36
J. Polania eta!.
cation TSS concentration plummets to 15 mg I- 1 • The organic matter fraction ofTSS tends to increase from 28% in the inlet to 60% towards the Fundaci6n River. However, rivers that drain Sierra Nevada de Santa Marta do
not appear to be an important source of suspended solids for the CGSM.
The concentration of nutrients (nitrogen, phosphate, silicate) fluctuates
between months and years and follows steep horizontal gradients. The N:P
ratio in the CGSM tends to increase with salinity; however, in the center of
the lagoon the ratio increases during rainy seasons at low salinity.
Although dissolved nitrogen concentrations have remained about constant
in the CGSM during the last 10 years, chlorophyll concentrations have
increased. As a result increasing phosphorus levels may have initiated a
eutrophication process.
2.3 Biotic Components
2.3.1 Plankton
The phytoplankton community in the CGSM is comprised of pennate (91
species) and centric diatoms (48), dinoflagellates (34), Chlorophyta (31),
Euglenophyta (21 ), and Cyanobacteria ( 17; Vidal1995 ). Some of the typical
brackish water species are continuously present at high numbers and may
exceed densities of 2 x 10 6 cells m- 3 • The distribution of zooplankton varies
between seasons and with depth. Microzooplankton species are responsible for high abundance during the rainy season, in which three species may
account for 84% of abundance. Macrozooplankton and ichthyoplankton
species have higher abundance during the dry season. Zooplankton density gradients in the water column may be pronounced during the wet seasons but vertical distribution is uniform during the dry season. Salinity
changes and predation by ichthyoplankton influence successional changes
between micro- and macrozooplankton components.
2.3.2 Invertebrates
Among the invertebrate fauna, mollusks are represented by approximately
98 species ( 66 genera and 48 families) of which 61 are of marine origin. Six
species occur in mangrove sediments, Melampus coffeus being the most
abundant among the three gastropods. The fiddler crabs Uca rapax and U.
vocator are the most abundant crabs in areas of mangrove sediments. The
J. Polania eta!.
cation TSS concentration plummets to 15 mg I- 1 • The organic matter fraction ofTSS tends to increase from 28% in the inlet to 60% towards the Fundaci6n River. However, rivers that drain Sierra Nevada de Santa Marta do
not appear to be an important source of suspended solids for the CGSM.
The concentration of nutrients (nitrogen, phosphate, silicate) fluctuates
between months and years and follows steep horizontal gradients. The N:P
ratio in the CGSM tends to increase with salinity; however, in the center of
the lagoon the ratio increases during rainy seasons at low salinity.
Although dissolved nitrogen concentrations have remained about constant
in the CGSM during the last 10 years, chlorophyll concentrations have
increased. As a result increasing phosphorus levels may have initiated a
eutrophication process.
2.3 Biotic Components
2.3.1 Plankton
The phytoplankton community in the CGSM is comprised of pennate (91
species) and centric diatoms (48), dinoflagellates (34), Chlorophyta (31),
Euglenophyta (21 ), and Cyanobacteria ( 17; Vidal1995 ). Some of the typical
brackish water species are continuously present at high numbers and may
exceed densities of 2 x 10 6 cells m- 3 • The distribution of zooplankton varies
between seasons and with depth. Microzooplankton species are responsible for high abundance during the rainy season, in which three species may
account for 84% of abundance. Macrozooplankton and ichthyoplankton
species have higher abundance during the dry season. Zooplankton density gradients in the water column may be pronounced during the wet seasons but vertical distribution is uniform during the dry season. Salinity
changes and predation by ichthyoplankton influence successional changes
between micro- and macrozooplankton components.
2.3.2 Invertebrates
Among the invertebrate fauna, mollusks are represented by approximately
98 species ( 66 genera and 48 families) of which 61 are of marine origin. Six
species occur in mangrove sediments, Melampus coffeus being the most
abundant among the three gastropods. The fiddler crabs Uca rapax and U.
vocator are the most abundant crabs in areas of mangrove sediments. The