First Record of a Fertilized Female Blue Crab

Home , Callinectes sapidus

Aquatic Invasions (2010) Volume 5, Issue 2: 215-218 This is an Open Access article; doi: 10.3391/ai.2010.5.2.15 Open Access

Short communication

First record of a fertilized female blue crab, Callinectes sapidus Rathbun, 1896 (Crustacea: Decapoda: Brachyura), from the German Wadden Sea and subsequent secondary prevention measures

Stefan Nehring1* and Uilke van der Meer2 1Federal Agency for Nature Conservation, Konstantinstraße 110, 53179 Bonn, Germany 2National Park House, Wadden Sea of Lower Saxony, Oll Deep 7, 26553 Dornumersiel, Germany E-mail: [email protected] (SN), [email protected] (UVDM) * Corresponding author Received: 22 October 2009 / Accepted: 10 December 2009 / Published online: 15 January 2010

Abstract

A single female specimen of the blue crab Callinectes sapidus Rathbun, 1896 was captured by a fisherman on 26 May 2008 in the East Frisian Wadden Sea, National Park of Lower Saxony, Germany. The specimen was transferred to a public marine aquarium in Dorumersiel. On 9 June 2008 the female extruded masses of fertilized eggs. Due to nature conservation efforts in this national park, management instructions are implemented by the appropriate authority for further dealing with the captured specimen and its potential offspring. This is the second record of a mature female and the first record of a fertilized female blue crab from German coastal waters of the North Sea.

Key words: Callinectes sapidus, Crustacea, alien species, North Sea, Germany, management

A single fertilized female specimen of the Ame- specimens of the balanoid Balanus crenatus rican blue crab, Callinectes sapidus Rathbun, Bruguière, 1789 (Figure 1) which indicates a 1896, was caught by a shrimp fisherman using a considerable period of time since its last molt shrimp beam trawl on 26 May 2008 while fishing took place. According to Hill et al. (1989) they in the East Frisian Wadden Sea at the Accumer- copulate only once in their lives, the sperm from sieler Balje (53°43.7'N and 7°27.1'E), the tidal this mating is stored in seminal receptacles and inlet between the German islands Baltrum and may be used as often as a female spawns, Langeoog at a water depth of 8 m (Figure 1, generally two or more times during a one to two Table 1). The carapace length was 8.3 cm, total year period. carapace width was 16.5 cm and 12.5 cm width On 12 June 2008, immediately after the egg- when excluding the longest lateral spines. It carrying status of the captured female became weighed 190 g. The specimen was directly known, the Lower Saxony Wadden Sea National transferred to the public marine aquarium of the Park Authority decreed that a release of this National Park House in Dorumersiel. specimen into the wild would not be allowed. By After fourteen days in the aquarium at a producing this order the deliberate release of a salinity of 30 PSU and water temperature of potentially invasive alien species into the 19°C, normal for Wadden Sea summers, Wadden Sea, which is a multiple protected fertilized eggs were extruded within a period of marine nature reserve (see Nehring and Hesse two hours to form a cohesive mass on the 2008), was prevented. This management underside of the abdomen. Mating will have instruction is in fully agreement with the taken place some time before its capture because ‘Guiding Principles of the Convention of most females spawn for the first time two to nine Biodiversity’ (CBD 2002) and the ‘European months after mating (Hill et al. 1989). Moreover Strategy on Invasive Alien Species’ (Council of mating occurs when the female is ready to molt Europe 2003) which oblige member states to into the mature stage (Hill et al. 1989). The prevent unwanted (re)introductions of alien captured specimen had an extensive covering of species. Additionally the national park authority

