Biological Control of the European Green Crab, Carcinus Maenas: Natural Enemy Evaluation and Analysis of Host Specificity

Many introduced marine organisms are ecological and economic pests. Nevertheless, no management approach is available to mitigate their impacts. Now, a theoretical perspective borrows principles from classical biological control, as widely applied to terrestrial and fresh water systems, to control the abundance of introduced marine pests. A banner example of a marine pest is the European green crab, Carcinus maenas (L.) (Brachyura: Cancridae). This crab invaded San Francisco Bay in the late 1980s and has expanded its geographic range at a record rate. Studies on the Pacific coast of the U.S.A. and elsewhere strongly indicate that it is a worst-case introduction, affecting native organisms and potentially harming fisheries and aquaculture. Extensive studies show that a significant element of its success, where introduced, has been release from its natural enemies, notably parasites. Natural enemies are infectious agents with potential to contribute to green crab biological control include two parasitic castrators: Sacculina carcini Thompson (Rhizocephala: Sacculinidae) and, Portunion maenadis Giard (Isopoda: Entoniscidae), the parasitoid flatworm, Fecampia erythrocephala Giard (Fecampiida: Fecampiidae), and the symbiotic nemertean egg predator, Carcinonemertes carcinophila (Kolliker) (Hoplonemertea: Carcinonemertidae). Evidence for their potential efficacy derives from quantitative natural history studies and ecological modeling. Their safety with respect to non-target organisms is of great concern. Relevant information is available from qualitative field studies, host specificity experimentation, evolutionary theory, and the ability to detect and estimate the frequency of unsuccessful parasite attack rates in natural populations. _______________________________________________ Biological Control of the European Green Crab Second International Symposium on Biological Control of Arthropods 103 We interpret host specificity in the context of the double filter paradigm of Combes (2001). For a host to be suitable, two filters must be partially open. When the encounter filter is open, the infective stage can locate and enter the host because it shares the appropriate habitat and has suitable host location and attack behaviors. For the parasite to be successful, the compatibility filter must also be partially open. This occurs if the host provides appropriate nutrition and its defensive mechanisms cannot kill nor block reproduction of the infectious agent. For both rhizocephalan barnacles and entoniscid isopods in native (coevolved) regions, potential alternative hosts appear to be protected via inability to encounter the host, or due to incompatibility, or both filters are closed. Naïve hosts from an introduced area are located under permissive encounter experimental conditions, but the compatibility filter is closed.