Effect of limpets on the fouling of ships in the Mediterranean

Limpets reduce the cover of algae and barnacles on intertidal rocks, but do not inhabit ship-fouling communities. Patella caerulea (L.) from Israeli Mediterranean shores were successfully transplanted onto 20x20 cm initially non-fouled steel panels in 1983–1984, hung vertically in a commercial port at depths of 1 and 5.5 m. The limpets (15 individuals of ca 20 to 25 cm in length on each panel) controlled the fouling organisms that settled on the panels throughout a month of lowest settlement (December) and throughout a month of highest settlement (August). After 7 d of immersion the limpets restricted the total cover of fouling organisms from 2.4 and 4.8% to 0.6 and 0.2% (at 1 and 5.5 m depths, respectively), and brought down the barnacle density from 1.2 and 2.6 to 0.3 and 0.4 individuals per cm² (at 1 and 5.5 m depth, respectively). After 26 d the equivalent figures were a cover of 72 and 92% reduced to 14 and 9% and a density of 2.9 and 1.1 reduced to 0.3 and 0.2 individuals per cm². The limpets presumably achieved this by preventing the attachment of propagules and by removing already settled organisms through their movements during grazing excursions.