Community structure of the intertidal meiofauna along a gradient of morphodynamic sandy beach types in southern Chile

Se estudiaron tres playas arenosas del sur de Chile (Gaviotas, Guabun y Mar Brava; ca. 42o S) durante el verano del 2000 para analizar los patrones de abundancia y biomasa de la meiofauna a lo largo de un gradiente de tipos morfodinamicos de playas. Se recolectaron muestras de sedimento con cilindros metalicos (23 cm2 de area, 120 cm de longitud) en diez niveles espaciados a intervalos regulares a lo largo de seis transectos separados de 5 a 10 m y extendidos desde un punto sobre el nivel de marea alta y el nivel de marea baja. En cada nivel de muestreo se midio porosidad, fuerza de cizalla, contenido de agua, penetrabilidad y tamano del grano. La meiofauna estuvo primariamente representada por Nematoda y Copepoda Harpacticoidea. Las mayores densidades y biomasas medias por unidad de area se encontraron en la playa reflectiva de Gaviotas (6.172 ind 10 cm-2 y 2,38 g m-2, peso seco libre de cenizas) en comparacion con la playa intermedia de Guabun (3.390 ind 10 cm-2 y 1,70 g m-2) y la playa disipativa de Mar Brava (3.667 ind 10 cm-2 y 0,86 g m-2). La abundancia y biomasa total de la meiofauna por metro lineal de playa (i.e., meiofauna total contenida en un transecto intermareal de 1 m de ancho) fueron mayores en Mar Brava (506 x 106 ind m-1 y 119,4 g m-1) versus Gaviotas (271 x 106 ind m-1 y 101,7 g m-1) y Guabun (143 x 106 ind m-1 y 73,9 g m-1). Por lo tanto, estos ultimos resultados muestran una tendencia de aumento de abundancia y biomasa de la meiofauna intermareal hacia el tipo disipativo dentro del gradiente estudiado de tipos de playas. Los valores mas altos de densidad y biomasa de la meiofauna se encontraron en los niveles superiores y medio de cada playa. En la playa disipativa, se encontro la menor variabilidad en abundancia y biomasa de la meiofauna a lo ancho del intermareal. Segun la prueba de permutacion de Monte Carlo, el contenido de agua, penetrabilidad y tamano del grano fueron las variables que mejor predicen la variabilidad de las densidades de la meiofauna. Los tamanos corporales de nematodos, copepodos, turbelarios, halacaridos y ostracodos estuvieron correlacionados con las caracteristicas del sedimento. En general, las relaciones entre estructura comunitaria de la meiofauna y morfodinamica de playas, fueron similares a aquellas encontradas para la macroinfauna de diferentes playas arenosas alrededor del mundo, lo que sugiere que la meiofauna y macroinfauna son afectadas similarmente por los procesos fisicos asociados a diferentes tipos de playas


INTRODUCTION
The intertidal sediments of exposed sandy beaches harbour a diverse and abundant meiofauna and macroinfauna (Brown & McLachlan 1990).Nematoda, Harpacticoidea, Turbellaria and Oligochaeta stand among the most common meiofaunal taxa (McLachlan 1988), while Crustacea, Polychaeta and Bivalvia are the most frequent macroinfaunal taxa (Brown & McLachlan 1990).Although several studies have analysed the responses of macroinfauna and meiofauna to single sediment characteristics, such as mean grain size and sorting of particles (see reviews by McLachlan 1983 andCoull 1988), composite abiotic indexes created to characterize morphodynamic beach states were not used until the 90's.The pioneer studies of McLachlan (1990) and McLachlan et al. (1993) (1994) predicted that optimum conditions for the development of a diverse and abundant meiofauna are likely to occur in intermediate beaches.Their prediction was based upon the fact that beaches with intermediate morphodynamic characteristits represent an equilibrium state between organic inputs (which increases towards the dissipative beach state) and aerobic interstitial conditions (which increases towards the reflective beach state).Both factors are the most favorable to the presence on meiofauna in intertidal habitats (e.g., Giere 1993).To test this prediction, a number of beaches covering the full spectrum of morphodynamic beach states should be sampled.
The northern coast of Isla de Chiloe (southern Chile, circa 42° S) is ideal to examine the earlier prediction, since reflective, intermediate and dissipative beaches alternate in a reduced geographic area (Jaramillo et al. 2000).That allows to avoid eventual effects of confoundig factors which may vary geographically (e.g., sea water temperature, species replacement) along larger latitudinal gradients.While the sandy beach macroinfauna of this area of the the Chilean coast has been previously studied (Jaramillo eta!. 2000), no meiofaunal studies have been conducted here or elsewhere along the wave exposed sandy beach of this coast.Since community structure and zonation of the intertidal meiofauna are highly affected by sediment (Hicks & Coull 1983, Giere 1993) and beach characteristics (McIntyre 1971, McLachlan 1980, McLachlan et a!. 1981 ), it is reasonable to hypothesise that the community structure of the Chilean meiofauna is related to beach morphodynamics; i.e., it changes according to changes in physical characteristics occurring along a gradient of beach morphodynamic types (e.g., changes in grain sizes, porosity, water table depth).To provide a preliminary evaluation of this hypothesis and the prediction of McLachlan & Turner (1994) (i.e., higher densities and biomass of meiofauna in intermediate beaches), we sampled three morphodynamic beach types in the northern coast of Isla de Chiloe.

