131

Senckenbergiana maritima I 29 I (I/6) [ 131-138 I Frankfurt am Main, 15. 12. 1998

Effects of the Tube-Building conchilega (PALLAS) on Benthic Macrofauna and Nematodes in an Intertidal Sandflat

RUTH Z• & DIETRICH BLOME & KARL HEINZ VAN BERNEM & SABINE DITTMANN

With 4 Text-Figures and 2 Tables

Key words: , tube-dwelling, biogenic structures, arificial tube fields, benthic macrofauna, Nematodes.

Abstract

[ZOHLKE, R. & BLOME, D. & VAN BERNEM,K. H. & DITTMANN,S. (1998): Effects of the tube building polychaete Lanice conchilega (PALLAS) on benthic macrofauna and nematodes in an intertidal sandflat. - Senckenbergiana marit., 29 (1/6): 131-138, 4 figs., 2 tabs.; Frankfurt a. M.]

Biogenic habitat structures playa major role for distribution pattems of benthic fauna. Tube-dwelling provide one of the main features in the otherwise re[atively low structured sandy intertidal. The airn ofthis study was to investigate the effect of the tube-dwel[ing sand-mason Lanfce conchilega on macro- fauna and nematodes in an intertidal sandflat in the area offthe German coast. Field smdies and experiments were carried out on the associated macrobenthic fauna of natural L. concbilega aggregates and of artificial tubes. Furthermore, the distribution of nematode at increasing distances along transects arising from individual L. conchilega mbes, was investigated. Natural as well as artificial tubes had positive effects on numbers of macrofaunal species and indivi- duals. Yet, juvenile Mya arenaria were the only species appearing in higher numbers in both L. conchilega aggregates and artificial tube fields. They used the tube structure to attach themselves with their byssus threads. The polychaete Malmgrenidla lunulata only occurred in natural L. conchilega aggregates and was ofien found inside the polychaetes' tubes. It is possibly a commensal associated to L. conchilega. In artificial mbe fiel&, opportunistic spionids and Capitella capitata settled in higher numbers. This might be due to colonisation ofsediment accumulating in the tube fiel&, utilisation of the tubes as an attachment sufface or refuge from predation. However, two predatory polychaetes, Eteone Ionga and Nereis diversicolor, were also found in higher abundance in natural or artificial tube fields. Nematode abundances were considerably higher next to ~ndividual L. conchilega tubes ata distance of 0.5 cm. This distribution was mainly caused by a group ofthreadlike species with a thin cuticle, which are thought to be adapted to epidermal uptake of dissolved organic matter. Ir is suggested that there might be a linkage between predatory polychaetes and the distribution partero found for nematodes around the tubes ofL. concbilega.

Authors' addresses: R. ZOHLKE) University ofSwansea, School ofBiolog~cal Science, Singleton Park, Swansea, SA2 8PP, Great B¡ -D. BLOME, Universidit Hamburg, Institut fª Hydrobiologie und Fischereiwissenschaft, Zeiseweg 9, D-22765 Hamburg, Germany. -K. H. VAN BERNI/M,GKSS-Forschungszentrum Geesthacht, Posffach 1160, D-21494 Geesthacht, Germany. -S. D ITrMANN, Forschungszentrum Terramare, Schleusenstrage 1, D-26382 Wilhelms- haven, Germany. 132

Introduction

The effects ofhabitat complexity in the benthic system are 1993) or serve as a refuge from predation (WooDIN 1978). widely appreciated (BELL 1991). Especially in rather low struc- Along the Wadden Sea coast Lanice conchilega is the most con- tured soft sediments, biotic features play a major role for spe- spicuous widely distributed tube-dweller which forms exten- cies diversity and distribution patterns. Besides'macroalge, sive populations with densities ofup to several thousand indi- mussel- and seagras beds, polychaete dwelling tubes are regard- viduals per m ~ (BuHR & WINTEg 1976). The goal ofour study ed asa main habitat structure in the intertidal (BANDEIRA was to evaluate (1) whether certain species and funetional 1995; EVERETT 1991; SEBENS 1991). They potentially modify groups are affected by L. conchilega tube aggregates, (2) whether small-scale hydrodynamics (ECKMANN et al. 1981), provide an effects ate due to the physical structure only and 3) whether attachment surface for filamentous algae (ScHogIES & REISE effects on the macrofauna and nematodes show any correlation.

