BULLETIN DE L' INSTITUT ROYAL DES SC IENCES NATURELLES DE BELG IQUE ENTm.'IOLOG IE. 70: 97 -1 07 . 2000 BULLETIN VAN HET KONINKLIJK BELGISC H INSTITUU T VOOR NATUURWETENSC I-I A PP EN ENTOMOLOG IE. 70 : 97 -1 07,2000

The richness and paucity of the fauna of the Belgian coast

By Jean-Pierre MAELFAIT, Leon BAERT, Dries BONTE and Frederik HENDRICKX

Abstract Table I - Number of species per Red li st category of the spider fauna of . A compari son is made between the spider species composi ti on of twelve sandy natural areas in Flanders along a gradi ent from th e coast dunes and sa lt marshes in th e west to the large heath land areas in the Red list-catego1y (RLC) Nu mber east. All th ese natural areas have large numbers of rare and threatened Extinct (EX) species. The relati ve paucity in spider species in coastal reserves is 8 caused by the lack of species bound to ombrotrophic Sphagnu 111 bog Critical (CR) 58 vegetation and to wet o li gotrophic grasslands. Endangered (EN) 83 Keywords: , Belgian coast, coastal dunes, sa lt marshes, heath lands, peat bogs, oli gotrophi c grasslands. Vulnerable (VU ) 63 Restricted Geographically 65 (RG: N-, S- or W-limit) Intt-oduction Indeterminate (IN) 12 Recently a Red li st for th e spider fauna of Flanders was Insuffic iently Known (IK) 24 compiled ( M AELFAIT et a!., 1998). Flanders is the north­ Safe, low ri sk 29 1 ern part of the federal state of . It has a surface of approximately 13.500 knl, whilst th e total surface of TOTAL 604 Belgium is 30.5 00 km2. The spider fauna of Belgium comprises 689 species; th at of Flanders 604. As can be found in the above mentioned Red list only about half of the 604 spider species belongs to the "Safe or at Table 2 - Number of species belonging to th e Red li st low ri sk" -category. This hi gh degree of threat is under­ categories Extinct, Critical, Endangered and standable when one realises that human population den­ Vulnerable per habitat type. sity in Flanders is more than 420/km, i.e. more than three times the mean of the population density of the European Habitat Number community. Consequently, the remaining natural and Forest, deciduous, dry (Fdd) 26 semi-natural areas and nature reserves are scarce in Flan­ ders; they are small and isolated from each other. Forest, deciduous, marshy (Fdm) 6 Other categori es distingui shed in the Red li st are: Ex­ Forest, deciduous, wet (Fdw) 7 tinct, Threatened (with three different degrees: Critical , Grassland, oligotrophic, dry (God) 78 Endangered and Vulnerable), Indeterminate (species as­ sumed to be in threat but of whi ch there is not enough Grassland, oli gotrophic, wet (Gow) 22 informati on to decide which of th e threat categories is Heathland, dry (l-Id) 19 appropriate), Restricted geographically (species which are rare in the considered region due to th eir geographical Heathl and, wet (Hw) 16 di stribution, i.e. species for which Flanders lays at the Marshland (M) 24 northern , southern or western limit of th eir di stribution Riparian habitat (R) 6 range) and Insufficiently known (species for whose there is in sufficient information to judge into whi ch category Saltmarsh (Sa) 6 th ey should be placed and also those species menti oned Water habitat, eutrophi c (We) 2 doubtfully to occur in our region). The number of species TOTAL belonging to each category is li sted in Tabl e I. For each 2 12 98 Jean-Pierre MAELF AIT et a!. II

