Atlantic Coastal Biome
239
numerous warm-water species that dominate the zooplankton taxonomically. The fidelity
of Calanoides to upwelling cells is shown by the fact that I observed it abundantly on
the shelf off Lagos, Nigeria, on only one occasion—during a brief upwelling episode in
a region where upwelling episodes are very rare.
Off Ghana, Mensah (1974) showed that only the C5s survived the end of the upwelling
season, during which three or four generations appeared, with the development from
egg to adult taking only 14–18 days. During the nonupwelling season, the population
is maintained as C5s that remain dormant beyond the shelf, at deeper than 500 m.
Because this period of 7–8 months could not be sustained on the oil sac accumulated
during diatom feeding during the upwelling period, Mensah investigated feeding at
depth and found this species could also capture bacterioplankton. In the C5 instar,
maxillary setules have an interval of 1–4 m. The same cycle was observed on the Central
African shelf by Petit and Courties (1976), who followed six to eight generations during
the upwelling period but found only C5s, and only at 800 m off the shelf, during the
remainder of the year. The flexibility of life history schedules with the particular seasonal
sequence of phytoplankton production each year off the Central African coast, and
the fidelity between Calanoides numbers and patchiness of phytoplankton biomass, is
remarkable.
These large calanoid copepods are a principal food of the West African sardine (Sardinella aurita), whose annual appearance off Ghana and Ivory Coast (Cury and Roy,
1987) coincides with the rise of Calanoides to the surface waters. In fact, here as elsewhere
in some minor low-latitude upwelling regions, these two species (or their ecological
equivalents) are closely linked. There is a simple relationship between SST, zooplankton
abundance (dominated by Calanoides), Sardinella gonad maturation, and egg production
off Ghana (Quaatey and Maravelas, 1999). From June, as the seasonal SST minimum
approaches, sardine gonads mature. Sardine ova take maximal abundance in the water
column in July–August, corresponding closely with the peak zooplankton abundance of
August–September. In 1986, the SST minimum occurred in June, and in 1988–91 in July.
Sardine ova extrusion followed the same pattern. In 1987, upwelling failed, zooplankton abundance was minimal, but sardine ova were produced in normal numbers. One
wonders what became of that year-class of sardines?
On both the Guinea and Central African coasts, the changing relative abundance of
sardines and other pelagic fish has attracted much attention (Gammelsrd et al., 1998).
During “Benguela Niños,” the advent of warm water off the Congo and Angola is associated with mortality of Sardinops sagax and T. trachurus and a southward displacement
of sardine stocks. Off the Congo, the cold-water Sardinella maderensis dominated the
fishery from 1964 to 1983, when substantial warming was associated with the replacement of this species by S. aurita. The effect of a “Guinea Niño,” associated with the
transport of warm Bight of Biafra water south along Gabon, may be to force S. aurita
offshore and S. maderensis even further south to the Congo fishery. Along the Guinea
coast, it is postulated that the more extensive Ekman upwelling events of the 1980s
may have favored an expansion of the Ghana stock of S. aurita eastward to the Ivory
Coast.
Regional Benthic and Demersal Ecology
The ecology of the benthic communities and of the demersal fish associated with them
responds primarily to the presence of the permanent, shallow thermocline along almost
the entire continental shelf; there are basically two habitats—one of warm, sunlit water
at shallow depths and the other of cool water, deeper on the shelf, and dark.
In this province, we are fortunate in having the results of what is certainly the most
complete survey of an almost pristine demersal fish fauna that has been performed
239
numerous warm-water species that dominate the zooplankton taxonomically. The fidelity
of Calanoides to upwelling cells is shown by the fact that I observed it abundantly on
the shelf off Lagos, Nigeria, on only one occasion—during a brief upwelling episode in
a region where upwelling episodes are very rare.
Off Ghana, Mensah (1974) showed that only the C5s survived the end of the upwelling
season, during which three or four generations appeared, with the development from
egg to adult taking only 14–18 days. During the nonupwelling season, the population
is maintained as C5s that remain dormant beyond the shelf, at deeper than 500 m.
Because this period of 7–8 months could not be sustained on the oil sac accumulated
during diatom feeding during the upwelling period, Mensah investigated feeding at
depth and found this species could also capture bacterioplankton. In the C5 instar,
maxillary setules have an interval of 1–4 m. The same cycle was observed on the Central
African shelf by Petit and Courties (1976), who followed six to eight generations during
the upwelling period but found only C5s, and only at 800 m off the shelf, during the
remainder of the year. The flexibility of life history schedules with the particular seasonal
sequence of phytoplankton production each year off the Central African coast, and
the fidelity between Calanoides numbers and patchiness of phytoplankton biomass, is
remarkable.
These large calanoid copepods are a principal food of the West African sardine (Sardinella aurita), whose annual appearance off Ghana and Ivory Coast (Cury and Roy,
1987) coincides with the rise of Calanoides to the surface waters. In fact, here as elsewhere
in some minor low-latitude upwelling regions, these two species (or their ecological
equivalents) are closely linked. There is a simple relationship between SST, zooplankton
abundance (dominated by Calanoides), Sardinella gonad maturation, and egg production
off Ghana (Quaatey and Maravelas, 1999). From June, as the seasonal SST minimum
approaches, sardine gonads mature. Sardine ova take maximal abundance in the water
column in July–August, corresponding closely with the peak zooplankton abundance of
August–September. In 1986, the SST minimum occurred in June, and in 1988–91 in July.
Sardine ova extrusion followed the same pattern. In 1987, upwelling failed, zooplankton abundance was minimal, but sardine ova were produced in normal numbers. One
wonders what became of that year-class of sardines?
On both the Guinea and Central African coasts, the changing relative abundance of
sardines and other pelagic fish has attracted much attention (Gammelsrd et al., 1998).
During “Benguela Niños,” the advent of warm water off the Congo and Angola is associated with mortality of Sardinops sagax and T. trachurus and a southward displacement
of sardine stocks. Off the Congo, the cold-water Sardinella maderensis dominated the
fishery from 1964 to 1983, when substantial warming was associated with the replacement of this species by S. aurita. The effect of a “Guinea Niño,” associated with the
transport of warm Bight of Biafra water south along Gabon, may be to force S. aurita
offshore and S. maderensis even further south to the Congo fishery. Along the Guinea
coast, it is postulated that the more extensive Ekman upwelling events of the 1980s
may have favored an expansion of the Ghana stock of S. aurita eastward to the Ivory
Coast.
Regional Benthic and Demersal Ecology
The ecology of the benthic communities and of the demersal fish associated with them
responds primarily to the presence of the permanent, shallow thermocline along almost
the entire continental shelf; there are basically two habitats—one of warm, sunlit water
at shallow depths and the other of cool water, deeper on the shelf, and dark.
In this province, we are fortunate in having the results of what is certainly the most
complete survey of an almost pristine demersal fish fauna that has been performed