76
C. Medeiros et a!.
5.5 Biota
Mangrove forests (approx. 28km 2 ) occupy the lowlands along the inner
portion of the Santa Cruz Channel and the lower part of tributaries. The
dominant species is the red mangrove (Rhizophora mangle), followed by
white mangrove (Laguncularia racemosa) and the less common black
mangrove (Avicennia schaueriana) and button mangrove (Conocarpus
erectus; Silva 1995). Enhanced mangrove growth and size of trees in areas
around the nodal point of tides may be due to deposition of fine-grained,
nutrient-rich sediment from freshwater runoff. A large part of the organic
matter production originates from Rhizophora mangle litter (7 tons dry
weight per ha and year). Additionally, high net productivity of associated
primary producers (i.e., the red alga Bostrichia 52.4 mg C h- 1 m- 2 and periphyton 208.3 mg C h- 1 m- 2 ) contributes significantly to total annual carbon
production.
The phytoplankton community in the Santa Cruz Channel is composed
of 78 species, 85% of which are diatoms. Phytoplankton density is highest
in the Orange inlet ( 4.46 x 10 6 cells 1- 1 ) during the rainy season. Phytoplankton biomass decreases rapidly from the northern (796 mg m- 3 ) and
southern inlet (1,052 mg m- 3 ) towards oceanic regions ( <60 mg m- 3 ).
Owing to high solar radiation and nutrient concentrations (N limiting factor, N:P ratio < 10:1), phytoplankton primary productivity in the Santa
Cruz channel is high (2.25-39.0 mg C h- 1 m- 3 ). Lower mean productivity
values occur in the northern Catuama (10.2 mg C h- 1 m- 3 ) and southern
Orange entrance (18.8 mg C h- 1 m- 3 ), decreasing even further ( < 1.0 mg
C h- 1 m- 3 ) beyond the reef line over the adjacent continental shelf. Similarly, elevated chlorophyll a concentrations in both channel inlets (mean
12.0mgm- 3 ) decrease towards nearshore (0.34mgm- 3 ) and offshore
(0.01 mgm- 3 ) regions.
A large number of benthic organisms (19% Foraminifera) compose the
zooplankton community. Meroplankton (i. e.,larvae ofbivalves,gastropods,
polychaetes) comprise about 20% of the microzooplankton but copepods
(27 species) and Tintinnina (15 species) are the dominant euryhaline marine species (Eskinazi-Leya 197 4). The abundance of microzooplankton in the
Orange inlet (22,449-244,216 org. m- 3 ) tends to decrease towards oligotrophic shelf waters. Macrozooplankton ( 49 taxa) is characterized by the dominance of copepods, Brachyura zoeae (Decapoda), followed by Lucifer sp.,
Chaetognatha, Larvacea, fish eggs, gastropods, and Upogebidae zoeae. Meroplankton represents approximately 35% (Paranagua and Nascimento
1973). Ctenophores prevail during dry periods and polychaetes associated
with rotifers are common in upstream areas and at the mouths of tributa-
C. Medeiros et a!.
5.5 Biota
Mangrove forests (approx. 28km 2 ) occupy the lowlands along the inner
portion of the Santa Cruz Channel and the lower part of tributaries. The
dominant species is the red mangrove (Rhizophora mangle), followed by
white mangrove (Laguncularia racemosa) and the less common black
mangrove (Avicennia schaueriana) and button mangrove (Conocarpus
erectus; Silva 1995). Enhanced mangrove growth and size of trees in areas
around the nodal point of tides may be due to deposition of fine-grained,
nutrient-rich sediment from freshwater runoff. A large part of the organic
matter production originates from Rhizophora mangle litter (7 tons dry
weight per ha and year). Additionally, high net productivity of associated
primary producers (i.e., the red alga Bostrichia 52.4 mg C h- 1 m- 2 and periphyton 208.3 mg C h- 1 m- 2 ) contributes significantly to total annual carbon
production.
The phytoplankton community in the Santa Cruz Channel is composed
of 78 species, 85% of which are diatoms. Phytoplankton density is highest
in the Orange inlet ( 4.46 x 10 6 cells 1- 1 ) during the rainy season. Phytoplankton biomass decreases rapidly from the northern (796 mg m- 3 ) and
southern inlet (1,052 mg m- 3 ) towards oceanic regions ( <60 mg m- 3 ).
Owing to high solar radiation and nutrient concentrations (N limiting factor, N:P ratio < 10:1), phytoplankton primary productivity in the Santa
Cruz channel is high (2.25-39.0 mg C h- 1 m- 3 ). Lower mean productivity
values occur in the northern Catuama (10.2 mg C h- 1 m- 3 ) and southern
Orange entrance (18.8 mg C h- 1 m- 3 ), decreasing even further ( < 1.0 mg
C h- 1 m- 3 ) beyond the reef line over the adjacent continental shelf. Similarly, elevated chlorophyll a concentrations in both channel inlets (mean
12.0mgm- 3 ) decrease towards nearshore (0.34mgm- 3 ) and offshore
(0.01 mgm- 3 ) regions.
A large number of benthic organisms (19% Foraminifera) compose the
zooplankton community. Meroplankton (i. e.,larvae ofbivalves,gastropods,
polychaetes) comprise about 20% of the microzooplankton but copepods
(27 species) and Tintinnina (15 species) are the dominant euryhaline marine species (Eskinazi-Leya 197 4). The abundance of microzooplankton in the
Orange inlet (22,449-244,216 org. m- 3 ) tends to decrease towards oligotrophic shelf waters. Macrozooplankton ( 49 taxa) is characterized by the dominance of copepods, Brachyura zoeae (Decapoda), followed by Lucifer sp.,
Chaetognatha, Larvacea, fish eggs, gastropods, and Upogebidae zoeae. Meroplankton represents approximately 35% (Paranagua and Nascimento
1973). Ctenophores prevail during dry periods and polychaetes associated
with rotifers are common in upstream areas and at the mouths of tributa-