New records of Assiminea grayana Fleming, 1828, Myosotella myosotis (Draparnaud, 1801) and Pisidium subtruncatum Malm, 1855 (Mollusca: Gastropoda, Bivalvia) in the Scheldt estuary

4 Pages·2000·0.74 MB·English

by  Bruyndoncx, L

II
BULLETIN DE L'INSTITUT ROYAL DES SCIENCES NATURELLES DE BELGIQUE, BIOLOGIE, 70: I03-I06, 2000
BULLETIN VAN HET KONINKLIJK BELGISCH INSTITUUT YOOR NATUURWETENSCHAPPEN, BIOLOGIE, 70: I03-I06, 2000
New records of AssiwLinea grayana FLEMING, 1828, Myosotella 1nyosotis
(DRAPARNAUD, 1801) and Pisidiwn subtruncatwn MALM, 1855
(Mollusca: Gastropoda, Bivalvia) in the Scheidt estuary
by L. BRUYNDONCX, K. JORDAENS, H. DE WOLF, P. MEIRE & T. BACKELJAU
Abstract Material and methods
The mollusc fauna of the tidal marshes along the river Scheidt was The river Scheidt originates in France (Saint-Quentin), runs
investigated. To this end, 31 marshes were sampled along a salinity through Belgium and flows into the North Sea near
gradient from Berlare (Belgium; freshwater) to Ylissingen (the Vlissingen (the Netherlands) (Fig. 1). The part of the river
Netherlands; marine). Our faunistic survey yielded eight new lo
between Ghent and Vlissingen (i.e. Scheidt estuary) is sub
calities for the caenogastropod Assiminea grayana, of which
ject to tidal conditions, resulting in a salinity gradient which
seven in the Belgian part. In the marsh of Doel ("Prosperhaven")
ranges from sea-water at the river mouth (30 %a) over brack
we discovered the first inland population of the pulmonate mollusc
ish conditions, between Hansweert and Kruibeke ( 18 %a to
Myosotella myosotis, a species which in Belgium was hitherto only
known from three coastal localities. Finally, additional 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, Assiminea grayana, Myosotella myosotis, able, both seasonally and between years.
Pisidiwn sllbtruncalllm, Scheidt estuary, faunistics. From October 1998 till April I 999, molluscs were sampled
along the entire salinity gradient of the Scheidt estuary. Sam
pling was restricted to marshes, i.e. areas that are regularly
Resume inundated during spring tides, but not during daily high tides.
Sixty-four sampling sites were surveyed in 31 marshes.
La faune 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
que; eau douce) et Vlissingen (Pays-Bas; eau salee). Trente-et-un
eye", collected in a frame of 20 x 20 em (Marquet, 1979).
« schorres » ont ete echantillonnes. La distribution du Only living specimens were considered. The collection has
caenogasteropode Assiminea grayana dans Ie Bas-Escaut a ete
been deposited in the Royal Belgian Institute of Natural Sci
completee avec huit nouvelles localites, dont sept dans Ia partie
ences, Brussels where it is registered under catalogue
beige du Bas-Escaut. Dans Je « schorre >>de Doe! ("Prosperhaven"),
number IG 28791. Here we present a brief account of the new
on a decouvert Ia quatrieme population du gasteropode pulmone
Myosotel/a myosotis en Belgique, Jes trois autres populations belges faunistic observations.
connues vivant dans Ia region cotiere. Finalement, des nouvelles
observations du bivalve Pisidium subtrunca/UI/l ont ete faites dans
l 'estuaire du Bas-Escaut. Assiminea grayana FLEMING, 1828
Mots-clefs: Mollusca, Assiminea grayana, Myosotella myosotis,
Pisidium subtruncatum, estuaire du Bas-Escaut, faunistique. Assiminea grayana (fam. Assimineidae) is a small
caenogastropod (maximal height 7,5 mm) that lives 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, while of Antwerp. These sites were confirmed by DUMOULIN
GITTENBERGER et al. (1998), provided an extensive review (1989), who specified the presence of A. grayana at the
for the Netherlands. marshes of Doe!, Lillo and Liefkenshoek and the polder of
While making a survey of the molluscs inhabiting the Lillo. MARQUET (1985) mentioned another four sites along
marshes along the river 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 considerably by adding seven new locali
gastropods Assiminea grayana FLEMING, 1828, Myosotella ties, six of which are situated upstream of Antwerp (Table I,
m)'osotis (DRAPARNAUD, 1801) and the freshwater bivalve Fig. 1).
Pisidium subtrun.catum MALM, 1855. For the following UTM squares, ES96 and ES86, no previ-
II
I 04 L. BRUYNDONCX, K. JORDAENS, H. DE WOLF, P. MEIRE & T. BACKELJAU
~ / .......... f (l "--J
........,
VLISSINGEN Q
0 HANSWEERT
51"27" N NORTH
SEA
BELGIUM
DURMEMONDING
GHENT
KONKELSCHOOR
'
' '..._
10 km 4"25" E
Fig. I -Distribwion of Assiminea grayana and Belgian records ofMyosotella myosotis and Pisidium subtruncatum along the Schelcil estuary:
e neu· records ofA . grayana; • confirmation ofp revious records of A. grayana; 0 records ofA . grayanajimn the literature; t; previous
sampling sites ofPisidium. 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 situated season, population densities may reach more than 40 000
sampling site of A. grayana, since the Durmemonding specimens per m2 (DUMOULIN, 1989). We estimated popula
marshland, located a few kilometres more upstream, was tion densities at 12 000 animals per m2 in the marsh at Doe!
also repeatedly investigated, 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 found A. grayana more upstream in the es Myosotella myosotis (fam. Ellobiidae) 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 fluctuations in salt concentra the Mediterranean and the Black Sea (GITTENBERGER et al.,
tions and as a consequence the species 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
tidal areas for its reproduction, since eggs need to be flooded Sea coast (DUMOULIN, 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 found 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) described an association be ity of M. myosotis along the river Scheidt.
tween A. grayana and Phragmites australis and In the Netherlands M. myosotis is common in the Frisian Is
Puccinelietum maritima, we found no connection with spe- lands and in Zeeland (GITTENBERGER et al., 1998). We sam-
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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 ("Ballooi") and five 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 genus 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 athericus 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
lives 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 ofA ssimea grayana, B: Belgium; NL: the Netherlands.
Salinity is expressed in g salts per kg water: the figures are average values for 1996 (Institute of Nature Conservation, 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 Ellewoutsdijk (Zuidgors) NL ES59 27,12 10/04/99 II (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 18/10/98 871 (4)
7 Beveren (Doel) B ES88 10,87 21/10/98 2321 (6)
8 Antwerpen (Liefkenshoek) B ES88 10,32 I 27/10/98 149 (I)
9 Antwerpen (Cauwelaertsluis) B ES98 6,00 I 31/10/98 745 (I)
10 Antwerpen (Oosterweel) B ES97 3,28 31/10/98 448 (I)
II Antwerpen (Sint Annastrand) B ES97 3,28 31/10/98 176 (I)
12 Burcht (Galgenweel) B ES97 2,38 13/10/98 190 (3)
13 Kruibeke (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 10/11/98 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
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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 bioiogischen Grenze
96.01). We wish to thank H. VAN PAESSCHEN for his help Meer-Land durch Mollusken. Untersuchungen an Alderia modesra
with the illustrations. (Opisth.) und Ova tel/a myosoris (Pulmonat.). Oecologia, I: I 30-
I54.
SEELEMAN, U., 1968b. Zur Uberwindung der biologischen Grenze
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