Rasprostranjenost i biometrijska obilježja hridinskog (Paracentrotus lividus (Lamarck, 1816)) i crnog ježinca (Arbacia lixula (Linnaeus, 1758)) uz istočnu obalu otoka Cresa

Urchins (Echinoidea) are distributed all over the oceans and just in the Adriatic Sea there are 20 species. From the group of Regularia, most common in the Adriatic Sea are purple sea urchin Paracentrotus lividus (Lamarck, 1816) and black sea urchin Arbacia lixula (Linnaeus, 1758). Purple sea urchin inhabits shallow infralittoral, vegetation-covered sea bottom. Black sea urchin inhabits infralittoral zone at depths up to 50 meters attached on the hard sea bottom. In this research, on locations on the Island of Cres, sea urchins were photodocumented on depths close to 3 meters. Two found species ware analysed and their biometrical characteristics were measured. The results have shown that purple sea urchin is more frequent species. Analysis of the results on frequency, density and biometrical characteristics of sea urchins has given a view in reasons why certain species are more abundant than other in certain locations. Environmental conditions determine the distribution, abundance and biometrical characteristics of sea urchins.