Northeastern Naturalist Vol. 25, No. 1 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 161 2018 NORTHEASTERN NATURALIST 25(1):161–180 Distribution and Habitat Use of the Invasive Carcinus maenas L. (European Green Crab) and the Native Cancer irroratus (Say) (Rock Crab) in Intertidal Zones in the Upper Bay of Fundy, Canada Amelia J. MacDonald1,2,*, Hannah M. Kienzle1,3, David Drolet1,4, and Diana J. Hamilton1 Abstract - Carcinus maenas (European Green Crab) is an invasive marine portunid crab that has established populations globally outside of its native range and has been implicated in declines of benthic invertebrates in invaded ecosystems. Observations of Green Crab on intertidal mudflats in the upper Bay of Fundy have increased in recent years. We assessed the distribution and relative abundance of crab populations in Chignecto Bay, an arm of the upper Bay of Fundy, by trapping Green Crab and native Cancer irroratus (Say) (Rock Crab) at mudflats and in rocky intertidal zones in 2013 and 2014. Spatial distribution of Green Crabs indicated a preference for rocky intertidal habitats and greater abundance geographically lower in the Bay, which would correspond with an initial introduction at the mouth of the Bay and subsequent inward expansion. Abundance declined drastically from 2013 to 2014, suggesting that Green Crab may not yet be well established in Chignecto Bay. Carapace width indicated that crab age may be less variable further into the Bay, suggesting these sites may only be colonized in years with favorable environmental conditions. The population may be vulnerable under poorer conditions in other years, like 2014, when high overwintering mortality is a possible cause for the observed decline. There was not a corresponding decline in native Rock Crab. While Green Crab abundance is currently relatively low in Chignecto Bay, and their impact on mudflats likely minimal, prolonged favorable environmental conditions could lead to an increased presence. Introduction The portunid crab Carcinus maenas L. (European Green Crab; Fig. 1A) is native to the eastern Atlantic from northern Africa to Norway, but has established invasive populations worldwide (Carlton and Cohen 2003, Klassen and Locke 2007). Green Crabs occupy both hard and soft substrate habitats on exposed coast and in protected embayments (Grosholz and Ruiz 1995). They can be found from the shallow subtidal to the upper intertidal zone. Adult Green Crabs can survive freezing temperatures, but prefer temperatures above 0 ºC (Klassen and Locke 1Department of Biology, Mount Allison University, 63B York Street, Sackville, NB, Canada, E4L 1G7. 2Current address - Department of Biology, Trent University, 1600 West Bank Drive, Peterborough, ON, Canada K9L 1Z8. 3Current address - Department of Biological Sciences, 507 Campus Drive NW, University of Calgary, 2500 University Drive NW, Calgary, AB, Canada T2N 1N4. 4Fisheries and Oceans Canada, Institut Maurice-Lamontagne, 850 Route de la Mer, Mont-Joli, QC, Canada G5H 3Z4. *Corresponding author - ajmacdonald3@gmail.com. Manuscript Editor: Thomas Trott Northeastern Naturalist 162 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 Vol. 25, No. 1 2007). The Green Crab is an aggressive competitor, and may outcompete sympatric native crustaceans (Haarr and Rochette 2012, MacDonald et al. 2007, McDonald et al. 2001). It has a generalist diet, and has had negative effects on several invertebrate species, notably bivalves (DFO 2011, Klassen and Locke 2007), but also polychaetes (Estelle and Grosholz 2012, Gregory and Quijón 2011) and amphipods (Grosholz and Ruiz 1995). Green Crabs can destroy Zostera marina L. (Eelgrass) beds (DFO 2011, Garbary et al. 2014, Neckles 2015, Matheson et al. 2016), and their foraging behavior has the potential to affect shorebird prey consumption by altering the availability of benthic invertebrates (Estelle and Grosholz 2012). The Green Crab was first introduced to the eastern US around 1817 and was detected in Atlantic Canada in rocky intertidal areas of the outer Bay of Fundy in 1951 (Klassen and Locke 2007). Green Crabs were found along the southeastern coast of Nova Scotia by the mid-1960s, but were not reported for the northeastern coast until the early 1980s. Genetic analysis suggests that multiple introductions have occurred in the Maritime Provinces since the 1980s. These crabs likely originated from a more northerly region of their native range than earlier arrivals, making these recently introduced crabs and their descendants more tolerant of cold temperatures (Roman 2006). The hardier northern crabs are also more effective predators (Haarr and Rochette 2012, Rossong et al. 2012), and these traits may have facilitated their rapid invasion of the Northumberland Strait, Prince Edward Island, and Newfoundland. They may have also spread southward and into the outer Bay of Fundy, mixing with crabs descended from the original introduction (Jeffery et al. 2017, Klassen and Locke 2007). The Green Crab’s broad geographic range in Atlantic Canada overlaps with that of the native crab Cancer irroratus (Say) (Rock Crab; Fig. 1B), and both species share similar requirements for food and habitat (Bélair and Miron 2009). Caging experiments examining competition between the 2 species have revealed mixed results. In a microcosm experiment, larger Green Crabs often out-competed smaller Rock Crabs for Mytilus edulis L. (Blue Mussel), particularly in warmer water temperatures (Matheson and Gagnon 2012). In another study, each species reduced foraging efficiency of the other at high densities (Gregory and Quijón 2011). There is also evidence that Figure 1. (A) Invasive Carcinus maenas (European Green Crab) and (B) native Cancer irroratus (Rock Crab). Photographs © A.J. MacDonald and H.M. Kienzle. Northeastern Naturalist Vol. 25, No. 1 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 163 the 2 species may coexist by reducing interspecific competition through temporal and spatial segregation (Bélair and Miron 2009). The Bay of Fundy is characterized by some of the highest tides in the world. The upper arms, Chignecto Bay and Minas Basin, include ~35,000 ha of intertidal mudflat ecosystems (Hicklin 1987) in addition to rocky intertidal habitats. The upper Bay of Fundy is a critical migratory stopover site for shorebirds, particularly Calidris pusilla L. (Semipalmated Sandpiper) (Hicklin 1987). Shorebirds, as well as benthic and demersal fish, forage extensively on mudflat invertebrates and biofilm (Gerwing et al. 2016, McCurdy et al. 2005, Quinn and Hamilton 2012), highlighting the ecological significance of these systems. We have worked in the upper Bay of Fundy for over 15 y and first detected Green Crabs on mudflats in Chignecto Bay in 2012 (D. Drolet, pers. observ.). A local naturalist also noticed an increase in Green Crab carapaces on shores in recent years (D. Christie, Naturalist, Harvey, NB, Canada, pers. comm.), and 12 Green Crabs were caught in the lower Minas Basin in 2001 (Roman 