Figure 8. Le Roux et al 1990.
| Index | Europe | East N. America |
| West N. America | Other Invasions | Conclusions |
| Bibliography | Characteristics | Megan McCormick 1999 |
C. maenas has been established in Australia since at least 1900 (Le Roux et al. 1990). In 1900, it was reported as 'plentifully distributed' in Port Phillip, Victoria (Cohen et al. 1995). Its current range includes New South Wales, Victoria, and South Australia (Le Roux et al. 1990). The crab is localized to a few small areas that have favorable habitat, and it was thought that no further dispersal would occur, due to unsuitable habitats along the coast. In Australia, the crab is found in bay and estuarine mudflats, among seagrasses, or occasionally in weedy regions of rocky platforms (Museum Victoria 1999). The latest movement was to South Australia, where its presence was noted in and around Port Adelaide in 1978. Ballast water transport was implicated in a few instances of dispersal, but with the discovery in 1986 of a specimen in the Coorong, predictions of no further dispersal proved inaccurate (Zeidler 1988).
The first known record of C. maenas in South Africa is in 1983, in Cape Town (Le Roux et al. 1990). By 1990, the range had expanded at least 100 km. 1992 estimates place the range from Saldanha Bay to Camps Bay. The rate of expansion has been calculated at 16 km/year (Grosholz and Ruiz 1996). In Africa, specimens aren't found on exposed shores (Le Roux et al. 1990). Breeding populations were established by 1984 (Griffiths et al. 1992), and females with eggs are found from July to November. It is interesting that the crabs are reproducing at roughly the same time as their European counterparts, even with the reversal of seasonality in South Africa (Le Roux et al. 1990).
The diet of the crab mostly consists of gastropods, isopods and polychaetes. The younger animals appear to be eating smaller, more readily available prey on the mussel beds, while the larger animals are eating the bivalves themselves. Mussels were surprisingly not found in gut content analysis, but it may be due to the fact that large specimens of Aulacomya ater and Choromytilus meridionalis appear to be invulnerable to attack (Le Roux et al. 1990). For this reason, there is little worry about the effects of the crab on these two populations.
Consistent with European behavior, the crab refuses to eat the native sea urchin Paraechinus angulosus, even when it is the only prey present. The feeding behaviors and preferences don't seem to overlap with that of the native crabs, so competition with native crustaceans isn't an area of great concern (Grosholz and Ruiz 1996).
The wave beaten nature of most of the South African coast has probably limited the crab's range expansion (Le Roux et al. 1990). This may help limit the impact on native communities. Areas of concern include predation on gastropods. Native species Oxystele variegata and Oxystele tigrina were both highly vulnerable to crab predation in lab experiments. The crab appears to have different diet preferences than the two native crab species it may interact with. The shore crab Cyclograpsus punctatus is largely herbivorous. The Cape rock crab Plagusia chabrus is broadly herbivorous. Habitat preferences also differ: C. punctatus is most abundant in the mid to upper high intertidal, and P. chabrus is usually found clinging to rocks subtidally or low on the shore (Griffiths et al. 1992).
The spread of the crab to Saldanha Bay is of particular concern, as it is an important center of mariculture (Griffiths et al 1992).
Other areas where possible invasions have occurred include Brazil, the Bay of Panama, Hawaii, Ceylon, Madagascar (Le Roux et al. 1990), Burma (Cohen et al. 1995), and Japan (Lafferty and Kuris 1996). These areas have yet to report a breeding population. Hawaii is particulary vulnerable to invasions due to shipping, because of its reliance on shipping for trade, the high volume of dry bulk imports, and the wide geographic spread of its receiving ports (Cullins 1997).
One method of control is to introduce a known predator or parasite. However, the introduction of yet another species must be considered carefully, as once it is done, it is irreversible. While it may prove to be an effective means of controlling the population, it can also have disastrous effects. The introduction of the mongoose to Hawaii to control rats wiped out ground dwelling birds instead (Tangley 1998). Several options for controlling C. maenas exist, such as the nemertean egg predator Carcinonemertes epialti, which infects Hemigrapsus oregonensis, and is already available in San Francisco. However, because of this possible cross infection, this is not a viable option for the U.S. west coast (Lafferty and Kuris 1996). Another option is the barnacle Sacculina carcini, which is specific to Carcinus (Lafferty and Kuris 1996). S. carcini is known as a parasitic castrator, because it makes the host sterile by attaching to the gonads and using them to incubate its own offspring (Tangley 1998).
Another method to control the population is to introduce a fishery. In Japan, the Mediterranean version of the crab is commonly used in soups, and has not become a pest in the area (Lafferty and Kuris 1996). The crabs are commonly used for bait in Europe and the American East Coast.
A further method of control is to prevent the introduction entirely. One of the most effective ways to do this is to monitor ballast water. A common way to prevent ballast water introduction is to exchange ballast water on the open ocean. Exchanging ballast water only in port allows the movement of shallow water species into a similar environment but in a different place. This can be bypassed by exchanging port water into the open sea, and vice versa. Most open ocean species are unique to the high seas and can't survive in coastal environments (Cullins 1997). If open water species are present in the ballast, it is then acceptable to exchange the water in port, as none of the species contained within will survive. Disinfect processes using ozone, ultraviolet light, or filtration are also used for ballast water control (Cullins 1997).