marshland, riparian habitat, salt marsh or unpolluted eu­ trophic water habitat. In Table 2 the number of the threatened species per habitat type is given. Figure I visualises the relative frequency of the habitat types in which the 204 Threatened and 8 Extinct species occur or occurred. We thus can conclude that the vast majority of species in the threatened part of the spider biodiversity of Flanders occur in dry and wet open habitats, i.e. grass­ land, heath land, marshland, riparian habitat, salt marsh and water habitats. Of the whole of the natural and semi-natural areas, which have been sampled quite exhaustively for their spider fauna, the highest spider biodiversity is found in the sandy regions of Flanders (MAELFAIT & BAERT, 1999). The most typical biotic elements of these regions are species bound to open habitats (non-forest species). Therefore, we compare and analyse the relative richness of the different Flemish sandy regions based on rare and threatened spiders of open habitats. One sandy part of Flanders occurs along the coast (Fig. 2). It is a nan-ow zone of a few kilometres wide with Fig. I - Habitats preferred by the Extinct, Critical, Endange­ two salt marshes and some thousand five hundred hectares red and Vulnerable spider species of Flanders. highly fragmented dry and wet coastal dune habitats. Dry dune tops with ma.Tam grass, sedge-, and lichen- and moss-vegetation contrast with waterlogged dune slacks. species, which belong to the categories Threatened and The dune soil is made up of quaternary deposits of lime Extinct, the habitat could be characterised as being one of rich sand. A large pati of Flanders is made up of the loamy the following types: dry, marshy or wet deciduous forest, sand region. Some parts of this region are sandier. They dry or wet oligotrophic grassland, dry or wet heath land, occur south of Bruges in the notih of the province of

Dunes & Loamy sand saltmarshes region Campine region Loam region

COAST WE-FL ANTWE LIMBU

Brussels Fig. 2 Localisation of the twelve sa ndy areas for which the biodiversity in sp iders fauna is compared. Further explanation: see text. Spider fauna of the Belgian coast 99

Table 3 - R ed list species (forest bound species excluded) present in: (I ) each of the twelve considered areas, (2) each group ofthree areas, (3) all of the twelve areas (ALL 12) and (4) Flanders (FLAND). For each species its Red list category and its preferred habitat is i ndicated (further explanation: see text an T ables I and 2).

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S~i e 1 D\1 HI' \IH LI\IBG BR BU KH A\ni'E GP &I w 1\HL LO 1\'H Z\1' COAST ALL ll FL\\D RLC HAB Marp issa ni voyi I I I I I I EN God Marp issa pomati a I CR M Marp issa rad iata I I I I vu M Neon valentulus I I I I I I CR Hw

Pell enes tripu nctatus I I I I EN God Philodromus buxi I RG N Phil odromus fa ll ax I I I I I CR God Philodromus hi strio I I I I I I vu Hd Philodro mus ru fus I RG N Phl egra fa sciata I I I I I I I I I I I I vu God Sitticus caric is I I I I I I I I EN M Sitti cus disti nguendus I EN God Sitticus fl oricola I I I I vu M Sitticus saltator I I I I I I I I I I EN God Synageles hil aru lus I I I I I RG N Thanatus stri atus I I I I I I I I I I I I I I I vu God Tibellus maritimus I I I I I I I I vu Gow Tibellus ob longus I I I I I I I I I vu Gow Oxyopes lineatus I RG N Oxyopes ramosus I I I I I vu Hd Alopecosa barbipes I I I I I I I I I I I I I I vu God Alopecosa cuneata I I I I I I I I I I vu God Alopecosa fab rili s I I I I I I I I I EN God Alopecosa tae ni ata I RG s Arctosa cinerea I CR R Arctosa fi gurata I I I I I I RG N Arctosa leopa rdus I I I I I I I I I I I I I I I vu Gow Arcto sa peri ta I I I I I I I I I I I I EN God Ca lli lepis nocturna I RG N Drassodes pubescens I I I I I I I I I I I EN God Gnaphosa lepori na I I I I I I I EN Hw Gnaphosa lucifuga I CR God Gnaphosa nigerrima I I I I CR Hw Gnaphosa opaca I RG N Haplodrassus da lm atensis I I I I I I I I I I EN God Haplodrassus umbrati lis I CR God Micaria di ves I I I I I I I I I CR God Mica ria ful gens I I I I I I EN God Mic ar ia romana I I I I I RG N Mica ri a silesiaca I I I I I RG N Pardosa agresti s I EN R Spider fauna of the Belgian coast I 0 I

