A study was conducted on the population of Paracentrotus lividus (Lamarck, 1816) in a Mediterranean infralittoral bottom of southern of Spain to characterize the relationships between the macroalgal food ingested and the gut and gonad conditions of individuals. Over a full annual cycle (November 2008 to October 2009) composition of the gut content was analyzed monthly and seasonally, the gastrointestinal (GII), repletion (RI) and gonadosomatic (gonad) (GI) indices were calculated, and the stage of gonad maturity of the population was assessed. The GII and RI were found to be strongly correlated, so only the RI was considered in the subsequent analysis. The prevalence of Phaeophyceae and local species of this macroalgal group in the gut content of the sea urchins throughout the year suggests that in conditions of abundant resources, with high levels of algal diversity and no effective limits on supply, brown algae are the main component of the natural diet of P. lividus. Comparison of the physiological indices and the algal fractions of gut content identified relationships throughout the year between RI, the stage of gonad maturity and GI. Specifically, these indices were found to be associated with the abundance of Rhodophyta ingested, although in different ways: GI was related to the consumption of fleshy (non-calcified) red algae and the RI, though less statistically significantly, to the consumption of calcified (articulate and encrusting).

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