2006). Further, previous surveys at 5 mudflats in the Minas Basin in 2013, each comprising two 800-m transects perpendicular to shore and one 100-m transect parallel to shore at the high-tide line, reported a molted carapace density of 0.014m-2 (MacDonald 2014). Green Crabs have reduced amphipod and polychaete densities in enclosure experiments (Estelle and Grosholz 2012, Gregory and Quijón 2011, Grosholz and Ruiz 1995). These mudflat invertebrates provide important resources for native species; thus, the current status—early phase of establishment if Green Crab abundance is lower than Rock Crab, middle phase if abundances are similar, and late phase if Green Crabs are significantly more abundant than Rock Crabs (sensu O’Connor 2014)—of the Green Crab population in Chignecto Bay merits investigation. We monitored Green Crabs and their potential competitors, native Rock Crabs, at mudflats and adjacent rocky intertidal sites in Chignecto Bay from May 2013 to January 2014 and June 2014 to January 2015 to assess their current distribution and relative abundance. Field-site Description We surveyed Green Crab and Rock Crab populations at 3 mudflats in Chignecto Bay, an arm of the upper Bay of Fundy, bordered by New Brunswick and Nova Scotia, Canada (Fig. 2). Pecks Cove mudflat (45º45'21.6''N, 64º29'13.2''W) extends about 850 m at low tide, Minudie mudflat (45º45'39.6''N, 64º23'42.0''W) extends between 500 m and 1500 m, and Mary’s Point mudflat (45º43'26.4''N, 64º40'01.2''W) extends ~1500 m at low tide. Common invertebrates at these mudflat sites include the amphipod Corophium volutator (Pallas), Tritia obsoleta (Say) (Eastern Mudsnail), and Macoma spp. (clams). Gerwing et al. (2015) provide biotic and abiotic characteristics of the sites. We also monitored Green Crabs and Rock Crabs at rocky intertidal areas adjacent to the mudflat sites. Slack’s Cove (45º43'30.0''N, 64º32'49.2''W) was paired with Pecks Cove, Joggins (45º41'52.8''N, 64º27'7.2''W) with Minudie mudflat, and Two Rivers (45º39'07.2''N, 64º43'30.2''W) with Mary’s Point mudflat (Fig. 2). Intertidal zones at rocky sites generally had a steeper slope and were characterized by large outcrops of bedrock, Fucus sp. (wrack), and Northeastern Naturalist 164 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 Vol. 25, No. 1 Ascophyllum sp. (rockweed) with some surrounding sand and mud. C. volutator, Macoma spp., Semibalanus balanoides L. (Acorn Barnacle), and Littorina littorea L. (Common Periwinkle) were some invertebrate taxa found at these sites (Kienzle 2015). We considered Pecks Cove, Slack’s Cove, Minudie, and Joggins as upper Chignecto Bay, and Mary’s Point and Two Rivers as lower Chignecto Bay because these sites were geographically closer to the mouth of the Bay of Fundy and the location of the earliest detection of Green Crab in the Bay of Fundy. Methods Population surveys We surveyed crabs using crab-specific 60 cm x 40 cm x 20-cm Fukui traps (Fukui North America, Eganville, ON, Canada) with 12-mm mesh, and horizontal slits running the full width of the trap. We deployed 15 traps at each site, with 5 traps at each of 3 distances, corresponding to low, intermediate, and high tidal elevation. We placed low traps 50 m above the low-tide line, high traps 50 m below the Figure 2. Sites in Chignecto Bay, an arm of the upper Bay of Fundy, Canada, where we surveyed Green Crab and Rock Crab populations in 2013 and 2014. Mudflat sites are denoted by circles, and rocky intertidal sites are marked by triangles. NB refers to New Brunswick, and NS indicates Nova Scotia. Northeastern Naturalist Vol. 25, No. 1 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 165 high-tide line, and intermediate traps at the midpoint between high and low traps. Submersion time varied with tidal elevation—traps closer to the low tide line were under water longer than those closer to the high-tide line. At each level, we placed traps 3–5 m apart and parallel to the water so that openings were positioned in line with main currents (Drolet et al. 2012). At most sites, we secured the traps to 2 rebar posts so that their position remained the same during every sampling period. We marked trap locations at Two Rivers with a GPS unit and secured traps with rocks because bedrock prevented the use of rebar posts. We baited all traps on each deployment with herring in perforated bait buckets that allowed odors to diffuse. We set all traps at low tide and returned after ~24 h to collect them the following day shortly after they became exposed. We sampled pairs of sites sequentially with deployment and collection days for each site, which amounted to a 6-d survey period to cover all sites once. We identified to species, sexed, measured carapace width with calipers (±1 mm) between the last antero-lateral points, and released all captured crabs. We conducted surveys at all sites once every 3 weeks from May through August in 2013, then monthly from September through December, though Mary’s Point and Two Rivers were surveyed in January 2014 rather than December 2013 due to inclement weather. We surveyed sites monthly from June through December 2014, though Pecks Cove and Slack’s Cove were sampled in January 2015 rather than December 2014 because the sites were temporarily inaccessible. We considered sampling conducted during December and January as a single survey period. Although our methods did not exclude recaptures between sampling periods, we marked Green Crabs at Two Rivers in 2014 and found an extremely low rate of recapture, with only 3 crabs recaptured between June and December (Kienzle 2015); thus, recaptures are highly unlikely to have in fluenced results. Statistical analysis We analyzed Green Crab and Rock Crab abundance separately using generalized linear models with negative binomial distributions and log-link functions to account for overdispersed count data (Norušis 2008). We defined survey period, site, and year as fixed factors; the number of crabs caught per trap per 24-h deployment period, or catch per unit effort (CPUE), was the dependent variable. We dealt with significant interactions by splitting the data by site to examine temporal effects and by year to examine spatial effects. We then reran models and performed biologically meaningful specific contrasts with applied alpha-level corrections (sensu Benjamini and Hochberg 1995). Contrasts were designed to examine temporal, spatial, and site type (mudflat versus rocky intertidal) variability. We also compared Green Crab and Rock Crab abundance using generalized linear models. When this comparison resulted in significant interactions, we split the data by site and year to examine differences between species. We excluded Pecks Cove and Minudie from this analysis because of very low sample size (≤3 Green Crabs were caught at these sites in either year). We employed a Kruskal-Wallis test to compare Green Crab and Rock Crab size among sites. We considered variability in carapace width as a proxy for the breadth of ages