II BULLETIN DE L'INSTITUT ROYAL DES SCIENCES NATURELLES DE BELGIQUE, BIOLOGIE, 70: I03- I06, 2000 BULLETIN VAN HET KO NINKLIJK BELGISCH INS TITUUT YOOR NATU URWETENSCHAPPEN, BIOLOGIE, 70: I03 -I 06, 2000

New records of AssiwLinea grayana FLEMING, 1828, 1nyosotis (DRAPARNAUD, 1801) and Pisidiwn subtruncatwn MALM, 1855 (: , Bivalvia) in the Scheidt estuary

by L. BRUYNDONCX, K. JORDAENS, H. DE WOLF, P. MEIRE & T. BACKELJAU

Abstract Material and methods

The mollusc fa un a of the tid al marshes along the river Scheidt was The river Scheidt ori gi nates in France (Saint-Quentin), runs investi gated. To th is end, 31 marshes were sampled along a salinity through Belgium and fl ows into the North Sea near gradient from Berlare (Belgium ; fres hwater) to Ylissingen (th e Vlissingen (the Netherlands) (Fig. 1). The part of the river Netherlands; marine). Our fauni sti c survey yielded eight new lo­ between Ghent and Vlissingen (i.e. Scheidt estuary) is sub­ calities for the caenogastropod grayana, of which ject to tidal conditions, resulting in a salinity gradient whi ch seven in th e Belgian part. In the mars h of Doel ("Prosperhaven") ranges from sea-water at the ri ver mouth (30 %a) over brack­ we di scovered the first inland population of th e pulmonate mollusc , a speci es whi ch in Belgium was hitherto only ish conditions, between Hansweert and Kruibeke ( 18 %a to known from three coastal localities. Finally, ad ditional records of 0,5 %a), to freshwater (< 0,5 %a) (VAN DAM MEet a!. , 1995). Pisidium subtruncat11m for the Scheidt estuary are reported. The upstream limit of sea-water penetration is highly vari­ Key-words: Mollusca, , Myosotella myosotis, ab le, both seasonall y and between years. Pisidiwn sllbtruncalllm , Scheidt estuary, faunistic s. From October 1998 till April I 999, molluscs were sampled along the en tire salinity grad ient of the Scheidt estuary. Sam­ pling was restricted to marshes, i.e. areas that are regularly Resume inundated during sprin g tides, but not during dai ly high tides. Sixty-four sampling sites were surveyed in 31 marshes. La faun e malacologique des << schorres » intertidaux du Bas-Escaut Sampling was done by hand picking for 20 minutes in an area a ete exploree Ie long d'un gradient de salinite entre Berlare (Belgi­ of I 0 m2 by two persons and by sifting out surface litter "by qu e; eau douce) et Vli ssingen (Pays-B as; eau salee). Trente-et-un eye", collected in a frame of 20 x 20 em (Marquet, 1979). « sc horres » ont ete echantillonn es . La distribution du Only li ving specimens were considered. The collecti on has caenogasteropode Assiminea grayana dans Ie Bas-Escaut a ete been deposited in the Royal Belgian In stitute of Natural Sci­ completee avec hui t nouvelles localites , dont sept dans Ia partie ences, Brussels where it is registered under catalogue beige du Bas-Escaut. Dans Je « schorre >>de Doe! ("Prosperh aven"), on a decouvert Ia quatrieme pop ul ati on du gasteropode pulmone number IG 28791. Here we present a brief account of the new Myosotel/a myosotis en Belgique, Jes trois autres populations belges faunistic observati ons. co nnues viva nt dans Ia region cotiere. Finalement, des nou velles observations du bivalve Pisidium subtrunca/UI/l ont ete faites dans l 'es tu aire du Bas -Escaut. Assiminea grayana FLEMING, 1828 Mots-clefs: Mollusca, Assiminea grayana, Myosotella myosotis, Pisidium subtruncatum, estuaire du Bas -Escaut, fa uni stique. Assiminea grayana (fam. ) is a small caenogastropod (maximal height 7,5 mm) that li ves along the European Atlantic coasts, from the Wadden Sea to the North­ Introduction west of Spain (VERDONSCHOT & DE WOLF, 1980). ADAM ( 194 7, 1960) reported A. gray ana from three sites in Bel­ The most recent general faunistic accounts of the brackish gium, i.e. near the coast at Knokke (Zwin) and Nieuwpoort and freshwater molluscs of Belgium were published by (IJzermonding), and along the Scheidt estuary downstream DUMOULIN ( 1989) and ADAM (194 7) respectively, whil e of Antwerp. These sites were confirmed by DUMOULI N GITTENBERGER et al. (1998), provided an extensive review (1989), who specifi ed the presence of A. grayana at the fo r the Netherlands. marshes of Doe!, Lillo and Liefkenshoek and the polder of While making a survey of the molluscs inhabiting the Lillo. MARQUET (1985) menti oned another four sites along marshes along the ri ver Scheidt, a number of new faunistic the Scheidt just north of Antwerp. Our study extends this dis­ observations were made with respect to the brackish water tribution pattern considerab ly by adding seven new locali­ gastropods Assiminea grayana FLEM ING, 1828, Myosotella ties, six of which are si tuated upstream of Antwerp (Table I, m )'osotis (DR APARNAUD, 1801) and the freshwater bivalve Fig. 1). Pisidium subtrun.catum MALM , 1855. For the fo llowin g UTM squares, ES96 and ES86, no previ- II I 04 L. BRUYNDONCX, K. JORDAENS, H. DE WOLF, P. ME IRE & T. BACKELJAU

