Hydrobi%gia 529: 205-224, 2004.., @ 2004 K/Ull'er Academic Publishers. Printed in the Netherlands. 205

Spatial patterns of the surf zone hyperbenthic fauna of Valdivia Bay (Ecuador)

Luis Dominguez Grandal,*, Nancy Fockedel'*, Micheline De Mey2, Bregje Beyst2,Maria del Pilar Cornejol, Jorge Calderon3 & Magda Vincx2'Facultad de Ingenieria Maritima y Ciencias del Mar (FlMCM), Escuela Superior Po/iu?cnica del Litoral(ESPOL). Campus Gustavo Galindo, Km. 30.5 Via Perimetral. P.O. Box 09-01-5863. Guayaquil. Ecuador2Marine Biology Section. Department of Biology. Ghent University. Krijgslaan 281/S8, B-9000 Gent. Belgium'Centro Nacional de Acuicultura e Investigaciones Marinas (CENAIM). Campus Gustavo Galindo, Km. 30.5Via Perimetral, P.O. Box 09-01-4519. Guayaquil. Ecuador(*Authors for correspondence: Tel.: + 32-9-264-8518, Fax: + 32-9-264-8598,E-mails:nancyfockedey@Ugent.be(NancyFockedey)..ldomingu@espol.edu.ec (Luis Dominguez Granda)

Received 30 September 2003; in revised form 2 April 2004; accepted 19 April 2004

Key words: hyperbenthos, Mysidacea, sandy beach, surf zone, tropical southeast Pacific

Abstract

The present research is a first attempt to study the hyperbenthic fauna of the surf zone of Valdivia Bay(South East Pacific - Ecuador), an exposed low tide terrace - rip beach. The aims of the study were tocontribute to the inventory of the surf zone fauna of the tropical southeast Pacific coast, to investigatespatial distribution patterns along the bay and to search for possible tidal effects on the hyperbenthiccomposition. Samples were taken during daylight with a hyperbenthic sledge on 6 consecutive days inAugust 1999 at high tide, low tide and mid tide. The hyperbenthic community was characterized byquantifying the higher taxa, their density and the relative composition of the dominant groups. No tidaleffect could be observed, but two main geographically distinct hyperbenthic assemblages were distinguishedalong the bay, related to hydrodynamic factors (local current velocity, intertidal beach slope and suspendedparticulate matter). In the turbulent northern part of the bay the highest densities were encountered andhyperbenthos was, next to the dominant mysid Metamysidopsis sp., mainly composed of planktonicorganisms (calanoid copepods, chaetognaths and fish eggs). In the calmer southern part of the bay Meta-mysidopsis sp. dominated as well, but the community was completed with other mysid species, and early lifestages of Brachyura and fish. Most striking was the general dominance of the mysid Metamysidopsis sp. inall the samples (97%, max. density of 62000 indo 100 m-2) and the high amount of unknown species.Penaeid shrimp larvae, important for the local shrimp industry, were only found in very low densitiesduring the sampling period (",1%). Compared to other studies on the whole surf zone hyperbenthic com-munity of sandy beaches, the average densities encountered in Valdivia Bay can be considered to berelatively high (2500-6000 indo 100 m-2). Although limited in time and performed with a limited taxonomicresolution, the results indicate a high contribution of early life stages of invertebrate and fish species to thebiodiversity of the intertidal hyperbenthic community in comparison with temperate regions.

Introduction and were thought to offer little variability in termsof habitat diversity, cover or productivity. Recentevidence however, suggest that fluctuations incertain physical variables such as the degree of

For many years surf zone habitats were charac-terized as structurally homogeneous environments

206

wave exposure, sediment particle size and turbidityhave a strong influence on the relative abundanceof certain species and may alter the compositionand species richness of surf zone assemblages(Clark et aI., 1996). The occurrence of diatomplumes, detached macrophyte accumulations andthe proximity of subtidal reefs, rocky jetties,estuarine habitats and seagrass beds may all con-tribute to the spatial variability in the surfzone faunal composition (Wooldridge, 1983,1989; Robertson & Lenanton, 1984; Romer &McLachlan, 1986; Wright, 1989; Romer, 1990;Odebrecht et aI., 1995).

The main component of this surf zone faunaconsists of peracarid organisms, but it also in-cludes decapods, pycnogonids, euphausiids, cope-pods and early life stages of teleosts (M unilla et aI.,1998). It is important to note that many fish spe-cies and macro-invertebrates use the surf zone as anursery area (Lasiak, 1981, 1986; Senta & Ki-noshita, 1985).

