Management of Biological Invasions (2013) Volume 4 in press © 2013 The Author(s). Journal compilation © 2013 REABIC
Open Access
Research Article CORRECTED PROOF
Additional records and distribution (2011-2012) of Hemigrapsus sanguineus (De Haan, 1835) along the French coast of the English Channel Moâna Gothland 1*, Jean-Claude Dauvin 2, Lionel Denis1, Sandra Jobert2, Julien Ovaert1, Jean-Philippe Pezy2 and Nicolas Spilmont 1,3 1 Université de Lille Nord de France; Université Lille 1, Laboratoire d’Océanologie et Géosciences, CNRS UMR 8187 LOG, BP 80, F_62930 Wimereux, France 2 Normandie Université, UNICAEN, Laboratoire Morphodynamique Continentale et Côtière, CNRS UMR 6143 M2C, 24 rue des Tilleuls, F-14000 Caen, France 3 Environmental Futures Centre, Griffith University, Gold Coast QLD 4222, Australia
*Corresponding author E-mail:
[email protected] Received: 30 May 2013 / Accepted: 21 October 2013 / Published online: 25 November 2013 Handling editor: Justin MacDonald
Abstract The invasion process can be described as a succession of stages initiated by the transport of organisms from their native range to a new area where they persist, proliferate and spread. It is important to monitor the demographic development of invaders for management purposes. This study focuses on the different stages of population development during the invasion process and underlines the importance of understanding and monitoring the ‘persistence phase’. The distribution of Hemigrapsus sanguineus (Asian shore crab) in the English Channel, along the French coast, was first undertaken in 2008. In 2010, 35 sites were surveyed and it appeared that the abundance of this species had already established a 2–5 fold increase since 2008. The present study presents the geographical distribution of H. sanguineus in 2011 and 2012 which includes a further 39 sites (72 sampling stations in 2012). All populations observed during previous years persisted in 2011 and 2012. In 2012, H. sanguineus was detected at 61 sites; 36 intensely colonised (including 3 newly colonised sites compared to 2011); 22 had trace numbers and 3 sites had ‘proven presence’. In addition to males with carapaces up to 39 mm width (CW), abundances increased by a factor of 2 since 2010, which testifies for the naturalized status of the species along the French coast of the English Channel. Since 2008, La Hougue proved to be the most abundantly colonised site along the French coast. By 2011 it had an average density of 101±19 ind.m-2 , with an abundance of 258±54 individuals (under 30 boulders). Populations were subsequently halved in 2012. Increasing densities and abundances recorded between 2008 and 2011 at la Hougue suggest that H. sanguineus had reached the ‘expansion phase’, but the dynamics of H. sanguineus populations at the most colonised sites (12 sampling sites with abundance >200 individuals under 30 boulders), suggest that maximum values had already peaked and that the ‘persistence phase’ was probably reached. The implementation of pluri-annual surveys seems of prime importance to correctly evaluate population dynamics of alien species. Key words: Hemigrapsus sanguineus; Asian shore crab; invasive marine species; English Channel
Introduction The collection of basic information on the occurrence and spatial distribution of alien species, their rate of spread and their biological and ecological traits is a stepping stone for the assessment of biological invasions (Katsanevakis et al. 2013). More specifically, it is necessary to assess the demographic strategies and ecological characteristics of alien species to estimate their impact on ecosystems. Invasive species can change the structure and the functioning of marine ecosystems (Grosholz 2002) at all biological levels
(genome, individual, population, species, communities and ecosystem) via predation, parasitism, pathogen transfers and also physical and chemical modifications of habitats (Beisel and Lévêque 2010). Hemigrapsus sanguineus (De Haan, 1835), one of today’s most studied invaders in the USA is native to the north-western Pacific, and was observed for the first time in France in 1999 at Le Havre (Breton et al. 2002). A survey of the spread of this species along the French coast of the English Channel was not initiated until the spring of 2008 (Dauvin et al. 2009). The crab
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was detected at 35 sites in the upper and middle mediolittoral zones, under boulders. Regular harvesting of juveniles and ovigerous females and the extent of the breeding season the small size of the first spawning (carapace witdth 10 ind. under 30 boulders), proven presence. (Di: Dielette; GP: Gatteville-Phare; GM: Grancamp-Maisy; SH: St Honorine des Pertes; LM: Longues sur Mer; AM: St Aubin sur Mer; LsM: Lion sur Mer; TM: Trouville sur Mer; BO: Boulogne-sur-Mer harbour; W: Wimereux; CA: Calais harbour; DH: Dunkirk harbour).