...... f ~ / "--J ...... , VLISSINGEN (l Q 0 HANSWEERT

51"27" N NORTH SEA

BELGIUM

DURMEMONDING

GHENT

KONKELSCHOOR ' ' '..._ 10 km 4"25" E

Fig. I - Distribwion of Ass iminea grayana and Belgian records ofMyosotell a myosotis and Pisidium subtruncatum along the Schelcil estuary: e neu· records ofA. grayana; • confirmation ofpr evious records of A. grayana; 0 records ofA. grayana jimn the literature; t; previous sampling sites ofPi sidium. Locality numbers refer to table /. ous records were available. The marsh at Hingene cific plants. In a favourable habitat and depending of the ("Notelaar", 0,57 %o) seems to be the most inland si tuated season, population densities may reach more than 40 000 samp li ng site of A. grayana, since the Durmemonding specimens per m2 (DUMOULI N, 1989). We estimated popula­ marshl and , located a few kilometres more upstream, was ti on densities at 12 000 per m2 in the marsh at Doe! also repeatedly in vesti gated, but without yielding any speci­ (Table I ). men of A. grayana (Fig. I). In the Netherlands, A. grayana occurs at the Frisian Islands, the saltmarshes of Groningen and nine saltmarshes along the Myosotella myosotis (DRAPARNAUD, 1801 ) river Scheidt (GITTENBERGER et al., 1998). Compared to these records, we fo und A. grayana more upstream in the es­ Myosotella myosotis (fam. ) is a pulmonate mol­ tuary at the saltmarsh of Biervliet (Paulinapolder) (Fig. I). lusc, which is distributed from Great Britain and Denmark to A. grayana withstands large fluctuati ons in salt concentra­ the Mediterranean and the Black Sea (GITTENBERGER et al., ti ons and as a consequence the occurs in salt- as well 1998). In Belgium, M. myosotis has hitherto been recorded as in brackish and freshwater marshes with an optimal salin­ from only three sites, i.e. at Knokke (Zwin), Nieuwpoort ity between 9 %o and 18 %o. The species is restricted to inter­ (IJzermonding) and Bredene, all of them situated at the North ti dal areas for its reproducti on, since eggs need to be flooded Sea coast (DUMOULI N, 1989). We discovered a fourth popu­ before they can hatch (SEELEMAN , 1968b). According to lation of M. myosotis at the marsh of Doe\ (Fig.!). The speci­ GITTENBERGER et a/. ( 1998), A. grayana occurs on muddy mens were fo und under stones near the dike, between the sediments and in litter on higher, drier parts of the mar h. grass vegetation. This site is probably the most inland local­ Although DUMOULIN ( 1989) descri bed an association be­ ity of M. myosotis along the river Scheidt. tween A. grayana and Phragmites australis and In the Netherl ands M. myosotis is common in the Frisian Is­ Puccinelietum maritima, we fo und no connection with spe- lands and in Zeeland (GITTENBERGER et al., 1998). We sam- ' ' New records of mollusca in the Scheidt estuary. 105

