Recent introductiona of North American marine invertebrates in the North Sea and Baltic Sea. K. Essink. rjjkewaterstaat

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1 Recent introductiona of North American marine invertebrates in the North Sea and Baltic Sea. K. Essink Notitie GWAO rjjkewaterstaat dienst gotijdewataren bibliotheek grenadietsweg PG middelburg This short report is based on a poster presented at the Symposium on the Ecology of the North Sea, held at Texel, The Netherlands, May 23-27, Rijkswaterstaat Tidal Waters Division P.O. Box AE Haren The Netherlands

2 1, INTRODUCTION -1- dienst qoti dewateren bibliotheek grenadioisweg PG rniddeiburcj During the past ten years two invertebrate species, a bivalve mollusc and a polychaetous worm, which are common along the East Coast of North America were found in N.W. European waters. As there is no evidence for a step-bystep dispersal across the North Atlantic it is supposed that the dispersal of these species was intermediated by man. 2. ENSIS DIRECTUS (CONRAD, 1843) The American jack-knife clam (Ensis directus) is a common bivalve along the East coast of North America. It ranges from South Carolina (USA) to Newfoundland (Canada) (fig. 1). Figure 1. Distribution of Ensis directus in North America. The first specimens in Europe were found subtidally in 1979 in the inner German Bight (Von Cosel et al, 1982). It is supposed that larvae did reach this area with tanker ballast water in In the years following Ensis directus dispersed along the European coasts. At present it ranges from the Kattegat (Denmark) to Ostende (Belgium) (fig. 2). The mechanisms involved

3 -2- in the diapersal towards the Southwest, i.e. against the net yearly water current along the east coast of the North Sea, and described by Essink (1985). Fed.Rep.GERMANY NETHERLANDS FRANCE Figure 2. Dispersal of Ensis directus in NW Europe. The species does also occur on intertidal flats, where birds do prey upon it (Swennen et al., 1985). Differences in shell characteristics between Ensis directus and the most resetnbling European species, Ensis arcuatus, are given in figure 3. (See also APPENDIX). As the species is presently present in Belgian coastal waters it is not unlikely to appear along the coasts of SE England in due time.

4 Figure 3. Interior of ai Kr sis americanus (Binney), bs En~sis arcuatus (Jeffr.) l«anterior adductor scar 2-ligament insertion (end of the ligament) 3=foot-retractor scar 4»posterior adductor scar 5 a pallial sinus 6«ventral pallial scar 7-anterior pallial scar (Also published in: de Boer, 1984) References; Boer, T.W. de, The American jack-knife clam Ensis directus {Conrad, 1843) in Europe. Boll. malac. 20t Burger, A.W., Aanvulling op het voorkomen van Eneis directus (Conrad, 1843) in Noordwest Europe. De Kreukel 21t Cosel, R, von, J. Dörjee & U. Mühlenhardt-Siegel, Die amerikanische Scnwertmuschel Ensis directus (Conrad) in der Deutschen Bucht I. Zoögeographie und Taxonomie im Vergleich mit den einheimischen Schwertmuschel-Arten. Senckenberg. marit. 14: Essink, K., On the occurrence of the American jack-knife dam Ensis directus (Conrad, 1843) (Bivalvia, Cultellidae) in the Dutch Wadden Sea. Basteria 49: Essink, K., Note on the distribution of the American jack-knife clam Ensis directus (Conrad, 1843) in N.W. Europe (Bivalvia, Cultellidae). Basteria, 50: Kerkhof, F. & E. Dumoulin, 1987, Eerste vondsten van de amerikaanae Zwaardschede Ensis directus {Conrad, 1843) langs de Belgische kust. De Strandvlo 7:

5 Mühlenhardt-Siegel, U., J. Dörjes & R. von Cosel, Die Amerikanische Schwertmuschel Ensis directus (Conrad) In der Deutschen Bucht II. Populationsdynamik. Senckenberg. marit. 15: Swennen, C., M.F. Leopold & M. Stock, Notes on growth and behaviour of the American razor clam Ensis directus in the Wadden Sea and the predation on it by birds. Helgol. meeresunters. 39: Urk, R.M. van, Ensis americanus (BINNEY) (syn. E. directus auct. non. CONRAD) a recent introduction from Atlantic North America. J. conch. 32: MARENZELLERIA VIRIDIS (VERRILL. 1873) Marenzelleria viridis is a spionid polychaete, cowmon in estuaries along the East coast of North America. It is synonymous to Scolecolepides viridis (Maciolek, 1984). It ranges from Georgia (USA) to Nova Scotia (Canada) (fig. 4). CANADA Figure 4. Distribution of Marenzelleria viridis in North America.