215 S. Nehring and U. van der Meer required that measures were taken to prevent the water of the aquarium, in which the female crab was held, to reach the Wadden Sea. Otherwise blue crab larvae may reach the environment. According to our current state of knowledge, this is the first time such secondary prevention measures for a captured aquatic alien species were ordered in Germany for the Wadden Sea National Park. Initially the egg mass was orange-yellow in color, but it gradually darkened to black. After two weeks the eggs hatched and released an unknown number of blue crab larvae. Sandoz and Rogers (1944) reported that hatching of blue crab eggs must occur at salinities of 23 to 33 PSU and water temperatures of 19 to 29°C, conditions occurring in the aquarium. A release of crab larvae to the Wadden Sea was prevented Figure 1. Mature female of Callinectes sapidus Rathbun, by rigorous management of the closed water 1896 caught in the German Wadden Sea on 26th of May 2008. circulation system at the aquarium. Additionally The carapace is covered by specimens of the barnacle Balanus crenatus Bruguière, 1789 (photo by M. Kröger). all hatched larvae were extracted through continuous filtration and no juvenile crab was observed in the aquarium afterwards. On 2 July 2009 the captured blue crab died a natural death in the aquarium and was preserved.

Figure 2. Occurrence and (first) records of living Callinectes sapidus Rathbun, 1896 in German and adjacent waters (Data sources: Adema 1991, Wolff 2005, Tendal and Flintegaard 2007, Nehring et al. 2008, present study).

216 Fertilized Callinectes sapidus from the German Wadden Sea

Table 1. Records of Callinectes sapidus in German waters in 1964-2008. Site Geographic coordinates No. Location Species Record date Sex Phase Reference (Map (River, site name) Latitude, Longitude, abundance Ref.) °N °E Elbe estuary, near 1 53°53.2' 08°43.2' 12.09.1964 1 male mature Kühl 1965 Cuxhaven Weser estuary, near 2 53°32.1' 08°33.7' ca. 1965 1 unknown unknown Nehring et al. 2008 Blexen Weser estuary, Power U. Ocken in 3 station at Bremen 53°07.1' 08°43.4' ca. 1990 1 male mature? Nehring et al. 2008 harbour Weser estuary, Power U. Ocken in 4 station at Bremen 53°07.1' 08°43.4' ca. 1990 1 male mature? Nehring et al. 2008 harbour Weser estuary, inner 5 53°23.4'a 08°29.4'a 04.11.1998 1 male mature Geiter 2000 estuary Weser estuary, near 6 Mellumplate - Hohe 53°47.0' 08°07.8' 20.07.2007 1 female mature Nehring et al. 2008 Weg roads Eastfrisian Wadden mature, 7 Sea, Accumersieler 53°43.7' 08°27.1' 26.05.2008 1 female present study fertilized Balje a Coordinates are not exactly known.

Live specimens of C. sapidus were recorded passive dispersal of larvae with water currents or from the German North Sea coast in 1964, ca. the transport of juvenile or adult specimens as 1965, ca. 1990 and 1998 (Nehring et al. 2008) hitchhikers on a ships’ hull are also possible (Figure 2, Table 1). These were males except for pathways of introduction. The use of the the second record where sex was not determined. barnacles on the carapace as a biogeographically The first mature female, an unfertilized marker is not really helpful in this case (Figure specimen, was caught by a German shrimp 1) because the circumpolar species B. crenatus fisherman in the outer Weser estuary in 2007 indicates only that, since its last molt, the (Figure 2, Table 1) and died in a public marine captured blue crab has lived in European waters aquarium 16 months later (Nehring et al. 2008, or elsewhere in the Northern hemisphere Gabriele Speckels pers. comm.). The present (Hutchins 1952). However, it is conceivable that record in 2008 is the first record of a fertilized the captured blue crab has lived for a more or female blue crab from German coastal waters of less prolonged period on the German North Sea the North Sea. Elsewhere ovigerous females coast before it was caught. It is very likely that have been recorded from the northern coasts of C. sapidus can survive German winters with France, Belgium and the Netherlands (ICES lowest water temperatures of about 2°C (Otto et WGITMO 2001, 2006, 2007; Wolff 2005) al. 1990) because blue crabs can tolerate even (Figure 2). Hill et al. (1989) noted that adult blue acute periods of freezing temperatures (Bauer crabs are excellent swimmers and can migrate 2006). At temperatures below 5°C, blue crabs several hundred kilometers (Callinectes, from enter a dormant phase during which they bury the Greek calos = “strenuous”, nectes = “swim- into the sediments, by which means they are mer”, sensu Stimpson 1860). Migrations of insulated from cold water to some extent (Hill et females are usually associated with mating, al. 1989; Hill 2004). gonadal maturation and spawning (Hill et al. Within the native range of C. sapidus at the 1989). And so an active migration of the Atlantic coast of America blue crabs occupy captured fertilized female from Benelux, where water ranging from a near-ocean salinity of 34 the occurrence of permanently established PSU to freshwater in rivers as far as 195 km populations of C. sapidus is very likely upstream from the coast (Hill et al. 1989). (Kerckhof et al. 2007; Wolff 2005), and to the However, male and female blue crabs gather in German North Sea coast is plausible. However, different areas of salinity, with adult males

