The Gulf of Guayaquil and the Guayas River Estuary, Ecuador
253
17 .4.2 Plankton
A total of 159 species of phytoplankton have been identified in the Guayas
River estuary (C. Cajas, unpubl. data), compared to earlier surveys of diatoms and silicoflagellates (189) and dinoflagellates (103; Jimenez 1980).
Throughout the year, the phytoplankton community composition is dominated by diatoms (i.e., Skeletonema costatum, Polymyxus coronalis, Coscinodiscus lineatus, Actinoptychus undulatus, Biddulphia sinensis, Thalassionema nitzschioides; Cardenas 1995). Mean values for the Churute,
Guayas, and Salado subestuaries are 3.6, 3.3, and 2.0 x 10 5 cells ml- 1 , respectively (Cardenas 1995) and mean values for cyanobacteria and dinoflagellates vary between 5-19 and 9-80 cells ml- 1 , respectively. Chlorophyll-a
concentrations range from 1 to 5 mg m- 3 (De Peribonio 1981; Stevenson
1981), with highest concentrations (5mg m- 3 ) in the inner Gulf and lower
Guayas River estuary and mean concentrations of 15, 14, and 6mg m- 3 in
the Guayas, Churute, and Salado subestuaries, respectively (Cardenas
1995). Toxic phytoplankton blooms (Gonyaulax catenella, G. monilata,
Gymnodium breve) are a common occurrence in the Gulf of Guayaquil and
the Guayas River estuary (Jimenez 1980; de Arcos 1982) and have caused
fish kills and mortality of post-larvae in shrimp hatcheries (Jimenez 1989).
Blooms also occur in the Guayas River ( Gyrodinium stratum, Prorocentrum maximum, Nitzschia sp., and Mesodinium rubrum), Estero Salado
(Mesodinium rubrum), and coastal waters of the Gulf of Guayaquil (Thalassiosira sp.; de Arcos 1982).
The zooplankton community in the Guayas River estuary is composed
of 101 species. Arthropods, dominated by copepods (mean 300 ind. cm- 3 ),
and protozoans are the major components (C. de Cajas, unpubl. data). High
zooplankton biomass outside the Gulf of Guayaquil is largely comprised of
cope pods while fish eggs dominate zooplankton inside the Gulf (de Cajas
1982). Ichthyoplankton is represented by 29 families, the most abundant
are Engraulidae (Anchoa sp., Engraulis sp., E. ringens, Cetengraulis mysticetus, Anchovia), Sciaenidae, Gobiidae, and Carangidae (Luzuriaga et al.
1998). Engraulidae and Gobiidae dominate in surface waters and Sciaenidae in deeper waters. The highest density of larvae occurs from May to
July and is correlated with high concentrations of phytoplankton.
17 .4.3 Benthos
Several macrobenthic species, like the oysters Crassostrea columbiensis
(Hanley) and C. iridiscens (Hanley), the mangrove crab Ucides occidentalis, and Mytella guyanensis (Lamarck), M. strigata (Hanley), and Ala-
253
17 .4.2 Plankton
A total of 159 species of phytoplankton have been identified in the Guayas
River estuary (C. Cajas, unpubl. data), compared to earlier surveys of diatoms and silicoflagellates (189) and dinoflagellates (103; Jimenez 1980).
Throughout the year, the phytoplankton community composition is dominated by diatoms (i.e., Skeletonema costatum, Polymyxus coronalis, Coscinodiscus lineatus, Actinoptychus undulatus, Biddulphia sinensis, Thalassionema nitzschioides; Cardenas 1995). Mean values for the Churute,
Guayas, and Salado subestuaries are 3.6, 3.3, and 2.0 x 10 5 cells ml- 1 , respectively (Cardenas 1995) and mean values for cyanobacteria and dinoflagellates vary between 5-19 and 9-80 cells ml- 1 , respectively. Chlorophyll-a
concentrations range from 1 to 5 mg m- 3 (De Peribonio 1981; Stevenson
1981), with highest concentrations (5mg m- 3 ) in the inner Gulf and lower
Guayas River estuary and mean concentrations of 15, 14, and 6mg m- 3 in
the Guayas, Churute, and Salado subestuaries, respectively (Cardenas
1995). Toxic phytoplankton blooms (Gonyaulax catenella, G. monilata,
Gymnodium breve) are a common occurrence in the Gulf of Guayaquil and
the Guayas River estuary (Jimenez 1980; de Arcos 1982) and have caused
fish kills and mortality of post-larvae in shrimp hatcheries (Jimenez 1989).
Blooms also occur in the Guayas River ( Gyrodinium stratum, Prorocentrum maximum, Nitzschia sp., and Mesodinium rubrum), Estero Salado
(Mesodinium rubrum), and coastal waters of the Gulf of Guayaquil (Thalassiosira sp.; de Arcos 1982).
The zooplankton community in the Guayas River estuary is composed
of 101 species. Arthropods, dominated by copepods (mean 300 ind. cm- 3 ),
and protozoans are the major components (C. de Cajas, unpubl. data). High
zooplankton biomass outside the Gulf of Guayaquil is largely comprised of
cope pods while fish eggs dominate zooplankton inside the Gulf (de Cajas
1982). Ichthyoplankton is represented by 29 families, the most abundant
are Engraulidae (Anchoa sp., Engraulis sp., E. ringens, Cetengraulis mysticetus, Anchovia), Sciaenidae, Gobiidae, and Carangidae (Luzuriaga et al.
1998). Engraulidae and Gobiidae dominate in surface waters and Sciaenidae in deeper waters. The highest density of larvae occurs from May to
July and is correlated with high concentrations of phytoplankton.
17 .4.3 Benthos
Several macrobenthic species, like the oysters Crassostrea columbiensis
(Hanley) and C. iridiscens (Hanley), the mangrove crab Ucides occidentalis, and Mytella guyanensis (Lamarck), M. strigata (Hanley), and Ala-