The reproductive strategies of the sea urchin, Paracentrotus lividus, were studied in the Bay of Tunis.
Samples were collected monthly, from September 1993 to August 1995, in two sites which differ in their
marine vegetation and their exposure to wave action. Histological examination demonstrated a cycle of
gametogenesis with six reproductive stages and a main breeding period occurring between April and
June. Gonad indices varied between sites and years, the sheltered site presenting a higher investment in
reproduction.This difference was essentially induced by the largest sea urchins (above 40 mm in diameter).
Repletion indices showed a clear pattern without difference between sites and years. The sea urchin
increase in feeding activity was controlled by the need to allocate nutrient to the gonad during the
mature stage. But the gonad investment was not correlated with the intensity of food intake. Hydrodynamic
conditions might play a key role in diverting energy to the maintenance in an exposed
environment at the expense of reproduction.