represented in trapped crabs and used Bartlett’s test to assess this variable among sites. A wider range of ages may indicate a longer Green Crab Northeastern Naturalist 166 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 Vol. 25, No. 1 presence at a site, rather than a single strong age class (Grosholz and Ruiz 1995). We excluded Pecks Cove and Minudie from this analysis due to low sample size. We examined sex ratios for each species in each year using chi-square contingency tests. To obtain an index of winter severity and conditions relative to seasonal norms, we retrieved from the Environment Canada Historical Climate Database (Environment Canada 2015) daily air temperatures for the winters before each year of the study (December 2012–March 2013 and December 2013–March 2014), daily summer (May–August) air temperatures during the study, and average monthly air temperatures calculated from climate data collected from 1981–2010. Data were collected at Moncton International Airport (46°06'43.2''N, 64°40'44.4''W) and Moncton, NB (46º06'03.6''N, 64º47'24.0''W), and thus, while not exact for our study locations, serve as a proxy for the weather conditions at our sites. We compared the winter thermal environment experienced by crabs across months and years using a 2-way analysis of variance (ANOVA). Using the historical monthly average temperatures (1981–2010) as a baseline, we calculated the difference between the daily winter air temperatures during our study period and the historical average to detect any sustained anomalous temperatures during our study. We specified post-hoc contrasts that examined differences between years and applied an alpha-level correction (sensu Benjamini and Hochberg 1995). We also employed 1-sample t-tests to compare monthly winter temperatures directly to corresponding historical averages. Further, we calculated mean summer air temperature (±1 SD). We conducted all analyses in R v. 3.0.2 (R Core Team 2013) using the MASS (Venables and Ripley 2002), multcomp (Hothorn et al. 2008), and pgirmess (Giraudoux 2013) packages. We created figures in ArcMap 10.3 (ESRI 2014), and R v. 3.0.2 (R Core Team 2013) using the ggplot2 package (Wickham 2009). Results Temporal effects In 2013, we caught Green Crabs at all 6 sites, totaling 1488 crabs. In 2014, numbers declined substantially and we caught 402 crabs at 5 sites. CPUE (individuals caught per trap in ~24 h) varied from 0 to 90 in 2013 and 0 to 25 in 2014. Differences in crab abundance between years varied among sites (site x year interaction, Dev5, 1511 = 72.53, P < 0.001), but abundance was higher in 2013 than 2014 at Slack’s Cove (Dev1, 254 = 3.88, P = 0.049), Joggins (Dev1, 254 = 5.71, P = 0.017), Mary’s Point (Dev1, 254 = 17.86, P < 0.001), and Two Rivers (Dev1, 254 = 323.36, P < 0.001). We also caught more crabs at Pecks Cove and Minudie in 2013 than 2014, but did not evaluate these sites statistically because we caught ≤3 crabs at either site each year. Despite lower numbers in 2014, we observed a similar trend in abundance across survey periods in both years (survey x year interaction, Dev1, 1516 = 0.27, P = 0.602), where numbers increased as the year progressed, peaked in October, and declined drastically in December/January (Fig. 3). We caught 396 and 111 Green Crabs in October in 2013 and 2014, respectively, whereas we caught only 6 and 2 crabs in December/January during the 1st and 2nd years of the study, respectively. Northeastern Naturalist Vol. 25, No. 1 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 167 Contrary to the decrease in Green Crab abundance, native Rock Crab numbers increased from 2013 to 2014 (Dev1, 1522 = 5.41, P = 0.020), though the increase was not as pronounced as the decline in Green Crabs. We caught 819 Rock Crabs in 2013 and 994 in 2014, and CPUE varied from 0 to 28 and 0 to 66 in the 2 years, respectively. This increase was consistent across most survey periods (survey x year interaction, Dev1, 1516 = 0.87, P = 0.351; Fig. 3), and there was no significant difference among sites (site x year interaction, Dev5, 1511 = 10.39, P = 0.065; Table 1), though some survey periods and sites showed larger increases than others. Whether Green Crabs outnumbered native Rock Crabs depended on site and year (site x year x species interaction, Dev5, 3036 = 31.44, P < 0.001; Table 1). At Slack’s Cove, CPUE for Green Crab and CPUE for Rock Crab were not significantly different in 2013, but CPUE for Rock Crab was higher than that of Green Crab in 2014. At Joggins, Rock Crab was more abundant than Green Crab in both 2013 and 2014. Table 1. Total numbers of Green Crabs and Rock Crabs caught at each site in Chignecto Bay in 2013 and 2014. Green Crab Rock Crab Site type Site 2013 2014 2013 2014 Mudflat Pecks Cove 3 2 38 28 Mudflat Minudie 2 0 2 6 Mudflat Mary’s Point 488 23 81 177 Rocky Slack’s Cove 144 1 169 125 Rocky Joggins 138 13 327 312 Rocky Two Rivers 713 363 202 346 Figure 3. Catch per unit effort (±1 SE) of (A) Green Crab (n = 1890) and (B) Rock Crab (n = 1813) for all sites across survey periods per year. Points correspond to the first day of each survey period. Circles represent data collected in 2013, and triangles represent data collected in 2014. Northeastern Naturalist 168 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 Vol. 25, No. 1 At Mary’s Point, Green Crab CPUE was higher in 2013. This trend was reversed in 2014 when Rock Crab CPUE was higher. Green Crab CPUE was greater at Two Rivers in both 2013 and 2014 (Table 2). The total number of Rock Crabs exceeded the total number of Green Crabs caught at Pecks Cove in both years and at Minudie in 2014. Equal numbers of Green Crab and Rock Crab were caught at Minudie in 2013 (Table 1). In 2013, the ratio of male to female Green Crabs decreased as the season progressed (χ2 = 100.92, df = 8, P < 0.001). The proportion of Green Crabs trapped that were female was also higher in fall 2014 (χ 2 = 17.354, df = 7, P = 0.015; Fig. 4). Male-to-female ratio varied across the season for Rock Crabs in 2013 (χ 2 = 71.588, Figure 4. Total counts of male versus female Green and Rock Crabs throughout the trapping season in each year. Points correspond to the first day of each survey period. Table 2. Results of generalized linear models comparing Green Crab and Rock Crab CPUE at 4 study sites each year. Pecks Cove and Minudie were not statistically analyzed due to low Green Crab numbers. Site Year Direction of difference, if any df Residual df Deviance P-value Slack’s Cove 2013 No significant difference 2 268 0.71 0.703 2014 Green Crab < Rock Crab 2 238 59.93 less than 0.001 Joggins 2013 Green Crab < Rock Crab 2 268 34.56less than 0.001 2014 Green Crab < Rock Crab 2 238 118.07 less than 0.001 Mary’s Point 2013 Green Crab > Rock Crab 2 268 62.35 less than 0.001 2014 Green Crab < Rock Crab 2 238 17.73 less than 0.001 Two Rivers 2013 Green Crab > Rock Crab 2 268 244.61 less than 0.001 2014 Green Crab > Rock Crab 2 238 85.16 less than 0.001 Northeastern Naturalist Vol. 25, No. 1 