Study area
The sites selected for sampling were at the central areas of the beaches ofGuabun (41 o 48'S, 74° 01' W) and Mar Brava (41 ° 54'S, 73° 59' W), located on the exposed coast of Isla de Chiloe (i.e., fully exposed to the Pacific Ocean, Fig. 1 ), and at the central area of the beach of Gaviotas ( 41 o 51' S, 73° 45' W), located on the less exposed coast of Golfo de Ancud (Fig. 1 ).Tides in this region are semidiurnal with maximum tide ranges close to 2 m.A previous study characterised Gaviotas as a reflective beach, Guabun as intermediate and Mar Brava as dissipative (Jaramillo et a!. 2000).

Meiofauna sampling
Samplings were carried out during spring tides of January 2000.Sediment samples were collected with metallic cylinders (23 cm 2 cross sectional area, 120 em long) at ten equally spaced levels along six replicated transects (separated haphazardly between 5 and 10 m) and extending from above the drift line to the swash zone.The uppermost station was located above the drift line (level 1 0), the second at the drift line (level9) and the last (level 1) at the lowest limit of the swash zone (indicated by bore collapse).Previous studies of vertical distribution of meiofauna in exposed beaches (e.g., McLachlan 1980)   to upper beach levels (i.e., from 40 to 120 em).Each sediment sample was homogeneised by hand in a small plastic tube before collecting subsamples of 100 cm 3 and 40 cm 3 with plastic corers for meiofaunal and sedimentological analyses, respectively.Subsamples for meiofauna were kept in 250 cm 3 plastic jars with 40 cm 3 of seawater previously filtered through APFF Millipore glass microfibre filters.40-100 μg of menthol were added to each jar as an anaesthetic.After 24 h, the samples were stored in formaldehyde 6 % with Rose Bengal and borax.To extract the meiofauna, water was added to each sample which was stirred and later on decanted for less than 10 seconds in a plastic graduated cylinder (6.4 em in diameter, 33 em length).After decantation, the supernatant was filtered through a 42 μm sieve (Pfannkuche & Thiel 1988).This procedure was repeated six times resulting in an extraction efficiency of about 97% (efficiency estimated by examination at 40x of residual sediment of six samples ramdomly selected).Meiofaunal samples retained in the 42 μm sieve were separated through a set of sieves of different mesh sizes: 1,000, 500, 200, 100 and 42 μm.The meiofauna was sorted to major taxa using an inverted microscope ( 100 x) in a modified Bogorov zooplankton tray.Indirect estimates of biomass (ash free dry weights) were carried out by using the individual weights previously measured in meiofaunal taxa by McLachlan (1977b), Faubel (1982) and Widbom (1984).Abundance and biomass values per running meter of beach (i.e., estimates of total meiofauna in an intertidal across shore transect of 1 m wide) were obtained by linear interpolation between sampling stations, after obtaining mean values of biomass and abundances per m 2 at each sampling station.An indirect average size of the meiofauna was calculated for each major taxa by pondering mesh size of sieves with the relative abundances of organisms retained in each sieve (e.g., if 50 % of the organisms of a major taxa are retained in a mesh sieve of 1 00 μm mesh and 50 % are retained in a mesh sieve of 42, the estimated indirect average size is 71 μm).

