ABSTRACT
The seagrass Posidonia oceanica is an important primary producer in the mediterranean sea with large production rates and a high biomass. Sea urchins, the most important macroconsumers of that seagrass, showed strong feeding preferences among different parts of the plant, as well as between Posidonia and epiphytic algae. The consumption rates of the sea urchins and the quota of Posidonia in their gut contents has been measured, particle size and number of torn off blades were investigated, in order to obtain the factor of the plant materials physical de gradation, caused by the sea urchins. Some time after egestion, the sea urchins faeces become strongly overgrown by microorganisms and serve as a food resource for a number of small crustaceans (harpacticids, isopods, amphipods ) and holothurians.
