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Home , Carcinus, Carcinus aestuarii, Carcinus maenas, Hemigrapsus oregonensis, Portunidae

Pacific Northwest aquatic invasive profile:

the European green , maenas (Linnaeus, 1758)

Joseph J. Bizzarro

December 20, 2009

BC Growers Association Figure 1. Dorsal and ventral (male at left, female at right) views of the European green crab, .

www.biolib.cz McDonald 2006 Jenson 1995 Behrens–Yamada 2001 Figure 2. Color morphs of the European green crab, Carcinus maenas. Diagnostic Information 2). Green and red crabs can be found in Scientific name all size classes, but the relative proportion of red Order: Latreille, crabs increases dramatically at sizes > 50–60 1802 mm carapace width (CW) (Wolf 1998; Family: Rafinesque, Styrishave et al. 2004). Ventral coloration may 1815 be shades of yellow, light green, orange, or red /Species: Carcinus maenas (Behrens–Yamada 2001; Fig. 2). (Linnaeus, 1758)

Common names: European green crab, European shore crab, green shore crab, green crab, shore crab, Joe rocker

Basic identification key The European green crab, Carcinus maenas (Fig. 1), is placed within the Figure 3. Diagnostic information used to identify the order Decapoda, a well–studied group that European green crab. Note: shell width and coloration includes many commercially important species information indicate typical conditions, but larger of crabs, lobsters, and shrimps. Within the sizes and a range of colors have been reported (image decapods, C. maenas is considered a true crab of courtesy of New South Wales Government). the Infraorder Brachyura and placed in family Regardless of its highly variable coloration, C. the Portunidae, the swimming crabs (Martin and maenas is easily identified from other Pacific Davis 2001). Only two species of Carcinus are Northwest (PNW) species by meristic counts currently recognized, C. maenas and the and morphology. It is the only PWN species closely–related Mediterranean shore crab, C. with five teeth, which are evenly spaced along aestuarii (Behrens–Yamada and Hauck 2001). each side of the anterior–lateral margins of the Although known as the European green crab, carapace (Behrens–Yamada, 2001; McDonald color is highly variable in this species and 2006; Fig. 3). This species also has three lobed, therefore a poor character for identification. frontal teeth between the eye stalks and a Individual dorsal coloration is typically mottled carapace that is nearly as long as it is wide and varies from light green/yellow to bright or (Behrens–Yamada and Hauck 2001). Among dark green, olive–brown, or red, with lighter and portunid crabs, C. maenas is somewhat more mottled coloration typical in small anomalous in morphology and behavior, in that specimens (Crothers 1968; McDonald 2006; Fig. it is adapted for walking rather than swimming. Although its fifth pair of legs are flattened, they are not nearly as flattened as those of other portunids and lack the typical portunid paddle– shape (Jenson 1995; Behrens–Yamada 2001; Fig. 3). Carcinus maenas reaches a maximum size of 100 mm CW, with males larger than females (< 79 mm CW; Behrens–Yamada et al. 2005). Figure 4. Carcinus maenas megalopae.

Life History and Basic Ecology After mating, a female can produce one or more broods. Eggs are fertilized as they descend the Life cycle reproductive tract, encased in a sticky Mating in C. maenas occurs membrane, and attached to the hairs of the immediately after adult females moult, typically pleopods where they engulf the abdomen to with males of larger sizes (Behrens–Yamada form a “sponge” (Fig. 4). The number of eggs 2001). In the Pacific Northwest, this commonly per brood increases with size of the female occurs during summer months. Prior to (Behrens–Yamada 2001), and > 185,000 eggs moulting, females release a powerful pheremone have been reported from a relatively small that attracts males (Bambler and Naylor 1997). female (Broekhuysen 1936). Brooding females An attracted male will grasp the female beneath migrate to deeper waters during winter months it and carry her in a precopulatory embrace for in the Pacific Northwest where salinity and two to sixteen days (Behrens–Yamada 2001). temperature are more stable and either hide in After the female moults, mating occurs during rocky structure or bury themselves in soft which the male injects sperm packets into the sediments (Dries and Adelung 1982). The paired gonopores of the female. Stored sperm duration of brooding is contingent on water can remain viable for up to a year (Behrens– temperature. Captive females kept at 12° in a Yamada 2001). Since copulation can take seawater tank in brooded eggs for just almost three days, the mating pair shelters over two months (Behrens–Yamada 2001). during this time. After copulation, the male During this time, they remove foreign materials continues to hold the female for a time period from the sponge and aerate the eggs with their ranging from less than a day (no other males pleopods. Hatching typically occurs at night at present) to more than two days (other males the ebb of a high tide so that the eggs are carried present) (Behrens–Yamada 2001). out to sea (Queiroga et al. 1994; Zeng and crabs stop feeding and seek shelter, and 10° C, when crabs stop molting (Ropes 1968; Eriksson and Edlund 1977). Water temperatures in the Pacific Northwest are typically > 10° C for most of the year, facilitating relatively rapid growth and development in this region (Table 1). Based on data collected in Oregon and during 1998, crabs grew to sizes of

