Comparative Temporal Analysis of Demographic and Morphometric Traits in Patella ferruginea

This study presents the results of monitoring the endangered gastropod Patella ferruginea within a Marine Protected Area in Sardinia. A detailed map of the species distribution was created, and individual density and population structure were analysed by comparing data collected during monitoring campaigns in 2014, 2018, and 2023. A total of 206, 203, and 109 individuals were recorded in 2014, 2018, and 2023, respectively. In 2014 and 2018, 24 and 26 specimens with a maximum diameter of ≥6 cm were observed, while in 2023, only 11 individuals reached this size, with a single specimen measuring 6.5 cm. Linear density showed an average reduction of approximately 37% in the latest campaign compared to the previous one. The coastline under analysis was divided into five sectors based on the degree of protection and exposure to prevailing winds. The overall decline of approximately 50% in the population indicates a decrease affecting all size classes, although it is more pronounced in the larger size classes. Furthermore, analyses of spatial structure using the Minimum Spanning Tree (MST), Clark and Evans’ R index, and Nearest Neighbour Distance (NND) indicate a dispersed distribution already in 2018, which became more pronounced in 2023. These results indicate that current protection measures within the MPA may not be sufficient to ensure long-term population stability, suggesting that conservation strategies for this species should be assessed on a site-specific basis.