The Rio de Ia Plata Estuary, Argentina-Uruguay
193
13.3.2.4 Mammals and Birds
Dolphins, mainly Pontoporia blainvillei and Tursiops gephyreus, are frequent in the Rio de la Plata estuary (Boschi 1988) and the sea lion Otaria
flavescens also occurs (Vaz-Ferreira and Ponce de Leon 1984). Phalacrocoracidae, Ardeidae, Phoenicopteridae, Anatidae, Charadriidae, Scolopacidae, Laridae, and Passeriform represent common aquatic birds in Rio de la
Plata wetlands (Bonetto and Hurtado 1998). In the salt marshes of Samboromb6n Bay, Calidris canutus rufa, C. fuscicoloris, Limosa haemastica,
Tringa flavipes, Himantopus melanurus, Charadrius falklandicus, C. semipalmatus, C. collaris, Pluvialis dominica, and Arenaria interpres feed on
polychaetes (Laeonereis acuta, Heteromastus simmili, Neanthes succinea)
and bivalves (Tagelus plebeius; Botto et al. 1998). Pluvialis dominica P.
squatarola, Arenaria interpres, and Numenius phaeopus forage on the fiddler crab Uca uruguayensis (Iribarne and Martinez 1999), which constitutes
an important food source.
13.3.3 Continental Shelf Environment
13.3.3.1 Plankton
The phytoplankton of shelf areas adjacent to the mouth of the Rio de la Plata (depth >50m) is richer in species than mixohaline waters (Negri et al.
1988). The community is composed of centric diatoms like Chaetoceros curvisetus, Bacteriatrum hyalinum, and Rhizosolenia delicatula, and pennate
diatoms (i.e., Asterionella glacial is, Thalassionema nitzschioides; Elgue et
al. 1991), dinoflagellates ( Ceratium tripos, C. lineatum, C. horridum), and
silicoflagellates. Generally, diatom abundance is highest in spring. Over the
Uruguayan shelf dinoflagellates and coccolithophores dominate ( Gayoso
1996) and blooms of toxic dinoflagellates (Alexandrium tamarense and
Gymnodinium catenatum) have been reported (Carreto and Akselman
1996). Coastal areas under estuarine influence are characterized by Acartia
tonsa, Euterpina acutifrons, Parae alan us parvus, Oithona nana, and dadocera (Evadne nordmani, Podon polyphemoides, Penilia avirostris; Fermindez Anioz et al. 1991 ), while Scyphomedusae (Aurelia aurita, Chrysaora lactea, Lichnorhiza lucerna) occur mainly off Punta del Este (Mianzan et al.
1988).
Eggs and larvae of Engraulis anchoita (Sanchez and Ciechomski 1995),
which has a protracted reproductive season with a peak in late spring/early
summer (November-January), dominated the ichthyoplankton of shelf
193
13.3.2.4 Mammals and Birds
Dolphins, mainly Pontoporia blainvillei and Tursiops gephyreus, are frequent in the Rio de la Plata estuary (Boschi 1988) and the sea lion Otaria
flavescens also occurs (Vaz-Ferreira and Ponce de Leon 1984). Phalacrocoracidae, Ardeidae, Phoenicopteridae, Anatidae, Charadriidae, Scolopacidae, Laridae, and Passeriform represent common aquatic birds in Rio de la
Plata wetlands (Bonetto and Hurtado 1998). In the salt marshes of Samboromb6n Bay, Calidris canutus rufa, C. fuscicoloris, Limosa haemastica,
Tringa flavipes, Himantopus melanurus, Charadrius falklandicus, C. semipalmatus, C. collaris, Pluvialis dominica, and Arenaria interpres feed on
polychaetes (Laeonereis acuta, Heteromastus simmili, Neanthes succinea)
and bivalves (Tagelus plebeius; Botto et al. 1998). Pluvialis dominica P.
squatarola, Arenaria interpres, and Numenius phaeopus forage on the fiddler crab Uca uruguayensis (Iribarne and Martinez 1999), which constitutes
an important food source.
13.3.3 Continental Shelf Environment
13.3.3.1 Plankton
The phytoplankton of shelf areas adjacent to the mouth of the Rio de la Plata (depth >50m) is richer in species than mixohaline waters (Negri et al.
1988). The community is composed of centric diatoms like Chaetoceros curvisetus, Bacteriatrum hyalinum, and Rhizosolenia delicatula, and pennate
diatoms (i.e., Asterionella glacial is, Thalassionema nitzschioides; Elgue et
al. 1991), dinoflagellates ( Ceratium tripos, C. lineatum, C. horridum), and
silicoflagellates. Generally, diatom abundance is highest in spring. Over the
Uruguayan shelf dinoflagellates and coccolithophores dominate ( Gayoso
1996) and blooms of toxic dinoflagellates (Alexandrium tamarense and
Gymnodinium catenatum) have been reported (Carreto and Akselman
1996). Coastal areas under estuarine influence are characterized by Acartia
tonsa, Euterpina acutifrons, Parae alan us parvus, Oithona nana, and dadocera (Evadne nordmani, Podon polyphemoides, Penilia avirostris; Fermindez Anioz et al. 1991 ), while Scyphomedusae (Aurelia aurita, Chrysaora lactea, Lichnorhiza lucerna) occur mainly off Punta del Este (Mianzan et al.
1988).
Eggs and larvae of Engraulis anchoita (Sanchez and Ciechomski 1995),
which has a protracted reproductive season with a peak in late spring/early
summer (November-January), dominated the ichthyoplankton of shelf