Figure 5. Carcinus maenas with egg sponge. 32–60 mm DW at the onset of their first winter, during which growth stopped until May. By the Naylor 1996a). In the Pacific Northwest, onset of winter 1999, sizes ranged from 52–80 hatching usually occurs during winter months. mm CW (Behrens–Yamada et al. 2005), with There are six larval stages in C. maenas; one sizes 60–92 reported during winter 2000 extremely short protozoea stage, four zoea (Behrens–Yamada 2001). This facilitates very stages, and one megalopa stage (Fig. 5). Total short generation times in the Pacific Northwest, planktonic development is estimated at 62 days typically less than one year as compared to two at 12° and 32 days at 18° (Dawirs 1985). to three years in (Berrill 1982) Gravid Vertical migration to surface waters occurs early females may be observed in this region from 8– in the first zoeae stage, which facilitates 12 months/year (Behrens–Yamada et al. 2005). transport out to sea on the ebb tide (Queiroga et al. 1994). Conversely, late megalopa migrate to Feeding habits the surface just after a low tide and are carried Organisms from at least 104 families in shoreward on high flood tides (Zeng and Naylor 14 and 5 plant and protist phyla have 1996b). Settlement and metamorphosis of been recorded in the diet of C. maenas (Cohen et megalopae occurs in the upper tidal zone to al. 1995). This species is also cannibalistic, and ensure that new recruits are left in the intertidal small individuals can be an important food after the high tide recedes, as refuge against source for larger C. maenas (Moksnes et al. . Recruitment in the Pacific Northwest 1998). Although such a diverse diet would typically takes place during late winter and suggest an opportunistic feeding strategy, C. spring. maenas has been shown to select prey by size Growth rates are highly variable in C. maenas, and species in a substantial number of laboratory but conditions in the Pacific Northwest favor experiments (Cohen et al. 1995). Additionally, rapid growth compared to other regions (Table the diet of C. maenas has been shown to vary by 1). Key thresholds are reported at 7° C, when size, location, time of year, and occasionally sex Table 1. Comparison of life history characteristics of Carcinus maenas from different regions of the world (from Behrens–Yamada et al. 2005)

(Cohen et al. 1995; Behrens–Yamada et al. detecting moving prey (Hughes and Seed 1995). 2001). Therefore, this crab be characterized as Carcinus maenas commonly excavates buried having immense dietary plasticity, but exhibits bivalves and other infauna to depths of 15 cm specific prey preferences under different life deep (Smith and Chin 1951). These digging history and environmental conditions. A efforts can cause considerable environmental sampling of prey items include: bacteria and disturbance, and can substantially modify foraminiferans, carrion, snail eggs, marsh community structure (Congleton et al. 2005; vegetation, algae, , , Garbary and Miller 2006). insects, bivalves, gastropods, urchins, fishes, tunicates and jellyfishes. Carcinus maenas Reproductive strategies becomes more carnivorous with age and older, Male C. maenas exfhibit two different larger individuals show a strong preference for reproductive strategies, with trade offs in bivalves (Behrens–Yamada 2001). This species reproductive fitness and C. maenas, and is a voracious predator and has been shown to aggressive encounters are common among males consume up to 62.3 bivalves (19–23 mm) per (Styrishave et al. 2004). Long thought to be day in laboratory experiments (Palacois and simply a consequence of different intermoult Ferraro 2003). periods, the red and green coloration in male C. Carcinus maenas is thought to be mainly a maenas are now understood to infer tactile and chemosensory rather than visual considerable physiological and ecological predator (Cohen et al. 1995). Visual cues are differences (Reid et al. 1997; Wolf 1998). Red mainly limited to assessing prey size and males remain in intermoult for longer durations, intertidal regions, to changes in their surrounding environment, and to the effects of pollution (Reid et al. 1997; Styrishave et al. 2004).

Environmental optima and tolerance Carcinus maenas exhibits an extremely wide physiological tolerance of temperature but will only persist in a much more limited range. Adult C. maenas can tolerate temperatures between 0° C and 33° C (Eriksson et al. 1975). However, the minimum temperature needed for growth and molting is 10° C (Berrill 1982). Upper temperature limits are 18° C for brooding and 26° C for long–term survival. Therefore, for long term sustainability and population growth, optimal temperatures for C. maenas range from 10° C to 18° C (Behrens–Yamada 2001). Similarly, although adult C. maenas can tolerate a considerable ranges of salinities, optimum salinity conditions are much narrower. Carcinus maenas can survive at salinities ranging from 4‰ to 54‰ (Eriksson et al. 1975), but are much