Substrate characteristics
At each beach level, a superficial sampling (0-6.5 em of depth) of sediment was taken along one of the central transects to determine porosity, water content and granulometry.Porosity and water content were estimated by gravimetric differences (Giere et al. 1988).Grain size of sands was analysed by using a Coulter LS 200 laser diffraction particle size analyser, while that of the coarser fraction by dry sieving (Folk 1980).Penetrability and shear strength were measured (n = 6) at the same beach levels where sediment samples were collected.Penetrability and shear strength were measured with a penetrometer and a shear vane meter.The penetrometer was a 120 g metal rod, 35 em in length and 7.5 mm diameter, which was dropped from 1 m above ground level.The vane tester (English Drilling Equipment Co. Ltd., England) comprises a torque head with a direct reading scale which is turned by hand.A non -return pointer indicates the reading.The vane (33 mm diameter) which is screwed into the rear of the torque head was pushed 5 em into the sediment (the same extension of the vane).The readings are given in kPa.The beach face slope at the site of the transects was analysed with Emery's profiling technique (Emery 1961 ).

Statistical analyses
Non-metric multidimensional scaling ordination (MDS) with the Bray-Curtis similarity measure and cluster analysis (Bray-Curtis index, groupaverage linkage) were performed on double square root transformed abundance of major taxa.Pairwise analysis of similarities (ANOSIM, Clarke 1993) was carried out to test the null-hypothesis that there were no differences (at α= 0.05) in the composition of the meiofaunal assemblage at different beaches.MDS, cluster analysis and ANOSIM were performed using the software package PRIMER, developed at the Plymouth Marine Laboratory (Clarke & Warwick 1994 ).Redundancy analysis (RDA) was used to evaluate the relation between the average density of the meiofauna per tidal level and the environmental variables.RDA is the canonical form of principal component analysis, a form of direct gradient analysis (ter Braak 1995).Linearity between the abundances of the major taxa and the

The physical environment
The beaches of Gaviotas and Guabun had similar intertidal widths and beach profiles, while Mar Brava (135 m) was about three times wider and four times flatter (Fig. 2).The substrate characteristics of the beaches are shown in Table 1.Sands from the reflective beach of Gaviotas corresponded to coarse and very coarse sands, that of the intermediate site at Guabun to medium sands, while that of the dissipative beach at Mar Brava corresponded to fine sands (sensu Folk 1980).In Gaviotas and Mar Brava, sands were coarser at the lower shore levels, while at Guabun

Mar Bravo m from tide
Fig. 2: Beach face slopes at the sites studied.
Perfiles de playa en los sitios estudiados.the coarsest sands were found up shore (Table 1).
The worst and best selected sediments were found at Gaviotas and Mar Brava, respectively.Porosity ranged between 30-35 % at Gaviotas and 40-42 % and 36-43 % at Guabun and Mar Brava, respectively (Table 1).Water saturation increased from the dry zone to the resurgence and swash zones at Gaviotas and Guabun, while it was quite homogeneous at Mar Brava.Penetrability and shear strength values indicate that the sediments of Mar Brava had a higher compaction than those of Gaviotas and Guabun (i.e., harder sands) (Table 1).

Composition and abundance of the meiofauna
Meiofauna was primarily represented by Nematoda and Copepoda Harpacticoidea.Crustacean nauplii, oligochaetes, halacarids, turbellarians, mystacocarids, ostracods, tardigrades, gastrotrichs, kinorhynchs and foraminiferans were also present but in lower abundances.Pre-zoea larvae and zoea of Emerita (at the two lowest levels of Gaviotas and Guabun), interstitial polychaetes, insects, syncarids (at the four lowest levels of Gaviotas) and interstitial isopods (at the lowest level of Gaviotas) were also found.
The number of major taxa was higher at the reflective beach of Gaviotas (15) and the intermediate site of Guabun ( 14 ), and lower at the dissipative beach of Mar Brava (6) ( The highest density and biomass of the meiofauna were found at the upper and mid shore levels of Gaviotas.Density and biomass values as high as 11,550-13,992 ind 10 cmˉ² and 4.02-4.61g mˉ² were estimated for this beach (Table 3).The highest density and biomass estimated for the beaches of Guabun and Mar Brava were 7,110-9,900 ind 10 cmˉ² and 3.76-4.10g mˉ² and 4,250-7,504 ind 10 cmˉ² and 1.08-1.75g mˉ², respectively (Table 3).The highest total abundance and biomass of the meiofauna per linear meter of beach (i.e., abundance and biomass of the meiofauna in an intertidal across-shore transect l m wide) were estimated for Mar Brava (506 x 10 6 ind m 1 and 119.4 g mˉ¹ ), as compared with Gaviotas (271 x 10 6 ind mˉ¹ and 101.7 g mˉ¹) and Guabun (143 x 10 6 ind m 1 and 73.9 g mˉ¹) (Table 2).