~~ff i 11 D\1 HV ~I ll LI\IBU BR Bli Kll A\111'[ Gf ~ \Y 1\HL LO lrH Z\\' C0 :1ST .\LL 1l FU\D RLC HAB Pardosa ag ri co la 1 CR R Pardosa hortensis I 1 1 1 1 1 1 1 R G N Pardosa monti co1a 1 1 1 1 1 1 1 1 1 1 1 EN God Pardosa prati vaga 1 1 1 1 1 1 1 1 1 1 vu M Pardosa proxima I I I I I I RG N Pardosa purbeckensis I I I I I CR Sa Pardosa sphagn icola 1 I I 1 1 1 1 1 I 1 I I CR M Phaeocedus braccatus 1 1 1 1 1 I 1 EN Hd Pirata pi scatorius 1 1 1 1 1 1 1 1 1 1 EN M Pirata tenuitarsis 1 1 I I I I 1 I 1 1 CR M Pirata ul iginosus 1 1 I 1 1 1 1 1 1 1 CR Hw Poec ilochroa conspicua I RG N Trochosa robusta 1 CR God Troch osa spini·palpis 1 1 1 1 1 I 1 I I vu Gow Xero lycosa mini ata 1 1 1 I 1 1 1 1 I 1 1 EN God Zelotes aeneus 1 RG N Ze lotes electus 1 I I I I I I I I 1 I vu God Ze lotes longipes 1 1 1 1 1 1 1 1 I 1 1 1 1 vu God Zelotes luteti anus I I I 1 1 1 1 EN Gow Ze lotes pedestris I 1 1 1 1 I I 1 I EN God Ze lotes petrensis 1 1 1 1 1 1 1 1 I 1 I 1 vu God Ze lotes prae ficu s 1 1 1 1 CR He! Cheiracanthium pennyi I 1 1 1 RG N Cheiracanthium virescens I I 1 1 I I I I 1 1 1 1 1 EN God Cheiracantium mo ntanum 1 I 1 1 RG N Clu biona fr isia I I 1 I I I vu God Club io na genevensis I CR God Clubi ona juven is I CR M Clubiona subsultans 1 1 1 1 RG s Clubi ona tri vial is 1 1 1 1 1 I 1 1 1 vu God Dolomedes fimbriatus 1 1 1 1 1 1 CR M Dolomedes pl antarius I CR We Agraec ina lineata 1 RG N Agroeca cuprea 1 1 1 I 1 1 EN God Agroeca dentigera I I I I I I I CR Hw Agroeca lusatica I I 1 I 1 I I I I I I I vu God Argyroneta aquati ca I I I I I I I I I I vu We Phrurolithus minimus I CR God Scotin a celans I I 1 I RG N Scot ina gracilipes 1 I I I CR l-Id Coelotes inenni s 1 RG N 102 Jean-Pierre MAELF AIT et a/. I I

SJII!irl D\1 HI" \IH Ll\18~ 8R 8~ KH A\1\\I Gf ~ IT 1\HL LO lrH Z\1' COAST ALLil fLI.\0 RLC H.\8 Histopona torpida I RG N Zora si lvestris I I I I Et Hd Hahnia candida I RG N Hahnia nava I I I I I I I I I I EN God Ero aphana l l l l RG N Ero tuberculata l I I l vu God Achaearanea riparia I vu God Anelosimus aulicus I I I I RG N Anelosimus pulchellus I RG N Crustulina guttata I l l I I I I l l l I vu God Crustulina sticta I I I I CR M Dipoena inornata I I l l CR Hd Dipoena melanogaster I l I I I I l E N God

Dipoena prona I I l I EN God Dipoena tristis I I I I I I I CR God Enoplognatha mordax l I l l vu God Enoplognatha oelandica l l l l l EN God Enoplognatha tecta l I l I RG N Episinus truncatus l CR God Eutyopis fl avomaculata l I l l I l l l l I l l l l vu God Pholcomma gibbum I I I I I I I I I I I I I I I vu God Robertus arundineti I I I I I I I EN Gow rtus scoticus I Robe .. RG s Steatoda albomaculata I I I l I I I l vu Hd Steatoda phalerata I I l I I l l vu Hd Theonoe minutissima I I I I vu Hw Theridion instabile I EN M Theridion uhlighi I I I I I l CR Hd Tetragnatha reimoseri I CR M Tetragnatha striata I EN M Agalenatea redii I I I I I I I I I I vu God Argiope bruennichi I I I I RG N Cyclosa oculata I I I I RG N Hypsosinga albovittata I I I I I I I I I vu God Hypsosinga heri I I I I l l EN Gow Hypsosinga pygmaea I I l I EN Hw Hypsosinga sanguinea I I I I I I l EN Hd Singa hamata I EN Gow Acartauchenius scurri lis I I I I I I I I I l EN G od Araeoncus crassiceps I I I I I I I I EN Hw Baryphyma duffeyi I I I I I CR Sa Spider fauna of the Belgian coast I 03