Figure 6. Color–based mating trials (Reid et al. 1997). more affected by low salinities. The minimum salinity for long–term survival is 11‰ developing stronger, thicker carapaces and (Behrens–Yamada 2001). Additionally, there is chelae and routinely winning mating conflicts a trade–off between salinity and temperature over similarly–sized green males (Fig. 6). By tolerances. Carcinus maenas is also well exerting greater forces with their chelae, red adapted to low oxygen conditions and can males are also able to eat larger and higher survive at low tide in near anoxic tide pools quality prey organisms (Kaiser et al. 1990; Reid (Klein–Breteler 1981). et al. 1997). This advantage comes at the cost of Recruitment is an important part of the life reduced physiological tolerance, however. history of C. maenas and megalopae prefer to Green crabs are better adapted to living in recruit to protected upper–intertidal habitats (Behrens–Yamada 2001). New recruits are typically occupied during summer and of lowest typically found in sea grass bed, on filamentous abundance in winter (Aagaard et al. 1995). green algae, in muddy regions, along cord grass banks, in beds, and in gravel beds. Biotic associations Carcinus maenas does not typically recruit to Carcinus maenas has a variety of sandy habitats (Klein–Breteler, 1976). Mussel parasites and pathogens in its home range and in beds have been reported as optimum habitat for other invaded regions, but largely exhibits an recruits as they provide a natural refuge from enemy release in the Pacific Northwest (Torchin predators as well as abundant food resources et al. 2001). This is likely one of the reasons (Thiel and Dernedde 1994; Gunther, 1996). why C. maenas individuals in the Pacific However, it seems that survival of new recruits Northwest are largest recorded (McDonald is actually greater in filamentous algae, whereas 2006). In its native habitat, parasites include: predatory juvenile crabs move preferentially to the protozoan Thelothania maenadis, the mussel beds (Hedvall et al. 1998). flatworms Fecampia erythrocephala, Adult C. maenas are common in protected Microphallus similis and M. primas, the marine and estuarine habitats to depths of 60 m acanthocephalan botulus, the (typically < 6 m), but are scarce in high–energy, nemertean Carcinonemertes carcinophila, the outer–coast regions (Cohen et al. 1995). This is parasitic carcini, the isopod especially true in the Pacific Northwest, where Portunion maenadis, the dinoflagellate the occurrence of C. maenas is limited to bays Hematodinium perezi, and nicothoid copepods and (Behrens–Yamada 2001). Adults (Behrens–Yamada 2001; Stentiford and Feist typically occur on rocky shores, under rocks, in 2005). Additionally, filamentous bacteria and macroalgae or eelgrass beds, in marshes, or ciliates have been detected on the gill lamellae burrowed into cordgrass beds (Behrens–Yamada of C. maenas (Stentiford and Feist 2005). One 2001). Carcinus maenas is itinerant, and does parasite that has affected populations not maintain a permanent home shelter (Singh of C. maenas is Carcinonemertes epialti, which 1991). Juveniles and young adults can live is native to the West Coast of the . above the high water mark in marsh burrows or This nemertean worm is an egg predator that under algae for up to 10 days. As crabs grow, typically preys on native crabs, but has infected they occupy lower portions of their depth the C. maenas population in Bodega Harbor ranges, moving from intertidal regions to the with 11–93% prevalence depending on sex and subtidal zone (Behrens–Yamada 2001). season (Torchin et al. 1996). To date, this Additionally, intertidal regions are more parasite has not been reported in C. maenas populations for the Pacific Northwest. Pathogens in C. maenas include baculoviruses, a parovirus, reoviruses, and a bunyalike virus (Brock and Lightner 1990).

Current Geographic Distribution

Carcinus maenas is currently found along the Northeast and West coasts of . In the northeast, it is distributed continuously from Virginia (Perry 2009) to Nova Scotia (Cameron 2003; Fig. 7). The West Coast distribution of C. maenas is much more patchy. In this region, it is confined to estuaries, bays, and other protected coastal and inland waters from Morro Bay, California to the west coast of Vancouver Island, (Fig. 7; Behrens–Yamada 2001; Behrens– Yamada and Gillespie 2008). Figure 8. Known range of Carcinus maenas in the In the Pacific Northwest, C. maenas is Pacific Northwest (Behrens–Yamada and established in several coastal estuaries and Gillespie 2008) wave–protected embayments in Oregon, Vancouver Island (McDonald 2006). Its range in Washington, and along the west coast of this region extends from the Coquille River, Oregon to Kyoquot Sound, British Columbia (Behrens–Yamada and Gillespie 2008; Fig. 8). Contrary to McDonald, 2006, it has not been reported from the inland sea between Vancouver Island and the mainland (Behrens–Yamada and Gillespie, 2008). Population levels are still believed to be relatively low in the Pacific Northwest compared to the Northeast, though it has established breeding populations throughout

Figure 7. Current range of Carcinus maenas in the the region (Behrens–Yamada and Gillespie United States (USGS). 2008). Figure 9. Global distribution map of C. maenas as of 2003 (Carlton and Cohen 2003).

