AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, VOL. 6, 299-31 1 (1996)

Effects of human trampling on tidalflat infauna

W. U. CHANDRASEKARA and C. L. J. FRID Dove Murinr Laboratory, University of’ Neitulstle upon Tyne, Cullerrouts, North Shields, T j w und Weur NE30 4PZ, U K

ABSTRACT

1 . Human trampling has been shown to be detrimental to the survival of fauna of terrestrial habitats and on rocky coastal areas. However, its effects on saltmarsh benthic infauna were not known.

2. The abundance of macro-benthic fauna at five locations on a transect across a footpath on the emergent marsh and on the tidalflat at Lindisfarne NNR were sampled during the summer I994 and winter 1995.

3. The abundances of dominant taxa increased in summer in the intensely trampled path on the unvegetated tidalflat leading to a change in the community structure. These changes were not apparent when the trampling intensity was lower in winter.

4. The abundances of dominant taxa at a less intensively trampled site in the vegetated emergent marsh did not change in either season.

5. The susceptibility of the saltmarsh infauna to human trampling depends on the intensity of trampling disturbance and on the nature of the habitat. The possible effects of human trampling on the macrofauna in these intertidal habitats are discussed with reference to coastal management. 31, 1996 by John Wiley & Sons, Ltd.

INTRODUCTION

There has been a rapid growth of human outdoor leisure activities since the beginning of the twentieth century (Patmore, 1970). Coastal areas rank among the most attractive sites for these activities (Andersen, 1995) as these areas are rich in faunal and floral diversity (Klucas and Duncan, 1967) and scenic beauty. The increased visitor activities, however, can have severe effects on the areas, and contribute to their destruction and reduction of their nature and recreational values. A direct effect is the disturbance to the fauna and flora by human trampling.

Systematic studies to investigate the effects of repeated human trampling on natural communities can be traced to Bates (1935). Some of the direct impacts are, the disappearance of vulnerable species (Bates, 1935; Chappell et al., 1971), reduction in number of flowering species (Goldsmith et d., 1970; Hylgaard, 1980), decrease in biomass production (Edmond, 1962; Liddle and Greig-Smith, 1975b), decrease of vegetation cover (Burden and Randerson, 1972; Bowles and Maun, 1982), interference in natural succession (Goldsmith et al., 1970; Hoiser and Eaton, 1980) and loss of biodiversity (McDonell, 1981). The communities may also be impacted indirectly by soil erosion (Carlson and Godfrey, 1989), alteration of the substrate structure (Chappell et al., 1971), creation of footpaths (Bayfield, 1973; Hylgaard and Liddle, 1981), reduction of soil organic matter (Boorman and Fuller, 1977; Hylgaard and Liddle, 1981) and soil compaction (Bates, 1935; Liddle and Greig-Smith, 1975a). These effects are likely to increase as use of the area concerned increases (Brosnan and Crumrine, 1994). However, most of these studies have been primarily targeted at investigating the changes brought about on the flora or on the soil structure and only

CCC 1052-761 3/96/040299-13$17.50 ((,I996 by John Wiley & Sons, Ltd

Received December 1995 Accepted September 1996

300 W U CHANDRASEKARA A N D C. L. J. FRlD

a few accounts (e.g. Chappell ct ul., 1971; Duffey, 1975; Meyer, 1993) are available of its effects on the fauna.

Duffey (1975) demonstrated that the invertebrate fauna of grassland litter appeared to be affected by levels of trampling much lower than those required to produce changes in the structure and abundance of living plants and that the fauna declined markedly in terms of numbers and species. Some species such as woodlice in particular, were very sensitive to trampling. He also concluded that at lower trampling intensities, the changes brought about in the fauna were negligible. Massoud ct ul. (1984) showed that human trampling decreased the density of collembolan communities in litter and soil in a French forest area. The species richness and the diversity of the ground living enchytraeid fauna on a hiking trial in a Hungarian forest decreased significantly due to continuous trampling (Dozsa-Farkas, 1987). Investigating the effects of skiing and trampling on Alpine soils, Meyer ( 1 993) demonstrated that every kind of touristic impacts on the natural landscape had a negative effect on the soil fauna. He also observed that the abundance of earthworms diminished by 85% in trekked areas and the recovery of ground living fauna at high altitudes proceeded extremely slowly.

