Crustacean Research 2019 Vol.48: 23–37 ©Carcinological Society of Japan. doi: 10.18353/crustacea.48.0_23 Callinectes sapidus Rathbun, 1896 (Brachyura: Portunidae): An assess- ment on its diet and foraging behaviour, Thermaikos Gulf, NW Aegean Sea, Greece: Evidence for ecological and economic impacts Thodoros E. Kampouris, Joanne S. Porter, William G. Sanderson Abstract.̶ The blue crab, Callinectes sapidus Rathbun, 1896, is native to the Atlantic coasts of the Americas and globally one of the most highly invasive marine species. In the present study, the species’ diet and the foraging behaviour was studied in the Thermaikos Gulf and Papapouli Lagoon for the first time. Surveys were undertaken using fyke nets, shore surveys, scuba and snorkelling. Additional data were compiled from systematic interviews with mussel farmers, shellfish traders and fishermen. In both Thermaikos Gulf and Papapouli Lagoon C. sapidus was found to prey on a wide variety of species including economically important molluscs, fishes, and crustaceans, indicating a substantial potential impact on fisheries and aquaculture in the region. Observation showed that over 6 (2009–2014) years, the blue crabs became dominant in Papapouli Lagoon at the expense of the native commercially fished crab Carcinus aestuarii Nardo, 1847 according to fisheries data. Potential management implications are discussed. Key words: blue crab, alien species, ecological imbalances, invasive species, biodiversity, East Mediterranean Sea ■ Introduction alien decapods from the Mediterranean. Main vectors of introduction are the Suez Canal, ship- According to the European Commission ping and accidental escapes from aquaculture (2014), Invasive Alien Species (IAS) are those (Galil, 2011; Katsanevakis et al., 2014). with ‘a significant negative impact on biodiver- The blue crab̶Callinectes sapidus Rathbun, sity as well as serious economic and social con- 1896, is native to the Atlantic coast of the Amer- sequences’ and the EU Marine Strategy Frame- icas and is distributed from Nova Scotia to Uru- work Directive and the EU Regulation guay and Argentina including the Gulf of Mexi- 1143/2014 on the prevention and management co and the Caribbean Sea. The species inhabits a of the introduction and spread of invasive alien wide variety of marine, brackish and freshwater species establishes monitoring requirements that environments (Hill et al., 1989; Carr et al., have yet to be implemented (Lehtiniemi et al., 2004). It can be found on the continental shelf in 2015). In the Mediterranean Sea, IAS are a ma- estuaries, lagoons and near-shore waters from jor source of biodiversity loss (Galil, 2011; depths of 0 to 90 m on sandy and muddy sub- Mačić et al., 2018). For instance, Galil (2011) strates with or without vegetation (Millikin and reports 100 alien crustacean species. Further- Williams, 1984; Mizerek et al., 2011). more, Manfrin et al. (2018) report more than 86 In Europe, blue crabs were reported from non-indigenous decapod species. Also, Galil et 1900 from the Atlantic coast of France (Neh- al. (2015), under different criteria, indicated 91 ring, 2011). It has since been introduced to the Received: 21 Nov 2018. Accepted: 8 Feb 2019. Published online: 2 Apr 2019. 23 THODOROS E. KAMPOURIS, JOANNE S. PORTER, WILLIAM G. SANDERSON European North East Atlantic in Denmark, mains; Benedict, 1940). The species may also Germany, United Kingdom, Netherlands and consume detritus and a minor proportion of the France (Ingle, 1997; Nehring, 2011), with no diet consists of plant matter (Darnell, 1958). clear vector of introduction (Nehring, 2011). In Almost exclusively, the literature on the feed- the Mediterranean, the blue crab appeared in ing behaviour and prey preferences of the blue 1949 or earlier (Nehring 2011; Mancinelli et crab C. sapidus is based on its native range. In al., 2016) with the most recent observations re- the U.S.A., Brazil and in some Western Euro- corded by Mancinelli et al., (2017a, 2017b). In pean countries (e.g. UK) C. sapidus has a sig- addition, C. sapidus was recored in Hawaii nificant economic value (Stagg and Whilden, (Eldredge, 1995) and in Japan (Doi, et al. 1997; Severino-Rodrigues et al., 2013). The 2011), making it one of the world’s most suc- main products are soft shell crabs or live bait. cessful invasive species. In the Mediterranean, an important fishery ex- In their native habitats, blue crabs are among ists in Turkey (Tureli-Bilen and Yesilyurt, the most well studied decapods. The species is 2014) and a smaller scale fishery exists in the opportunistic in its feeding habits (Carrozzo et Adriatic Sea (Manfrin et al., 2015) and Egypt al., 2014) consuming small crustaceans, mol- (Abdel Razek et al., 2016). In Greece, though luscs, plants and fishes. Blue crabs have been that a relative fishery is developed (Perdikaris shown to have