6 In. Europe the first specimens were found In 1983 in the inner part of the Ems Estuary (Essink & Kleef, 1988). Figure 5 shows the distribution of Marenzelleria in October In May 1988 densities of 0-group individuals of more than per m 2 were found in the SE corner of the Dollard (H.L. Kleef, pers. conrai.). In the Dollard densities of M. viridia increased with time, whereas those of an other polychaete, Nereis diversicolor seemed to decrease (fig. 6). This may suggest some competitive interaction. EMDENN \ f 0 1 % v.v.; Qdult + juvenile && m" 2 juvenile «CQ. tooo.m juvenile,16600.fn'2 Figure 5. Distribution of Marenzelleria viridis in the Dollard (Ems BstüaryJ in October 1986.

7 -6- n.m 2000 H 1600H 1200H 800 H 400 H I I -in I I n* I 87 Figure 6. Density of Nereis diversicolor ( ( ) at a transect in the Dollard. ) and Marenzelleria viridis Around the North Sea Marenzelleria viridis was also found in other estuariess Elbe (A. Leling, 1987)j Weser (M. Grotjahn and A. Künitzer, pers. comm.); Tay (Atkins et al, 1987) j Forth (Garwood, pers. comm.) and Humber (R. Barr, pers. comm.) (Fig. 7). The species was also reported from the Zingst-Darss estuary (G.D.R.) in the Baltic Sea, where it is present since 1985 {A. Bick, pers. comm.). References! Atkins, S.M., A.M. Jones P.R. Garwood, The ecology and reproduction cycle of a population of Marenzelleria viridis (Annelidat Polychaetaj Spionidae) in the Tay Estuary. Proc. Royal. Soc. Edinburgh 92Bs Essink, K. & H.L. Kleef, Marenzelleria viridis (Verrill, 1873) (Polychaeta: Spionidae)! a new record from the Ems Estuary (The Netherlands/Federal Republic of Germany). Zool. Bijdragen, Leiden 38: Leling, A., Untersuchungen zur HUufigkeit und Verteilung des Makrobenthos in der Unterelbe. Diplomarbeit, University of Hamburg (F.R.G.), 117 pp.

8 -7- Maciolek, N.J., New records and species of Marenzelleria Mesnil and Scolecolepides Ehlers (Polychaeta; Spionidae) from North-eastern North America. - Proc. First Internat. Polychaete Conf., Sydney (P.A. Hutchings ed.), The Linnean Society of New South Wales; Weser-1986 Figure 7, Firtst records of Marenzelleria viridis in estuaries around the North Sea. Arrows give possible routes of dispersal.

9 APPENDIX Characters for recognizing Ensis americanus (Syn. E. directus) and E. arcuatus, according to Van ürk (1987). CHARACTERS AND RECOGNITION Comparing E. americanus with the Europcan species of the genus it looks most like E. arcuatus (Jeflr.), the following characters serving to distinguish the two species: E. americanus 1. Anterior adductor scar as long as the. ligament or slightly longer only. 2. Foot-retractor scar opposite to the insertion marking the end of the ligament. 3. Posterior adductor scar very close to the paüial sinus, nearly bordering it. 4. Pallial sinus (often) pointing to posterior adductor scar. 5. Lcngth/height ratio 6:1. 6. Colour greyish violet with olive green periostracum. 7. Anterior adductor scar (usually) narrowly pointed anteriorly, more or less directed downwards posteriorly. 8. Young specimens: anterior pallial scar markedly cioser to the anterior sheu margin than the adjacent ventral pallial scar to the ventral shell margin. E. arcuatus Anterior adductor scar more than lè X the ligament (var. norvegica: ± \{ X the ligament). Foot-retractor scar posterior to the ligament insertion {var. norvegica: opposite to it). Posterior adductor scar at about its own length from the pallial sinus. Not so pointing. Length/height ration about 8:1. Colour fleshy pink with brown periostracum. Anterior adductor scar moderately nar* rowed anteriorly, slightly directed downwards or almost parallel to the dorsal shell margin. Both at about the same distance, or the anterior pallial scar only slightly cioser to the anterior shell margin. The first three of these characters are constant and reliable, revealing the identity of the species at once. The other characters may show more or less variation, but they are useful in different situations, thus for instance the colour (only E. siligua (L.) may show a more or less similar tinge) and l/h ratio when collecting on the beach, or character 8 when dealing with small specimens. E. arcuatus var. norvegica, a large, broad form of E. arcuatus, approaches E, americanus in external appearance and the position of the foot-retractor scar (compare 1 & 2), but otherwise its internat characters, and also the colour, are those of E. arcuatus.