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 169 df = 7, P < 0.001), with particularly high numbers of females trapped in September, but did not vary in 2014 (χ 2 = 2.32, df = 7, P = 0.940; Fig. 4) The temporal profile of winter air temperatures varied between study years (year x month interaction, F3, 209 = 6.30, P < 0.001). Deviation from historical climate averages differed significantly between study years in December and March. December 2013 was significantly colder relative to climate norms than December 2012 (adjusted α = 0.03, P = 0.015), as was March 2014 compared to March 2013 (adjusted α = 0.03, P < 0.001). Further, December 2013 was significantly colder than the historical average (t = -2.93, P = 0.006), whereas December 2012 was not (t = 0.78, P = 0.444). March 2014 was also colder than the historical average (t = -4.63, P < 0.001), while March 2013 was warmer (t = 2.57, P = 0.016; Fig. 5B). Deviation from historical average temperatures did not differ significantly between January 2013 and 2014 (adjusted α = 0.03, P = 0.056) or February 2013 and 2014 (adjusted α = 0.03, P = 0.748). Neither January 2013 nor 2014 differed from the historical average (t = -1.59, P = 0.126; t = 0.61, P = 0.546). February 2013 and 2014 were also similar to climate norms (t = 0.41, P = 0.687; t = -0.05, P = 0.960; Fig. 5). Average winter temperature preceding the 1st year of the study was -5.1 ºC and was -7.1 ºC preceding the second year; however, December 2013–March 2014 was characterized by a period of relatively consistent cold, while temperatures from December 2012–March 2013 were more variable (Fig. 5A). Average summer air temperature was similar in 2013 (16.5 ± 4.8 ºC) and 2014 (16.1 ± 5.2 ºC). Spatial effects Green Crab abundance varied with site in both 2013 (Dev6, 804 = 458.88, P less than 0.001) and 2014 (Dev6, 714 = 380.55, P < 0.001). In 2013, CPUE was significantly higher at Slack’s Cove and Joggins than at their respective mudflat pairs, Peck’s Cove and Minudie, while CPUE did not differ significantly between Two Rivers and Mary’s Point (Table 3). In 2014, greater abundance at Two Rivers than Mary’s Point was the only significant difference between site pairs. Table 3. Post-hoc comparisons examining differences in Green Crab CPUE between mudflat and rocky site pairs and upper and lower Chignecto Bay rocky sites in 2013 and 2014. Comparisons between mudflat sites were not performed due to low crab numbers at Pecks Cove and Minudie. The adjusted alpha-level (α = 0.03) is based on Benjamini and Hochberg’s (1995) correction. Year Comparison Sites and direction of difference, if any P-value 2013 Mudflat vs. rocky site Pecks Cove < Slack’s Cove less than 0.001 2013 Mudflat vs. rocky site Minudie less than Joggins less than 0.001 2013 Mudflat vs. rocky site Mary’s Point–Two Rivers 0.104 2013 Upper vs. upper Bay Slack’s Cove–Joggins 0.868 2013 Upper vs. lower Bay Slack’s Cove less than Two Rivers less than 0.001 2013 Upper vs. lower Bay Joggins < Two Rivers less than 0.001 2014 Mudflat vs. rocky site Pecks Cove–Slack’s Cove 0.580 2014 Mudflat vs. rocky site Minudie–Joggins 0.990 2014 Mudflat vs. rocky site Mary’s Point < Two Rivers less than 0.001 2014 Upper vs. upper Bay Slack’s Cove < Joggins 0.017 2014 Upper vs. lower Bay Slack’s Cove < Two Rivers less than 0.001 2014 Upper vs. lower Bay Joggins < Two Rivers less than 0.001 Northeastern Naturalist 170 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 Vol. 25, No. 1 In both years, we caught more Green Crabs at Two Rivers than at either rocky site geographically further into Chignecto Bay (Table 3). CPUE did not differ significantly between Slack’s Cove and Joggins in 2013, but abundance was greater at Joggins than Slack’s Cove in 2014 (Table 3). We caught 713, 144, and 138 Green Crabs in 2013 at Two Rivers, Slack’s Cove, and Joggins, respectively. In 2014, we trapped 363 crabs at Two Rivers, 1 crab at Slack’s Cove, and 13 crabs at Joggins. We did not statistically compare upper vs. lower Bay mudflat sites due to low crab Figure 5. (A) Average temperature (±1 SE) at Moncton International Airport during winters directly preceding each crab trapping season. (B) Average deviation in winter temperatures during the study period from monthly climate norms based on temperature data collected from 1981–2010. Northeastern Naturalist Vol. 25, No. 1 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 171 numbers. However, abundance was greater at Mary’s Point than at Pecks Cove and Minudie, most notably in 2013, when we caught 488 Green Crabs at Mary’s Point, 3 at Pecks Cove, and 2 at Minudie. In 2014 we trapped 23 crabs at Mary’s Point, 2 at Pecks Cove, and 0 at Minudie (Table 1). Green Crab carapace width varied across sites (H = 21.46, df = 3, P < 0.001), though median width only ranged from 40 mm to 45 mm among sites (Fig. 6A). The variability in carapace width also differed among sites (K2 = 23.99, df = 3, P less than Figure 6. Variability in (A) Green Crab and (B) Rock Crab carapace width across sites, excluding Pecks Cove and Minudie. Carapace width is divided into 5-mm–interval size classes. Northeastern Naturalist 172 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 Vol. 25, No. 1 0.001). Mary’s Point and Two Rivers had a broader range of sizes than Slack’s Cove and Joggins (Fig. 6A). Rock Crab carapace width also varied among sites (H = 257.83, df = 3, P < 0.001), with median width varying from 69 to 79 mm. Variability in carapace width also differed among sites as well (K2 = 15.84, df = 3, P = 0.001). Two Rivers and Joggins had a wider range of Rock Crab sizes than Slack’s Cove and Mary’s Point (Fig. 6B). Discussion This study is, to the best of our knowledge, the first formal survey of the Green Crab in Chignecto Bay. Our capture data show that Green Crabs are present in Chignecto Bay, though abundance varied substantially among sites and between years. Green Crabs have been documented on rocky flats of the lower Bay of Fundy since the 1950s (MacPhail and Lord 1954). We present evidence that they have expanded into the upper Bay. This area is characterized by extensive intertidal mudflats (Gerwing et al. 2015), which are unique to the region and provide a novel habitat for the species. Rocky flats, more similar to habitat wh ere Green Crabs occur in the lower Bay and elsewhere in their introduced range throughout the world, are also present in Chignecto Bay. We found that the spatial distribution of Green Crabs varied with geographical location and habitat type within Chignecto Bay. Abundance was higher at sites geographically lower in the Bay of Fundy. This finding suggests that Green Crabs are expanding from lower regions into upper regions of the Bay, consistent with the idea that they entered the Bay of Fundy at its mouth and have since moved further up its coast (Klassen and Locke 2007). Hardier crabs that stemmed from later introductions (Roman 2006) may have driven the spread into the upper Bay of Fundy. These crabs moved north into