2,4-Decadienal: Exploring a novel approach for the control of polychaete pests on cultured abalone

Infestations by shell-boring polychaete worms represent a threat to the continued growth of the abalone culture industry. The South African cultivated abalone, Haliotis midae, is affected by 3 species; the spionids Boccardia proboscidea and Polydora hoplura and the sabellid, Terebrasabella heterouncinata. Currently there are no effective treatments that do not cause undue harm to the abalone host while proving effective against the worms. Here we report on the efficacy of the diatom-derived polyunsaturated aldehyde 2,4-decadienal as a potential chemotherapeutic agent against shell-infesting polychaetes. Exposure to decadienal had pronounced dose- and time-dependent negative effects on larval mortality, growth and developmental rate. There was a variation in the response to treatment in relation to larval strategy, with planktotrophic B. proboscidea larvae more susceptible than adelphophagic larvae, and species, with lecithotrophic T. heterouncinata generally more sensitive than planktotrophic B. proboscidea larvae. Emergent larvae were more susceptible than encapsulated larvae. The egg capsule appears to provide an effective barrier to decadienal exposure. Decadienal could therefore prove effective as a control agent at several life history stages by reducing the number of larvae that survive and are able to settle, and also the fitness of the larvae that do survive and settle.