Some surf zone inhabitants live specifically inthe lowest layers of the water column, close tothe bottom (Colman & Segrove, 1955; Fincham,1970). Generally, a lot of names have been givento this faunal assemblage, such as suprabenthos,hypoplankton, benthopelagic plankton, demersalzooplankton, benthic boundary layer fauna andnektobenthos. In the present study the term hy-perbenthos will be used, as suggested by Ham-erlynck & Mees (1991). The hyperbenthic faunacan be specified as all those animals that live inthe lower layers of the water column but are inclose association with the seabed. The followingorganisms are included in the community: (I)species living permanently in the lower layers ofthe water column (e.g., mysids, chaetognaths,copepods), (2) species with a mainly endobenthiclifestyle but making short excursions from theseabed for feeding, mating and dispersion (e.g.,some amphipods, isopods, cumaceans, hippidcrabs and some polychaets) and (3) early lifestages of epibenthic species (e.g., larvae andjuveniles of several decapod and fish species).The first two categories are usually groupedunder the term holohyperbenthic animals, whilethe third group is specified as merohyperbenthicfauna.

Recently quite some ecological investigationsof sandy beach fauna are published, but they are

often limited to particular taxonomical groups,like Mysidacea (Mauchline, 1980; Wooldridge,1981, 1983, 1989; Webb & Wooldridge, 1990; Ta-kahashi & Kawaguchi, 1995, 1998; Hanamura,1999; Nel et aI., 1999; San Vicente & M unilla,2000), Isopoda (De Ruyck et aI., 1991a, b, 1992;Jones & Pierpont, 1997), anomuran Hippidae(Dugan & Hubbard, 1996; Amend & Shanks,1999; Jaramillo et aI., 2000; Lastra et aI., 2002;Defeo et aI., 2001; Defeo & Cardoso, 2002), Pyc-nogonida (Munilla & San Vicente, 2000), Cum a-cea (Corbera et aI., 2000), Amphipoda (Fincham,1970; Yu et aI., 2002) and fish larvae (e.g. Ross,1983; Senta & Kinoshita, 1985; Kinoshita, 1993;Cornejo et aI., 1993; Harris & Cyrus, 1996). Fewstudies discuss the entire hyperbenthic communityof the surf zone (see Table 4).

Most studies are situated in temperate regionsand almost no information is available on thetropics. Tropical beaches, in general, have beenexamined over shorter periods and in less detailthan temperate beaches (Dexter, 1992). Moreover,most of the investigations in subtropical andtropical environments deal with sandy lagoons incoral reef areas (Mees & Jones, 1997).

In this paper, we present the results of a studyin an exposed bay situated along the southeastPacific coast of Ecuador. The aims of the study are(a) to evaluate the heterogeneity of the surf zonehyperbenthic communities along a bay, relatingthe spatial and tidal distribution with environ-mental variables, (b) to determine the dominantcomponents of the distinguished communities, and(c) to contribute to the inventory of the surf zonehyperbenthic fauna of the tropical southeast Pa-cific coast.

Material and methods

Description of the study area

The sampling site is situated in Valdivia Bay(Ecuador), along the west coast of South-America(Fig. I). The bay consists of an 8 km long sandybeach directly exposed to the Pacific Ocean. Dur-ing summer months, the bay is intensively used byartisanal fishermen for catching penaeid shrimplarvae in the surf zone. This activity is mainlyconcentrated in the southern part of the bay (pers.

41' 80045W

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207

1°55'S

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Figure I. Map of the Ecuadorian coast showing the region of study (inset) and the locations of the six transects.

comm., Cornejo). However, on the moment ofsampling this was not the case.

Along the Ecuadorian coast there is a semi-diurnal tidal regime, with a periodicity of 11.5-13.5 h, and with a mean tidal range of 2.6 m(mesotidal). The beach is, in terms of exposi-tion (McLachlan, 1980) and morphodynamics(Masselink & Short, 1993), classified as an ex-posed, low tide terrace - rip beach (Aerts et aI.,2004). The Ecuadorian coastal zone is character-ized by two seasons: a dry/cool (winter) and a wet/warm period (summer). The climate is influencedby the currents in the southeast Pacific. The cold«22 DC) Humbolt current with a relatively high

salinity (>35 psu) is coming from the south anddominates in the period from July till October,while the warm (>25 DC)low salinity «34 psu) EINino-current, coming from the north, dominatesfrom January till April (Cucalon, 1989).

Sampling and processing of samples

Six transects along Valdivia Bay were sampled(Fig. 1). The distribution of the selected beachesalong the bay was based upon their accessibility.

