somewhat variable between years, with two
regional maxima in boreal summer, the second corresponding to the shoulder on the
productivity curve. However, the accumulation of chlorophyll in data aggregated for the
entire province (Fig. 9.14) is largely influenced by the late summer events in the southeastern Caribbean, when the highly pigmented water of the Orinoco discharge plume
passes into this province, and this may account for the second “chlorophyll” peak.
Western Tropical Atlantic Province (WTRA)
Extent of the Province
The WTRA comprises the tropical Atlantic west of 15
W, lying between NATR to the
north and SATL to the south. The northern boundary is the southern flank of the NEC
193
effluents. The community structure of the benthic infauna has been little investigated
in this region, despite the great commercial importance of the macrobenthic epifauna,
dominated by Penaeus setiferus and P. aztecus and the swimming crabs Callinectes spp. As
noted earlier, the De Soto canyon isolates the muddy “shrimp ground” of the Mississippi
sedimentary regime from the west shelf of Florida, populated by a variety of hard-ground,
warm-water epibenthic species.
In tropical seas, the nature of the fish fauna is dominated both by deposit type and by
water mass. Because the tropical surface water extends so deep on the shelf here, there is
no equivalent in the Caribbean to the passage of a subtropical sparid fauna through the
tropical region, deep on the shelf and in cooler water, as occurs in the eastern Atlantic.
The turbid waters and muddy deposits of the coastal regions are populated especially by
catfish, threadfins, and small sciaenids and everywhere it is the nature of the deposits
that chiefly determines the characteristic species associations of fish: softer deposits are
inhabited by a fauna of large sciaenids (Micropogon, Cynoscion), grunts (Haemulon),
and threadfins (Polynemus), much more diverse than that of the eastern Atlantic. On
sandy deposits and stony bottoms species associations occur in which lutjanids, sparids,
and pomadaysids are important. On the Campeche Bank, for instance, three species
associations having different core species of these families have been found to occur in
different microhabitats that are distinguished by deposit type and relative depth.
Here, we first meet the mass occurrence of the phytophagous, filter-feeding clupeid
fishes that we shall find are typical of warm seas where strong blooms of large diatoms
occur. In the case of the CARB province, this niche is occupied by the Gulf menhaden
(Brevoortia patronus), especially typical of the northern coast of the Gulf, where local
diatom blooms associated with river discharges are rather widespread. Menhaden have
a very fine filter-basket formed by their gill rakers, and diatoms such as Coscinodiscus
dominate their diet. Rather extensive migrations are undertaken to maintain the fish
in regions of appropriate blooms and when these are not accessible, they resort to a
maintenance diet of microzooplankton. The stocks of B. tyrannus of the eastern coast
of North America enter the Gulf of Mexico to spawn. Unlike the ecologically similar
Ethmalosa of the eastern Atlantic, Brevoortia does not occupy the lowest latitudes. A very
large biomass is maintained and has supported major industrial fisheries.
Synopsis
Case 4—Small-amplitude response to trade wind seasonality—The density-dependent
mixed layer undergoes weak boreal winter excursion from <20 m in June–September to
35 m in February while Z eu remains 45–50 m in all months; the thermocline is therefore
permanently illuminated. Productivity follows the irradiance cycle with a shoulder (as
so frequently is observed elsewhere) on the descending limb of the curve. Seasonality
in chlorophyll accumulation is complex and somewhat variable between years, with two
regional maxima in boreal summer, the second corresponding to the shoulder on the
productivity curve. However, the accumulation of chlorophyll in data aggregated for the
entire province (Fig. 9.14) is largely influenced by the late summer events in the southeastern Caribbean, when the highly pigmented water of the Orinoco discharge plume
passes into this province, and this may account for the second “chlorophyll” peak.
Western Tropical Atlantic Province (WTRA)
Extent of the Province
The WTRA comprises the tropical Atlantic west of 15
W, lying between NATR to the
north and SATL to the south. The northern boundary is the southern flank of the NEC