Stock evaluation of three littoral echinoid species on the Catalan coast (North-Western Mediterranean)

We estimated the abundances of the three common littoral echinoid species P aracentrotus lividus, Arbacia lixula and Sphaerechinus granularis is in a l ittoral zone (between 0 and 10 m depth) on the Catalan shores (NE Spain). D ensities of each species were estimated from a total number of 11 571 x 1 m (2) sampling units deployed at 152 sites along the 13 zones into which the coast was divided. The surface area available in each of these zones was es timated at the scale of the sampling unit (1 m(2)) taking into account the fractal dimension of the shore. The stocks (individuals > 2 cm test diamete r) of these species for the whole Catalan shore (approximate to 300 km. str aight-line distance) were estimated to be about 279.1 x 10(6) individuals f or P. lividus, 25.9 x 10(6) individuals for A. lixula and 10.9 x 10(6) indi viduals for S. granularis. These sea-urchins are key species in the regulat ion of algal communities and some of them (P. lividus, S. granularis) are o f commercial interest. This information will provide a tool for the future monitoring and management of this resource, which now faces diverse pressur es of human origin.