Sampling was done during 6 successive days (31August - 05 September 1999; waning quartermoon). From north to south, the stations wereBruja, Casa, Valdivia, San Pedro, Cenaim andPunta. Each day a different, randomly selectedstation was sampled 3 times during the recession ofthe tide: at high tide, 3 h later and at low tide. Allsamples were taken in daylight hours. In one sta-tion (Casa), the low tide hyperbenthos samplingwas cancelled because of too strong currents.

The surf zone was sampled using a hyperben-thic sledge of 70 cm wide and 50 cm high, equip-ped with a 4 m long net (mesh size of 1 x 1 mm).It was pulled over a distance of 400 m (200 m backand forth) by two persons walking parallel to thecoastline in the surf zone at waist depth (:I:1 m),i.e. some 30-100 m offshore of the swash linedependent on the inclination of the sampled tran-sect. The organisms caught were immediatelypreserved in neutral formaldehyde (final concen-tration 7-8%).

The salinity and water temperature wererecorded in situ using a hand refractometer anda mercury thermometer on each sample occasion.Water samples were taken to determine chlorophyll

~.~~oo~

100 120 140 160 180 0 20 40 60

Distance from MLWS (m)

Figure 2. Beach profiles of the six transects between the low water sampling point and the vegetation line; (8) indicating the height of

the sampling stations at high water, 3 h later, and at low water. The dashed line indicates the calculated intertidal slope (%).

208

a (chla) and chlorophyll c (chIc) contents, suspendedparticulate matter (SPM) and particulate organicmatter (POM) concentrations. For SPM and POManalyses, water samples were passed through pre-dried-tarred Whatman GF IC filters (65°C; for 2 h).The filters were dried at 105°C for 24 h to get theSPM value (by weight difference), and subsequentlyburned at 550°C for 2 h to calculate the POM.Water samples for chlorophyll analyses were filteredover Whatman GF IC filters and immediately fro-zen. In the laboratory, an extraction with acetone(90%) was done prior the analysis. The concentra-tion of chla and chIc was determined with a Gilsonhigh-performance liquid chromatograph, using aslightly modified method of Wright & Jeffrey (1997).

Along each transect, the relative height of 7-9points between the vegetation line and the lowwater line were measured using an altimeter. Therelative height of the low water point was com-bined with the local tide table values of La Li-bertad (INOCAR) to obtain its absolute height inrelation to the mean low water level at spring tide(ML WS), from which the absolute elevation of allhigher points was calculated and the beach profilesconstructed (Fig. 2). The beach intertidal slope

g

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was calculated as the inclination of the line ob-tained between the low and high water point (in%). The beach width is expressed as the distancebetween low and high water (in m). Also, at eachsampling occasion a sediment sample of the swashzone was taken and analysed for its granulometry.Median grain size between 0.4 and 900 11m wasobtained with a COULTER@ LS100 particle sizeanalyser. The local current was measured by theLagrangian method and the current velocity isgiven as the average speed used by a sub-surfacedrifter to cross 50 m parallel to the coast. Themacrobenthos of the bay was simultaneouslystudied and is published in Aerts et al. (2004).

In the laboratory all animals were sorted,counted and identified, when possible to specieslevel, using the identification keys of Rose (1933),Tattersall & Tattersall (1951), Russel (1953), Loesh& Avila (1964), Fonseca (1970), Keen (1971), King(1974), Russel (1976), Fauchald (1977), Kabata(1979), Lincoln (1979), Smaldon (1979), Mauchline(1980), Mendez (1981), Basurto & Naranjo (1983),Bonilla (1983), Massay (1983), Kensley & Schotte(1989), Dall et al. (1990), Barnard & Karaman(1991), Fisher et al. (1995), Hendler et al. (1995),

40[230 4%2.0

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100 120 140 160 180

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Hartmann-Schroder (1996) and Todd et a\. (1996).Different developmental stages of the organismswere treated as separate functional 'species'. Whena specimen could not be identified with certainty tospecies level, but if a clear (external) morphologicalcontrast between different individuals of the samegenus, family or even a higher taxonomic levelexisted, it was defined as a specific morphospecies(sp. I, sp. 2, etc.). Several morphospecies within thePycnogonida, Brachyura, Ophiuroidea and fishlarvae were distinguished according to the externalmorphologic characteristics summarised in Table Iand kept in a reference collection in the laboratory.For the calanoid copepods and fish eggs no mor-phospecies were defined. All the identificationswere done in a consistent way for all samples byone person. An inventory of the hyperbenthicfauna of Valdivia Bay is presented in Table 2. Thedistinction between holo- and merohyperbenthicspecies is indicated.

Data analysis

The sampling sites were characterised in terms ofenvironmental variables and the tidal variation ofthese variables in the bay was examined usingKruskal-Wallis analyses.