Sjll!in D\1 HI' \IH LI\IBC BR BC KH A.\1111 Gr SJ IT IIHL LO 1\'H Z\1 com .\llll fLl\D RLC HAB Baryphyma maritimum I I I I I I EN God Baryphyma pratense I I I I I I vu Gow Baryphyma trifrons I CR Hd Ceratinopsis romana I I I I I I I EN God Ceratinopsis stativa I I I I RG N Di smodicus elevatus I I I I RG s Entelecara congenera I I I I I I RG s Entelecara errata I RG N Entelecara media I I I I RG s Entelecara omissa I I I I CR Gow Erigone promiscua I I I I I I I CR God Erigonella hiemalis I I I I I I RG s Erigonella ignobilis I I I I EN Gow Glyphesis cottonae I I I I CR Hw Gongylidiellum murc idum I CR M Hylyphantes nigritus I RG N Hypomma fulvum I vu M Hypseli stes jacksoni I I I I I EN Hw Maso gallicus I I I I I I I EN Gow Metopobactrus prominulus I I I I I I I I I I I vu God Mioxena blanda I I I I I I I I I RG N Monocephalus castaneipes I I I I RG s Notioscopus sarc inatus I CR Hw Pelecopsis nemoralis I I I I I EN God Pseudocarorita thal eri I RG s Pseudomaro ae ni gma ticus I RG N Satilatlas britteni I I I I I I I CR Hw Savignya frontata I vu Gow Silometopus ambi guus I I I I I CR Sa Si lometopus boness i I I I I CR Hd Silometopus elegans I I I I I I I I I I vu Gow Silometopus incurvatus I I I I I I I I I EN God Silometopus reussi I I I I I I vu Gow Thyreostenius biovatu s I CR God Tmeti cus affinis I vu M Trichoncus hackmanni I I I I CR R Tri chopterna cito I I I I I I I I I I I YU God Trichopterna thorelli I I I I I I I I EN Gow Walckenaeria alticeps I I I I I CR M Wa lckenaeri a kochi I I I I I I RG s Walckenaeria nodosa I I I I I I EN Gow 104 Jean-Pierre MAELFATT eta/. I I

SJ11Cio D\1 HI' \Ill LLIIBl" BR sr KH mwE GP SJ IT \IHL LO 1\'H lW COAST ALL ll FL\.\0 RLC IIAB Walckenaeria styli frons I I I I I EN God Allomengea scopigera I I I I CR Sa Allomengea vidua I I I I vu Gow Aphileta misera I I I I I I I I E Hw Bathyphantes setiger I I I I I I I I I I EN Hw Bolyphantes luteolus I I I I I I RG s Carorita paludosa I EN M Centromerus capucinus I I I I RG N Centromerus incultus I I I I I EN Hw Centromerus leruthi I RG N Centromerus levitarsus I I I I CR M Centromerus pabulator I I I I I I RG w Centromerus serratus I RG N Donacochara speciosa I I I I vu Gow Drepanotylus uncatus I I I I I I I EN M Frontinellina frutetorum I RG w Halorates distinctus I EN Gow Haloratus reprobus I CR Sa Kaestneria dorsa lis I I I I I I vu God Lepthyphantes I RG w lepthyphanti form is Leptorhoptrum robustum I vu R Leptothrix hardyi I I I I EN Gow Linyphia tenuipalpis I CR Hd Macrargus carpenteri I I I I RG s Meioneta beata I I I I I I I I I I I EN God Meioneta fuscipalpis I RG w Microlinyphia impigra I I I I I I vu M Taranucnus setosus I I I I I I I I vu Hw