Material and Methods Study Site Faunal Sampling

Benthic species assemblages associated with Lanice conchi- Macrofauna in Lanice conchilega-Aggregates lega were studied in 1995 at the Gr6ninger Plate, an intertidal sandflat between the coastline of Lower Saxony, Germany, and In August and September 1995 (31,08., 25.09.) samples the backbarrier island ofSpiekeroog (Fig. 1). The northem part were taken from randomly chosen L. conchilega-aggregates and of the Gr6ninger Plate was characterized by a L. concbilega intermediate L. conchilega-free areas. To avoid pseudorepli- population with densities ofabout 1,000 ind./mL The small- cation (HURLBERT 1984) jUSt one sample was taken from each scale distribution pattern ofL. conchilega was patchy: L. con- aggregate or tube-free area. Samples were taken with a corer of chilega-aggregates of approximately 1-5 m 2 alternated with 0.32 cm 2 surface area to a sediment depth of 10 cm. On each tube-free areas ofabout the same size. This distribution pat- sampling day, six replicates were taken from L. conchilega-aggre- tern created a surface structure ofgentle mounds with tube- gates and intermediate tube-free areas respectively. The samples aggregates and shallow depressions in the spaces between. were taken to the laboratory and sieved using a 0.5 mm mesh. A field experiment with artificial tubes was carried out in Species of the unpreserved samples were sorted, identified to the vicinity of the L. conchilega area at a distance of about the lowest practica1 taxonomic unit and counted. 100 m.

t.an~oog

8o~~roo0 wan0r

Fig. 1. Location of study site Gr6niger Plate (,) between the Gerrnan coastline and the island of Spiekeroog. 133

Fig. 2. One ofsix 1 m ~fields with 1000 artificial tubes.

Macrofauna in Artificial Tube Fields transects arising from three L. concbilega tubes (two transects each tube) using drinking straws of 0.5 cm diameter (0.2 cm 2 In July 1995 six 1 m 2 fields with artificial tubes were area). Up to a distance of 2 cm from the tubes the straws were established (Fig. 2). Each field consisted of 1,000 metal sticks, inserted into the sediment to a depth of 5 cm. Controls were 25 cm long with a diameter of 4 mm. They were inserted into sampled in the transects at distances of 5 and 10 cm (5 repli- the sediment with the upper 2-3 cm protruding ffom the sur- cates each). AII corresponding samples were treated as replica- face. To take into account the possible impact of the metal, tes. Furthermore reference samples were taken in the vicinity three fields were established with artificial tubes inserted flush of the L. conchilega area. with the surface. Furthermore, seven untreated reference fields The samples were fixed in 4% formaldehyde (bulk fixation) were staked out. All field variations (artificial tubes, referen- immediately after retrieval. The total meiofauna was extracted ces, controls)were randomly distributed in an area of about using a beaker, suspending the sediment cores and decanting 500 mL Samples were taken in August and September 1995 the fauna. Nematodes were separated and mounted in un- (22.08, 12.09.). On each sampling day one sample was taken hydrous glycerine after dehydration. from every field. Sample size and treatment were as described above. An increase in surface height within the artificial tube fiel& occurred due to sediment trapping or sedimentation. The increase ranged between 1-3 cm. To avoid covering of the Data Analysis artificial tubes they were regularly adjusted. The univariate Mann-Whitney-U-Test was applied to test for differences between numbers ofindividuals of natural as Nematodes well a~ artificial tube fields and their respective references or controls. Additionally differences between species assemblages Nematodes associated to Lanice concbilega tubes with living were tested using the multivariate ANOSIM (CLARKE & worms inside were sampled on 15 September 1995. For WAXWICK 1994). Multivariate analysis was carried out using sampling nematodes, sediment cores were gathered along six the PRIMER software.

Results Macrofauna aggregates than in the intermediate L. concbilega free areas (Tabs 1-2). Altogether about 20 species were identified in The macrobenthic fauna at the Gr6ninger Plate consisted L. conchilega aggregates whereas only 12 species occurred in mainly of polychaetes (65-80%) and bivalves (20-30%). the intermediate tube free areas. Mainly mobile polychaete Densities ofL. conchilega varied in aggregates between 600 and species were missing like Eumida spp. or Scoloplos armiger, but 1,800 ind./mL The associated fauna ofL. conchilega was nume- also tubificoid oligochaetes and amphipodes. rically dominated by small species such as the polychaete Bivalve abundance was generally higher in L. concbilega Pygospio elegans or Thatyx killariensis and juveniles of the aggregates whereas overall polychaete abundance was not bivalve Mya arenaria. found to be significantly higher in L. conchilega aggregates on either sampling date. At species level two bivalves and two polychaetes were Lanice conchilega-Aggregates found to be more abundant in L. concbilega aggregates. High numbers ofjuvenile Mytilus edulis and Mya arenaria were atta- The overall mean macrobenthic abundance as well as total ched to the tentacle crowns. The predatory polychaete Eteone and mean numbers of species were higher in L. conchilega Ionga appeared in significantly higher abundance in Sep- 134

