border of the shelf. This front has mild gradients in density controlled mainly by
temperature in summer and by salinity in winter. The dynamics of the Malvinas
Current affects the latitudinal and seasonal variation of the front, moving offshore
during summer and onshore during spring and autumn (Olson et al. 1988; Fedulov
et al. 1990; Carreto et al. 1995; Acha et al. 2004). The front extends from the
Burwood Bank along the shelf-break and around Malvinas Islands (Guerrero et al.
1999) to the Brazil/Malvinas confluence in the North, producing a large region of
interrelated fronts (Acha et al. 2004).
The ACS, particularly the Patagonian shelf, is identified as a high primary
productivity area (Rivas et al. 2006). The ecology and reproduction of echinoderms inhabiting the coastal, shelf and shelf-break region of the ACS are affected
by variations of the primary productivity and oceanographic variables (e.g.
Brogger et al. 2004, 2010; Rubilar et al. 2005, 2008a; Marzinelli et al. 2006; Gil
and Zaixso 2007; Martinez 2008; Pérez et al. 2008; Gil et al. 2009).
The ACS is characterized by a homogeneous layer of unimodal fine and
medium size sand, which is the main component of the sediment. In some areas,
this layer is up to 2 m thick (Urien and Ewing 1974; Bastida and Urien 1981).
Although some places show a high percentage of gravel, other areas associated
with estuaries, gulfs and bays have fine sediments (mud-sand). Hard-bottom areas
with rocky shores seem to be scarce (Bastida et al. 1992).
The fauna of the Argentine shelf can be separated into two biogeographic
provinces: the Argentine and the Magellanic. These are part of the Subtropical and
Subantarctic Regions (Boschi 1979; Balech and Ehrlich 2008). The Argentine
province is a warm-temperate subregion extending from the littoral of Buenos
Aires southward to the coastal waters of northern Chubut (43–44°S). The depths of
the external boundaries range between 40 and 60 m. Water temperature varies
latitudinally and seasonally from 8 to 23 °C (Boschi 1979). This subregion also
reaches northward to Cabo Frio, (Brazil; 23°S, 42°W) having seasonal fluctuations
in the southern area. On the other hand, the Magellanic province is a cold-temperate subregion. At latitudes of 44–45°S it leaves the coastal region following the
Malvinas Current, upon reaching 37°S. This province extends about 150-200 km
from the continent, with depths greater than 80 m. The northern boundary of this
subregion can be tentatively placed at 34–35°S. Water temperature varies seasonally from 4 to 16 °C. This subregion extends to the Pacific Ocean along the
southern coastline of Chile (Boschi 1979).
11.2 Diversity and Distribution of Echinoderms
11.2.1 Expeditions to the Argentine Sea
The first campaign in the Argentine Sea was the Eugenie (1851–1853), which
explored the Río de la Plata and the Magellan Strait. From the collections of this
expedition, Ljungman (1867) studied the ophiuroids and Ekman (1925) studied the
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M. I. Brogger et al.
temperature in summer and by salinity in winter. The dynamics of the Malvinas
Current affects the latitudinal and seasonal variation of the front, moving offshore
during summer and onshore during spring and autumn (Olson et al. 1988; Fedulov
et al. 1990; Carreto et al. 1995; Acha et al. 2004). The front extends from the
Burwood Bank along the shelf-break and around Malvinas Islands (Guerrero et al.
1999) to the Brazil/Malvinas confluence in the North, producing a large region of
interrelated fronts (Acha et al. 2004).
The ACS, particularly the Patagonian shelf, is identified as a high primary
productivity area (Rivas et al. 2006). The ecology and reproduction of echinoderms inhabiting the coastal, shelf and shelf-break region of the ACS are affected
by variations of the primary productivity and oceanographic variables (e.g.
Brogger et al. 2004, 2010; Rubilar et al. 2005, 2008a; Marzinelli et al. 2006; Gil
and Zaixso 2007; Martinez 2008; Pérez et al. 2008; Gil et al. 2009).
The ACS is characterized by a homogeneous layer of unimodal fine and
medium size sand, which is the main component of the sediment. In some areas,
this layer is up to 2 m thick (Urien and Ewing 1974; Bastida and Urien 1981).
Although some places show a high percentage of gravel, other areas associated
with estuaries, gulfs and bays have fine sediments (mud-sand). Hard-bottom areas
with rocky shores seem to be scarce (Bastida et al. 1992).
The fauna of the Argentine shelf can be separated into two biogeographic
provinces: the Argentine and the Magellanic. These are part of the Subtropical and
Subantarctic Regions (Boschi 1979; Balech and Ehrlich 2008). The Argentine
province is a warm-temperate subregion extending from the littoral of Buenos
Aires southward to the coastal waters of northern Chubut (43–44°S). The depths of
the external boundaries range between 40 and 60 m. Water temperature varies
latitudinally and seasonally from 8 to 23 °C (Boschi 1979). This subregion also
reaches northward to Cabo Frio, (Brazil; 23°S, 42°W) having seasonal fluctuations
in the southern area. On the other hand, the Magellanic province is a cold-temperate subregion. At latitudes of 44–45°S it leaves the coastal region following the
Malvinas Current, upon reaching 37°S. This province extends about 150-200 km
from the continent, with depths greater than 80 m. The northern boundary of this
subregion can be tentatively placed at 34–35°S. Water temperature varies seasonally from 4 to 16 °C. This subregion extends to the Pacific Ocean along the
southern coastline of Chile (Boschi 1979).
11.2 Diversity and Distribution of Echinoderms
11.2.1 Expeditions to the Argentine Sea
The first campaign in the Argentine Sea was the Eugenie (1851–1853), which
explored the Río de la Plata and the Magellan Strait. From the collections of this
expedition, Ljungman (1867) studied the ophiuroids and Ekman (1925) studied the
364
M. I. Brogger et al.