Western Flanders (WE-FL). The o ther reall y sandy region the . Niveo-eolian sands cover it. Soils are is the Campine region. As already mentioned, as well as distinctly podsolized so that they have an endured horizon the coastal regions, the Campine region has also a very of ill uvial h umus a nd/or iron, about 30 to 40 centimetres high biodiversity in its spider fauna. below surface. This gives the Campine soils the charac­ teristics of being both sandy and waterlogged, with water accumulating on the impermeable hori zon of the soil Methods profile. Hence, we find in the remaining natural areas a fine mosaic of very dry sandy a reas and dunes on the one We compiled the list (Table 3) of the Threatened and hand and lakes, marshes and peat bogs on the other hand. Geographicall y restricted species occurring in twelve areas Until the nineteenth century the region wa~ almost com­ distributed over the sandy regions of Flanders (Figure 2). pletely covered by heathland, which h ad been developed Three of the study areas are localised in the eastern part under a balanced agro-pastoral system. Drainage, irriga­ of the Campine region in the province of (LIM­ tion, pine wood plantation and the use of fertilisers dra­ BU): Mechelse heide (MH), De Maten (DM) and Hage­ maticall y transformed it. There are however still impor­ ven (HV). This region stretches across the north-east of tant remnants of heathland. Each of these areas has a Spider fauna of the Belgian coast 'I 105

80

50

• LIMBU DANTWE 40 •WE-FL DCOAST DFLAND 30

RG God Hd Gow Hw M R Sa We

Fig. 3 - Number of species per habitat type per group of three areas and in Flanders.

surface area of at least hundred hectares. The spiders of the river lJzer and (WI-I): a few hundred hec­ these three nature reserves were sampled by JANSSEN tares of wet and dry dune habitats at the French border ( 19 80, 1987, 199 1). (B AERT & DESENDE R, 1993; BA ERT & MAELFA IT , 1999; Three other areas were loca li sed in the western part of BONTE et al. , 1999; 1-I UB LI~. 1975, 1976; MA ELFA IT et al. , the Campine region (province of An twerp : ANTWE): 1997; Nus, 1976) Kalmthoutse heide (KH), Brecht's groot sc hi etveld (BR) and Buitengoor (BU). The first is a Flemish nature reserve of more than thousand hectares. The second is Results military area of almost two thousand hectares. BU is a sma ll area in the va ll ey of a rivulet of only some forty Of the 269 sp ider species of Flanders which are threa­ hectares. The sp iders occurring in these areas were ten ed and restricted geographicall y, 230 are not bound to sampled by 1-I ENDR ICKX (unpublished data), JOCQUE forest habitats (Table 3, co lumn FLAND). Of these 230 ( 1986), LAVRYSSEN ( 1993) and MAELFA IT eta/. ( 1993). species 164 occur in the twelve study areas (column Three very small natural areas of on ly a few to a few ALL 12). This confirms that here, we are really dealing tens of hectares are situated in the more sandy parts of the here with hot spots of biodiversity and that we have province of Western Flanders (WE-FL) in the vicinity of included a signifi cant part of the sp ider fauna for analysis. Bruges: Vloethemveld (VV), Schobbejakshoogte (SJ) By far the largest number of species occurs in the most and Gulke putten (GP) (MAELFAIT, unpublished data; eastern province of the Ca mpine region (L imburg: LlM­ MA ELFA IT & JANSSEN, unpublished data; ALDERWE IRELDT BU), rather less in (ANTWE), much less in the & POLLET, 1990). three sma ll reserves in Western Flanders (WE-FL) and All these inland sites were compared with three coastal again only a bit less in the three coastal areas taken areas : Zwin (ZW): some two hundred hectares of salt together (COAST). When we subtract fro m these species marsh and dune habitats at the Dutch border; Lombard­ numbers the rare species at the limit of their distribution sijde (LO): dunes and sa lt marshes along the estuary of (RG-species), the difference between Limburg and the 106 Jean-Pierre MAELF AIT et a/. ''

Table 4 - Number of Red list species per categoty per eoncus crassiceps, the lycosids Pardosa sphagnicola, group of three areas, in all twelve areas and Pirata piscatorius, Pir ata tenuitarsis and Pirata uligino­ in Flanders. sus, the salticid Sitticus caricis and the pisaurid Dolo­ medes flmbriatus. RLC LIMBV ANTIVE W£-FL COAST ALL12 FLAND