encountered. Frequency distributions (%) of carapace- width (1 mm classes) were also determined. A t-test was used to determine differences in abundance of H. sanguineus between 2010–2011 and 2011–2012 for each study area (e.g. Cotentin Peninsula). Data examined for 2010 is from Dauvin and Dufossé (2011). A Mann-Whitney Wilcoxon test was used to determine differences in abundance between 2010–2011 and 2011–2012 for the sampling sites (e.g. La Hougue). For all statistical tests, the risk level was set at 5%. Results Hemigrapsus sanguineus distribution In 2012, H. sanguineus was detected at 61 sites out of a total 72 sampled (Figure 1b). Three new sites supported the Asian crab, namely Dielette in the Cotentin Peninsula, and Grancamp-Maisy and St Aubin sur Mer along the Calvados coast. The presence of the crab was considered as ‘trace’ at 22 sites, ‘colonised’ at 36 sites and ‘proven presence’ at the remaining 3 sites. The most colonised areas were the Northern and the Eastern parts of the Cotentin Peninsula, the Calvados coast, South of the Albâtre Coast and North of the Opal Coast (Boulogne-sur-Mer to Dunkirk harbour) (Table 1, Table 2 and Figure 1).
Figure 2. Size distribution (%) of carapace width classes (CW; mm) of H. sanguineus sampled along the French coast of the English Channel in 2012 (a. white: size distribution of both sexes, black: size distribution of females; b. grey: size distribution of ovigerous females).
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Table 1. Abundance (individuals under 30 boulders, mean ± s.d.; rounded up to the nearest unit), density (ind.m-2 , mean ± s.d.; rounded up to the nearest unit), sex ratio (male/female) and % of ovigerous females (number of ovigerous females/total number of females) of Hemigrapsus sanguineus along the Opal Coast (sampled spring 2012) and the Albâtre and Picarde coast (sampled summer 2012). See Appendices 1 and 4 for sampling dates. Location The Opal Coast Berck Le Touquet Le Portel Boulogne harbour site ‘roro’ Boulogne harbour Wimereux ‘Pointe de la Crèche’ Wimereux ‘Fort de Croy’ Wimereux ‘Pointe aux Oies’ Ambleteuse Gris Nez Cap Blanc Nez Cap Calais harbour Grand-Fort-Philippe (Aa) Dunkirk harbour The Albâtre and Picarde Coast Ault St Martin en Campagne Dieppe outside harbour Saint-Aubin Saint-Valéry Veulettes Grandes Dalles Senneville Benouville Etretat St Jouin de Bruneval Ste Adresse Le Havre
Abundance Under 30 boulders
Density
Sex ratio M/F
% of Ovigerous Females
1±0 0 16±1 16±12 2±1 97±25 209±106 42±12 32±14 38±26 1±1 2±1 1±1 77±12
4±3 1±1 1±1 16±6 5±3 0 5±4 0 3±4 6±3
1.54 1.11 0.92 1.40 0.78 0.68 1.00 1.07
0 0 0 3.01 0 0 3.70 0 0 0
2±3 0 55±3 20±4 8±3 24±12 18±3 6±1 23±4 7±1 33±5 11±3 62±5
9±1 3±2 9±2 5±1 3±1 8±3 3±1 10±3 4±1 19±5
0.50 1.10 2.23 2.89 1.13 1.65 7.67 1.27 3.00 0.92 1.93 0.97
0 12.82 59.09 22.22 61.70 38.46 66.67 48.78 57.14 44.78 46.67 37.70
Size distribution and sex-ratio
Abundances and densities
A total of 6,792 individuals were collected in 2012 with sizes ranging from 1–39 mm (carapace width, CW) for males and from 3–29 mm for females (Figure 2). Three modal classes were observed: 4–5 mm CW for very young individuals, 11–12 mm for medium-sized individuals and 18– 19 mm for large individuals. Medium and large individuals were observed during spring and summer, contrary to very young individuals which were generally observed in the spring. In 2012, 443 ovigerous females were observed throughout the sampling area (essentially during the summer); ranging from 6 to 29 mm; 53.1% were mature before reaching 19 mm (CW; Figure 2). The male/female sex ratio was examined during the reproductive period in summer 2012. Male/female sex ratio favoured males with a ratio of > 1 for all four geographical areas. An increased ratio of 1.79 was found along the Cotentin Peninsula, but an even greater ratio of 2.89 was found along the Albâtre and Picarde coast.
Population abundances remained unchanged in all areas between 2010–2011 and 2011–2012 (t-test, p>0.05). Heavily colonised sites in 2012 (i.e. >200 individuals under 90 boulders), were numerous and included Gatteville-Phare, La Hougue, St Honorine des Pertes, Longues sur Mer, Lion sur Mer, Trouville sur Mer, Honfleur 2, Wimereux ‘Fort de Croy’, Wimereux ‘Pointe de la Crèche’ and Dunkirk harbour (Figure 1b). In 2012, densities ranged from 1 ind.m-2 to 70±21 ind.m-2 (St Honorine des Pertes in the ‘Calvados Department’; Table 1 and 2). At Wimereux ‘Pointe de la Crèche’, Dunkirk harbour, St. Honorine des Pertes and Honfleur 2, abundances were higher than during previous years (Wilcoxon-Mann-Whitney test, p
