The Bahia Blanca Estuary, Argentina
213
sated for by active mixing of the water column by winds; thus, chlorophyll-a concentrations ( 40-54jlg 1- 1 ) and net primary production
values (>200 jlg C 1- 1 h- 1 ) reflect high photosynthetic activity and, at the
end of blooms, nitrate, phosphate, and silicate are almost completely
depleted.
In general, composition and spatial distribution of zooplankton in the
Bahia Blanca Estuary is influenced by highly variable environmental parameters in the inner estuary and more stable conditions of the coastal and
marine environment. Coastal ciliates without a lorica, like the abundant
Strombidium sulcatum, Strombidium sp., and Cyrtostrombidium sp., are
among the principal components of the microzooplankton community.
Tintinnidium balechi is most abundant and, together with Tintinnopsis sp.,
serves as an indicator of water quality in the Bahia Blanca Estuary (Barria
de Cao 1992). The presence of typical warm water species (i.e., Tintinnopsis radix) and Stylicauda platensis of the Brazil Current suggests mixture of
warm and cold waters. The meso- and macrozooplankton community
(0-4 m depth) is composed of Cnidaria, Ctenophora, Lophochordata, Mollusca, Chaetognata, Annelida, Arthropoda (Copepoda), and Chordata
(Hoffmeyer 1994). During the entire year, the calanoid copepod Acartia
tonsa is the most frequent holoplanktonic species, followed by Paracalanus
parvus and Euterpina acutifrons. Meroplankton (35 taxa) and freshwater
elements (Daphnia sp., Boeckella poopensis) dominate the estuarine zooplankton community. The eggs of the cupleid Brevoortia aurea and larval
stages of Conopeum sp. and Chasmagnatus granulata are frequent in summer (20 oC) and fall ( 18.2 °C). The zoe a larvae and megalopa forms of
Chasmagnatus granulata are important elements in spring (October 78 %)
and fall (March 51%). Most zoea larvae of the Grapsidae (Pachysteles haigae), Caridae (Pagurus sp.), and Majidae (Pilumnus reticulatus, Peisos
petrunkevitchi) are widely distributed in the estuary and well adapted to
temperature changes (Cervellini 1987). Other species, like Caridea (Betaeus lilianae and Latreutes parvulus) have coastal preference or are stenothermal (i.e., Corystoides chilensis, Artemesia longinaris, Pleoticus muelleri). Stenohaline forms of decapods tend to remain near the estuary
entrance.
14.4.3 Nekton
Important components of the estuarine ichthiofauna are Brevoortia a urea,
the whitemouth croaker Micropogonas furneri, the striped weakfish Cynoscion striatus, Odontesthes bonaerensis, and Mustellus schmitti. The adults
of Brevoortia aurea migrate into the estuary during spawning in spring
213
sated for by active mixing of the water column by winds; thus, chlorophyll-a concentrations ( 40-54jlg 1- 1 ) and net primary production
values (>200 jlg C 1- 1 h- 1 ) reflect high photosynthetic activity and, at the
end of blooms, nitrate, phosphate, and silicate are almost completely
depleted.
In general, composition and spatial distribution of zooplankton in the
Bahia Blanca Estuary is influenced by highly variable environmental parameters in the inner estuary and more stable conditions of the coastal and
marine environment. Coastal ciliates without a lorica, like the abundant
Strombidium sulcatum, Strombidium sp., and Cyrtostrombidium sp., are
among the principal components of the microzooplankton community.
Tintinnidium balechi is most abundant and, together with Tintinnopsis sp.,
serves as an indicator of water quality in the Bahia Blanca Estuary (Barria
de Cao 1992). The presence of typical warm water species (i.e., Tintinnopsis radix) and Stylicauda platensis of the Brazil Current suggests mixture of
warm and cold waters. The meso- and macrozooplankton community
(0-4 m depth) is composed of Cnidaria, Ctenophora, Lophochordata, Mollusca, Chaetognata, Annelida, Arthropoda (Copepoda), and Chordata
(Hoffmeyer 1994). During the entire year, the calanoid copepod Acartia
tonsa is the most frequent holoplanktonic species, followed by Paracalanus
parvus and Euterpina acutifrons. Meroplankton (35 taxa) and freshwater
elements (Daphnia sp., Boeckella poopensis) dominate the estuarine zooplankton community. The eggs of the cupleid Brevoortia aurea and larval
stages of Conopeum sp. and Chasmagnatus granulata are frequent in summer (20 oC) and fall ( 18.2 °C). The zoe a larvae and megalopa forms of
Chasmagnatus granulata are important elements in spring (October 78 %)
and fall (March 51%). Most zoea larvae of the Grapsidae (Pachysteles haigae), Caridae (Pagurus sp.), and Majidae (Pilumnus reticulatus, Peisos
petrunkevitchi) are widely distributed in the estuary and well adapted to
temperature changes (Cervellini 1987). Other species, like Caridea (Betaeus lilianae and Latreutes parvulus) have coastal preference or are stenothermal (i.e., Corystoides chilensis, Artemesia longinaris, Pleoticus muelleri). Stenohaline forms of decapods tend to remain near the estuary
entrance.
14.4.3 Nekton
Important components of the estuarine ichthiofauna are Brevoortia a urea,
the whitemouth croaker Micropogonas furneri, the striped weakfish Cynoscion striatus, Odontesthes bonaerensis, and Mustellus schmitti. The adults
of Brevoortia aurea migrate into the estuary during spawning in spring