Saltmarshes and the associated tidalflats in the coastal environment attract bird lovers, bird hunters and visitors looking for ‘natural recreational’ areas due to their natural beauty, peacefulness and the rich avian diversity (Long and Mason, 1983). The tidalflats are also a centre for activities such as bait-collecting (Jackson and James, 1979; McLusky et al., 1983; Wynberg and Branch, 1991, 1994). Schroeder (1978) reported that bait-worm digging is the fifth largest fishery in Maine, USA, and employs more than a thousand diggers. The occurrence of recreational visitors, naturalists and bait-collectors on these coastal habitats could bring about a high intensity of human trampling and consequent disturbance to the sediment structure.

The passage of even a single person across a saltmarsh leaves a trail discernible for weeks. However, few studies have been carried out so far to investigate the effects of visitor pressure on the community structure of these coastal soft-bottom habitats. Dalby (1970) showed that varying intensities of repeated trampling resulted in changes in the vegetation structure in a Pembrokeshire saltmarsh. Usually long recovery times are predicted, e.g. it takes between 4 and 15 years for the vegetation to recover to its original level and between 10 to 50 years were required when the soil structure had been altered (Beeftink, 1979). Results of the survey by Andersen (1995) on the effects of human trampling on Danish saltmarsh vegetation types were contradictory. He found that saltmarsh vegetation was resistant to repeated trampling, hence the plant diversity was not changed by this process. The effects of this type of disturbance on the infauna in these coastal habitats have been largely neglected.

This study investigates the changes brought about in the benthic fauna of two established footpaths on saltmarshes and associated tidalflats which were subjected to repeated trampling. The benthic community structure and the abundances of the benthid fauna of footpaths were compared with those of the neighbouring areas in order to determine whether the continuous trampling disturbance has had any effect on the soft-bottom benthic fauna. It also examines the effects of seasonality on the degree of impact on the fauna of these paths.

MATERIALS AND METHODS

Study sites

The two habitats selected for the study were located within the Lindisfarne National Nature Reserve (UK grid ref NU850 420) on the north-east coast of England (Figure 1). Lindisfarne NNR is an extensive tidalflat and saltmarsh area. The area is intensively used by bait diggers and bird watchers. At high tide, the sea isolates Lindisfarne (Holy Island) from the mainland. It is a holy site for pilgrims. During the summer these pilgrims walk to Lindisfarne along a traditional path, the Pilgrims Way, which stretches across the

TRAMPLING ON TIDALFLAT INFAUNA 30 1

England s Figure 1. Pilgrims Way (A) and ‘Old track’ (B) at Lindisfarne NNR in north-east coast of England.

unvegetated tidalflat. This path runs south of the modern causeway and is marked by a series of wooden stakes driven into the soft mud. Another footpath to the north of the causeway runs mainly through the heavily vegetated emergent marsh. Previously, it was used by 4-wheel drive vehicles but is now only used by bait diggers and naturalists.

Sampling

One transect perpendicular to each footpath was sampled on 16 August 1994 (summer) and again, on 17 February 1995 (winter). On each transect, five 1 m x 1 m sampling quadrate locations were established in such a way that one was on the path centre and two quadrates were on either side of the path. In Pilgrims Way, sample quadrate locations were established on the transect 5m from each other, whereas in ‘Old track’ the distances to the two quadrate locations on either side of the path were 2 m and 3 m respectively from the centre of the path. Each quadrate was subdivided into a lOcm x lOcm grid, with the sample location pre-determined by random coordinates. A 6 cm diameter cylindrical corer was used to retrieve 5 samples to a depth of lOcm from within each quadrate position for faunal analysis (see Dicks and Iball (1982) for a justification of the number and the size of the core). Sediment pH in each quadrate location was determined in situ, using a pH meter (model: JENWAY 3097) and the depth of the redox discontinuity layer in sediment was measured in a 20 cm deep sediment core retrieved on to the sediment surface. In addition, four further randomly located sediment cores were retrieved from within each quadrate location for sediment analysis.

302 W U. CHANDRASEKARA A N D C. L. J. FRID

On return to the laboratory, faunal samples were preserved in a solution of 40% formalin containing 5% Rose Bcngal. Thcy wcre thcn washed through a 0.5 mni incsh. Animals retained on the mcsh wcrc idcntificd and enumerated under a binocular microscope. Organic matter content of sediment was determined by the loss of dry weight of sediment igniting at 550°C for 24 h. Silt clay content was determined by the loss of weight after wet sieving a sediment sample through a 63 pm mesh (Buchanan, 1984).

