Life-history patterns of populations of the limpet Patella granularis: the dominant roles of food supply and mortality rate

Population Characteristics of the Limpet Patella caerulea (Linnaeus, 1758) in Eastern Mediterranean (Central Greece)

Limpets are pivotal for structuring and regulating the ecological balance of littoral communities and are widely collected for human consumption and as fishing bait. Limpets of the species Patella caerulea were collected between April 2016 and April 2017 from two sites, and two samplings per each site with varying degree of exposure to wave action and anthropogenic pressure, in Eastern Mediterranean (Pagasitikos Gulf, Central Greece). This study addresses a knowledge gap on population characteristics of P. caerulea populations in Eastern Mediterranean, assesses population structure, allometric relationships, and reproductive status. Morphometric characteristics exhibited spatio-temporal variation. Population density was significantly higher at the exposed site. Spatial relationship between members of the population exhibited clumped pattern of dispersion during spring. Broadcast spawning of the population occurred during summer. Seven dominant age groups were identified, with the dominant cohort in the third-year class. Significant negative allometric relationships were exhibited between morphometric characteristics. Differences in growth patterns among populations were indicated.

Food supply, grazing activity and growth rate in the limpet Patella vulgata L.: a comparison between exposed and sheltered shores

The limpet Patella vulgata L. is an important microphagous grazer on intertidal rocky shores of north-west Europe, occurring across the wave exposure gradient. Groups of P. vulgata were selected at mid-tide level of two exposed shores and two sheltered, fucoid dominated shores on the Isle of Man, British Isles, and manipulated to equivalent densities and population structure. The level of grazing activity and growth rate were determined over a 1-year period. At the same time, the abundance of epilithic microalgae, measured as the concentration of chlorophyll a, was determined as an estimate of food supply. Microagal abundance showed a seasonal pattern in both exposed and sheltered conditions, with higher levels in winter compared to summer. In both seasons, the microalgal resource was more abundant on the sheltered shore studied. The level of grazing activity in P. vulgata showed a seasonal pattern on the exposed but not the sheltered shores. Averaged over the year, grazing activity on the exposed shores was over double that on sheltered shores. Thus, in sheltered conditions, food supply for limpets was high and grazing activity low; in exposed conditions, food supply was low and grazing activity high. The growth rate of P. vulgata, measured as increase in shell length, showed no significant difference between exposed and sheltered shores. Growth rate was also determined in P. vulgata at natural densities. Although the overall density declined with decreasing exposure to wave action, the density per unit area of grazeable substance was higher in shelter. In these populations, the mean growth rate was over twice as high on exposed compared to sheltered shores.