areas previously considered to be too cold for Green Crab (Roman 2006) and may be capable of tolerating harsher conditions in the upper Bay, such as colder temperatures and extreme tides. Some crabs collected in the Bay of Fundy had haplotypes linked to later introductions, though the majority of haplotypes from this location could be linked to the original New England introduction (Blakeslee et al. 2010, Roman 2006). Similarly, Williams et al. (2015) found that northern haplotypes stemming from later introductions were uncommon on the northern US Atlantic coast. This distribution of haplotypes suggests that northward expansion in the Bay of Fundy may be currently limited, and that perhaps only a subset of the crabs present have the capacity to persist in these areas. Over time, selection in the region for these hardier haplotypes could lead to larger populations in the upper Bay of Fundy. Overall, we caught more Green Crabs at rocky sites than at mudflats. As crabs expanded further into the Bay of Fundy, they may have continued to colonize areas similar to previous habitat in the lower Bay. Movement onto mudflats in Chignecto Bay would require an adjustment to the prey base, which differs from prey available at rocky intertidal sites. Rocky intertidal zones may also provide better protection from predation for juvenile Green Crabs than the relatively homogenous mudflat substrate. Megalopa larvae experience lower predation and settling mortality on Northeastern Naturalist Vol. 25, No. 1 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 173 structurally complex substrates (Moksnes et al. 1998) and actively select such habitats (Hedvall et al. 1998). Thus, Green Crab larvae may be preferentially settling in rocky habitats over mudflats in Chignecto Bay, or experiencing greater survivorship in these areas. However, while the rocky intertidal appears to be a more suitable habitat for Green Crab, numbers observed at Mary’s Point in 2013 suggest that they can survive on mudflats. It is also possible that our sampling design may have influenced the comparison between the 2 habitat types. Rocky sites have steeper slopes than mudflats, resulting in smaller intertidal zones. If Green Crabs are moving in and out of the intertidal zone with the tide cycle (e.g., Aagaard et al. 1995), and if they are relatively evenly distributed within habitats (which is probably not the case), it is possible that more crabs would be caught in the higher traps at rocky intertidal sites because crabs would not need to travel as far to reach the higher traps. Conversely, due to greater distance between trap levels at mudflat sites, we surveyed a larger mudflat than rocky area, which could lead to increased capture rates on mudflats, generating the opposite effect of the steeper slope at rocky sites. We observed a substantial decline in Green Crab abundance from 2013 to 2014. Two Rivers was the only site at which Green Crabs were still regularly caught in 2014, and we trapped roughly 50% fewer crabs even there. Similar declines in Green Crab abundance were observed in other parts of Atlantic Canada in 2014 (N. Simard, Department of Fisheries and Oceans Canada, Mont-Joli, QC, Canada [DFO], pers. comm.). We speculate that this decline was related to over-winter mortality in 2013–2014. The winter of 2013–2014 is best characterized as a 4-month period of relatively consistent cold, in contrast to 2012–2013, when similar temperatures were experienced in only January and February. Additionally, December 2013 and March 2014 were colder than historical temperature averages for those months (Fig. 5). Green Crab abundance has declined following harsh winters in their native range (Beukema 1991), and cold temperatures have been cited as a limiting factor in their northward progression in Atlantic Canada (Audet et al. 2003). Thus, it is possible that the particularly long winter of 2014 may have caused the Chignecto Bay Green Crab population to decline dramatically at recently invaded sites, potentially due to both reduced larval recruitment and adult mortality. We did not observe any newly settled crabs in 2014, and we caught fewer crabs around the age of maturity (Sharp et al. 2003), suggesting low recruitment. We also caught fewer large adults in 2014, indicating some mortality may have occurred. Habitat differs between the upper and lower Bay of Fundy, and sites further into Chignecto Bay may function as marginal habitat where Green Crabs have an appreciably greater presence in years with favorable conditions but struggle under unfavorable conditions. We speculate that the extra length of winter in 2013–2014 may have reduced Green Crab survivorship. Further, crab size was less variable at Joggins and Slack’s Cove than at Two Rivers and Mary’s Point, sites geographically lower in the Bay. This finding suggests that crabs at these upper sites may have been from fewer cohorts, only colonizing these areas in years with favorable conditions, whereas Green Crabs may be more established at sites lower in the Bay where more age classes may be present. Ocean conditions have been linked with year-class strength of Green Crabs Northeastern Naturalist 174 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 Vol. 25, No. 1 (Behrens-Yamada and Kosro 2010), and in a location where abundance remains low compared to other areas of the Atlantic coast, the population in Chignecto Bay may be particularly susceptible to environmental stressors, as occurred in winter 2013–2014. Although the substantial decline of Green Crabs in 2014 suggests they are not yet well established in Chignecto Bay, a series of strong year-classes could lead to a stable or increasing population. Green Crab numbers decreased when temperatures were below average; thus, increases of winter temperatures predicted by climate change models (Stachowicz et al. 2002) could lead to population increases in this region and result in the formation of established populations. We caught 2 ovigerous Green Crabs at Joggins in June 2013, indicating that they were breeding at the site following a relatively mild winter (A.J. MacDonald, unpubl. data). More winters like this could lead to additional reproduction in these upper areas of the Bay. Although the mesh size of the Fukui traps prevented us from cap turing particularly small crabs, we observed newly settled Green Crabs at Slack’s Cove and Mary’s Point in August and September 2013 (A.J. MacDonald, pers. observ.). Only 1 month in winter 2012–2013 was warmer than historical averages, whereas 2 months in winter 2013–2014 were colder than climate norms. Green Crab numbers decreased when air temperatures were below average. If winter temperatures increase due to climate change, population increases in this region are a clear possibility in coming years and could lead to formation of established populations. Green Crab populations declined from 2013 to 2014, but Rock Crab abundance increased slightly. The lack of a decline in Rock Crabs is not surprising, and