fluctuated between 70,000 and 100,000 eggs/gonad. The reproductive cycle produced a fully synchronous spawning event between late winter and early spring.
A new gametic proliferation may occur during the spring with subsequent partial
spawning in the summer (Orler 1992). At NG a main spawning event occurrs in
winter and a second minor event during the summer (Marzinelli et al. 2006). The
gonad index at NG was negatively correlated with photoperiod and water temperature with a lag period of 3 mo. Egg strain values are high in eggs spawned
by small individuals. According to Marzinelli et al. (2006) the jelly coat of eggs of
P. magellanicus may protect them from the forces experienced during spawning,
thus allowing reproductive success.
Diet was studied by Penchaszadeh et al. (2004). The authors suggested an
omnivorous behaviour related to different ecological conditions. The diet spectrum
of P. magellanicus depends mostly on the habitat and biotic community in which
they occur. The species has been identified as a grazer in the benthos, associated
with Macrocystis pyrifera forests in Beagle Channel (Ojeda and Santelices 1984;
Vásquez et al. 1984; Adami and Gordillo 1999), and as a secondary consumer in
circalittoral mussel banks, feeding on barnacles, polychaetes, bivalve recruits,
small gastropods and crustaceans (Penchaszadeh 1979). It can also feed on drifting
or detached algae (Castilla and Moreno 1982; Penchaszadeh et al. 2004).
According to Penchaszadeh et al. (2004) this species can play an important role in
the community structure of the circalittoral beds of Mytilus edulis platensis,
mainly through intense predation on bivalve spat.
Due to the invasion of the kelp Undaria pinnatifida in Argentine Patagonia, the
potential role of invertebrate grazers, such as the sea urchins P. magellanicus and
A. dufresnii were preliminarily analyzed by Teso et al. (2009). They found that
both species of sea urchins fed on the alga at a low rate. In this context, they are
unlikely to play a role in the control of the seaweed because of the high rates of
recruitment and growth of U. pinnatifida.
The edible sea urchin Loxechinus albus has a wide geographic distribution
along the Pacific coast, from Ecuador (6°S) to south of TF including the Magellan
Strait and Beagle Channel (BC) (Bernasconi 1947, 1953) and Malvinas Islands
(Schuhbauer et al. 2010). Growth was analysed by Schuhbauer et al. (2010) in the
Malvinas Islands and growth curves were found to be asymptotic with the von
Bertalanffy growth model as the best predictor. The authors argue that the relatively short period of optimal water temperatures limited this species’ final size
compared to populations in regions with higher seasonal temperatures (e.g. central
Chilean coasts). Reproductive aspects of L. albus populations have been studied
along the Chilean Pacific coast (Gutiérrez and Otsú 1975; Zamora and Stotz 1992),
in the Magellanic region (Bay-Schmith et al. 1981; Oyarzún et al. 1999), in the
Beagle Channel (Orler 1992; Pérez et al. 2008, 2010, 2009) and at the Malvinas
Islands (Schuhbauer et al. 2010). The BC population of L. albus represents the
southernmost limit of distribution. There it is exposed to strong variations in
photoperiod, temperature, and marked seasonal fluctuations in primary productivity (Hernando 2006). In BC, a major peak of gonadal index occurred in winter,
followed by spawning in spring. A minor gonadal index peak occurred in autumn,
11 Echinoderms from Argentina
377
A new gametic proliferation may occur during the spring with subsequent partial
spawning in the summer (Orler 1992). At NG a main spawning event occurrs in
winter and a second minor event during the summer (Marzinelli et al. 2006). The
gonad index at NG was negatively correlated with photoperiod and water temperature with a lag period of 3 mo. Egg strain values are high in eggs spawned
by small individuals. According to Marzinelli et al. (2006) the jelly coat of eggs of
P. magellanicus may protect them from the forces experienced during spawning,
thus allowing reproductive success.
Diet was studied by Penchaszadeh et al. (2004). The authors suggested an
omnivorous behaviour related to different ecological conditions. The diet spectrum
of P. magellanicus depends mostly on the habitat and biotic community in which
they occur. The species has been identified as a grazer in the benthos, associated
with Macrocystis pyrifera forests in Beagle Channel (Ojeda and Santelices 1984;
Vásquez et al. 1984; Adami and Gordillo 1999), and as a secondary consumer in
circalittoral mussel banks, feeding on barnacles, polychaetes, bivalve recruits,
small gastropods and crustaceans (Penchaszadeh 1979). It can also feed on drifting
or detached algae (Castilla and Moreno 1982; Penchaszadeh et al. 2004).
According to Penchaszadeh et al. (2004) this species can play an important role in
the community structure of the circalittoral beds of Mytilus edulis platensis,
mainly through intense predation on bivalve spat.
Due to the invasion of the kelp Undaria pinnatifida in Argentine Patagonia, the
potential role of invertebrate grazers, such as the sea urchins P. magellanicus and
A. dufresnii were preliminarily analyzed by Teso et al. (2009). They found that
both species of sea urchins fed on the alga at a low rate. In this context, they are
unlikely to play a role in the control of the seaweed because of the high rates of
recruitment and growth of U. pinnatifida.
The edible sea urchin Loxechinus albus has a wide geographic distribution
along the Pacific coast, from Ecuador (6°S) to south of TF including the Magellan
Strait and Beagle Channel (BC) (Bernasconi 1947, 1953) and Malvinas Islands
(Schuhbauer et al. 2010). Growth was analysed by Schuhbauer et al. (2010) in the
Malvinas Islands and growth curves were found to be asymptotic with the von
Bertalanffy growth model as the best predictor. The authors argue that the relatively short period of optimal water temperatures limited this species’ final size
compared to populations in regions with higher seasonal temperatures (e.g. central
Chilean coasts). Reproductive aspects of L. albus populations have been studied
along the Chilean Pacific coast (Gutiérrez and Otsú 1975; Zamora and Stotz 1992),
in the Magellanic region (Bay-Schmith et al. 1981; Oyarzún et al. 1999), in the
Beagle Channel (Orler 1992; Pérez et al. 2008, 2010, 2009) and at the Malvinas
Islands (Schuhbauer et al. 2010). The BC population of L. albus represents the
southernmost limit of distribution. There it is exposed to strong variations in
photoperiod, temperature, and marked seasonal fluctuations in primary productivity (Hernando 2006). In BC, a major peak of gonadal index occurred in winter,
followed by spawning in spring. A minor gonadal index peak occurred in autumn,
11 Echinoderms from Argentina
377