pled M. myosotis at six marshes (Ritthem, N=53; Hoofdplaat, were very muddy and were inundated regularly during high N= 133; Biervliet, N=67; Ellewoutsdijk, N=46 I ; Hontenisse, tides. Previous records of Pisidium in the Scheidt estuary N=22; Prosperpolder, N=21) along the Scheidt, two of which date from I 989 (ROSSAERT, I 989), who found a single speci­ are new records, i.e. the saltmarshes at Biervliet and men at Temse ("Bal looi") and fi ve specimens at the marsh of Hoofdplaat. Similar to GITTENBERGER et al. (1998), M. Steendorp (" Kijkverdriet") (Fig. 1). Yet, the specimens were myosotis was always sampled on the higher, drier parts of the only identified at the level. In Belgium, P. marsh, where the animals lived on the soil between the dense subtruncatwn is common in running waters, bu.t scarce in vegetation, with Elymus ath ericus and Halimione stagnant waters (ADAM, 1960). In the Netherlands, it is the portulacoides as the dominant plant species. M. myosotis most common Pisidium species and is for instance very li ves in salt- as well as in freshwater, but the optimum salin­ abundant in the mudnats of the tidal freshwater areas, where ity for growth and egg production is I 0 %o (SEELEMAN, it can reach densities of 777 specimens per m2 near the low I 968a). water level (KUIPER & WOLFF, I 970). Sometimes P. subtruncatum is observed on land, but only in very wet sites (DEVRIESE et al., 1997). The species is rather resistant to Pisidiwn subtruncatum MALM , I 855 pollution (KUIPER & WOLFF, I 970) and withstands relatively high salinity concentrations (max. 3 %o) (GITTENBERGER et Pisidium subtru11.catum (fam. Sphaeriidae) is widely distrib­ al. , 1998). uted in Europe (GITTENBERGER et al., 1998). ADAM (1947) described this species as common in a large part of Belgium and although he mentioned the Scheidt basin as distribution Acknowledgements area (p. 236), his map (p. 265) shows only one sampling site along the Scheidt, situated in the brackish part near Lillo. This work was realised within the Belgian-Federal research In this work, P. subtruncatum was sampled at two freshwater program "Genetische karakterisatie van perifere en marshes, in Tielrode (Dunnemonding, UTM ES86, March­ ge"lsoleerde dierlijke populaties in Belgie, in uitvoering van April 1999, N=29) and in Berlare (Konkelschoor, UTM de verplichtingen onder het Verdrag van Rio" ("Meerjaren­ ES75, 14 October 1998, N= I) (Fig. !). Both sampling sites plan van de werkgelegenheid") and was supported by a grant

TABLE I

Sampling sites and numbers of individuals (N, number of plots per sampling site in parentheses) collected ofAs simea grayana, B: Belgium ; NL: the Netherlands. Salini tey is xpressed in g salts per kg water: the fi gures are average values for 1996 (Institute of Nature Conservati on, Brussels).

No Sampling sites Country UTM Salinity Date N Ritthem (Rammekenshoek) NL ES49 30,55 I 10/04/99 0 Hoofdplaat NL ES49 30,55 09/04/99 0

Borssele (Kaloot) NL ES49 30,55 10/04/99 0

I Biervliet (Paulinapolder) NL ES48 28,93 14/1298 9 (I)

2 Ellewout sdijk (Zuidgors) NL ES59 27, 12 10/04/99 I I (I)

3 Hontenisse (Hellegatspolder) NL ES69 24,41 14/ 12/98 100 (2) 4 Prosperpolder (Saeftinge) NL ES79 18,09 2-1/04/99 903 (2) 5 Bath NL ES89 15,56 01/12/98 953 (2)

6 Zandvliet (Groot Buitenschoor) B ES89 11 ,41 18/10/98 87 1 (4)

7 Beveren (Doel) B ES88 10,87 2 1/10/98 2321 (6) 8 Antwerpen (Liefkenshoek) B ES88 10,32 I 27/ 10/98 149 (I ) 9 Antwerpen (Cauwelaertsluis) B ES98 6,00 I 31 /1 0/98 745 (I) 10 Antwerpen (Oosterweel) B ES97 3,28 3 1/1 0/98 448 (I )

II Antwerpen (Sint Ann astrand) B ES97 3,28 31/10/98 176 (I )

12 Burcht (Galgenweel) B ES97 2,38 13/ 10/98 190 (3)

13 Krui beke (Barbierbeek) B ES96 1,48 07111/98 52 (2) 14 Hemiksem (Kallcbeekveer) I B ES96 0,93 07/11/98 8 (I) 15 Rupelmonde B ES96 0,93 10/1 1/98 I (I) 16 Hingene (Notelaar) B ES86 0,57 I 03/11 /98 I (I ) 17 I Tiel rode (Durmemonding) B ES86 0,39 I 25/ 10/98 0 '' 106 L. BRUYNDONCX , K. JORDAENS , H. DE WOLF, P. ME!RE & T. BACKELJAU

