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J.L. Valentin
upwelled water and wave action. Strong wave action of exposed rocky
shores and high phytoplankton biomass also favor the development of
banks of the mussel Perna perna, associated with rich algal communities
and dense populations of cirri peds. The distribution of benthic organisms
is influenced by local hydrodynamics which directly affect recruitment of
the propagules and larvae, post-settling mortality, and grazing by the
gastropod Littorina ziczac on cyanophyceans and the crab Pachygrapsus
transversus on Ulvales and Ectocarpales (Coutinho 1995).
The impact of SACW on the structure of benthic communities of the
continental shelf varies with the nature of the substrate. North of the cape
(23°S), conglomerates of lithothamnioid calcareous algae and almost permanently cold waters favor recruitment and establishment of extensive
Laminaria abyssalis banks (50-110m depth). The conditions for the completion of the Laminaria life cycle and maximum growth of sporophytes
(18 °C, 20 f.lM N0 3 - , and 35 f.lmol photons m- 2 s- 1 of blue light) are provided
by SACW at depths below 50m (Yoneshigue-Valentin 1990). Laminaria
beds are habitat for a rich demersal fauna.
South of 23°S, unconsolidated substrates are composed of medium sand
(30-45 m) and fine sand and mud (below 60 m). The action of currents,
together with strong thermal gradients during frequent upwelling in
spring and summer, determine the structure of benthic and demersal communities. Sea stars are an ecologically important and numerically dominant group of the soft-bottom community. The distribution of the common Astropecten cingulatus, followed by Astropecten brasiliensis, Luidia
ludwigi scotti, Luidia alternata, and Tethyaster vestitus, seems to follow
depth-related sediment characteristics. The 45-m isobath appears to represent a transitional depth for echinoderms and pelecypods, which are the
principal prey of sea stars (Gomes 1989; Ventura and Fernandes 1995). The
reproductive peak of Astropecten brasiliensis coincides with upwelling
periods. The larvae benefit from abundant phytoplankton, and large quantities of prey (bivalves and crustaceans, mainly cumaceans) are ingested
during the major feeding period in summer (Ventura et al. 1997). Similarly, depth-related sediment particle size seems to be the main factor for the
distribution of bivalves. The common Mactra petiti, Tell ina petitiana, Tellina gibber, and Crassinella lunulata are abundant in neashore areas down
to 30m depth where high turbulence and resuspension of sediment favors
the dominance of sediment-feeders. The organic enrichment of inner shelf
sediments by upwelling promotes the presence of detritivorous bivalves
like Nucula puelcha and Corbula patagonica (below 30m depth) and Malletia cumingii (below 60 m; Gomes 1989). Another important element of
the inner shelf is crustaceans, like Brachyura (Portunus spinicarpus; Brisson 1992) and Anomoura (Dardanus arrosor insignis; da Gama and Fer-
J.L. Valentin
upwelled water and wave action. Strong wave action of exposed rocky
shores and high phytoplankton biomass also favor the development of
banks of the mussel Perna perna, associated with rich algal communities
and dense populations of cirri peds. The distribution of benthic organisms
is influenced by local hydrodynamics which directly affect recruitment of
the propagules and larvae, post-settling mortality, and grazing by the
gastropod Littorina ziczac on cyanophyceans and the crab Pachygrapsus
transversus on Ulvales and Ectocarpales (Coutinho 1995).
The impact of SACW on the structure of benthic communities of the
continental shelf varies with the nature of the substrate. North of the cape
(23°S), conglomerates of lithothamnioid calcareous algae and almost permanently cold waters favor recruitment and establishment of extensive
Laminaria abyssalis banks (50-110m depth). The conditions for the completion of the Laminaria life cycle and maximum growth of sporophytes
(18 °C, 20 f.lM N0 3 - , and 35 f.lmol photons m- 2 s- 1 of blue light) are provided
by SACW at depths below 50m (Yoneshigue-Valentin 1990). Laminaria
beds are habitat for a rich demersal fauna.
South of 23°S, unconsolidated substrates are composed of medium sand
(30-45 m) and fine sand and mud (below 60 m). The action of currents,
together with strong thermal gradients during frequent upwelling in
spring and summer, determine the structure of benthic and demersal communities. Sea stars are an ecologically important and numerically dominant group of the soft-bottom community. The distribution of the common Astropecten cingulatus, followed by Astropecten brasiliensis, Luidia
ludwigi scotti, Luidia alternata, and Tethyaster vestitus, seems to follow
depth-related sediment characteristics. The 45-m isobath appears to represent a transitional depth for echinoderms and pelecypods, which are the
principal prey of sea stars (Gomes 1989; Ventura and Fernandes 1995). The
reproductive peak of Astropecten brasiliensis coincides with upwelling
periods. The larvae benefit from abundant phytoplankton, and large quantities of prey (bivalves and crustaceans, mainly cumaceans) are ingested
during the major feeding period in summer (Ventura et al. 1997). Similarly, depth-related sediment particle size seems to be the main factor for the
distribution of bivalves. The common Mactra petiti, Tell ina petitiana, Tellina gibber, and Crassinella lunulata are abundant in neashore areas down
to 30m depth where high turbulence and resuspension of sediment favors
the dominance of sediment-feeders. The organic enrichment of inner shelf
sediments by upwelling promotes the presence of detritivorous bivalves
like Nucula puelcha and Corbula patagonica (below 30m depth) and Malletia cumingii (below 60 m; Gomes 1989). Another important element of
the inner shelf is crustaceans, like Brachyura (Portunus spinicarpus; Brisson 1992) and Anomoura (Dardanus arrosor insignis; da Gama and Fer-