The impact of commercial and recreational harvesting for Paracentrotus lividus on shallow rocky reef sea urchin communities in North-western Sardinia, Italy

The fishery for the edible sea urchin Paracentrotus lividus is of great importance to many European regions, although in some of them this
species has shown a wide scale decline in recent years. This paper reports on direct (on P. lividus) and indirect (on the co-occurring but not fished
echinoid, Arbacia lixula) effects of sea urchin harvesting in shallow rocky reefs in North-western Sardinia (Italy, central-western Mediterranean
Sea), where this activity is intensively practised. Density, size (test diameter), and biomass of both species were assessed in autumn 2004 at two
locations impacted by P. lividus fishery, and at two controls within an adjacent Marine Protected Area. Density of P. lividus and A. lixula was
significantly greater at the controls than at the exploited locations. The average test diameter of P. lividus was also significantly larger at the
controls, where large-sized specimens (i.e. >5 cm) were notably more abundant. The average size of A. lixula did not significantly differ between
the impacted locations and the controls. The average biomass of P. lividus was significantly greater at the controls than at the exploited locations,
whereas no differences were detected for A. lixula. These results reveal the existence of a heavy fishing impact on P. lividus in North-western
Sardinia and the need for regulation of its harvesting to prevent severe direct effects on its populations. Since no indirect effects on A. lixula have
been detected, it could be hypothesized that this species did not benefit from P. lividus fishery due to an only moderate competition for habitat
and resources between these two echinoids. Implications for management of edible sea urchin fishery are also discussed.