Control of the herbivorous gastropod Fissurella mutabilis (Sow.) in a land-based integrated abalone–seaweed culture

High quantities of macrofauna pests in aquaculture systems can result in decreased production of target species. Methods for controlling outbreaks of the Cape keyhole limpet Fissurella mutabilis in integrated abalone–seaweed cultures were investigated. Limpets were exposed to freshwater and CO2 saturated seawater in the laboratory for different periods of time. The exposure times to freshwater (0.32 psu) and hypoxia (DO ≤ 0.1 mg L− 1) that killed 90% of F. mutabilis were 142 (95% CI: 134, 152) and 154 min (95% CI: 138, 180), respectively. A freshwater treatment of > 200 min resulted in 100% mortality, while at the maximum exposure time of the CO2/hypoxia experiment (180 min) the observed mortality was < 100%. In accordance with other studies, freshwater is suggested to be a suitable treatment for different types of pests in macroalgae cultivation systems. It killed off F. mutabilis within treatment times suggested to have minor impacts on the cultivated Ulva spp. (Chloropyta) and previously shown to not have significant effects on the production of Gracilaria gracilis (Rhodophyta). A CO2/hypoxia treatment can alternatively be used to control macrofauna pests, especially in areas where freshwater is limited.