History of Invasiveness the late 1990s it had reached the eastern shore of Prince Edward Island and is now found Carcinus maenas is native to the throughout Nova Scotia (Cameron 2003; Carlton Atlantic shores of Europe, the North Sea, and and Cohen 2003). the western (Carlton and Cohen Several additional reports of introductions are 2003). Its natural range also includes available during the 1800s. In the mid century, Northwest Africa from Morocco to Mauritania, C. maenas was collected from Rio de Janeiro, the , the British Isles, southern (1857), the Bay of (1866), Sri , and northern Norway (Fig. 9). In total, Lanka (1866 or 1867), and the Hawaiian Islands the native ranged spans 49° of latitude (1873). By the turn of the century, it had also (Behrens–Yamada 2001). been reported in Pernambuco, Brazil, but no Carcinus maenas was first reported outside of its collection date was given. All these native range from the 1817, but did not introductions failed to establish viable establish a viable population (Carlton and Cohen populations (Carlton and Cohen 2003). 2003). During the same year, it was reported In , C. maenas was reported as from the east coast of the United States but a abundant around Port Phillip, Victoria in 1900, specific location was not provided. By 1871, C. but information regarding its initial occurrence maenas was distributed from New Jersey to is vague (Carlton and Cohen 2003). It may have Cape Cod, . It reached Maine in arrived by the 1870s or 1880s but remained a the 1890s and the Canadian border in 1951. By small founder population at that time. After a was invaded by C. maenas in 1983, when this species was collected at Table Bay, (Cohen and Carlton 2003). By 1988, it had spread north to Melkboostrand (20 km) and south to Camps Bay (15 km). This remains the established range, and an observation 117 km north of Cape Town is the only record outside the area of original spread (Carlton and Cohen 2003). Green crabs identified as C. aestuarii were collected in Tokyo Bay, Japan during 1984 and in Sagami, Osaka, and Dokai bay in the 1990s (Cohen and Carlton 2003). However, recent genetic evidence has shown this invasion to actually consist of a of C. maenas and C. aestuarii. It has not spread outside these Figure 10. Sightings of Carcinus maenas on the west extremely polluted bays, possibly because of coast of North American through 2000 (from biotic resistance from a high diversity of native Behrens–Yamada 2001). crabs (Behrens–Yamada 2001). The west coast of the United States was invaded long quiescent period, much like the situation in in the late 20th century. An established the Northwest Atlantic, C. maenas dispersed population was discovered in along the Australian coast. In 1971 and 1976, it in 1989, indicating a much earlier, unnoticed was reported to the north and west of Victoria, arrival (Cohen et al. 1995). Molecular evidence respectively. It reached Tasmania in 1993 indicated that the founding population was from (Carlton and Cohen 2003). th the east coast of the United States (Bagley and During the early to mid 20 century, there were Geller 2000). Also in 1989, a single individual few reports of C. maenas from new locations. of C. maenas was collected from Estero All verified records are from the greater Indian Americano, a small 45 km to the north Ocean, including: Nossi, (1922); (Carlton and Cohen 2003). During 1993, newly Maungmagan, (1933); Perth Australia recruited C. maenas spread north to Bolinas (1965); Karachi, (1971). None of these Lagoon, Drakes Estero, Tomales Bay, and introductions resulted in established populations Bodega Harbor (80 km north of San Francisco (Carlton and Cohen 2003). Bay) (Grosholz and Ruiz 1995). By 1994, it was observed 150 km south of San Francisco at Invasion Process Elkhorn Slough and by 1998, it had reached Pathways, vectors, and routes of introduction Morro Bay, 220 km further (Cartlon and Cohen Anthropogenic activities have been 2003). This embayment remains the southern solely implicated in the transoceanic extent of its West Coast distribution. Northward introductions of C. maenas (Carlton and Cohen expansion was more rapid and extensive. 2003). Rafting via floating algae, wood, or other Specimens were found in , 320 flotsam has not been observed for this species km north of Bodega Bay, in 1995. Based on and planktonic larval duration is not long observations of early adult crabs in Coos Bay enough to facilitate the of extreme long (300 km north of Humboldt Bay), Oregon distance dispersal necessary to transport ocean during 1997 and sightings of the same cohort in basins (Cohen et al. 1995; Carlton and Cohen five more Oregon estuaries, Willapa Bay and 2003). International trade is a primary invasion Grays Harbor, WA during 1998 (400 km from pathway for C. maenas, and shipping has been Coos Bay), is was deduced that a colonization implicated as the likely vector for several event occurred in the Pacific Northwest during introductions. Ship boring and fouling or solid 1995 or 1996 (Behrens–Yamada 2001; Carlton ballast transport are the probable mechanisms and Cohen 2003). Carcinus maenas was for all invasions noted during the 1800s (Carlton subsequently reported in British Columbia in and Cohen 2003). During the early and mid 1999 and 2000 and now ranges throughout the 1900s, the opening of the Suez Canal (1969) is west coast of Vancouver Island (Behrens– the likely source of several failed introductions Yamada and Gillespie 2008). to the Indian Ocean, and ballast water began to In 2003, C. maenas was found in Camarones be a major transport vector during this time Bay, Argentina, on the Atlantic coast of (Carlton and Cohen 2003). Introduction of C. (Hidalgo et al. 2005). Size frequency maenas to South Africa was also believed