Data analysis

Species abundance data were log (x + 1) transformed prior to analysis. Species which comprised more than 5% of the total individuals in each sample set were deemed to be in sufficient numbers to analyse parametrically. Before performing any parametric tests, transformed data were tested for homogeneity of variance using the Bartlett’s test (a = 0.05) (Zar, 1996). Differences in the transformed abundance data of the most abundant species and the physico-chemical factors between the 5 quadrate locations on each transect were tested using one-way ANOVA (a = 0.05). When the ANOVA indicated significant differences the Tukey’s multiple comparison tests were carried out in order to test for significant differences between any pair of quadrate locations (Zar, 1996).

Non-metric Multi Dimensional Scaling (MDS) plots and the associated dendrograms based on the Bray- Curtis similarity index (Clarke and Warwick, 1994) were constructed for each transect at each sampling time. All the species recorded were used in preparing dendrograms and MDS plots. Differences in community compositions between the cores retrieved from within the footpath and the four other sites were determined by one-way ANOSIM (Analysis of Similarity; a = 0.05).

The PRIMER multivariate analytical package (Ver. 4.2B) was used in the community data analysis and MINITAB (Ver. 10.2) for Windows was used to test differences in the densities of species and physico- chemical data between the five quadrate locations.

RESULTS

Pilgrims Way

The numbers of species recorded on the transect during the summer and winter were 24 and 20 respectively. Capitella capitata (Fabricus), Clitellio arenarius (Miiller), Tuhificoides pseudogaster (Dahl), Enchytrueus huclzholzi (Vejdorsky), Pygospio elegans (Claperede), Scoloplos armiger (Miiller) and the multispecies taxon nematodes dominated at both times. They represented 87.6% and 89.4% of the individuals during the summer and winter respectively.

Cluster analysis and the associated MDS plot (Figure 2a) clearly identified two groups in the summer data. All the samples from the footpath were tightly clustered together and were significantly different (ANOSIM; R=0.599, p=O.OOl) from the other cluster indicating that repeated trampling has had a significant impact on the benthic community during the summer. The summer abundances of all the dominant taxa varied significantly (ANOVA; p<O.O5) (Table 1) between the five locations along the transect. The abundances of C. arenarius, E. huchholzi, nematodes, T. pseudopster and P. eleguns significantly increased (Tukey’s pairwise tests; p < 0.05) while that of C. capitata and S. uriniger significantly decreased (Tukey’s pairwise tests; p<0.05) with respect to the location of the path (Figure 3).

In winter samples, cluster analysis and the M DS plot (Figure 2b) distinguished two significantly different (ANOSIM; R = 0.932, p = 0.001) clusters in the data, comprising locations to the south of the path and the path and sites to the north of it. In this latter cluster samples from the footpath were not significantly different from the remainder of samples ( R = 0.507; p = 0.07) implying that those samples shared the same community structure. The abundance of all the dominant taxa varied significantly between locations in winter (p<0.05) (Table I ) . The abundance of C. capitata significantly increased (Tukey’s pairwise test;

TRAMPLING ON TIDALFLAT INFAUNA 303

0 0 0 0

0 A 0

A

I [Stress = 0.1

I

0

I (Stress = 0.1

Figure 2. MDS ordination for summer (a) and winter (b) samples for the transect across Pilgrims Way, Lindisfarne NNR. Footpath samples (0) formed a distinct cluster in summer samples. This cluster is delimited by a line in the MDS ordination and its community structure was significantly different (ANOSIM; p=0.005) from that in the remainder of samples (0, a, 0, 0). In winter, footpath samples (0) clustered with the samples taken from locations to the north of the path (0, A). Samples from locations in the south of

the path (0, 0 ) clustered separately.

~ ~ 0 . 0 5 ) towards the centre of the path. However, the abundances of the remaining species showed no obvious pattern with respect to the location of the path at this time (Figure 3).

‘Old track’

The number of taxa recorded on the transect during the summer and winter were 19 and 18 respectively. Fabriciu subellu (Ehrenberg), Hydrobia ulvae (Pennant), Manayunkia aestuarina (Bourne), Clitellio arenarius, Tubificoides pseudogaster, Enchytraeus buchholzi, Pygospio elegans (Claperedae) and the multi- species taxon nematodes dominated at both times. These 8 taxa accounted for 90.5% and 92.7% of the individuals during the summer and winter respectively.

