الفهرس 
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Abstract
Sea urchins (Echinodermata: Echinoidae) are key species in the littoral rocky reef of the Mediterranean Basin. The current study examines the sea urchin species composition, size structure off Alexandria city and their potential for aquaculture. A genetic analysis confirmed the identity of five color morphs of sea urchin on the coast of Alexandria to be the two species, Paracentrotus lividus, Lamarck, 1816, and Arbacia lixula, Linnaeus, 1758. Haplotype diversity was examined and the results showed that P. lividus has high haplotype diversity with low nucleotide diversity. P. lividus is the most dominant species in all the stations throughout the study period. The associated fauna and flora with the sea urchin population were recorded revealing many groups of different taxa. An induction and fertilization of P. lividus were carried out in laboratory. The resulting larvae were fed four algal diets comprising three uni-algal diets (D1 = Chaetoceros calcitrans, D2 = Nannochloropsis oculata and D3 = Tetraselmis suecica) and D4 = algal-mix, which is a mixture of the previous strains with equal ratio (1:1:1). The results of this experiment revealed that larval competence and metamorphosis was achieved in P. lividus with the four algal diets. However, the larvae fed the algal-mix diet showed a relatively better growth performance than the other three uni-algal diets.