have distributions and reproductive condition of occurred several times via shipping vectors from females indicated that the introduction had the Northeast Atlantic, whereas the introduction occurred at least 3–4 years prior to discovery of hybrid Carcinus to Japan is believed to be and that the population was established (Hidalgo from a single shipping event from Europe et al. 2005). Niche modeling indicates a (Bagley and Geller 2001; Roman 2006). potential distribution on the east coast of South Expansion of C. maenas to Canada, often American from southern Brazil (29° S) to the believed to be directly from expansion of the Magellan Strait (52° S) (Hidalgo et al. 2005). Northwest Atlantic invasion, was actually augmented by multiple invasions via shipping events from the Northeast Atlantic (Roman 2006). The introduction of C. maenas to UK and has led to the transport of crabs within Argentina was also from a shipping vector, its native range (Sheehan et al. 2008). either through ballast water or hull fouling (Hidalgo et al. 2005). The Argentina Factors influencing establishment and spread introduction, like those of South Africa and Factors influencing establishment of C. Canada, was from a secondary invasion, in this maenas are largely based on a combination of case from Australia (Darling et al. 2008). By physiological suitability, environmental contrast, the source the C. maenas introduction suitability, and propagule pressure. Like many to San Francisco Bay is considered to be either invasive marine species, C. maenas has typically the live seafood or bait trade. The donor region become established in large, international for the San Francisco introduction was shipping ports where propagule number is likely determined to be the Northwest Atlantic, to be maximized (Behrens–Yamada 2001). precluding ocean shipping as a possible vector Furthermore, because crabs are short–lived (Bagley and Geller 2001). Lobsters (Homarus broadcast spawners, the persistence of americanus) and baitworms (glycerid and nereid introduced populations is dependent upon local polychaetes) are routinely packed in recruitment (Behrens–Yamada 2001; Behrens– and shipped cross–country and C. maenas has Yamada and Gillespie 2008). Carcinus maenas been observed hitchhiking on such shipments to populations therefore typically establish in sites California. The seaweed is routinely discarded where larvae are more likely to be retained and into coastal and estuarine waters by anglers and not flushed out to sea (Cohen et al. 1995; Banas restaurant owners (Carlton and Cohen 2003). et al. 2009). Although larval supply from Additional transport mechanisms of C. maenas regional populations is a key factor in increasing that have not been specifically implicated in genetic diversity and facilitating local population introductions include: 1) fouled seawater pipes establishment, local reproduction and or sea chests, and 2) the movement of fouled recruitment in these “closed” embayments may frames of exploratory drilling platforms, and 3) be enough to maintain a population (Behrens– scientific research activities. Carcinus maenas is Yamada et al. 2005). Because of their trophic routinely used in experimental studies and plasticity, food resources are unlikely to be a escape, accidental release, or intentional release limiting factor to establishment of C. maenas are all possible introduction vectors (Carlton and (Cohen et al. 1995). However, habitat selection Cohen, 2003). The relatively small size of C. is a key factor in determining recruitment maenas has so far precluded stocking to create success, as mortality of newly settled crabs is or for purposes, though a lowest in algal habitats or mussel beds of substantial bait is active in the southern inshore or protected coastal regions (Gunther 1996; Hedvall et al. 1998). In other habitats, The invasion of the Pacific Northwest by C. predation pressure or wave surge may severely maenas was greatly augmented by anomalously impact recruitment success. Although there have strong northern currents associated with the been many tropical introductions, all have failed 1997/1998 ENSO event (Jamieson et al. 2002; largely because they are above the 18° C Behrens–Yamada and Gillespie 2008). During threshold needed for sustainability (Behrens– this time, currents of up to 50 km/day resulted in Yamada 2001, Carlton and Cohen 2003). a considerable northward population expansion Spread of C. maenas can occur naturally or may of C. maenas to Oregon, Washington, and be mediated by human vectors, and often occurs British Columbia from California populations after a considerable lag time. Once a founding (Yamada et al. 2005; Tepolt et al. 2009). population is of sufficient size, it can produce Although populations persist, temperature enough larvae to seed additional sites via current regimes and current patterns have not facilitated transport (Behrens–Yamada 2001). Larval northern larval transport in subsequent years dispersal is thus the dominant mechanism for (Behrens–Yamada and Gillespie 2008). Another range expansion. However, the previously northern colonization event could occur with the identified human vectors that result in next ENSO, however, as warm years with introductions (e.g., live seafood trade, hull favorable currents have been linked to increased fouling, ballast water) have also been shown to larval production, survival, and dispersal in C. supplement the regional spread of C. maenas maenas regardless of location (Behrens–Yamada (Carlton and Cohen 2003). The spread of C. 2001). Under these circumstances, introductions maenas is typically episodic. Once established, of C. maenas are likely throughout expanded it may take decades before a C. maenas regions of British Columbia and into , as population to build up sufficient propagule size temperatures in these regions are adequate for to expand its range (Behrens–Yamada 2001). their long–term persistence (Cartlon and Cohen For example, in both the Northwest Atlantic and 2003). Ocean warming will serve a similar Australia, C. maenas spread after a long function in promoting northern population quiescent period (Carlton and Cohen 2003). expansion of C. maenas. Although currents are Additionally, even well established populations the dominant mechanism of spread in the Pacific of C. maenas can exhibit cycles of range Northwest, anthropogenic vectors could play a contractions and expansion. In the Northwest critical role in spreading C. maenas to the inland Atlantic, for example, C. maenas range contracts waters of Puget Sound and Dixon Strait after unusually cold winters but expand again (Behrens–Yamada 2001). when temperature regimes are more favorable (Behrens–Yamada 2001). Potential ecological and/or economic impacts thereby directly impacting restoration efforts Ecological impacts of C. maenas are (Davis et al. 1998; Garbary and Miller 2006). considerable in some regions, and include This species is a superior competitor for food effects of predation, competition, and behavior. over the native blue crab, sapidus, in Carcinus maenas can decimate bivalve the Northeast United States, and the yellow populations when it is present in high numbers shore crab ( oregonesis) on the as a result of its high consumption rate West Coast which may result in energetic losses compared to most other comparably sized crab to the natives (MacDonald et al. 2007). species (Behrens–Yamada 2001). One such The ecological impact of C. maenas on the West example is the invasion meltdown scenario Coast appears to be mitigated in relation to other created by C. maenas’ preference for native regions through biotic resistance from a (Nutricola spp.) over an introduced comparatively rich native crab fauna. This is species (Gemma gemma). A minor component especially true of comparisons to the Northwest of bay and estuarine communities since its Atlantic. For instance, whereas nine species of introduction over 50 years ago, populations of crabs or crab–like anomurans have been G. gemma have rapidly spread and greatly recorded form intertidal zones of Maine, increased as a result of competitive release in twenty–six are found in Washington at similar accordance with the arrival and spread of C. latitudes (Jensen et al. 2002). As a result of maenas (Grosholz 2005). The long–term competition and especially predation with a occurrence of C. maenas has also resulted in richer native fauna, C. maenas has been shell thickening in Northwest Atlantic bivalve excluded from hard substrates on the West Coast prey species such as Mytilus edulis and Littorina and is further restricted within soft bottom obtusa at energetic and developmental costs regions of inshore waters to shallow sloughs and (Freeman and Byers 2006; Brookes and mudflats far from the main channels (Jensen et Rochette 2007). In addition to single–species al. 2007). and to a lesser impacts, C. maenas predation can modify extent C. antennarius are the species largely community structure in intertidal sandflats controlling the distribution of C. maenas on the through predation and prey excavation West Coast through predation (Jensen et al. (Grosholz and Ruiz 1995), and can substantially 2007). is reduce population size of newly recruited competitively dominant over C. maenas in flatfish (Taylor 2005). Foraging and burrowing contests for shelter and further excludes it from (sheltering) behavior of C. maenas can also have complex habitat in intertidal regions (Jensen et considerable negative effects on eelgrass beds al. 2002). In addition, the Asian shore crab (H. and are especially disruptive to transplants, sanguineus) has been shown to outcompete C. maenas for both food and shelter in the maenas populations. Other factors such as Northwest Atlantic, where it has recently been increasing temperatures, disease, or the effects introduced (Jensen et al. 2002; Griffen et al. of other predators may have contributed, but 2008). The introduction of H. sanguineus to the losses in harvests occurred eight years West Coast would therefore probably further earlier in Massachusetts than Maine and impact C. maenas populations. In West Coast correspond well with the northward spread of C. regions where C. maenas has established, maenas (Smith 1950; Glude 1955). however, it reaches larger sizes than it does at Additionally, in the North Sea, C. maenas distant locations where it has a much broader predation on commercially important cockles habitat distribution, such as South Africa and the (Cerastoderma edule) and clams (Macoma Northwest Atlantic (Grosholz and Ruiz 1996). balthica, M. arenaria) severely impacts Carcinus maenas may therefore limit biotic recruitment, especially during mild winters resistance in the West Coast by occupying (Jensen and Jensen 1985). Recently, it has been intertidal habitats with high intertidal area–to– demonstrated that C. maenas may negatively boundary ratios where it is especially robust impact populations of newly recruited American because of predatory release from parasites. In lobsters (Homerus americanus) through these warmer, shallow regions C. maenas can predation (Rossong et al. 2006). However, C. occur at high densities and under such maenas is also prey for larger size classes of conditions will have intense, localized effects on lobster and this association is of greater benthic community structure and stability magnitude (League–Pike and Shulman 2009; (Jensen et al. 2007). Such are the scenarios on Lynch and Rochette 2009). sandy intertidal regions of Bodega Bay and On the