Aquatic Invasions (2011) Volume 6, Issue 3: 329–338 doi: 10.3391/ai.2011.6.3.09 Open Access © 2011 The Author(s). Journal compilation © 2011 REABIC Research Article Hemigrapsus sanguineus (De Haan, 1835) (Crustacea: Brachyura: Grapsoidea) a new invasive species in European waters: the case of the French English Channel coast (2008–2010) Jean-Claude Dauvin1* and Fabien Dufossé2 1Université de Caen Basse Normandie, Laboratoire Morphodynamique Continentale et Côtière, UMR CNRS 6143 M2C, 2-4 rue des Tilleuls, F-14000 Caen, France 2Université Lille1, UMR CNRS 8187 LOG, Station Marine de Wimereux, BP 80, 28 avenue Foch, F-62930 Wimereux, France E-mail: [email protected] (JCD), [email protected] (FD) *Corresponding author Received: 28 November 2010 / Accepted: 20 April 2011 / Published online: 11 May 2011 Abstract The unintentional introduction of the Asian shore crab, Hemigrapsus sanguineus, along the French coast during the mid 1990s has revealed the problematic effects that invasive species can have on biodiversity, entering into competition with native crab species. This invasion along coastal ecosystems of northern France has become an ineluctable, irreversible phenomenon. The present study describes the distribution and abundance of H. sanguineus along the French side of the English Channel from the Cotentin to the Opal Coast on the Dover Strait in spring and summer 2010. The results were compared with those obtained previously in 2008 and 2009 for the same areas and now show that the crab has increased in numbers since its first sighting in 1999. In 2010, the maximal abundance reached 51 ind.m-2 in Dunkirk harbour, and 69 ind.m-2 at La Hougue in the eastern part of the Cotentin Peninsula. Hemigrapsus sanguineus has been sighted all along the southern coastline of the English Channel to the North Sea (approximately 1,500 km). Its high colonisation potential suggests that this brachyuran could continue its invasion in European waters. Therefore a European surveillance network might be necessary to monitor its progression in the north-eastern Atlantic Ocean. Key words: Hemigrapsus sanguineus, Asian shore crab, invasive marine brachyuran, Crustacea, Decapoda, southern coastline of English Channel, North Sea Introduction often negative effects affect the flux of matter and the trophic chains causing the mortality of The Asian crab Hemigrapus sanguineus (De some autochthonous species due to great inter- Haan, 1835) has colonised most of the French species competition. In the case of H. sangui- English Channel coast since it was first neus, it is suspected that its introduction, as well introduced into Le Havre harbour in 1999 as another Asian crab (the brush-clawed shore (Breton et al. 2002; Dauvin 2009a, b; Dauvin et crab Hemigrapsus takanoi Asakura and al. 2009). Subsequently, the species has been Watanabe, 2005, could reduce the abundance of recorded all along the north-east European coast, the autochthonous green crab Carcinus maenas from the western coast of the Cotentin in the (Linnaeus, 1758) in the areas colonized by these English Channel to the North Sea coast species (Dauvin et al. 2009). The introduction of bordering the German state of Schleswig- invasive species is often irreversible in the Holstein (Dauvin et al. 2009). In addition, colonised environment (Clout 1998). However, H. sanguineus has formed abundant populations the speed with which an introduced species at some littoral sites in the eastern part of the extends its range varies greatly from one species Cotentin, a peninsula that divides the English to another, and also from the first colonized area Channel (north-eastern Atlantic) into two basins, (McDermott 1998). In the case of H. sanguineus, west and east (Dauvin 2009a, b) and the Dover its expansion rate has been estimated at 12 km Strait (Dauvin et al. 2009). per year along the eastern coast of the United Introduced species may have major effects on States (Leppäkoski and Olenin 2000). the characteristics and dynamics of the colonised According to Valéry et al. (2008) an invasive ecosystem (Occhipinti-Ambrogi 2007). These species has four main characteristics: 1) compe- 329 J.