provides additional support for our hypothesis that winter stressors, as opposed to some widespread habitat or food-base change, were responsible for the decline in Green Crabs. Native Rock Crabs are well adapted to cold and are sensitive to warm temperatures. Jost et al. (2012) found that Rock Crab righting-response time after being turned over slowed at 20 °C and stopped at 30 °C, whereas Green Crab response time did not slow and stopped at 34–36 °C. Although most invertebrate foraging is to some degree temperature-sensitive, foraging efficiency in Green Crabs has been shown to decrease markedly in colder water (Bélair and Miron 2009, Matheson and Gagnon 2012). Thus, while a colder winter would be of little consequence to Rock Crabs in Chignecto Bay, it would be detrimental to invasive Green Crabs. Further, Rock Crab CPUE was higher than that for Green Crab at every site in 2014 other than Two Rivers, where Green Crabs were most strongly established. In 2013, Rock Crab CPUE exceeded that of Green Crab at only Joggins and Pecks Cove. This result suggests that the Green Crab invasion of Chignecto Bay is in early stages at most locations, though the Green Crab appears to be a late-phase invader at Two Rivers (sensu O’Connor 2014). However, the changes in abundance between the 2 species at some sites over the course of our study indicate that invasion status could change quickly. We observed within-site spatial segregation between Green Crabs and Rock Crabs in 2013. Rock Crabs were primarily caught in the lower intertidal, while Green Crabs were more prevalent in the upper intertidal (MacDonald Northeastern Naturalist Vol. 25, No. 1 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 175 2014). Rock Crab distribution did not change in 2014 when Green Crab presence was minimal, suggesting that Rock Crabs may have been outcompeting Green Crabs in the low intertidal zone (Kienzle 2015). Despite the overall decline in Green Crab abundance from 2013 to 2014, both years showed the same within-year temporal trend. CPUE increased as the season progressed, peaking in October. We may have caught more crabs later in the season because of the age distribution at the sites we surveyed. Aagaard et al. (1995) found that adult males displayed greater tidal rhythmicity in foraging activity than juveniles, which remained in the low intertidal zone. Based on observed sizes, many Green Crabs caught at all sites were around the age of maturity (Sharp et al. 2003), though Two Rivers and Mary’s Point had several particularly large adults in 2013. Placement of traps may have generated a bias by catching few crabs early in the season if they were predominantly in the low intertidal or subtidal zones, and then catching more crabs later in the season when they began foraging in the upper intertidal zone after moulting during the summer (e.g., Aagaard et al. 1995). Additionally, an increase in females caught in fall (Fig. 4) may have contributed to the overall increase in CPUE. More female crabs may have entered traps after the summer breeding period because ovigerous females are less likely to be attracted to bait (Klassen and Locke 2007). Green Crab abundance currently appears to be lower in Chignecto Bay than in certain other invaded areas in Atlantic Canada. Average CPUE in Chignecto Bay was 1.84 Green Crabs per trap per 24 h in 2013 and 0.56 in 2014. Recent Green Crab monitoring programs led by the DFO used a protocol similar to our study, with Fukui traps deployed for 24 h. However, DFO set traps just below the low-tide line and they were submerged for the entire deployment (Simard et al. 2013, Vercaemer and Sephton 2016), whereas we placed traps in the intertidal zone, so time submerged varied. Further, our mudflat habitat was certainly distinct from anything found in these other study locations. Monitoring efforts from 2008 to 2015 (Vercaemer and Sephton 2016) that included the lower Bay of Fundy, southern and eastern shores of Nova Scotia, and Cape Breton reported an average CPUE of 12.54. Green Crabs were particularly abundant along the eastern shore and in Cape Breton with the maximum annual average CPUE reaching 52.0 and 43.0, respectively. Average CPUE for the lower Bay of Fundy was 20.1 in 2008, but only 0.1 in 2011. Mudflat invertebrate communities provide important food resources for fish and migrating shorebirds (Hamilton et al. 2003, McCurdy et al. 2005, McLean et al. 2013, Quinn and Hamilton 2012). Green Crabs are present in Chignecto Bay at all sites we surveyed, though the population does not yet appear to be widely established, given the limited abundance at many sites. Impacts of small Green Crabs (less than 40 mm carapace width) at relatively low densities on mudflat invertebrate biomass are likely negligible (MacDonald 2014). However, Green Crab predation rates increase substantially with crab size (Boudreau et al. 2013), so if the population stabilizes and older crabs become more prevalent, as could occur in the event of consecutive warm winters, mudflat invertebrate taxa could be affected. There is mixed evidence on the potential for adverse effects of a Green Crab invasion on Northeastern Naturalist 176 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 Vol. 25, No. 1 other trophic levels. In an enclosure experiment, Estelle and Grosholz (2012) found that Green Crabs reduced polychaete consumption by Calidris alpina L. (Dunlin). Wong and Dowd (2014) modeled the effects of a Green Crab removal program on an intertidal sand flat and predicted that removal of 50% or 95% of Green Crabs from the food web would result in increased Pluvialis squatarola L. (Black-bellied Plover) biomass and increased removal of benthic prey by migrating shorebirds. However, Grosholz et al. (2000) did not observe changes in shorebird abundance in a 9-y period following the introduction of Green Crabs to Bodega Bay Harbor, CA. Nevertheless, because polychaetes are an important prey item of Semipalmated Sandpipers in the upper Bay of Fundy (Quinn and Hamilton 2012), indirect effects of Green Crab predation could occur in the long term if the invasion is highly successful. Green Crabs also prey on amphipods and may reduce Corophium sp. densities (Grosholz and Ruiz 1995). Corophium volutator, a prey item for Semipalmated Sandpipers (Gerwing et al. 2016, Quinn and Hamilton 2012) and potentially Green Crabs, is usually the dominant species in Chignecto Bay’s mudflat invertebrate community (Drolet et al. 2012), thus creating an opportunity for competition to develop between the 2 species. Such competition, however, is likely only under extremely high crab densities. Green Crabs burrow and pit mudflat surfaces through foraging (Floyd and Williams 2004, Ropes 1968). We observed such pits on mudflats in Chignecto Bay (D. Drolet, pers. observ.), and changes to the structural integrity of mudflat sediments in Chignecto Bay under increased crab densities have the potential to affect the infaunal invertebrate community (e.g., Schratzberger and Warwick 