Growth model of the reared sea urchin Paracentrotus ... - SciViews

General introduction
mm (Spirlet et al, 1994). P. lividus becomes mature when it reaches a test
diameter of 20 to 25 mm (Grosjean, pers. obs.).
Figure 5. Mature adult Paracentrotus lividus with oral region removed showing the five
gonads. The individual at the top is a male, the two others are females (gonads of brighter
color).
Like any echinoderm, sea urchins have a water-vascular system which
is used for locomotion. Tube feet (podia) elongate and retract and their
sucker-shaped tip can glue and unglue to the substratum (Flammang, 1996;
Flammang et al, 1998). Locomotion in any direction is sometimes aided by
the movements of spines. P. lividus exhibits a gregarious behavior and
lives in aggregates where small individuals tend to stay under larger ones
(including inside holes, for populations living in rocky shores). This
behavior was clearly identified as a protective mechanism against
predators (Tegner & Dayton, 1977). Many sea urchins species, including
P. lividus, also cover their exposed aboral surfaces with shells, stones, and
algae for camouflage (Crook et al, 1999; see also Fig. 1).
Echinoids are key-species in several ecosystems such as kelp forests,
barren grounds or Posidonia beds (Tegner & Dayton, 1981; Rowley, 1989;
Fernandez, 1996; Leinass & Christie, 1996). Emson (1984) suggested that
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