Establishment and presumed causes of the trimodal distribution commonly observed in cultivated populations of juvenile Paracentrotus lividus

Multimodal distribution (i.e.: few individuals growing very fast and few individuals growing very slowly among an originally homogeneous group of sea-urchins P. lividus of the same strain) is often observed in controlled cultivation. The splitting of this group into homogeneous size-classed subgroups induces an increased growth of the smaller individuals that achieve the same size than the others in 3 months. This indicates that the smaller animals are not genetically less productive and suggests they are inhibited in their growth due to some environmental constraints.