304 W U CHANDRASEKAKA A N D C L J . F R l D

Table 1. Summary of the ANOVA on the abundance of dominant taxa between the 5 quadrate locations on the transect across the Pilgrims Way and ‘Old track’ at Lindisfarne N N R .

Footpath Species/Multi Time species taxa

~ ~~

DF ss MS F P

Pilgrims Way Cupitellu cupitutu

Clitellio urcwirius

Enchytraeus buchholzi

Nematoda

‘Old track‘

Pj,gospio eleguns

sl~oInpl0.F armiger

Tub~fifiidcs pseudogaster

Clitellio arenurius

Enchytraeu,c. huchholzi

Fubriciu sabella

Hydro b iu ulvue

Munuyunkiu uestuurinu

Nematodes

Summer Winter Summer Winter Summer Winter Summer Winter Summer Winter Summer Winter Summer Winter Summer Winter Summer Winter Summer Winter Summer Winter Summer Winter Summer Winter Summer Winter Summer Winter

4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4

1.923 2. I10 1.570 1.092 2.504 4.328 2.27 1 1.763 8.617 8.100 2.038 3.763 0.785 0.961 0.696 4.313 0.153 0.148 5.336 2.936 0.267 1.208 2.343 1.801 I .337 0.533 1.025 1.462 0.990 1.823

0.48 1 0.528 0.393 0.273 0.626 1.082 0.568 0.441 2.154 2.025 0.509 0.941 0.196 0.240 0.174 1.078 0.038 0.037 1.334 0.734 0.067 0.302 0.586 0.450 0.334 0. I33 0.256 0.365 0.248 0.456

8.05 4.10 7.24 5.97

17.11 24.80

5.71 8.40

78.52 30.1 1 10.29 39.67 4.04 2.53 3.50

17.22 0.85 0.75 8.95 3.61 1.83 1.16 7.97 2.38 2.X6 1.17 5.99 2.68 1.41 3.32

0.001 0.014 0.001 0.002 0.001 0.00 I 0.003 0.001 0.001 0.00 1 0.001 0.00 1 0.015 0.043 0.025 0.001 0.512 0.570 0.001 0.023 0.162 0.357 0.001 0.086 0.050 0.354 0.002 0.061 0.267 0.03 I

Dendrograms and the associated MDS plots showed the footpath samples to be interspersed between off path samples in both the summer (Figure 4a) and the winter (Figure 4b). The community structure of footpath samples was not significantly different from that of the remaining samples in either the summer (ANOSIM; R = - 0.149, p = 0.91) or the winter (ANOSIM; R = 0.026, p = 0.40). This illustrated that repeated trampling has not had any significant effect on the structure of the benthic community on the footpath at either time.

During the summer, the abundance of F. sabella, M . aestuarina, C. armarius, and P. elegans varied significantly between the five locations (ANOVA; p < 0.05) (Table 1). However, their abundances did not increase or decrease towards the centre of the path (Tukey’s multiple comparison test; p>O.O5) (Figure 5) . The winter abundances of F. sabellci, C. arenarius, and T. pseudogaster varied significantly (ANOVA; p<O.O5) (Table 1) between the five locations along the transect with no significant increase or decrease of their abundance towards the centre of the path. These results suggest that the dominant taxa on the footpath were not affected by trampling at either sampling time.

The depth of the redox discontinuity layer (RDL), organic matter content, silt-clay content and soil pH did not vary significantly between quadrate positions along the transect either in summer or winter (ANOVA; p > 0.05) at either site.

TRAMPLING ON TIDALFLAT INFAUNA

g 8 m

a n m 4

V c 6

C 2.-

07 2

305

- -

-- -- -- -

- I

10 5 0 5 10 10 5 0 5 10

9

10

m a 3 6 n

4

16

2 12

f 2 4 2

0 0 10 5 0 5 10 10 5 0 5 10

2007 120,

l o T

10 5 0 5 1U

I n :u 10 5 0 5 10

-r

10 5 0 5 10 Distance from the centre of the path

(metres)

Figure 3. Summer (0) and winter (m) abundances (no. per m2) of (a) Cupitella capitafa, (b) Clitellio arenarius, (c) Enchytraeus buchholzi, (d) Scoloplos urmiger, (e) nematodes, (f) Tubificoides pseudogater and (9 ) Pygospio elegans on the five positions along the

transect a t Pilgrims Way, Lindisfarne NNR.

