Effects of microhabitat on shell form, density and size structure of the limpet Cellana capensis (family Nacellidae) on South African rocky shores

Abstract

Rocky intertidal habitats are considered extreme environments, alternately exposed to air during low tide and then submerged during high tide. Among the organisms that thrive in these conditions is the Cape variable limpet Cellana capensis, which has developed various adaptations to endure the constantly shifting environment, including alterations in shell morphology. This study investigated the shell dimensions of C. capensis residing on emergent rocks versus those in rock pools, and estimated the mean density and mean shell length of C. capensis in these distinct microhabitats to better understand their local distribution pattern. Sampling took place at Dwesa-Cwebe Nature Reserve in the Transkei region of South Africa, during spring low tides, quarterly, from April 2010 to May 2011. Within the mid-intertidal zone, three sites were randomly selected, each located ∼100 m apart; at each site, four rock pools and four adjacent emergent rocks were examined. The linear regression results indicated significant differences in shell shape between the two microhabitats: shells from rock pools were taller and narrower, while those from emergent rocks were flatter and wider. The density of C. capensis was significantly higher in rock pools than on emergent rocks, peaking in autumn and reaching the lowest density in summer. Conversely, C. capensis in rock pools had a significantly smaller mean shell length than those on emergent rocks; the largest sizes were recorded in summer and the smallest in winter. These findings suggest that the microhabitat type on rocky shores could influence limpet abundance and shell form.