The Rio de Ia Plata Estuary, Argentina-Uruguay
191
crop to the surface (Mianzan and Guerrero in press). The dominant zooplankters in Samboromb6n Bay are Acartia tonsa (Copepoda), Neomysis
americana (Mysidacea), Mnemiopsis maccradyi, and Liriope tetraphylla
(Hydromedusae), with biomass peaks of M. maccradyi in spring and L.
tetraphylla in summer (Sorarrain 1998). Copepods (mainly Acartia tonsa)
and Sagitta friderichi are also the dominant zooplankton at the Uruguayan
coast, followed by N. americana, the cladoceran Pleopis polyphemoides,
chaetognats (Sagitta), larvae of cirripeds (Balanus; Mendez et al. 1997),
and Scyphomedusae (Lichnorhiza lucerna, Chrysaora lactea; Mianzan et
al. 1988).
Eggs and larvae of Micropogonias furnieri and Brevoortia aurea and larvae of Gobiosoma parri dominate the ichthyoplankton. The densities of
eggs and larvae of M. furnieri and B. a urea are highest at the bottom salinity front (Acha et al. 1999; Acha 1999) and near Montevideo (Acuna et al.
1997). Both species have reproductive peaks in spring and early summer
(October-December). The occurrence of larvae of Gobiosoma parri from
March through December indicates spawning from February to April
(Acha 1994). Anchoa marinii eggs occur mainly at the mouth of Rio de la
Plata and reach highest densities in front of Punta del Este (Cassia and
Booman 1985; Sanchez and Ciechomski 1995; Acha 1999). The planktonic
stages of most of these species (i.e., B. aurea, G. parri), as well as atherinid
larvae, larvae of Pogonias cromis and Cynoscion guatucupa, and small juveniles of Syngnathidae occur in Samboromb6n Bay (Cassia and Boo man
1985; Lasta and de Ciechomski 1988; Acha 1999).
13.3.2.2 Benthos
The muddy bottoms of the inner estuary (8- 15 m depth), including Samboromb6n and Montevideo bays, are characterized by abundant clams
(Mactra isabelleana, Angulus gibber), snails (Buccinanops duartei, B. globulosum, B. gradatum, Anachis isabellei, Turbonilla uruguayensis), worms
( Onuphis tenuis, Nephtys sp.), and crabs (Pinnixa brevipolex, Cyrtograpsus
affinis, C. altimanus). Most species are deposit feeders or carnivores and
highest densities (M. isabelleana, 1,500-2,700 ind. m- 2 ) occur near Barra
del Indio at 9- 11 m depth. Shannon species diversity values range between
1.29 and 2.44 (A. Roux and C. Bremec, unpubl. data).
Supralittoral levels of rocky promontories between Montevideo and
Cabo Polonio are dominated by lichens ( Caloplaca montevidensis, Verrucaria sp.), cyanophytes, crustaceans, and mollusks (Acmaea subrugosa and
Siphonaria lessoni). The upper midlittoral presents algae, cirri peds ( Chthamalus bisinuatus), polychaetes (Neanthes succinea), and mollusks (A. sub-
191
crop to the surface (Mianzan and Guerrero in press). The dominant zooplankters in Samboromb6n Bay are Acartia tonsa (Copepoda), Neomysis
americana (Mysidacea), Mnemiopsis maccradyi, and Liriope tetraphylla
(Hydromedusae), with biomass peaks of M. maccradyi in spring and L.
tetraphylla in summer (Sorarrain 1998). Copepods (mainly Acartia tonsa)
and Sagitta friderichi are also the dominant zooplankton at the Uruguayan
coast, followed by N. americana, the cladoceran Pleopis polyphemoides,
chaetognats (Sagitta), larvae of cirripeds (Balanus; Mendez et al. 1997),
and Scyphomedusae (Lichnorhiza lucerna, Chrysaora lactea; Mianzan et
al. 1988).
Eggs and larvae of Micropogonias furnieri and Brevoortia aurea and larvae of Gobiosoma parri dominate the ichthyoplankton. The densities of
eggs and larvae of M. furnieri and B. a urea are highest at the bottom salinity front (Acha et al. 1999; Acha 1999) and near Montevideo (Acuna et al.
1997). Both species have reproductive peaks in spring and early summer
(October-December). The occurrence of larvae of Gobiosoma parri from
March through December indicates spawning from February to April
(Acha 1994). Anchoa marinii eggs occur mainly at the mouth of Rio de la
Plata and reach highest densities in front of Punta del Este (Cassia and
Booman 1985; Sanchez and Ciechomski 1995; Acha 1999). The planktonic
stages of most of these species (i.e., B. aurea, G. parri), as well as atherinid
larvae, larvae of Pogonias cromis and Cynoscion guatucupa, and small juveniles of Syngnathidae occur in Samboromb6n Bay (Cassia and Boo man
1985; Lasta and de Ciechomski 1988; Acha 1999).
13.3.2.2 Benthos
The muddy bottoms of the inner estuary (8- 15 m depth), including Samboromb6n and Montevideo bays, are characterized by abundant clams
(Mactra isabelleana, Angulus gibber), snails (Buccinanops duartei, B. globulosum, B. gradatum, Anachis isabellei, Turbonilla uruguayensis), worms
( Onuphis tenuis, Nephtys sp.), and crabs (Pinnixa brevipolex, Cyrtograpsus
affinis, C. altimanus). Most species are deposit feeders or carnivores and
highest densities (M. isabelleana, 1,500-2,700 ind. m- 2 ) occur near Barra
del Indio at 9- 11 m depth. Shannon species diversity values range between
1.29 and 2.44 (A. Roux and C. Bremec, unpubl. data).
Supralittoral levels of rocky promontories between Montevideo and
Cabo Polonio are dominated by lichens ( Caloplaca montevidensis, Verrucaria sp.), cyanophytes, crustaceans, and mollusks (Acmaea subrugosa and
Siphonaria lessoni). The upper midlittoral presents algae, cirri peds ( Chthamalus bisinuatus), polychaetes (Neanthes succinea), and mollusks (A. sub-