of the Flemish Community (AMINAL/ Natuur/ VLINA/ SEELEIV!AN, U., I 968a. Zur Uberwindung der bioiogisc hen Grenze 96.01) . We wish to thank H. VAN PAESSCHEN fo r his help Meer-Land durch Mollusken . Untersuchungen an Alderia modesra with the illustrations. (Opisth .) und Ova tel/a myosoris (Pulmonat. ). Oecologia, I: I 30- I5 4. SEELEM AN, U. , 1968b. Zur Uberwindung der biologischen Grenze References Meer-Land durch Mollusken, II. Untersuchun gen an Limaponria capirara, Limaponria depressa und Assiminea grayana. Oecologia, ADAM , W. , 1947. Revi sion des Mollusques de Ia Belgique. I I : 356-368. Mollusques terrestres et dulcicoles. Menw ires du Musee royal VANDAMME, S., MEIRE, P. , MAECKELBERGHE, H., VERDJEVEL, M., d'Histoire naturelle de Belgique, I 06, 298 pp . BOURGOING , L., TAVERN IERS, E. , YSEBAERT, T. & WATTEL, G., ADAM , W., 1960. Faune de Belgique. Mollusques terrestres et I 995. De waterkwaiiteit van de Zeeschelde: evolutie in de voo rbije dul cicoles. lnstitut royal des Sciences naturelles de Belgique, 402 dertigjaar. Water, 85 : 244-256. pp. VERDONSCHOT, P.F.M . & DE WOLF, L., 1980. De levenscyc lus en DEVR IESE, R., WARMOES , T. & VERCOUTERE, B., 1997 . Land- en verspreiding van Assiminea grayana (FLEM ING, 1828). Rapporten zoetwater mollusken va n de Benelux. Jeugdbond voo r en Versiagen Delta lnstituut voor Hydrobiologisch Natuurstudi e en Milieubescherming, Gent, 192 pp. Onderzoek, Yerseke, I 2: I -25 . DUMOULIN, E. , 1989. Overzicht van de brakwatermollusken van Belgie. In : Verhandelingen van bet symposium "lnve rtebraten van Belgie", Brussel, 87-94. GITTENBERGER, E. , JANSSEN , A.W. , KUIJ PER , W.J ., KUIPER , J.G.J ., L. BRUYNDONCX & T. BACKELJ AU MEIJER, T., VAN DER VELDE , G. & DE VRIES , J.N. , 1998. De Royal Belgian Institute of Natural Sciences Nederlandse zoetwatermollu sken. Recente en foss iele weekdieren Malacology Section uit zoet en brak water. Nederl andse Faun a 2. Nati onaal Vautierstraat 29 Natu urhi storisch Museum Naturalis, KNNV Uitgeverij, Leid en, 288 pp. B-1 000 Brussels, Belgium KUI PER, J.G.J. & WOLFF, W.J., 1970. The mollusca of the estuarin e K. JORDAENS region of the ri vers Rhine, Meuse and Scheidt in relation to th e hydrography of the area. III The ge nu s Pisidiwn. Basteria, 34: 1- University of Antwerp (R.U.C.A.) 42. Evolutionary Biology Group Groenenborgerlaan 171 MARQUET, R., I 979. Terrestrisch ecologisch onderzoek toegepast op natuurbeheer. Verband tu ssen molluskenfau na en bodem. B-2020 Antwerp, Belgium Rijksuni versitair Centrum Antwerpen, Veldbiologisch Station Kaimthout Rapport 8, 62 pp . H. DEWOLF MARQUET, R., I 985 . The land molluscs of th e Antwerp harbour University of Antwerp (R.U.C.A.) area, with a new record of Cemuella cespitum (Draparnaud, I80I) Laboratory of Ecophysiology and Biochemistry fo r western Europe. Baste ria , 49: 3-10. Groenenborgerl aan 171 MEIRE, P. , ROSSAERT , G. , DEREGGE, N., YSEBAERT, T. & KUIJKEN , B-2020 Antwerp, Belgium E. , I 992. Het Schelde-estuarium: ecoiogische beschrij ving en een visie op de toekomst. Rapport Rijksuniversiteit Gent - WWE, P. MEIRE nr.28 , Rapport Instituut voor Natuurbehoud nr. A. 92.57, 150 pp. University of Antwerp (U.I.A.) ROSS AERT, G. 1989. Voorkomen van Watervogels la ngs de Ecosystem Management Research Group Zeeschelde: sterk beinvloed door de watervervuiling? Universiteitsplein 1 Licentiaatsveraandeling, Rijksuni versitei t Gent. B-2610 Wilrijk, Belgium