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| Safety and Efficacy of Green Crab Biological Control | |
| The European green crab has invaded the East Coast, USA; and West Coast, Australia (both Victoria and Tasmania) and South Africa. In these areas, it may reach pest status, decimating shellfish populations and altering natural ecosystems. To understand the reasons behind the introduced crab's enhanced performance, Dr. Kevin Lafferty of USGS is working with Dr. Armand Kuris, Dr. Jeff Goddard and Mark Torchin of the University of California, Santa Barbara, to compare population abundance, body size, rates of predation and parasitism between introduced and native green crabs. |  |
| The researchers have now extensively sampled green crab populations throughout their native and introduced ranges. In Europe, the crabs are small and less abundant in areas where they are infected by a parasitic barnacle (Sacculina carcini) that castrates infected crabs for life. Green crabs are not infected by parasitic barnacles where the crabs were introduced. In these areas, green crabs are larger and more abundant than they are in Europe, suggesting that their spectacular success in introduced regions is due to release from parasitic barnacles. This supports the proposition that biological control (by introducing parasitic barnacles to areas where the crab is a pest) may be a feasible means to reduce the impacts. Although biological control is commonly used to combat insect pests and weeds, it has never been used against a marine pest. |
| There are two scientific questions that must be addressed before embarking on a biological control program. The first is whether or not the agent is likely to control the pest. Because there was no information on parasitic castrators from traditional biological control studies, Dr. Lafferty analyzed data from field studies and developed mathematical models. Both efforts suggest that a parasitic castrator can impact its host population under a wide range of conditions. The second question, and the more important one, is whether or not the biological control agent will be safe. In other words, if introduced, will this parasitic barnacle impact other native or commerically important species? |
| Although Sacculina carcini appeared to be very host specific, the scientists conducted laboratory infection trials with a number of native Californian crabs to be sure. They first learned how to infect green crabs with the barnacle and watch it complete its development. When presented with Californian crabs, however, the barnacle was unable to complete development. Unfortunately, the barnacle was able to penetrate Californian crabs. In many cases, the Californian crabs could not mount a successful defense and died as a result of the infection. |
| Even though the researchers suspect that these results are partly a consequence of conducting experiments in the laboratory (where it is easy for barnacle larvae to encounter Californian crabs they might not normally be able to locate), their conservative concerns about safety cause them to question the suitability of the parasitic barnacle as a biological control agent for the introduced European green crab. A few other possible control agents exist in Europe and the researchers will be turning their attention to these in future studies. |
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