Intertidal zonation of the meiofauna
The intertidal variability in total abundance and biomass of the meiofauna and the across shore TABLE2 Density (ind 10 cm-2 ) and biomass (g m-2 ) of the total meiofauna at the beaches studied Densidad (ind 10 cm-2 ) y biomasa (g m-2 ) de la meiofauna total en las playas estudiadas Shore level Gaviotas Guabun (ind I 0 cm-2) (ind 10 cm-2) distribution of the major taxa is shown in Fig. 3.At Gaviotas, total abundance and biomass peaked at the sampling levels located at the retention zone (Fig. 3).At Guabun total abundance and biomass peaked at the drying zone and upper levels of the retention zone (Fig. 3 ).The total abundance and biomass showed less spatial variability at Mar Brava although slightly lower values were found at the upper shore levels (Fig. 3).
The density distribution of nematodes followed different patterns among the three beaches (Fig. 3).Nematodes at Gaviotas showed higher abundances at the retention and resurgence zone (3,900-10,600 ind 10 cm-2 versus densities of 55-372 ind 10 cm-2 in the swash zone).At Guabun, the density of this group was higher at the dry zone and the upper levels of retention zone, while at Mar Brava the intertidal distribution of nematodes did not show much spatial variability.While the harpacticoid copepods at Gaviotas showed low intertidal variability, they peaked at the dry zone and the upper levels of the retention zone at Guabun and at the dry and retention zones at Mar Brava (Fig. 3).At the latter, harpacticoid copepods were absent from the lowest shore levels (swash zone, Fig. 3 ).
The maximum number of nauplii larvae at Gaviotas occurred at the swash zone.At Guabun this group peaked significantly at the dry zone, while at Mar Brava they showed a fairly homogeneous distribution across the intertidal (Fig. 3).Foraminiferans were absent at the highest beach levels of the three beaches, specially at Mar Brava (Fig. 3).The intertidal distribution of turbellarians at Gaviotas showed maximum abundance values at the retention zone.At Guabun the maximum abundances of this group were found at the retention and swash zone, while at Mar Brava they showed a homogeneous distribution throughout most of the intertidal but the upper shore levels (dry zone) (Fig. 3).Halacarids and ostracods were absent from the lower shore levels at Guabun; at this beach, ostracods peaked at the retention zone.The intertidal distribution of Gastrotricha was wider at Mar Brava; at Gaviotas and Guabun they were absent from the upper shore levels (Fig. 3).Interstitial polychaetes and oligochaetes showed opposite patterns of distribution; polychaetes were primarily found in the lower shore levels, oligochaetes were mostly found at the upper shore levels.While tardigrades primarily occupied the upper shore levels of Gaviotas and Guabun, they were not found at Mar Brava (Fig. 3).Mystacocarids were only found at the lower shore of Guabun, while kinorhynchs and interstitial insects occurred only at Gaviotas and Guabun (Fig. 3).

Relationships between meiofauna and environmental variables
Figure 6 shows the RDA ordination biplot obtained for the major taxa of meiofauna.The Monte Carlo permutation test showed that the meiofauna community changed significantly with grain size (P < 0.001), water saturation (P < 0.05) and sediment penetrability (P < 0.001).The total explained variation was 36.6 %.The first and second axis, explained by the environmental variables, accounted for the 93.5 % of the speciesenvironment correlations.The sum of all canonical eigenvalues was 35.9 %.The position of the meiofaunal groups in the biplot reflects the contribution of each group to the variance explained by the first two axes.Thus, the numbers of turbellarians and foraminiferans were not correlated with environmental variables since their positions in the RDA were near the origin (Fig. 6).The angles between variables in the biplot reflect their correlations (Legendre & Legendre 1998): angles near 90° indicate no correlations, angles near oo indicate high positive correlation and angles near 180° indicate high negative correlation.Thus, the abundance of gastrotrichs was positively correlated with water saturation, while harpacticoid copepods and oligochaetes were negatively correlated with the same variable (Fig. 6).Copepods and nauplii larvae were positively correlated with grain size of sands, while the abundances of nematodes and gastrotrichs were negatively correlated with sand size (Fig. 6).Finally, the abundance of gastrotrichs was positively correlated with sediment penetrability; those of the harpacticoid copepods and oligochaetes were correlated negatively with the same variable (Fig. 6).

