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C. Odebrecht and J.P. Castello
cies without pelagic life-cycle phases (Capitoli 1997). Beyond the direct
influence of runoff, inner shelf sandy areas (10-15 m depth) are characterized by cumaceans, isopods, the penaeid Artemesia longinaris, and mollusks (Dorsanum moniliferum, Olivancillaria urceus, Adelomelon brasiliana, Mactra isabelleana). The mollusks Encope emarginata, Buccinanops
lamarcki, Loxopagurus loxochelis, Astropecten armatus, Adrana elect a, isopods, and polychaetes occupy deeper ( 15-25 m) areas with fine sand. Transitional sandy mud bottoms (25-50 m) between inner and intermediate
shelf regions are typical of Pitar rostratus, Corbula patagonica, Buccinanops gradatum, Mactra petiti, Dardanus arrosor, Persephona punctata,
Hepatus pudibundus, and ophiurids. Phyllochaetopterus socialis, Astrangia
rathbuni, serpulid polychaetes, and Crepidula pro tea are conspicuous organisms on consolidated substrate and beach rock outcrops (Capitoli 1997).
Further south (38°S), about 84 typical species occur on the inner shelf
( <60 m depth) on hard (e.g., Mytilus platensis, Lithophaga patagonica,
Lumbrineris tetraura, Crepidula aculeata, Tegula patagonica, Diopatra
viridis) and soft substrate (Nucula puelcha, Turbonilla uruguayensis, Olivella tehuelchana, Eunice argentinensis; Roux et al. 1993).
The mollusk Pi tar rostratus, polychaetes, amp hi pods, and ophiurids are
abundant on muddy sand bottoms (50-90 m) of the intermediate shelf between 32°S and 34°S. The highest faunal abundance (500-1,000 ind. m- 2 ) is
associated with extensive sandy mud bottoms of the intermediate shelf
(80-130 m), with species like Diopatra tridentata, Chasmocarcinus typicus,
Terebellides sp., Onuphis tenuis, Astropecten cingulatus, Squilla brasiliensis, and Portunus spinicarpus. In muddy bottoms (100-130m) this
assemblage is substituted by polychaetes (Eupanthalis rudipalpa, Panthalis oerstedi, Spirochaetopterus sp.) and sipunculids (Nephasomma sp.; Capftoli 1997). Eurybathic species (41; e.g., Amphiura eugeniae, Idanthyrsus
armatus, Philine argentina, Colpospirella algida, Hiatella salida, Limopsis
hirtella, Natica isabelleana, Ninoe brasiliensis, Epicodakia falklandica, Kellia suborbicularis, Yoldia eightsii, Ophiacanta vivipara) characterize bottoms at 38°S under the influence of SAW (Bastida et al. 1992; Roux et al.
1993).
At the outer shelf and slope (30-32°S) between 130 and 220m depth, low
abundance of gorgonians, echinoderms, isopods, barnacles, and serpulid
polychaetes (100-500 ind. m- 2 ) coincides with biodetritus bottoms. Slope
areas (200-500 m) have low density ( < 100 ind. m- 2 ) and different depths
strata (200-300 m and 300-500 m) and substrate types appear to select for
different species. Eunice frauenfeldi, Zoanthidea sp., and species of Porifera, Actinaria, and Ophiurida typically occupy consolidated substrates of
upper slope regions. Lower slopes are characterized by Acanella eburnea
and Flabellum brasiliensis (coral), Ophiurolepis sp. (ophiurid) and Priapu-
C. Odebrecht and J.P. Castello
cies without pelagic life-cycle phases (Capitoli 1997). Beyond the direct
influence of runoff, inner shelf sandy areas (10-15 m depth) are characterized by cumaceans, isopods, the penaeid Artemesia longinaris, and mollusks (Dorsanum moniliferum, Olivancillaria urceus, Adelomelon brasiliana, Mactra isabelleana). The mollusks Encope emarginata, Buccinanops
lamarcki, Loxopagurus loxochelis, Astropecten armatus, Adrana elect a, isopods, and polychaetes occupy deeper ( 15-25 m) areas with fine sand. Transitional sandy mud bottoms (25-50 m) between inner and intermediate
shelf regions are typical of Pitar rostratus, Corbula patagonica, Buccinanops gradatum, Mactra petiti, Dardanus arrosor, Persephona punctata,
Hepatus pudibundus, and ophiurids. Phyllochaetopterus socialis, Astrangia
rathbuni, serpulid polychaetes, and Crepidula pro tea are conspicuous organisms on consolidated substrate and beach rock outcrops (Capitoli 1997).
Further south (38°S), about 84 typical species occur on the inner shelf
( <60 m depth) on hard (e.g., Mytilus platensis, Lithophaga patagonica,
Lumbrineris tetraura, Crepidula aculeata, Tegula patagonica, Diopatra
viridis) and soft substrate (Nucula puelcha, Turbonilla uruguayensis, Olivella tehuelchana, Eunice argentinensis; Roux et al. 1993).
The mollusk Pi tar rostratus, polychaetes, amp hi pods, and ophiurids are
abundant on muddy sand bottoms (50-90 m) of the intermediate shelf between 32°S and 34°S. The highest faunal abundance (500-1,000 ind. m- 2 ) is
associated with extensive sandy mud bottoms of the intermediate shelf
(80-130 m), with species like Diopatra tridentata, Chasmocarcinus typicus,
Terebellides sp., Onuphis tenuis, Astropecten cingulatus, Squilla brasiliensis, and Portunus spinicarpus. In muddy bottoms (100-130m) this
assemblage is substituted by polychaetes (Eupanthalis rudipalpa, Panthalis oerstedi, Spirochaetopterus sp.) and sipunculids (Nephasomma sp.; Capftoli 1997). Eurybathic species (41; e.g., Amphiura eugeniae, Idanthyrsus
armatus, Philine argentina, Colpospirella algida, Hiatella salida, Limopsis
hirtella, Natica isabelleana, Ninoe brasiliensis, Epicodakia falklandica, Kellia suborbicularis, Yoldia eightsii, Ophiacanta vivipara) characterize bottoms at 38°S under the influence of SAW (Bastida et al. 1992; Roux et al.
1993).
At the outer shelf and slope (30-32°S) between 130 and 220m depth, low
abundance of gorgonians, echinoderms, isopods, barnacles, and serpulid
polychaetes (100-500 ind. m- 2 ) coincides with biodetritus bottoms. Slope
areas (200-500 m) have low density ( < 100 ind. m- 2 ) and different depths
strata (200-300 m and 300-500 m) and substrate types appear to select for
different species. Eunice frauenfeldi, Zoanthidea sp., and species of Porifera, Actinaria, and Ophiurida typically occupy consolidated substrates of
upper slope regions. Lower slopes are characterized by Acanella eburnea
and Flabellum brasiliensis (coral), Ophiurolepis sp. (ophiurid) and Priapu-