EXPERIMENTAL-STUDY OF GROWTH IN THE ECHINOID PARACENTROTUS-LIVIDUS (LAMARCK, 1816) (ECHINODERMATA)

Multimodal size frequency distribution (i.e., a few individuals growin g very fast and a few individuals growing very slowly) among an origin ally homogeneous cohort of juveniles Paracentrotus lividus is observed in reared conditions when they are 6-24 months old, The splitting of this cohort into homogeneous size-classed subgroups results in an incr eased growth of the smaller animals that catch up with the bigger ones in 4 months time. This indicates that the smaller animals are not gen etically less productive and suggests they were inhibited in their gro wth due to the presence of larger ones. Supposing such growth inhibiti on also occurs in the natural environment, the observed mechanism coul d be very efficient in stabilizing field populations of aggregative ec hinoid species by maintaining a protected pool of small individuals wi th high growth potential but inhibited by the density of larger ones.