Ta b le 1. Mean numbers (per 0.01 m 2) of the most abundant macrobenthic species of Lanice concbilega aggrrega- tes and experimental fie[ds with artificial tubes. -Standard deviations are given in parenthesis. Numbers of species were calcuIated from the original sample size of 32 cm 2. -Functional groups: Oz) fiherfeeder; (S) surface-feeder; (SS) subsurface-feeder; (C) commensal to L. concbilega; OZ) predator; (O) omnivor.

L.conchilega aggregates (LA)/ Artificial tube fields (ATF)/ L.conchilega free arcas (REF) Tube free araas (REF)/ Controll with totally inserted tubes (CON)

Aug. Sep. Aug. Sep.

LA REF LA REF ATF REF CON ATF REF CON

Lanice conchilega 6.3 11.5 1.8 0.5 0.5 0.4 (Palias, 1766) (3.4) (6.5) (2.5) (1.3) (1.3) (1.2)

Mytilus edulis (F) (1) 3.6 1.0 3.1 10.4 3.1 1.6 8.9 1.3 2.1 Linn› (3.1) (1.6) (2.8) (7.8) (7.0) (2.6) (11.4) (2.5) (3.6)

Cerastoderma edule (F) 4.2 6.3 3.1 4.7 1.0 0.9 0.5 1.6 0.9 1.0 (Linn› (3.2) (3.4) (3.4) (7.3) (1.6) (1.5) (1.3) (1.7) (2.4) (1.8)

Macoma balthica (S) 3.6 2.1 2.6 0.5 0.4 (Linn› (5.0) (3.8) (3.7) (1.3) (1.2)

Mya arenafia (F) 33.9 4.7 28.6 4.2 6.8 1.3 0.5 6.3 0.9 8.3 Linn› (17.9) (4.7) (23.7) (5.1) (3.1) (2.5) (1.3) (4.4) (2.4) (4.8)

Malmgreniella lunulata (G) 2.6 5.7 0.5 (Delle Chiaje, 1841 ) (2,4) (4.2) (1.3)

Eteone Ionga (P) 0.5 0.5 5.7 0.5 0.5 0.5 1.0 (Fabricius, 1780) (1.3) (1.3) (5.7) (1.3) (1.3) (1.3) (1.8)

Phyllocode mucosa (P) 03 (Oersted) (13)

Eumida sanguinea (P) 0.5 2.1 (Oersted, I843) (1.3) (2.6)

Nereis diversicolor (0) 1.6 3.6 0.5 0.5 O.F, Mª 1776 (3,8) (4.2) (1.3) (1.3)

Nephtys hombergi (P) 3,6 0.5 1.6 1.6 1.6 0.5 0.4 Savigny, 1818 (4.2) (1.3) (1.7) (1.7) (1.7) (1.3) (1.2)

Pygospio elagans (S) 85.4 37.0 30.7 15.6 94.3 23.2 19.8 78.6 17.4 28.1 Clapar~de, 1863 (62,1) (22.7) (24.1) (12.7) (77.1) (21.9) (17.8) (55.0) (10.8) (17.4)

Polydora comuta (S) 9.4 0.5 1.0 14.6 0.4 4.2 0.4 Bosc (11.9) (1.3) (2.6) (5.8) (1.2) (6.8) (1.2)

Thatyx killariensis (S) 27.1 24.5 29.7 27.6 3.6 4.0 2.1 10.4 4.0 5.2 (Saint-Joseph, 1894) (22.6) (17.5) (19.8) (26.0) (4.6) (8.0) (2.6) (5.8) (4.3) (6.5)

Capitella capitata (SS) 4.7 1.6 0.5 1.6 45.3 3.1 3.6 22.9 0.4 7.3 {Fabricius, 1780) (1.7) (1.7) (1.3) (1.7) (33.7) (4.0) (3.7) (14.9) (1.2) (12.6)

Heteromastus filiformis (SS) 2.1 0.5 2.1 0.5 (Clapar~de, 1864) (2.6) (1.3) (2.6) (1.3)

