Larval development of Arbacia lixula (Linneo, 1758) in two Marine Protected Area: preliminary data.

The sea urchin Arbacia lixula is a crucial species in driving the algal assemblages dynamic of the infralittoral zone. A. lixula is considered a thermophilic species and its increase in abundance in western Mediterranean waters, probably is due to an increase in seawater temperature. The aim of this study was to examine the reproductive success of A. lixula by larval development. The study was conducted within two Sicilian MPA (Capo Gallo-Isola delle Femmine and Ustica), characterized by photophilic algae, the same exposure and seawater temperature. In each area, twenty random specimens was sampled from May to September 2010, and mature gametes were collected from six males and six females to prepare embryos reared in experimental conditions. The larvae were monitored for 48h after the fertilization to assess the different stages and times of development. Our results showed a different larval development within two MPA, in time and quality of embryos. The samples from Ustica had a slower developmental rate and a higher mortality than samples from Capo Gallo. We hypothesize that in Ustica, A. lixula allocates almost resources into body components (Aristotele’s lantern) affecting reproductive success, than in Capo Gallo, probably due to an intra-specific competition relative to others factors here not investigated