The Cabo Frio Upwelling System, Brazil
99
ter favors remineralization. Silicate tends to increase with depth (> 1511M
Si0 4 -Si), though surface values (5-10 11M) also indicate occasional addition
through runoff from the Paraiba River north of Cabo Frio, which transports large quantities of silicate during the rainy season (> 140 11M; Valentin et al. 1978). The dissolved oxygen levels (annual mean 4-5mll- 1 ) are
stable and range from a minimum of 3 mll- 1 at the bottom (50 m depth) to
a maximum of 8 mll- 1 during algal blooms.
7.3 Biological Community
7.3.1 Plankton
The upwelling phenomenon has a direct impact on the composition of
species and trophic structure (Fig. 7.2). The vertical distribution and
intensity of phytoplankton blooms is controlled by the depth and intensity of the thermocline in the euphotic layer proximate to the coast controls. Despite elevated nitrate levels and rarely limiting irradiance
(1,500 11E m- 2 s- 1 ), chlorophyll (0.5-6.0 11g 1- 1 ) and primary production
(2-14mgC m- 3 h- 1 ) tend to be lower than in upwelling systems elsewhere,
probably owing to low initial biomass and reduced surface heating of
upwelled water. Furthermore, biomass tends to be effectively dispersed by
advection currents and strong winds and reduced by high zooplankton
grazing pressure (50%; Druehl and Yoneshigue-Braga 1976).Although biomass and primary production levels are similar during post-upwelling
phases in summer and non-upwelling in winter, they are still high when
compared to oligotrophic tropical water of the Brazil Current and the
abundant, probably resuspended organic detrital matter is an important
energy source for higher trophic levels, especially zooplankton.
The presence of different water masses induces spatial and temporal
variation in the composition and abundance of zooplankton, and community changes correlate with the upwelling cycles (Valentin and Moreira
1978; Valentin et al. 1987). The copepod species Calanoides carinatus,
Rhincalanus cornutus, Aetideus giesbrechti, and Heterorhabdus papilliger
are typical of deep SACW ( <18 °C, salinity <36). Warm tropical water
(>24 oc, salinity >36) of the Brazil Current with high diversity is dominated by copepods like Clausocalanus furcatus, Mecynocera clausi, Corycella
gracilis, Oithona setigera, Corycaeus typicus, Oncaea conifera, Undinula
vulgaris, Calocalanus pavo, and Lucicutia flavicornis, and the cladoceran
Evadne spinifera. Zooplankton densities tend to be > 10 org. l- 1 (annual
mean 66 mg ash-free dry weight m- 3 ) and may reach 100 org. 1- 1 during
99
ter favors remineralization. Silicate tends to increase with depth (> 1511M
Si0 4 -Si), though surface values (5-10 11M) also indicate occasional addition
through runoff from the Paraiba River north of Cabo Frio, which transports large quantities of silicate during the rainy season (> 140 11M; Valentin et al. 1978). The dissolved oxygen levels (annual mean 4-5mll- 1 ) are
stable and range from a minimum of 3 mll- 1 at the bottom (50 m depth) to
a maximum of 8 mll- 1 during algal blooms.
7.3 Biological Community
7.3.1 Plankton
The upwelling phenomenon has a direct impact on the composition of
species and trophic structure (Fig. 7.2). The vertical distribution and
intensity of phytoplankton blooms is controlled by the depth and intensity of the thermocline in the euphotic layer proximate to the coast controls. Despite elevated nitrate levels and rarely limiting irradiance
(1,500 11E m- 2 s- 1 ), chlorophyll (0.5-6.0 11g 1- 1 ) and primary production
(2-14mgC m- 3 h- 1 ) tend to be lower than in upwelling systems elsewhere,
probably owing to low initial biomass and reduced surface heating of
upwelled water. Furthermore, biomass tends to be effectively dispersed by
advection currents and strong winds and reduced by high zooplankton
grazing pressure (50%; Druehl and Yoneshigue-Braga 1976).Although biomass and primary production levels are similar during post-upwelling
phases in summer and non-upwelling in winter, they are still high when
compared to oligotrophic tropical water of the Brazil Current and the
abundant, probably resuspended organic detrital matter is an important
energy source for higher trophic levels, especially zooplankton.
The presence of different water masses induces spatial and temporal
variation in the composition and abundance of zooplankton, and community changes correlate with the upwelling cycles (Valentin and Moreira
1978; Valentin et al. 1987). The copepod species Calanoides carinatus,
Rhincalanus cornutus, Aetideus giesbrechti, and Heterorhabdus papilliger
are typical of deep SACW ( <18 °C, salinity <36). Warm tropical water
(>24 oc, salinity >36) of the Brazil Current with high diversity is dominated by copepods like Clausocalanus furcatus, Mecynocera clausi, Corycella
gracilis, Oithona setigera, Corycaeus typicus, Oncaea conifera, Undinula
vulgaris, Calocalanus pavo, and Lucicutia flavicornis, and the cladoceran
Evadne spinifera. Zooplankton densities tend to be > 10 org. l- 1 (annual
mean 66 mg ash-free dry weight m- 3 ) and may reach 100 org. 1- 1 during