Mean total number of 192.2 81.3 137.5 59.9 182.3 38.4 32.8 141.1 32.6 57.3 individuals (106.0) (34.0) (69.4) (28.0) (74.2) (28.3) (21.0) (78.0) (13.5) (41.3)

Mean number of individuals, 185.9 81.3 126.0 59.9 182.3 38.4 32.3 140.6 32.1 57.3 Lconchilega excluded (85.1) (34.0) (70.3) (28.0) (74.2) (28.3) (20.5) (78,4) (13.9) (41.3)

Mean number of species 10.5 5,8 11.0 5.0 7.2 3.1 4,4 7.0 4.0 4.2 (2.6) (1.0) (2.9) 1.2) (1.3) (1.8) (2.2) (1.8) (1.9) (2.0)

Total number of species 21 12 22 12 11 9 12 16 15 10

tember, Malmgreniella lunulata at both sampling dates. The lat- mediate areas. However, due to high variations the differences ter was regularly found inside the L. concbilega tubes whereas were not significant. No difference was found for several other no individual was found in the intermediate tube-free areas. abundant species like T. killariensis, Capitella capitata or Mean abundances of the spionid polychaete P elegans were at Nephtys hombergi and no species had higher abundance in the least twice as high in L. concbilega aggregates as in the inter- intermediate L. conchilega free areas. 135

Table 2. Mann-Whimey-U-Test results ofpairwise comparisons of species abundances or groups of species and ANOSIM results of mul- tivariate comparisons between species assemblages (Bray CurtŸ in&x, A q2 data transformation). -Tests were conducted between the macro- A benthic fauna of(l) L. conchilega aggregates and adjacent L. conchilega C free areas; (2) experimental fiel& with artificial tubes and tube-free A (~&'C c reference areas. Significantly higher numbers in L. concbilegaaggregates A or artificial-tube fileds: *: p<0.05; **: p<0.01; ***: p<0,005; -no signi- B D ficant difference, -- species not found. Classification of species is sho- B A wn in Tab. 1. B A D B L.conchilega- Artificial tube D B aggregates/ fields/ L.conchilega-free Tube-free areas areas Aug. Sept. Aug. Sept.

ANOSlM Total individuals ~t Total number of species *** *** Fig. 3. MDS plot for faunal assemblages ofL. concbilega aggregates and Number of polychaete species qr artficial tube fields, August 1995; stress 0.18 (Bray Curtis in&x, ,/2 data transformation). -(A) L. conchilegaaggregates; (B) Intermediate L. con- Taxonomical Group$ cbilega ffee areas; (C) Artificial tube fields; (D) Reference fields. Bivalves F~olychaetes tt~

Functional groups (1~ Surface feeders Subsurface feeders Predators Filter feeders In artificial tube fields both polychaete and bivalve abun- Species dances were significantly higher than in reference areas. ~ytilus edulis Altogether five species, four polychaetes and one bivalve, were ~fya arenaria found in higher numbers in artificial tube fields. Mainly ~falmgreniella lunulata juvenile forms smaller than 0.5 cm ofP. elegans and C. capitata =_teone Ionga were found in higher numbers on both sampling dates; Po~- Nereis diversicolor dora cornuta and Nereis diversicolor appeared in higher num- Pygospio elegans b** bers in August only. Juvenile M. arenaria settled preferably at Polydora comuta the protruding part of the metal sticks. Capitella capitata The most affected functional groups were surface and sub- surface feeders, which was due to the high numbers of the above mentioned spionid polychaetes and C. capitata. Similar to the L. concbilega aggregates filteffeeders were more abundant in artificial tube fields. This was related to high abundance of M. arenaria, although their overall numbers were considerably Considering functional groups, filterfeeders and predators lower in the artificial than in the natural tube aggregates. were more abundant in L. conchilega aggregates. The numeri- The multivariate compa¡ (ANOSIM) showed a signifi- cally dominating species of these groups were M. arenar& and cant difference between species" assemblages of artificial tube E. longa respectively. fields and reference fields which is visualized by distinctly The multivariate test ANOSIM (Tab. 2) indicated a signi- separated groups of samples in the MDS plot (Fig. 3). The ficant difference between the faunal assemblages. The corres- figure furthermore indicates that the fauna of the artificial tube ponding MDS-Plot (Fig. 3) showed a separation of samples fields was similar to the natural aggregates. from L. conchilega aggregates and intermediate L. concbilega free areas. Nematodes