RG 21 II 4 10 35 65 Discussion

Threatened 87 82 24 71 129 165 P. sphagnico/a and P. uliginosus are, in our country, TOTAL 108 93 28 81 164 230 bound to ombrotrophic Sphagnum (peat) bog situations (ALDERWEIR ELDT & MA ELFAIT, 1990). That is a habitat type occurring in the Campine region and not in our coastal region. Species bound to ol igotrophic wet grass­ other species rich regions (Antwerp and the coast) be­ lands with low sedges (vegetation of the Caricetum tri­ comes less pronounced (Table 4). The higher number of nervis-nigrae-type, WESTHOFF ex FOUCOUL T 1984; SCHA­ geographically restricted species in Limburg, compared MI EE et a!., 1995) such as Pirata piscatorius and P. with all other provinces, is caused by a high number of tenuitarsis are also absent in our coastal dunes. However, species having their northern limit in that region. They based on their habitat preference, we can assume that probably occur there and not in the rest of Flanders their absence may be the result of recent extinction because of the somewhat wanner summers and perhaps following habitat destruction. Oligotrophic dune slack because of the presence nearby of the river Rhine, which fens with analogue vegetation were present until the forms a corridor for southerly species to the north. 19th century along the Flemi sh West coast (DE RAEVE Excluding the regionally restricted species from the et al., 1983) on former fossil beach planes and along the comparison, the three coastal areas sti ll contain about dune-polder border zone. Due to the intensive agricultural I 0 to 15 species less than the Cam pine areas. To find land use and forestation of these wetlands with Alder the reason for that difference we compiled Figure 3. In (PROVOOST & HOFFMA NN, 1996a), the habitat disap­ that figure we have indicated for each preferred habitat peared. This is also the case for the mesotrophic fen sedge the number of species respectively occurring in (from left beds (C/adietum marisci-vegetation type, AL LORGE ex to right): Limburg (LIMB), Antwerp (ANTWE), the three ZOBR ES IT 1935; SCHAMINEE eta/., 1995), a typical former sandy areas in Western Flanders (W E-FL) and in the dune-polder habitat, characterised by stable high ground­ three coastal areas (COAST). At the outermost right, water levels and sand-silt substrate conditions. This is the we indicated the total number of Flemish threatened typical habitat of Dolomedes jimbriatus. The absence of species preferring that habitat category (FLAND). Here this species may thus also be the result of historical again, we see that in Limburg there occurs a considerable habitat loss. Indirect evidence for the above given expla­ larger number of geographically restricted species com­ nation for the absence of the three species bound to pared with the three other regions. The larger number of oligotrophic grassland conditions is their presence in threatened species bound to dry grassland, that occur in the nearby coastal dune region of northern (Bou­ the coast region, is compensated by the species restricted lonnais), where these habitats are still well preserved to dty heath land situations in Antwerp and Limburg. A (BONTE, unpublished data). comparable number of thTeatened species of wet grass­ Whether habitat restoration along the Flemish coasts lands is found in the eastern provinces and along the (as proposed by PROVOOST & HOFFMANN, 1996b) would coast. As this is the case for almost all other habitat lead to the re-colonisation by these species is question­ categories, the number of species belonging to the habitat able: colonisation depends both on the presence of neigh­ category "wet grasslands", occurring in the small re lict bouring populations and on the species specific dispersal heath lands near Bruges, in Western Flanders, is much capacities. Of these species, no nearby populations are lower than in the other regions. The number of marshland known, so a very well developed aerial dispersal would species is high in the two eastem provinces. That number probably be necessary to enhance (re-) colonisation. is not fully compensated by salt marsh-bound red list There are however no specific data on this behaviour. species of the coa t region. Besides the difference in We can conclude that the contemporary absence of the number of species between the Campine region and typical wet heath land spider species in the coast region the coast, there are about ten, wet heath land species of results from the geological, climatological and pedologi­ the Limburg and Antwerp areas, which are not repre­ cal impossibility for developing particular habitat types sented along the coast. It can be concluded that the (ombrotrophic Sphagnum bogs) as well as from historical threatened species bound to oligo- and mesotrophic wet­ anthropogenic habitat loss. It is the absence of these land habitats (incl. peat bogs) provide the difference particular wet heath land habitat types that makes that between the Campine region and the coast region. Their the spider fa una of the Belgian coast is what it is, and presence is responsib le for the hi gher spider bi odiversity although being a species rich fauna, it is markedly poorer of the Campine region in comparison with the coast than the spider fauna of the heath land areas in the region. Examples of such species are: the eri gonid Ara- Campine region. Spider fauna of the Belgian coast 107

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