Shape and growth in European Atlantic Patella limpets (Gastropoda, Mollusca). Ecological implications for survival

Abstract. Specimens of Patella intermedia, Patella rustica, Patella ulyssiponensis, and Patella vulgata were analyzed for shell and radula characteristics. Shell growth in P. rustica and P. ulyssiponensis was basically isometric, indicating that shell shape was constant during growth. On the contrary, shell growth in P. intermedia and P. vulgata was positively allometric, indicating that as shells increased in size, the base became more circular and the cone more centred and relatively higher. Radula relative size increased in the order P. ulyssiponensis, P. vulgata, P. intermedia and P. rustica, and had negative allometric growth in all species, indicating that radula grew less as shell increased in size. Data reported in the literature estimated that the lowest risk of dislodgment for a limpet is associated with a centred apex, and a (shell height)/(shell length) or (shell height)/(shell width) ratio of ca. 0.53. However, as reported for other limpets, in all four studied Patella species, shells were more eccentric and flat than this theoretical optimum. Data reported in the literature indicated that, in limpets, decreasing the (shell base perimeter)/(shell volume) or (shell surface area)/(shell volume) ratios by increasing size results in lower soft body temperature and desiccation. In the present study, P. rustica shells displayed the lowest ratios, and P. ulyssiponensis shells, the highest. Considering that the former species lives at high shore levels, and the latter species at low levels, it appeared that shell shape in European Atlantic limpets can be directly related to resistance to desiccation and high temperature stresses. Radula relative size (in relation to shell height) also increased with increasing level in the shore, suggesting that this might be due to a decreasing abundance of algae with increasing shore level.