306 W. U. CHANDRASEKARA AND C. L. J . FRID

0. 0

0

A

I (Stress = 0.17)

A

(Stress = 0.13)

Figure 4. MDS ordination for summer (a) and winter (b) data for the transect across the ‘Old track’, Lindisfarne NNR. Footpath samples (0) intersperse among the samples from the four other locations (0, A, 0, 0) along the transect without forming a

significantly different cluster at both sampling times.

DISCUSSION

Human trampling in coastal recreational areas including saltmarshes creates footpaths and reduces their natural beauty and amenity value (Vickery, 1995). It has been shown that human trampling has an impact on the saltmarsh flora (e.g. Dalby, 1970; Andersen, 1995). The present study appears to be the first to address the changes in the saltmarsh benthic fauna as a result of human trampling.

During a typical year, about 10 000 pilgrims walk to Lindisfarne along the Pilgrims Way, predominantly in the summer months between May and September (P. Davey, Warden, Lindisfarne NNR, personal communication). It is possible that the soft-bodied infauna that live at or very close to the sediment surface (Brenchly, 1981; Lopez and Levinton, 1987; Unsal, 1988) of the path are crushed and directly killed by trampling.

TRAMPLING O N TIDALFLAT INFAUNA 307

The fauna may also experience indirect mortality as a result of burial in the mud, through compaction of the sediment and reduction of its oxygen content leading to asphyxiation or displacement due to the collapsing of their burrows (Wynberg and Branch, 1994). The sediment disturbance could also bring the infauna onto the sediment surface exposing them to avian predation (Jackson and James, 1979; Heiligenberg, 1987; Wynberg and Branch, 1991). The intensity of trampling on the Pilgrims Way was sufficient to cause a shift in the composition of the benthic fauna (Figure 2a). The abundance of Capitella cupituta and Scoloplos armiger were reduced on the path (Figure 3). However, the remainder of the dominant taxa; Tuh$icoides pseudogaster, Clitellio arenarius, Enchytraeus buchholzi, Pygospio elegans and nematodes, appeared to have benefited from trampling. While the individuals of these species may also experience mortality due to human trampling, there must be a process going on which more than compensates for the removal of the dominant taxa. One possibility is that this occurs through the rapid recruitment of adult stages (Thistle, 1980 and 1981; Thrush, 1986, 1991; Thrush and Ropper, 1988; Thrush et al., 1995; Frid, 1989; Chandrasekara and Frid, 1996).

Human trampling churns the upper sediment layer of the path stimulating the bacterial growth on organic matter (Rhodes and Young, 1970). This may have made available food for the deposit-feeding infauna (Lopez and Levinton, 1987). In addition, the bodies of animals dead or injuried due to trampling may further enhance the food value of the sediment. This food may be attractive to dispersing infauna resulting in the observed increases in the abundance of some species. Similar patterns of increasing abundance of fauna in disturbed patches in soft sediments have been observed previously (Simon and Dauer, 1977; Thistle, 1980 and 1981; Wynberg and Branch, 1994).

The tidal flow over the tidalflats provides a mechanism which adult opportunistic colonists can use to move actively into the path from surrounding undisturbed areas (Thistle, 1980; McLusky et ul., 1983). Furthermore, the tide flowing over the tidalflat may erode the upper sediment layer, passively redistributing animals as bedload (Eckman, 1983) or moving them into the water column from where they can move actively with the inflowing water (Siegismund and Hylleberg, 1987). The Pilgrims Way is only 2 m wide but it extends about 3.5 km. The sides of the path are always in contact with the undisturbed areas so that colonization can be rapid.

It can be argued that changes in species abundance on the Pilgrims Way should decline soon after the pilgrimage season stops as there is no permanent source of disturbance. In winter, when the trampling has virtually ceased, it appears that the community on the path had reverted to a structure similar to that in adjacent areas (Figure 2b). The lack of significant differences in the winter abundances of the species which were impacted during the summer suggests that the changes brought about in these populations were rapidly removed by natural processes such as dispersal and sediment reworking (Probert, 1984). Nevertheless, there is still some evidence of a difference in the community structure on the Pilgrims Way even in winter.

The ‘Old track’ is clearly distinguishable on the vegetated marsh. Short rhizomous plants like Puccinellia maritima, Armeria maritima and Aster tripolium which grow as dense tufts or rosettes, cover a substantial part of the path. Although most of this saltmarsh vegetation is trampling resistant (Ranwell, 1972; Andersen, 1995), a decrease in the abundance of flora and consequent increase in bare mud has been brought about by the sustained human trampling (personal observation). This implies that the existing trampling intensity is strong enough to bring changes in the flora of the ‘Old track’.

