Population ecology ofGibbula umbilicarisandGibbula ardens(Gastropoda: Trochidae) in aPosidonia oceanicaseagrass bed

Population structures of the gastropods Gibbula umbilicaris and Gibbula ardens (Trochidae), the two most common species of the genus Gibbula living in shallow beds of the Mediterranean seagrass Posidonia oceanica, were investigated in the seagrass bed off Lacco Ameno of Ischia (Gulf of Naples), at six stations along a depth gradient (1, 3, 5, 10, 15 and 25 m). Sampling was performed on a monthly basis for 1 year. A total of 853 individuals were...