DISCUSSION
The results of this study show that the highest density and biomass values per unit area of the total meiofauna occurred at the reflective beach of Gaviotas, as compared to the intermediate and dissipative sites.However, and due to the fact that the beaches studied differed in the width of the sampling zone, interbeach comparisons of density values can be misleading since across shore distribution of the meiofauna is not accounted for.The following figures exemplify this: two beaches of similar length but different intertidal width (e.g., 100 versus 200 m) may have the same density of meiofauna per square meter.However, the wider beach will have twice the intertidal density.Thus, comparisons based on linear meter of beach sampled (i.e., estimations on an intertidal transect of 1-m wide) allow to truly know which beach harbours higher densities in its intertidal area.The comparative analyses of this study showed that abundance and biomass of the total meiofauna per linear meter of beach were higher towards the dissipative side of the beach spectrum analyzed.This trend is similar to that usually found for the sandy beach macroinfauna; i.e., abundance and biomass per linear meter of across shore intertidal increase from reflective to dissipative beaches (McLachlan eta!. 1993(McLachlan eta!. , 1996(McLachlan eta!. , 1998)).On the other hand, the trend shown by richness of major meiofaunal taxa was the opposite to that shown by the macroinfauna elsewhere.Thus, while species richness of the sandy beach macroinfauna increases from reflective to dissipative sites (McLachlan eta!. 1993(McLachlan eta!. , 1996(McLachlan eta!. , 1998)) Other studies have reported meiofaunal densities between 4 and 11,820 ind 10 cmˉ² (McIntyre 1969, Coull 1988), although most values for sandy beaches lie between 50 and 1,500 ind 10 cmˉ² (McIntyre 1969).Thus, while the densities estimated in this study (3,390-6, 171 ind 10 cm-2 ) can be considered high, the biomass values (0.86-2.38 g mˉ²) fit well within the biomass figures reported for the intertidal of exposed beaches, i.e., 0.020-4.4g m-2 on other coasts of the world (McLachlan 19 8 3).It was also found that nematodes and harpacticoid copepods were the most abundant taxa, which is typical in all kinds of sediments (Coull & Bell 1979, Coull 1988).
The intertidal distribution of the total meiofauna at Gaviotas and Guabun was noticeably compressed downshore as compared with that at Mar Brava (Fig. 3).McLachlan (1983) mentions that in exposed sandy beaches the zone of resurgence is the most suited for interstitial life, since there is a good balance among water content, oxygen and food supply and physical stability.Giere ( 1993) has mentioned that in exposed sandy beaches, the swash zone is characterised by an impoverished meiofauna.Similar compressed patterns of downshore distribution have been found at exposed beaches on the Pacific coast of USA (Wieser 1959), east coast of India (Ganapati & Rao 1962, McIntyre 1968) and east coast of South Africa (McLachlan 1977b ).The intertidal distribution of the numbers of the meiofauna at Mar Brava was the most uniform, as that found in other dissipative and/or relatively protected beaches ( cf. Harris 1972, McLachlan 1977b).The fact that at Mar Brava the zonation was more uniform might well be related to the lower variability of physical intertidal characteristics, specially water saturation (see Table 1).
Even when the three beaches studied are morphodynamically different, the zonation of the major taxa of meiofauna was quite similar at Gaviotas and Guabun (Fig. 3).Although the size of sand grains was quite different between these beaches, the beach face slope and water saturation were very similar.This suggests that the zonation of the intertidal meiofauna of exposed sandy beaches may be related to a combination of physical factors (such as the morphodynamic beach stage, sensu Short & Wright 1983) rather than to single ones, such as grain size.This would explain the low percentage (36 %) of the meiofaunal variability explained by the three physical variables included in the redundancy analysis.
Results presented in Fig. 3 show that the three beaches differ in the composition of their meiofauna, and mainly in the relative proportion of nematodes and crustaceans.This fact fits well with the hypothesis that the nematode/copepode ratio is negatively correlated with grain size in non-polluted sediments (Warwick 1981 ).McLachlan (1977a) found an increase in the proportion of crustacean with an increase in wave exposure.Thus, the relationship between nematodes and crustaceans could be an indicator of the energetic and morphodynamic conditions of exposed sandy beaches.
Sediment characteristics have a dominant role in meiobenthic ecology (Giere 1993).Indeed, grain size determines many physiographic parameters which are closely related to substrate such as porosity, permeability and oxygen supply (Giere et a!. 1988).Orren et a!.(1981) and Hennig et a!.(1983) found that the densities of nematodes and copepods were negatively correlated with grain size at exposed beaches of South Africa.In this study, the RDA showed correlations with nematodes, but not with copepods.This may be explained by the fact that the density of the copepods at the beaches studied was more influenced by sediment penetrability than by grain size.
Virtually all the meiofauna is interstitial (i.e., no burrowing) in sands coarser than 200 μ m median particle diameter (Wieser 1959).Body size of the meiofauna tends to decrease as grain size, and consequently pore size, decreases (Swedmark 1964 ).The results of this study show that the average sizes of copepods and ostracods were positively correlated with grain size (Fig. 7).Witte & Zijlstra (1984) also found this positive correlation for copepods.The fact that the size of some major taxa is negatively correlated with the shear strength can be due to the fact that the higher the physical alteration of the sediment (less shear strength), the higher the size the fauna that will bear the mechanical impact of that alteration.
In conclusion, this study has shown that the intertidal meiofauna inhabiting exposed sandy beaches of southern Chile is closely related to beach characteristics.While the highest density and biomass values per m 2 were found at the reflective side of the beach spectrum sampled, density and biomass per linear meter of beach were higher at the dissipative beach.Thus, these results do not agree at all with the prediction of McLachlan & Turner (1994); i.e., higher abundance of meiofauna at intermediate sandy beaches.If this trend still holds along a complete spectrum of beach types along the coast of southern Chile or elsewhere remains an open question.