Artificial Tubes Nematodes showed considerably higher abundances in samples immediately next to individual Lanice concbilega tubes As in natural Lanice conchilega aggregates, mean individu- than in controls or in the ambient sandflat without L. concbF al abundances and mean numbers ofspecies were significantly lega tubes. At a distance of 0.5 cm from the tubes 182+171 higher in the experimental fiel& with artificial tubes than in ind./0.2 cm 2 were found (Fig. 4) - about five times as many as untreated reference areas (Tab. 2). In contrast to natural tube in the vicinity of the L. conchilega area with densities of areas the total number of species did not differ markedly in 34.5+14.9 ind./0,2 cmL The latter value corresponds to a comparison to the reference fields. No differences in terms of mean nematode abundance of 34+15 ind./0.2 cm 2 at 5 cm numbers of species or individual abundance were found distance from the tubes, serving as control together with between the untreated reference areas and control fiel&, with samples from 10 cm distance, reveaIing a value of 58_+38 M. arenaria being the exception in September 1995 (Tab. 1). ind./0,2 cm 2. 136

200 The nematode density rapidly decreased within 2 cm distance from the worm tube. From about 1.5 cm distance with mean nematode densities ranging from 59+30 to 46+15 9DOM-feeders 150 ind./0.2 cm 2, values were similar to the background level. 9Diatom-feeders This general trend was especially due to a group ofnema- [] Others "E todes characterized by a very long and slender (threadlike) o habitus (GIERE 1993) with a thin and weak cuticle. This life 100 form is considered to be an adaptation to epidermal uptake of dissolved organic matter (DOM) (J~NSEN 1987). The dominant species of this group were Linhomoeidae like Metalinhomoeus 50 bformis, M. (ypicus, Paralinhomoeus ilenensis and P lepturus, Molgolaimidae (Molgolaimus cuanensis), Microlaimidae like Calomicrolaimus honestus, Calomicrolaimus sp., Microlaimus 0~ conotbelis, finally Odontophora rectangula and, perhaps, O. 0.5 1 1.5 2 5 10 armata. A reverse trend ofhigher densities with increasing distance Distance from L.conchflega tube [cm] from L. conchilega tubes became apparent for another group of nematodes sharing a common food resource: diatoms. Fig. 4. Mean numbers of nematodes along a transect arising from Dominant species ofthis group were Chromadoropsis vivipara, L. concbilegatubes (n = 6). Daptonema oxycerca, and D. setosum.

Discussion

This study showed significant effects of the tubes buih by Higher numbers of opportunistic polychaetes in artificial the polychaete Lanice conchilega on the distribution ofmacro- tube fields were presumably mainly related to sediment accu- faunal species and meiobenthic nematodes. Effects on macro- mulation inside the experimental fields. P. elegans, P. ligni and fauna were confirmed by the experiment with artificial tubes. C. capitata ate all known to be primary colonizers (McCALL 1977; GI~SSLE & GPa~SSLE 1974). They might either be passi- vely trapped, as ECKMANN (1979) suggests for Tanais sp. and Macrofauna Manayunkia aestuarina around simulated tubes, or migrate actively (ARMoNIES 1994). Justas the already mentioned Natural as well as artificial tubes were accompanied by bivalves, they might also use tubes asa settlement substrate, higher numbers of species and individuals in comparison with as BELL & COEN (1982b) found for P. ligni. tube free reference areas. WOODI~ (1978) described similar They presumably also benefit from decreased predatory findings when comparing the effect ofDiopatra cuprea tubes pressure as WOODIN (1978) stated in her refuge-hypothesis. P. and plastic straws and concluded that physical and biogenic elegans for example is exposed to damage from 0-group plaice entities affected infaunal abundance in the same way. and flounder (Muus 1967) which were certainly inhibited in However, in this study, juvenile Mya arenaria were the only their preying activities by the artificial tubes. Weaker sediment species appearing in higher numbers with both L. concbilega trapping and less effective refuge from predation by the more aggregates and artificial tubes. Most other species appearing in flexible natural L. concbilega tubes can explain the moderate higher numbers in artificial tube fields were opportunistic effect ofL. concbilega aggregates on the surface- and subsurface polychaetes, whereas natural L. conchilega aggregates were in- feeding opportunistic polychaetes. Again, the studies of habited by higher numbers ofa potentially commensal poly- WOODIN (1978) and own observations at sites with higher L. chaete and juvenile Mytilus edulis. Furthermore, two predatory concbilega densities showed that spionids can also be affected polychaetes were found in higher abundance: Eteone longa in by natural tube aggregates. the L. concbilega aggregates and Nereis diversicolor in artificial While tube structures provide shelter from epibenthic tube fields. predation, endobenthic predatores have access to abundant Juvenile M. arenaria and M. edulis used the tube structures prey. In our study the predatory polychaetes E. longa and asa primary settlement surface. Both bivalves are able to N. diversicolor were found in higher numbers in natural or arti- anchor in the sediment or attach to bard substratum with ficial tube aggregates, respectively. Thus, tube aggregates ate byssus-threads (G• 1992; LINKE 1939). by no means perfect refuges from predation. Malmgreniella lunulata was the only species presumably exhibiting an interspecific relationship to L. conchilega. Numerous individuals of the mobile polychaete were found in L. conchilega aggregates but none in fields with artificial Nematodes tubes or reference areas. HARTMANN-SCHR/3DER (1996) mentioned that M. lunulata lives asa commensal to other Effects ofmacrofaunal burrows, tubes or trails on meio- polychaetes including L. concbilega. It was found regularly fauna organisms have been reported from tidal flats around inside L. conchi/ega tubes (pers. observation). The artificial the world (BELL & COEY 1982a, b; DITTMANN 1996; REI- tubes were not hollow, which might have distorted the result. DENAVER 1989). Especially small-scale differences in distribu- The exact character of the relationship between L. conchilega tion ofmeiofauna, and thereofnematodes, with polychaetes and M. lunulata still remains unclear. ate well documented (ALoNCI 1985; BELL 1983;JE~sEN 1980, 137