1999). Given the ecological importance of mudflats in the region, the status of Green Crabs in Chignecto Bay merits continued monitoring. As average winter temperatures increase (Stachowicz et al. 2002), so too does the likelihood of a greater Green Crab presence in the upper Bay of Fundy. The invasion history of the Green Crab demonstrates its ability to detrimentally affect intertidal invertebrate populations (Floyd and Williams 2004, Grosholz and Ruiz 1995, Ropes 1968), which are essential to Bay of Fundy mudflats. An established population of invasive Green Crabs has the potential to negatively impact native species at multiple trophic levels through predation and both direct and indirect competition. Acknowledgments We thank Hilary Mann, Elizabeth MacDonald, Shaun Allain, Lauren Jonah, Jeremy Dussault, Sarah Neima, Brittany Dixon, Clay Steell, Marissa Hackman, Laura Steeves, Sebastian Carrera, Caila Henderson, Jeff Bell, Abby FitzGerald, Clara Doucette, Jacob Bach, Sylvain Lemieux, and Nicole Tweddle for assistance with fieldwork. Mary’s Point Shorebird Reserve, Joggins Fossil Centre, and Karin Bach provided access to field sites. The DFO provided Fukui traps, and Dawn Sephton, Benedikte Vercaemer, and Andrea Locke gave valuable advice during project design. We also thank 3 anonymous reviewers and manuscript editor Thomas Trott for their helpful comments that improved this manuscript. Funding was provided by a Natural Sciences and Engineering Research Council Discovery Grant (to D.J. Hamilton), the New Brunswick Wildlife Trust Fund ( to D. Drolet and D.J. Hamilton), NSERC Undergraduate Summer Research Awards (to A.J. MacDonald and H.M. Kienzle), and Mount Allison University. Northeastern Naturalist Vol. 25, No. 1 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 177 Literature Cited Aagaard, A., C.G. Warman, and M.H. Depledge. 1995. Tidal and seasonal changes in the temporal and spatial distribution of foraging Carcinus maenas in the weakly tidal littoral zone of Kerteminde Fjord, Denmark. Marine Ecology Progress Seri es 122:165–172. Audet, D., D.S. Davis, G. Miron, M. Moriyasu, K. Benhalima, and D. Campbell D. 2003. Geographical expansion of a nonindigenous crab, Carcinus maenas (L.), along the Nova Scotian shore into the southeastern Gulf of St. Lawrence, Canada. Journal of Shellfish Research 22:255–262. Behrens Yamada, S., and P.M. Kosro. 2010. Linking ocean conditions to year-class strength of the invasive European Green Crab, Carcinus maenas. Biological Invasions 12:1791–1804. Bélair, M.C., and G. Miron. 2009. Predation behaviour of Cancer irroratus and Carcinus maenas during conspecific and heterospecific challenges. Aquatic Biology 6:41–49. Benjamini, Y., and Y. Hochberg. 1995. Controlling the false discovery rate: A practical and powerful approach to multiple testing. Journal of the Royal Statistical Society: Series B 57:289–300. Beukema, J.J. 1991. The abundance of shore crabs Carcinus maenas (L.) on a tidal flat in the Wadden Sea after cold and mild winters. Journal of Experimental Marine Biology and Ecology 153:97–113. Blakeslee, A.M.H., C.H. McKenzie, J.A. Darling, J.E. Byers, J.M. Pringle, and J. Roman. 2010. A hitchhiker’s guide to the Maritimes: Anthropogenic transport facilitates longdistance dispersal of an invasive marine crab to Newfoundland. Diversity and Distributions 16:879–891. Boudreau, M.L., M.R. Boudreau, and D.J. Hamilton. 2013. The influence of body size on foraging facilitation and kleptoparasitic behavior in the Green Crab (Carcinus maenas). Journal of Experimental Marine Biology and Ecology 449:330–334. Carlton, J.T., and A.N. Cohen. 2003. Episodic global dispersal in shallow-water marine organisms: The case history of the European shore crabs Carcinus maenas and C. aestuarii. Journal of Biogeography 30:1809–1820. Department of Fisheries and Oceans (DFO). 2011. Proceedings of the Regional Advisory Process on Green Crab, Carcinus maenas: Populations and mitigations in the Newfoundland and Labrador region. St. John’s, Newfoundland and Labrador, Canada, 17 March 2010. Canadian Science Advisory Secretariat Proceedings Series 2011/020. Department of Fisheries and Oceans (DFO), St. John’s, NL, Canada. 22 pp. Drolet, D., T.T. Bringloe, M.R.S. Coffin, M.A. Barbeau, and D.J. Hamilton. 2012. Potential for between-mudflat movement and metapopulation dynamics in an intertidal burrowing amphipod. Marine Ecology Progress Series 449:197–209. Environment Canada. 2015. Historical climate data. Available online at http://climate. weather.gc.ca/. Accessed 11 February 2016. Environmental Systems Research Institute (ESRI). 2014. ArcGIS Desktop: Release 10.3, Redlands, CA. Estelle, V., and E.D. Grosholz. 2012. Experimental test of the effects of a non-native invasive species on a wintering shorebird. Conservation Biology 26: 472–481. Floyd, T., and J. Williams. 2004. Impact of Green Crab (Carcinus maenas L.) predation on a population of Soft-shell Clams (Mya arenaria L.) in the southern Gulf of St. Lawrence. Journal of Shellfish Research 23:457–462. Garbary, D.J., A.G. Miller, J. Williams, and N.R. Seymour. 2014. Drastic decline of an extensive Eelgrass bed in Nova Scotia due to the activity of the invasive Green Crab (Carcinus maenas). Marine Biology 161:3–15. Northeastern Naturalist 178 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 Vol. 25, No. 1 Gerwing, T.G., A.M. Allen Gerwing, D. Drolet, M.A. Barbeau, and D.J. Hamilton. 2015. Spatiotemporal variation in biotic and abiotic features of eight intertidal mudflats in the upper Bay of Fundy, Canada. Northeastern Naturalist 22(Monograph 12):1–44. Gerwing, T.G., J.H. Kim, D.J. Hamilton, M.A. Barbeau, and J.A. Addison. 2016. Diet reconstruction using next-generation sequencing increases the known ecosystem usage by a shorebird. Auk 133:168–177. Giraudoux, P. 2013. pgirmess: Data analysis in ecology. R package version 1.5.8. Available online at http://CRAN.R-project.org/package=pgirmess. Accessed February 2014. Gregory, G.J., and P.A. Quijón. 2011. The impact of a coastal invasive predator on infaunal communities: Assessing the roles of density and a native counterpart. Journal of Sea Research 66:181–186. Grosholz, E.D., and G.M. Ruiz. 1995. Spread and potential impact of the recently introduced European Green Crab, Carcinus maenas, in central California. Marine Biology 122:239–247. Grosholz, E.D., G.M. Ruiz, C.A. Dean, K.A. Shirley, J.L. Maron, and P.G. Connors. 2000. The impacts of a nonindigenous marine predator in a California bay. Ecology 81:1206–1224. Haarr, M.L., and R. Rochette. 2012. The effect of geographic origin on interactions between adult invasive Green Crabs, Carcinus maenas, and juvenile American Lobsters, Homarus americanus, in Atlantic Canada. Journal of Experimental Marine Biology and Ecology 422–423:88–100. Hamilton, D.J., M.A. Barbeau, and A.W. Diamond. 