217 S. Nehring and U. van der Meer tending to remain at lower salinities (Hill et al. Grabemann I, Krause G, Siedler G (1983) Langzeitige 1989). It is interesting that the known German Änderungen des Salzgehaltes der Unterweser. Deutsche Hydrographische Zeitschrift 36: 61-77, doi:10.1007/ records show a similar pattern (Figure 2, Table BF02313285 1). Males were found in the upper estuaries of Hill J, Fowler DL, Avyle MV van den (1989) Species the River Elbe and of the River Weser in a profiles: Life histories and environmental requirements of coastal fishes and invertebrates (Mid-Atlantic) - Blue salinity range of 1 to 23 PSU (Grabemann et al. crab. U.S. Fish and Widlife Service Biological Report 1993), while both females were captured in 82(11.100), 18 pp adjacent marine waters at salinities >30 PSU Hill K (2004) Callinectes sapidus. Smithsonian Marine (BLMP 2005). Due to the infrequent occurrence Station at Fort Pierce, http://www.sms.si.edu/IRLSpec/Callin_ sapidu.htm (Accessed 28 October 2009) of crabs in German waters the potentially Hutchins LW (1952) Geographical distribution. In: Woods invasive C. sapidus is not yet considered to be Hole Oceanographic Institution (ed) Marine fouling and established (cf. Gollasch and Nehring 2006, cf. its prevention, U. S. Naval Institute Annapolis, pp 91- Nehring et al. 2008). 101 ICES WGITMO (2001) Report of the Working group on Nevertheless, the recent record of a fertilized Introductions and Transfers of marine Organisms, female specimen of Callinectes sapidus in Barcelona, Spain, 21-23 March 2001. ICES CM German waters is remarkable as an introduced 2001/ACME:08, 104 pp mature female specimen has theoretically a ICES WGITMO (2006) Report of the Working group on Introductions and Transfers of marine Organisms, higher potential for the establishment of a Oostende, Belgium, 16-17 March 2006. ICES CM founder population compared to an introduced 2006/ACME:05, 330 pp male specimen because a single female crab may ICES WGITMO (2007) Report of the Working group on release millions of fertilized eggs. Therefore the Introductions and Transfers of marine Organisms, Dubrovnik, Croatia, 21-23 March 2007. ICES CM management instructions by the appropriate 2007/ACME:05, 160 pp authority were suitable and appropriate and must Kerckhof F, Haelters J, Gollasch S (2007) Alien species in the be permanent directives laid down in the marine and brackish ecosystem: the situation in Belgian trilateral alien management plan for the Wadden waters. Aquatic Invasions 2: 243-257, doi:10.3391/ai.2007. 2.3.9 Sea, which is actually in current preparation Kühl H (1965) Fang einer Blaukrabbe, Callinectes sapidus (Nehring et al. 2009). Rathbun (Crustacea, Portunidae) in der Elbmündung. 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