Painted topshell

The Painted topshell (Calliostoma zizyphinum) is a gastropod mollusk belonging to the order Trochida and the family Calliostomatidae. While primarily known as a marine gastropod, it can occasionally act as a nuisance in marine aquaculture environments, where it consumes commercial species of algae and sessile organisms.

In its natural habitat, the mollusk feeds on a variety of microalgae and organic debris. However, in controlled cultivation systems for seaweed, this species may cause significant damage by grazing on young shoots. Their feeding preference for soft algae tissue makes them a potential threat to nursery-stage aquatic plants that lack mature cell walls for protection.

The life cycle of Calliostoma zizyphinum involves a reproductive phase where eggs are deposited on rocky substrates. The resulting larvae are planktonic, allowing for widespread dispersal across coastal waters. Once settled, they develop into their characteristic conical shells and begin feeding on available vegetation, often colonizing infrastructure in aquaculture zones.

Damage caused by this mollusk is primarily physical, resulting from the use of the radula to scrape away plant tissue. This behavior compromises the integrity of the algae, leading to necrotic spots and stunted development. If the population density is high, the cumulative loss of biomass can be detrimental to the farm's total yield.

Management strategies focus on physical intervention and habitat manipulation. Regular manual inspection and removal of individuals from cultivation ropes are the most common practices. Furthermore, employing fine-mesh netting can help prevent the entry of larvae and juveniles into protected growing areas, ensuring that the crop remains free from biological interference.