2003. Shorebirds, mud snails, and Corophium volutator in the upper Bay of Fundy, Canada: Predicting bird activity on intertidal mudflats. Canadian Journal of Zoology 81:1358–1366. Hedvall, O., P.O. Moksnes, and L. Pihl. 1998. Active habitat-selection by megalopae and juvenile shore crabs Carcinus maenas: A laboratory study in an annular flume. Hydrobiologia 375:89–100. Hicklin, P.W. 1987. The migration of shorebirds in the Bay of Fundy. Wilson Bulletin 99:540–570. Hothorn, T., F. Bretz, and P. Westfall. 2008. Simultaneous inference in general parametric models. Biometrical Journal 50:346–363. Jeffery, N.W., C. DiBacco, B.F. Wringe1, R.R.E. Stanley, L.C. Hamilton, P.N. Ravindran, and I.R. Bradbury. 2017. Genomic evidence of hybridization between 2 independent invasions of European Green Crab (Carcinus maenas) in the Northwest Atlantic. Heredity: 1–12. doi:10.1038/hdy.2017.22. Jost, J.A., S.M. Podolski, and M. Frederich. 2012. Enhancing thermal tolerance by eliminating the pejus range: A comparative study with 3 decapod crustaceans. Marine Ecology Progress Series 444:263–274. doi: 10.3354/meps09379. Kienzle, H. 2015. Population dynamics and interactions between invasive Green Crabs (Carcinus maenas) and native Rock Crabs (Cancer irroratus) in intertidal zones in the upper Bay of Fundy. B.Sc. Honors Thesis. Mount Allison University, Sackville, NB, Canada. 41 pp. Klassen, G., and A. Locke. 2007. A biological synopsis of the European Green Crab, Carcinus maenas. Canadian Manuscript Report of Fisheries and Aquatic Sciences No 2818. Department of Fisheries and Oceans (DFO), Ottawa, ON, Canada. Vii + 75 pp. MacDonald, A.J. 2014. Distribution, habitat use, and impacts of invasive Green Crabs (Carcinus maenas) in intertidal zones in the upper Bay of Fundy. B.Sc. Honors Thesis. Mount Allison University, Sackville, NB, Canada. 55 pp. Northeastern Naturalist Vol. 25, No. 1 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 179 MacDonald, J.A., R. Roudez, T. Glover, and J.S. Weis. 2007. The invasive Green Crab and Japanese Shore Crab: Behavioural interactions with a native crab species, the Blue Crab. Biological Invasions 9:837–848. MacPhail, J.S., and E.I. Lord. 1954. Abundance and distribution of the Green Crab. Pp. 28, In J.L. Hart (Ed.). Report of the Atlantic Biological Station for 1954. Fisheries Research Board of Canada, Ottawa, ON, Canada. 171 pp. Matheson, K., and P. Gagnon. 2012. Effects of temperature, body size, and chela loss on competition for a limited food resource between indigenous Rock Crab (Cancer irroratus Say) and recently introduced Green Crab (Carcinus maenas L.). Journal of Experimental Marine Biology and Ecology 428:49–56. Matheson K., C.H. McKenzie, R.S. Gregory, D.A. Robichaud, I.R. Bradbury, P.V.R. Snelgrove, and G.A. Rose. 2016. Linking Eelgrass decline and impacts on associated fish communities to European Green Crab, Carcinus maenas, invasion. Marine Ecology Progress Series 548:31–45. McCurdy, D.G., M.R. Forbes, S.P. Logan, D. Lancaster, and S.I. Mautner. 2005. Foraging and impacts by benthic fish on the intertidal amphipod Corophium volutator. Journal of Crustacean Biology 25:558–564. McDonald, P.S., G.C. Jensen, and D.A. Armstrong. 2001. The competitive and predatory impacts of the nonindigenous crab Carcinus maenas (L.) on early benthic phase Dungeness Crab, Cancer magister Dana. Journal of Experimental Marine Biology and Ecology 258:39–54. McLean, M.F., M.J. Dadswell, and M.J.W. Stokesbury. 2013. Feeding ecology of Atlantic Sturgeon, Acipenser oxyrinchus Mitchill, 1815 on the infauna of intertidal mudflats of Minas Basin, Bay of Fundy. Journal of Applied Ichthyology 29:503–509. Moksnes, P.O., L. Pihl, and J. van Montfrans. 1998. Predation on postlarvae and juveniles of the shore crab Carcinus maenas: Importance of shelter, size, and cannibalism. Marine Ecology Progress Series 166:211–225. Neckles, H.A. 2015. Loss of Eelgrass in Casco Bay, Maine, linked to Green Crab disturbance. Northeastern Naturalist 22:478–500. Norušis, M.J. 2008. SPSS 16.0 Advanced Statistical Procedures Companion. Prentice Hall, Inc., Upper Saddle River, NJ. 432 pp. O’Connor, N. 2014. Invasion dynamics on a temperate rocky shore: From early invasion to establishment of a marine invader. Biological Invasions 16:73–87. Quinn, J.T., and D.J. Hamilton. 2012. Variation in diet of Semipalmated Sandpipers (Calidris pusilla) during stopover in the upper Bay of Fundy, Canada. Canadian Journal of Zoology 90:1181–1190. R Core Team. 2013. R: A language and environment for statistical computing. Version 3.0.2. R Foundation for Statistical Computing, Vienna, Austria. Roman, J. 2006. Diluting the founder effect: Cryptic invasions expand a marine invader’s range. Proceedings of the Royal Society B 273:2453–2459. Ropes, J.W. 1968. The feeding habits of the Green Crab, Carcinus maenas (L.). Fishery Bulletin 67:183–203. Rossong, M.A., P.A. Quijón, P.V.R. Snelgrove, T.J. Barrett, C.H. McKenzie, and A. Locke. 2012. Regional differences in foraging behavior of invasive Green Crab (Carcinus maenas) populations in Atlantic Canada. Biological Invasions 14:659–669. Schratzberger, M., and R.M. Warwick. 1999. Impact of predation and sediment disturbance by Carcinus maenas (L.) on free-living nematode community structure. Journal of Experimental Marine Biology and Ecology 235:255–271. Northeastern Naturalist 180 A.J. MacDonald, H.M. Kienzle, D. Drolet, and D.J. Hamilton 2018 Vol. 25, No. 1 Sharp, G., R. Semple, K. Conolly, R. Blok, D. Audet, D. Cairns, and S. Courtenay. 2003. Ecological assessment of the Basin Head lagoon: A proposed marine protected area. Canadian Manuscript Report of Fisheries and Aquatic Sciences No 2641. Department of Fisheries and Oceans (DFO), Ottawa, ON, Canada. vi + 70 pp. Simard, N., S. Pereira, R. Estrada, and M. Nadeau. 2013. État de la situation des espèces envahissantes marines au Québec. Rapport manuscrit canadien des sciences halieutiques et aquatiques 3020. Pêches et Océans Canada, Ottawa, ON, Canada . vii + 61 pp. Stachowicz, J.J., J.R. Terwin, R.B. Whitlatch, and R.W. Osman. 2002. Linking climate change and biological invasions: Ocean warming facilitates nonindigenous species invasions. Proceedings of the National Academy of Sciences 99:15497–15500. Venables, W.N., and B.D. Ripley. 2002. Modern Applied Statistics with S, 4th Edition. Springer, New York, NY. Xi + 495 pp. Vercaemer, B., and D. Sephton. 2016. European Green Crab (Carcinus maenas) monitoring in the Maritimes region 2008–2015. Canadian Technical Report of Fisheries and Aquatic Sciences 3147. Department of Fisheries and Oceans (DFO), Ottawa, ON, Canada. v+56 pp. Wickham, H. 2009. ggplot2: Elegant Graphics for Data Analysis. Springer, New York, NY. Viii + 213 pp. Williams, L.M., C.L. Nivison, W.G. Ambrose Jr., R. Dobbin, and W.L. Locke V. 2015. Lack of adult novel northern lineages of invasive Green Crab, Carcinus maenas, along much of the northern US Atlantic coast. Marine Ecology Progress Series 532:153–159. Wong, M.C., and M. Dowd. 2014. Role of invasive Green Crabs in the food web of an intertidal sand flat determined from field observations and a dynamic simulation model. Estuaries and Coasts 37:1004–1016.