West Coast of North America, there is muddy intertidal regions of San Francisco Bay currently no evidence that C. maenas is causing (Grosholz and Ruiz 1995; Grosholz 2005). significant economic impacts (Jensen et al. Economic impacts of C. maenas are primarily 2007). Although Lafferty and Kuris (1996) associated with reductions in population sizes of claimed that damage to commercial and commercially important bivalve species. The recreational fisheries and aquaculture by C. most cited example concerns the decimation of maenas could exceed $40 million/year in this the soft–shelled clam (Mya arenaria) fishery in region, economic losses thus far are limited to New England during the mid 1900s (Glude damage in 1993 sustained by one mariculture 1955). Although specific estimates of economic operation in Tomales Bay (Behrens–Yamada losses are not available, clam landings dropped 2001). This resulted in harvest reductions of from 6,664 metric tons in 1938 to 1,043 metric 23% (1.6 kg/bag) of cultured Manila clams tons in 1959 in association with expanding C. (). The primary reason Table 2. Commercial and recreational species on the west coast of North America Management Strategies and Control that could be impacted by Carcinus maenas (after Behrens-Yamada, 2001) Methods Common name Scientific name Landings (mt) $US Pacific Crassostrea gigas 8,400 25,000,000 Management and control of widespread Manila clam Venerupis philippinarum 3,448 14,800,000 marine species, such as C. maenas, is extremely Panopea abrupta Geoduck 4,027 34,500,000 difficult. Eradication is not a viable option for Native littleneck Prothaca staminea 164 320,000 Butter clam Saxidomis gigantes 1,280 113,000 C. maenas because adults are highly mobile (up Cockle Clinocardium nuttalli to 15 km; Gomes, 1991) and larvae are Bent-nose clam macoma nasuta Baltic Macoma macoma bathica planktonic. Since C. maenas has spread to Eastern soft-shell Mya arenaria establish satellite locations, removal of adults at Gaper clam Tresus sp. 8 10,000 one site will have no lasting effect as colonists Cancer magister 25,000 133,000,000 English sole Pleuronectes vetulus 2,100 1,500,000 from adjacent sites will keep arriving. For the same reason, containment efforts are also for these limited effects on the West Coast is unlikely to be successful. Control is therefore low abundance of C. maenas compared to other the only viable option (Behrens–Yamada 2001). regions. Reported densities range from up to Many control methods have been investigated 2 500/m on the east coast of North America for C. maenas, but none have proven effective. 2 (MacPhail 1955) to lows of 0.04– 0.4/m in Poisoned bait was tested in Maine but had little Bodega Bay, California (Grosholz et al. 2000). impact and may cause unintentional detrimental Furthermore, densities in the Pacific Northwest environmental and biological effects (Hanks are even lower than they are in Bodega Bay 1961). Fishing is a potential method for (Behrens–Yamada 2001). If West Coast controlling C. maenas populations, but this too populations increase, however, several has proven ineffective in practice. Long–term commercially important species could be fisheries have existed in Venice Lagoon, Italy affected (Table 2). In addition to bivalves, there and Ria de Aveiro, Portugal with no pronounced is some concern that C. maenas could impact long–term effects on abundance (Varagnolo Dungeness crab (Cancer magister) and flatfish 1968; Gomes 1991). In addition, a bait fishery fisheries in the Pacific Northwest through for C. maenas in the southwest United Kingdom predation on new recruits (Lafferty and Kuris has significantly increased abundance, 1996; Jamieson et al. 1998). apparently because the tiles used to catch crabs also serve as artificial habitat (Sheehan et al. 2008). In Massachusetts and Maine, where C. maenas is extremely common, communities have offered bounties for crabs or have required clam diggers to collect crabs before being issued The document is extensive and evaluates a harvesting permit (Behrens–Yamada 2001). management options for prevention, eradication, Trapping programs have also been conducted in and control. It has not been implemented, municipalities on Martha’s Vineyard, but have however. In reaction to the designation of C. proven ineffective (Walton 2000). Biological maenas as an ANS in 1998 and just prior to control has been proposed for C. maenas, but invasion, Washington made it illegal to possess has not been implemented. Carcinus maenas has or transport live C. maenas. Washington apparently undergone a predatory release in the Department of Fish and Wildlife (WDFW) Pacific Northwest and is largely free from monitoring and control programs were also parasites (Torchin et al. 2001). Parasitic initiated in Willapa Bay and Grays Harbor in castrators (e.g., , Portunion 1998, after C. maenas was locally discovered meanadis) and egg predators (Carcinonemertes (Figlar–Barnes et al. 2001). Trapping efforts led spp., nicothoid copepods) therefore hold to the capture of 94–303 crabs during 1998– promise as control agents, but are not host 2002. However, budget cuts in 2002 curtailed specific and therefore could have considerable the program and the C. maenas population in unintended negative consequence to native crab this region has persisted and become self– fauna (Behrens–Yamada 2001). Much more sustaining (Behrens–Yamada et al. 2005). research is needed before biological control During 1998, WDFW established a task force to agents can be considered a viable possibility. develop prevention and control strategies for Biological control may be better accomplished zebra and and C. maenas and this effort by enhancing habitat of native crabs who are is ongoing. predators and competitors of C. maenas