-C. Dauvin and F. Dufossé tition with autochthonous species; 2) a geo- Sampling procedure graphical discontinuity between the native area At each of the sampled sites (Appendix 1 and 2), and the colonised areas; 3) demonstrate a rapid Hemigrapsus sanguineus specimens were expansion; and 4) rapidly become a dominant counted underneath three groups of 30 boulders species in the colonised areas. The aim of this in the mid-littoral zone, for a total of 90 boulders paper is to illustrate the ability of Hemigrapsus per site. This sampling design has been adopted sanguineus to colonise and establish populations for estimating the abundances of shore crabs along the French coast of the English Channel. (Dauvin 2009a, b; Dauvin et al. 2009). In the sites corresponding to highly colonised zones – three sites in the Cotentin (Querqueville, Materials and methods Gatteville-Phare and La Houge) and three sites along the Opal Coast (Wimereux-Fort de Croy, Field sites Dunkirk harbour and Dunkirk outer harbour) – the population density estimations were made Opal Coast using 1m² quadrats, with three replicates being The 160 km of the French coast along the eastern undertaken at each of the sites (Table 6). Rocks English Channel, from the Authie estuary in the and boulders were turned over to collect the south to the Belgian border and the southern crabs; in some cases, it was also necessary to North Sea in the north, is known as the Opal extract the crabs from the burrows that they had Coast (Figure 1). This coastline is characterized dug. by a succession of sand dunes and rocky shores, extending from Boulogne-sur-mer to Gris Nez Laboratory observations Cape and Blanc Nez Cape. Hard substratum with dykes and boulders are also found in the Authie, Hemigrapsus sanguineus crabs were counted and Canche and Aa estuaries and in the three main sexed. Then the carapace width (CW) was harbours of the region: Boulogne-sur-mer, Calais measured between the third antero-lateral teeth and Dunkirk. As shown in Figure 1, a total of 16 (Delaney et al. 2008). Class-size histograms potential favourable crab habitats (Table 1; were then constructed for 2mm classes. Appendix 1) were sampled at the beginning of spring (i.e., from the end of March to the Results beginning of May) 2008 and 2010. Distribution and abundance The Cotentin Peninsula The 2010 observations confirmed those acquired In the Channel, the Cotentin Peninsula includes in 2008 and 2009. Along the Opal Coast, two the northern sector of the ‘Manche Department’, main areas colonized by Hemigrapsus from Saint-Jean-le-Thomas to Hague Cape sanguineus could be identified: 1) the sites in the (Goury) to the west and from Gatteville-Phare to southern part of Boulogne-sur-mer, which were the Bay of Veys to the east, including Cherbourg poorly colonised, with only one specimen harbour (Figure 1). From the Flamanville Cape collected at Berck and 11 at Le Portel in 2010, to Saint-Vaast-la-Houge, the coastline is mainly and 2) the sites from Boulogne-sur-mer to rocky shores. On the western part of the Dunkirk, which were abundantly colonised by Cotentin, south to Flamanville, the coastline is H. sanguineus, especially the sites with high essentially composed of sand dunes, except two hydrodynamics exposure outside the harbours rocky shore zones (i.e., the Barneville-Carteret and Granville capes). Some rocky outcrops (Figure 1, Table 1). In 2010, the western coast appear in the mid-littoral zone where there is a around the Cotentin Peninsula remained poorly sand dune habitat. Fifteen sites were sampled in colonised, whereas the north and eastern part of 2008; 19 sites were sampled in 2009 and 2010, the peninsula showed more abundantly colonized including three harbours (Granville, Carteret and sites (Figure 1, Table 2). Fermanville), three protected sites (Querqueville, For the most abundantly colonised sites, Table Salines and Saint-Vaast), and 13 other sites 3 gives the number of H. sanguineus collected around the Cotentin Peninsula located in areas underneath 90 boulders throughout the three with relatively high hydrodynamics (Figure 1, years of the survey. Except for some sites [i.e., Table 2, and Appendix 2). Salines (Cotentin Peninsula) and Dunkirk outer 330 Hemigrapsus sanguineus a new invasive species in European waters Figure 1. Location of the 16 sites that were sampled along the Opal Coast in April-May 2008 and 2010 (right above, see Table 1 for the abbreviations of the sampled locations) and the 19 sites that were sampled around the Cotentin Peninsula in July-August 2008, 2009 and 2010 (left above) (see table for the abbreviations of the site from the Opal coast). harbour (Opal Coast)], there was clearly a Size frequency general regular increase over the years of study An example of the yearly changes of the size- of the population abundances. Four high frequency (carapace-width) of H. sanguineus at colonisation sites appeared in the English La Houge site in the eastern part of the Cotentin Channel – Gatteville-Phare and La Hougue in the Peninsula for the three years of the survey are eastern part of the Cotentin Peninsula, and shown in Figure 2. Wimereux – ‘Fort de Croy’ and Griz Nez Cape In 2008, the size of sampled individuals on the Opal Coast – where the numbers of ranged from 6 to 32 mm, with the 16–18 mm size individuals underneath the boulders were more class being the most frequent. Three modes than 200. could be identified: young individuals around 6– 8 mm, medium individuals between 16–18 mm Density and the largest individuals varying between 28– In the most abundantly colonised sites, the 32 mm.