important influences on Ameri- et al., 2016; Mancinelli et al., 2017b; Kevreki- can food webs (Laughlin, 1982) and can alter dis and Antoniadou, 2018), blue crabs have a local benthic community structure and diversi- very low commercial value and are a by-catch ty by changing the distribution and abundance product, yet some quantities are exported (pers. of key species (Ebersole and Kennedy, 1995). com.). In Greece, the blue crab is not well- They also feed on economically important spe- studied, with only a handful of published data cies such as the winter flounder (Collier et al., being available (Kevrekidis et al., 2012, 2013; 2014). The species is pliable in its feeding hab- Perdikaris et al., 2016; Kevrekidis and Anto- its regionally and seasonally, consuming, for niadou, 2018). None of them is related with the example, more fish prey in late autumn and species’ feeding ecology. early winter and more shrimp during summer In the new era of science, cameras are used and fall in Florida (Laughlin, 1982). Juvenile frequently (Struthers et al., 2015), especially crabs prefer to feed during nighttime, while the when scuba diving (e.g. Cook et al., 2013) and adults are day-time feeders, mainly in the after- along with fisheries gear (Cairns et al., 2017; noon (Darnell, 1958). Larger crabs are active Merten et al., 2018). Moreover, the use of under- hunters, predating on mobile species (Laughlin, water photography and videography has proven 1982) like fishes, prawns and crabs and canni- to be useful at detecting alien species (e.g. Mar- balism of juveniles is also a wide spread be- celli et al., 2016). Furthermore, photographic haviour (Laughlin, 1982). Blue crabs often material and videos were used on the assessment swim to the water surface or to the water-air of foraging behaviour regarding crabs (Krieger interface to feed on abundant molluscs (e.g. et al., 2016) and turtles (Fujii et al., 2018). The Littorina irrorata; Hamilton, 1976) and on spat authors of the present study applied these meth- of small and large sized bivalves, like mussels, ods as well as conventional traps. oysters and clams (Blundon and Kennedy, The aim of the present study is to describe 1982; West and Williams, 1986). Blue crabs systematically the predation strategies and the are known to scavenge on terrestrial trapped, prey preferences of the invasive blue crab, C. dead or decaying animals (Darnell, 1958) and sapidus, across a wide sea area in its non-na- on animal tissues (e.g. skin, bones, fish re- tive eastern Mediterranean range for the first 24 Crustacean Research 48 BLUE CRAB DIET AND FORAGING BEHAVIOUR, AEGEAN SEA, GREECE time and compare this with accounts from the tions dictate a seasonality in sediment and sea Americas. The dominance of blue crabs is also water availability. The Papapouli wetland has investigated over time in a case-study of a la- been characterized as a wildlife refuge and it is goon complex within the study area. The re- an EU Habitat/Species Management Area IV sults are discussed in relation to the potential (European Environmental Agency, 2017). biodiversity impacts and economic importance of the blue crab in Thermaikos Gulf, Greek Survey methods waters and the eastern Mediterranean generally. Underwater and shore surveys.̶Eleven scu- ba diving surveys were conducted in six differ- ■ Material and Methods ent locations from 14 September to 9 November 2014 (Fig. 1): two at Plaka Beach Study areas (40°05′49.4″N, 22°34′07.7″E), two at Neoi Thermaikos Gulf is at the northwestern Ae- Poroi Beach (39°58′40.6″N, 22°39′22.5″E), one gean Sea (Fig. 1). It is the largest gulf at Pineios River estuaries (39°56′11.8″N (5,100 km2) in the area and is one of the most 22°43′07.3″E). Six more surveys were conduct- productive parts of the eastern Mediterranean ed at the east shores of Thermaikos Gulf: four at basin (Sakellariou and Alexandri, 2007) sup- Potamos Beach (40°22'32.8″N 22°53'49.9″E) porting the most important fishing activity in (ship wreck area), two at the saltworks of Epa- the Hellenic waters (Stergiou et al., 1997). nomi (40°26′17.1″N 22°51′47.6″E). All scuba Thermaikos Gulf has an extensive shelf, little dives were performed in morning hours from depth variation and it is dominated by soft sed- 09:00 to 12:30, standard protocols were fol- iments -amplified by the heavy trawling activi- lowed with two divers working together, freely ty (Dimitriadis et al., 2014). The main decapod searched foraging C. sapidus. The depth range species that support the regional fisheries are was 2–20 m. Additionally, 24 snorkel diving and the caramote prawn Penaeus kerathurus and beach surveys (09:00–14:00) were conducted at the pink shrimp Parapenaeus longirostris the aforementioned areas from 1 June to 20 July (Thessalou-Legaki, 2007). Moreover, Kam- 2014 and following the same protocol. The pouris et al.