1983; REISE 1981a; WARWICK et al. 1986) and the Arenicola Nematode-Macrofauna Relationship marina-system of the German Wadden Sea became a classic case (RtIst 1981b, 1985, 1987; SCHERER 1985; WE:rZEI. et al. DA, Ea et al. (1982) found significantly higher numbers of 1995). WETZEL et al. (1995) provide data on nematode species nematodes in experiments with artificial tubes and concluded from the tail shaft of A. marina and report distribution that this was due to spatial refuge from macrofaunal predation. pattems similar to those found in this study, for both total SCHUBERT & REISE (1986) and M,,s (1967) mentioned that numbers ofnematodes and the groups "slender nematodes" juvenile Nepblys hombergi and N. diversico[or possibly prey on (DOM-feeders) and "stout nematodes" (diatom feeders). nematodes. Thus. the distribution of endobenthic predators L. conchilega potentially produce bromophenols (GOERKr could be related to higher numbers ofnematodes associated & WEBER 1990, 1991), which are known to negatively effect with tube structures. meiofauna (ALoNGI 1987;JENSEN et al. 1992; STEWARD et al. In our study, the predatory polychaetes E. longa was more 1992). Prior to the investigations it was hypothesized that abundant in natural tube fields. This suggests that endobenthic nematode distribution pattems might correspond to concen- predators might benefit from high nematode densities. trations ofthis substance. However, sediment samples revealed Tubes may be an obstacle for subsufface predation as well, that bromophenol concentrations were of the same level as in which might explain the higher numbers ofnematodes in the the water column and showed no gradient associated to L. con- immediate vicinity of the tubes, in addition to a distribution chilega tubes (unpubl. own data). Due to these results and high of food resources for nematodes. nematode abundance close to the L. conchilega tubes it appears However, several studies on the effect of tube structures to be most unlikely that bromophenols had any effect on the could not find a clear correspondence between meio- and nematode distribution pattern. macrofaunal results (BELL & WOODIN 1984; DAUER et al. Nematodes might have utilized the dwelling tubes them- 1982) and the same certainly applies to the findings of this selves as a nutrient source e.g. polypeptides or polysacharides investigation. Further studies are needed to resolve meio- and (FRANKe 1994) or benefited from improved oxygen conditions macrobenthic interactions on the va¡ spatial scales of this through ventilation activities ofL. conchilega. intertidal assemblage.

Acknowledgements

Special thanks to INGRID LINKENBACHwho diligently assisted the 03F0112A. Responsibility for the content ofthis publication rests with macrofaunal part of the project, MICHAEL GROTJArfNfor his support the authors. This is publication number 245 of the "Ecosystem Research and to the Company GERDES & WENK (Norden, Germany), which Wadden Sea". donated 10.000 metal sticks for the experiment. This work was supported by the Bundesministerium fª Bildung, Wissenschaft, Forschung und Technologie (BMBF) under grant

Re fe rences

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