Fig. 1 :
Fig. 1: Location of the sandy beaches studied at Isla de Chi loé, southern Chile.Ubicaci6n de las playas arenosas estudiadas en Ia Isla de Chiloe, sur de Chile.

Fig. 3 :
Fig. 3: Distribution of the major taxa of the meiofauna at the intertidal of Gaviotas, Guabun and Mar Brava.Density values are expressed in numbers 10 cmˉ², biomass in g mˉ².Dashed lines separate the physical zones of the beaches (sensu Sal vat 1964): D =dry zone; Rt =retention zone; Rs =resurgence zone; S = swash zone.Distribuci6n de los taxa mayores de Ia meiofauna en el intermareal de Gaviotas, Guabun y Mar Brava.Los valores de densidad se expresan en numero 10 c m ˉ² , los de biomasa eng m ˉ² .Las lineas discontinuas separan las zonas ffsicas de las playas (sensu Sal vat 1964 ): D = zona de sec ado; Rt = zona de retenci6n; Rs = zona de resurgencia; S = zona de batido.

Figures 4
Figures 4 and 5 show the dendrogram and biplot resulting from the dendrogram and MDS analyses respectively.Meiofaunal assemblages from Guabun and Gaviotas were more similar between them (ANOSIM, R = 0.27) than between Guabun and Mar Brava (ANOSIM, R = 0.67) (higher R values indicate lower similarity, Legendre & Legendre 1998).Figures 4 and 5 suggest that Mar Brava was the beach with the lowest variation among sampling levels.

Fig. 5 :
Fig. 5: Biplot resulting from the multidimensional scaling analyses of the meiofauna.Lowe case letters indicate beaches while numbers represent sampling levels (see Fig. 4).

Fig. 6 :Fig. 7 :
Fig. 6: Biplot resulting from the redundancy analyses.Dashed arrows for the major taxa, full-line arrows for the environmental variables.The arrows indicate the direction of increase for the variables studied.Biplot resultante del analisis de redundancia.Flechas con lfneas discontinuas para los taxa mayores, flechas con lineas continuas para las variables ambientales.Las flechas indican !a direcci6n de aumento para las variables estudiadas.
related community structure of the intertidal macroinfauna to morphodynamic beach types (sensu Short & Wright 1983 ), showing that species richness, as well as, total abundance and biomass of the macroinfauna tended to increase from narrow beaches having coarse sands and steep slopes (reflective beaches, sensu Short & Wright 1983), to wider beaches having finer sands and flatter slopes (dissipative beaches, Short & Wright 1983).Similar studies have not been carried out with the sandy beach meiofauna, although McLachlan & Turner showed that the highest meiofaunal abundances are usually found in wet sands above the water table level; thus, for quantitative studies it is necessary to reach that level.Since water table depth increases up the beach, the sampling depth increased from lower

TABLE 1
Physical characteristics at each zone of the beaches studied: D = dry zone, Rt = retention zone, Rs = resurgence zone, S = swash zone Caracterfsticas ffsicas en cada una de las zonas de las playas estudiadas: D = zona de secado, Rt = zona de retenci6n, R s = zona de resurgencia, S = zona de batido de las alas