Duffey (1975) showed that ground living fauna of a grassland litter habitat can suffer damage by trampling intensities which are much lower than those required to bring about changes in the flora. Chappell et al. (1 97 1) showed that the abundance of earthworms and other ground living. animals were reduced on a footpath with increasing trampling intensity although there were no data available on the number of people causing the observed effects. In the present study neither the infaunal community structure (Figure 4a and 4b) nor the abundance of any of the dominant taxa (Figure 5) on the ‘Old track’ in the vegetated saltmarsh were impacted by repeated trampling.

308

70 - m 8

5 50.-

s U n m 30

5 2 0 2 - = 10

0 ,

W. U. CHANDRASEKARA AND C. L. J. FRID

a) e)

.-

40

20 .-

-- --

--

- ; 04 I

" T

3 2 0 2 3

70T T

3 2 0 2 3

3 2 0 2 3 3 2 0

3 2 0 2 3

2 3

3 2 0 2 3

T

3 2 0 2 3 3 2 0 2 3

Distance from the centre of the path Distance from the centre of the path (metres) (metres)

Figure 5. Sommer (0) and winter (m) abundances (no. per m2) of (a) Fahricio subella, (b) Hydrobiu ulvde, (c) Manayunkia ae.sruarinu, (d) nematodes, (e) Clitellio urenarius, (9 Enchytrueus hurhholzi, (g) Pygospio elegans and (h) Tuhificoides pseudogum on the five

positions along the transect at 'Old track', Lindisfarne NNR.

309 TRAMPLING ON TIDALFLAT INFAUNA

As all the dominant taxa at the study sites occupy the upper sediment layers and so might be expected to be exposed to the direct effect of trampling, the absence of any measurable effects by repeated trampling requires explanation. One possibility is that the presence of the vegetative cover on the footpath minimizes mechanical damage to the fauna. Although it is possible that trampling pressure causes mechanical injuries to the plants, the cover they provide on the ‘Old track’ may mitigate its effects by cushioning the impact on the fauna in the sediment layer underneath. The pressure per unit area transferred to the ground may be much lower with a shoe, particularly a rubber soled shoe (Cole and Bayfield, 1993) than that effected through a small surface, i.e. an animal hoof (Ranwell, 1972), thereby further lessening the damage.

Visible effects of human trampling on saltmarshes vary depending on the habitats concerned. Effects can usually be clearly observed in the submergent marsh where the substrate is more unconsolidated than in the emergent marsh. Visitors naturally avoid using this area for recreational activities due to the muddy nature of the substrate, hence limiting damage to this habitat. Visitor activities are usually centred on the emergent marsh, and while the plant cover in the emergent marsh resists occasional trampling, high trampling intensities over a long time damage the plant cover (Dalby, 1970). This leads to the creation of a path and a reduction in the natural beauty and amenity value (Vickery, 1995). Once a path is created people do not usually walk outside the path (Bayfield, 1971) thus the damage may persist (Dalby, 1970) but be restricted in area. Nevertheless, the altered vegetation cover appears to protect the fauna from the effects of trampling. Management should therefore encourage visitors to use established paths and so limit their impacts (Brosnan, 1992). In contrast, high levels of trampling on the unvegetated tidalflats lead to a change in the fauna. These changes, however, quickly disappear when trampling intensity is decreased. This suggests that paths in this habitat can be regarded as areas suffering temporary impacts.

The susceptibility of the benthic fauna to human trampling depends on the nature of the habitat and also on the trampling intensity. The observed changes in the fauna have occurred independent to the physico- chemical parameters of the sediment. Further research is required to clarify the threshold intensity at which the community responds to the trampling disturbance. These findings can then be used as a baseline in the formation of coastal management plans.

ACKNOWLEDGEMENTS

This work was carried out while WUC was in receipt of a scholarship from the Association of Commonwealth Universities. English Nature permitted the authors to carry out field experiments at Lindisfarne NNR. Phil Davey, Warden, Lindisfarne NNR, provided valuable information on the number of pilgrims at Lindisfarne. Assistance from Janaki Ranasinghe with the field work and constructive criticisms from two anonymous reviewers on the early draft are gratefully acknowledged.

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