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J Exp Mar Biol Torchin ME, Lafferty KD, Kuris AM (2001) Ecol 313: 317–336 Infestation of an introduced host, the European green crab, Carcinus maenas, by Taylor DL (2005) Predatory impact of the green a symbiotic nemertean egg predator, crab (Carcinus maenas Linnaeus) on post– Carcinonemertes epialti. J. Parasitology settlement 82(3): 449–453 (Pseudopleuronectes americanus Walbaum) as revealed by immunological Varagnolo S (1968) Fishery of the green crab dietary analysis. J Exp Mar Biol Ecol 324: (Carcinus maenas L.) and soft crab culture 112–126 in the Lagoon of Venice. Food and Agricultural Organization of the United Tepolt CK, Darling JA, Bagley MJ, Geller JB, Nations. General Fisheries Council for the Blum MJ, Grosholz ED (2009) European Mediterranean. Studies and Reviews green crabs (Carcinus maenas) in the 12(37): 1–13 northeastern Pacific: genetic evidence for high population connectivity and current– Walton WC (2000) Mitigating effects of mediated expansion from a single nonindigenous marine species: evaluation of selective harvest of the European green crab, Carcinus maenas. J Shellfish Res 4. Australian Marine Pests: 19(1): 634 http://www.marinepests.gov.au/__data/a ssets/pdf_file/0006/852108/Carcinus– Wolf F (1998) Red and green colour forms in maenas.pdf the common shore crab Carcinus maenas 5. Australian Marine Pests – National (L). (Crustacea: Brachyura: Portunidae): Management Plan: theoretical predictions and empirical data. J http://www.marinepests.gov.au/__data/a Nat Hist 32: 1807–1812 ssets/pdf_file/0003/952509/carcinus–ncp–08.pdf 6. BC Shellfish Growers Association: Zeng C, Naylor E (1996a) Synchronization of http://www.bcsga.ca/research– endogenous tidal vertical migration development/invasive–tunicates–monitoring– rhythms in laboratory–hatched larvae of the project/identifying– tunicates/european– crab Carcinus maenas. J Exp Mar Biol green–crab–carcinus–maenus Ecol. 198: 269–289 7. Fisheries and Oceans Canada – The Green Crab Invasion: Zeng C, Naylor E (1996b) Occurrence in coastal http://www.thefishsite.com/fishnews/70 water and endogenous tidal swimming 02/fisheries–and–oceans–canada–the–green– rhythms for late megalopae of the shore crab–alien– invasion crab Carcinus maenas: implications for 8. Global Invasive Species Database: onshore recruitment. Mar Ecol Prog Ser http://www.issg.org/database/species/ec 136: 69–79 ology.asp?si=114&fr=1&sts=&lang=EN 9. Oregon Department of Fish and Wildlife – Other Key Sources of Information Marine Resources Program – Shellfish Project: http://www.dfw.state.or.us/MRP/shellfis 1. Aquatic Nuisance Species Project: h/crab/green_crab.asp http://www.aquaticnuisance.org/fact– 10. Pacific States Marine Fisheries Commission sheets/european–green–crab – Aquatic Nuisance Species Prevention 2. Aquatic Nuisance Species Task Force: Program: http://www.anstaskforce.gov http://www.psmfc.org/Aquatic_Nuisanc 3. Aquatic Nuisance Species Task Force Green e_Species_Prevention_Program Crab Management Plan: 11. Prince William Sound Regional Citizens’ http://www.anstaskforce.gov/GreenCrab Advisory Council: ManagementPlan.pdf http://www.pwsrcac.org/docs/d0015300. pdf 12. Smithsonian Environmental Research Robertson. Rd., Delta, BC V4K 3N2; Center: [email protected], (604) 940–4674 http://www.serc.si.edu/labs/marine_inva Figlar–Barnes, R. Washington State Department sions/population_ecology/carcinus.aspx of Fish and Wildlife, P.O. Box 190, Ocean Park, 13. USDA National Invasive Species WA 98640 Information Center – Aquatic Species: Gillespie, Graham E. Fisheries and Oceans http://www.invasivespeciesinfo.gov/aqu Canada, Pacific Biological Station, 3190 atics/greencrab.shtml Hammond Bay Rd., Nanaimo, BC V9R 14. USGS – Non–Indigenous Aquatic Species: 6N7; graham.gillespie@dfo–mpo.gc.ca, (604) http://nas3.er.usgs.gov/queries/SpeciesL 666–0384 ist.aspx?group=&genus=carcinus&species=mae Hauck, Laura. – Zoology Department, Oregon nas State University, Corvallis, OR 97331–2914; 15. Washington Sea Grant: [email protected], (541) 737–4358 http://www.wsg.washington.edu/mas/ec Hunt, Christopher E. – Environmental Science ohealth/invasive_crabs/green_crab.html Program, Oregon State University, Corvallis, 16. WDFW – Aquatic Nuisance Species: OR 97331– 2914 http://wdfw.wa.gov/fish/ans/identify/ht Jamieson, Glen S., Fisheries and Oceans ml/index.php?species=carcinus_maenas Canada, Pacific Biological Station, 3190 Hammond Bay Rd., Nanaimo, BC V9R Expert Contact Information in the Pacific 6N7; glen.jamieson@dfo–mpo.gc.ca, (604) 666– Northwest 0384 Armstrong, David A. – School of Aquatic and Jensen, Gregory C. – School of Aquatic and Fishery Sciences, University of Washington, Fishery Sciences, University of Washington, Box 355020, Box 355020, Seattle, WA 98195; Seattle, WA 98195; [email protected], (206) 543–6132 [email protected], (206) 543–4270 McDonald, P. Sean. – School of Aquatic and Behrens–Yamada, Sylvia – Zoology Fishery Sciences, University of Washington, Department, Oregon State University, Corvallis, Box 355020, Seattle, WA 98195; OR 97331–2914; [email protected], (206) 914–1776 [email protected], (541) 737–5345 Elner, Robert W., Canadian Wildlife Service, Pacific Wildlife Research Centre, RR#1, 5421 Current Research and Management previously discussed monitoring and control Efforts plan was curtailed in 2002 because of budget cuts. The WDFW now relies on volunteers and Current research efforts focused on C. shellfish growers to monitor established C. maenas are extensive throughout its global maenas populations in Willapa Bay, Grays range. Topics of interest are widespread and Harbor, and a potential introduction to Puget include life history, genetics, parasitology, Sound. Biological and chemical methods to ecology, and aspects of invasion ecology (e.g., control C. maenas have been proposed through a invasion history, ecological and economic WDFW task force and recent published impacts, biotic resistance), among others. There literature. However, basic research necessary is no paucity of literature on this species, as for the implementation of these methods is literally hundred of peer reviewed publications lacking. The most effective control or are available. Most of the ongoing research on eradication measure available will be this species in the Pacific Northwest is being implemented in the event of a C. maenas conducted by the scientists identified in the introduction to Puget Sound. previous section of this document.

Although C. maenas has been afforded a substantial amount of scientific attention, federal and regional management efforts are lacking. The 2002 federal management plan has not been implemented. Possession of C. maenas in California and Oregon is prohibited, but no other management strategies are in place in these states. There are currently no laws in Alaska barring importation of C. maenas nor a management plan for this species. No government laws regarding C. maenas were found for British Columbia, although a risk assessment was prepared by the Oceans and Fisheries Department in Nanaimo, and monitoring is being conducted (Behrens– Yamada and Gillespie 2008). It is still illegal to possess or transport live C. maenas in Washington; however, funding for the