Densities are expressed as number of indi-viduals per 100 m2. Averages are always indi-cated with their standard error (SE). Densityvalues are considered as minimum estimatessince the net efficiency is unknown (Mees &Hamerlynck, 1992). The larger epibenthicorganisms, not efficiently caught by the sledge(e.g. juvenile Paguridae, Anthozoa, adultBrachyura and Echinodermata) were eliminatedfrom the data set for further statistical analysis.Also the parasitic copepods (Caligus sp.) andisopods (Gnathiidae larvae), and the endobenthicgastropods (Olivella semistriata and Mazatlaniasp.) were removed.

Species descriptions of hyperbenthic represen-tatives from this region of the world are often notavailable and forced us to further describe thehyperbenthic communities using a database withthe morphospecies grouped in 13 higher taxa(indicated in bold in Table 2). Those taxa pre-senting less than 0.002% of the total density likePolychaeta (0.0017%), Stomatopoda (0.0003%)and Euphausiacea (0.0007%) were no further in-

209

cluded in the dataset. In order to discover spatialand/or tidal patterns within the bay, the sampleswere classified using the classification programTWINSPAN (Two-Way INdicator SPeciesANalysis) (Hill, 1979). The cut levels used in theanalysis were 0, 10, 100, 1000 and 10000 indo100 m-2. To check the stability of the TWIN-SPAN results, a principal component analysis(PCA) was applied on the standardised data aftera DCA indicated that the unimodal responsemodel could be used (length of gradients 1.067SO). Vectors indicating the environmental vari-ables were later superimposed on the PCA output(using PCord 4.24; McCune & Mefford, 1999) toindicate their possible relation with the obtainedoutcome of the samples/taxa in the plot. Thedensity data were fourth-root transformed (Fieldet a\., 1982); the environmental data were stan-dardised by applying a relativisation to the stan-dard deviate. Environmental variables to beincluded in the analysis were previously submittedto a Pearson correlation analysis. If a relation wasfound between two or more variables, only one ofthem was used. The identified communities werefurther characterised and tested for differencesbetween the prevailing environmental variablesand densities of the main taxonomic groups bymeans of at-test.

The densities of the dominant mysid speciesMetamysidopis sp. were analysed for spatial andtidal differences with Kruskal-Wallis tests. Anadditional multiple regression analysis was per-formed to see what environmental variables wereexplaining the presence of the species.

Results

Environmental variables

The (means of the) environmental variablesmeasured in the 6 sampling stations are shownin Figure 3. The salinity in most of the bay was34 psu. Only in Cenaim a lower salinity of33 psu was recorded. The mean water tempera-ture in the surf zone varied between 24.0 and25.7 dc. Mean median grain size ranged between196 and 305 ,urn. A notably higher value wasfound in San Pedro at ebb tide (411 ,urn). Themean SPM values were very variable (63-

210

Table I. External morphologic characteristics used to distinguish between morphospecies within the Pycnogonidae, Brachyura,Ophiuroidea and fish larvae

Pycnogonlda

Body morphology

Ocular tubercle

ProboscisCheliceraePalps

Walking legs

Brachyura

Zoea

Carapace

Lateral spines

Rostral spinets)

Dorsal spine

Abdomen

Telson

Megalopa

Carapace

Rostral spinets)

Abdomen

Eye

Second antennae

Walking legs

Cheliped

Telson

Juvenile

Carapace

Eye

Walking legs

Cheliped

Opmuroidea

Disc

Arms

Fi.h laroae

General shape

Stage of development

Pigmentation

Gut shape

Fins

Head

Trunk stout, slender or disciform; segmentation of the trunk marked, diffuse or absent; segmentation of the trunk

marked, diffuse or absent; form of the cephalon; number and length of segments; lateral processes well separated or

continuous; terminal or dorsal abdomen

Position with respect to the basis of the 1st pair of ambulatory legs; tubercle elevation and form; position of the eyes

in the ocular elevation

Form and size in relation to the trunk; blunt or cylindrical

General length and width; length and width of claws

Presence/absence

Slender or stout; presence/absence and size of ventral spines/hairs; presence/absence of auxiliary claws (distal end of

the II tarsus)

Smooth or with spines

Relative length; directed anteriorly or posteriorly; curving ventraly or dorsally

Number; length in relation to the antennal protopod; directed ventrally or anteriorly (to a certain degree); presence/

absence of setae

Relative length; straight or curving posteriorly

Somites with posterolateral processes present/absent; presence/absence of spines or setae on the somite surface

Size and form of the furca; presence/absence of lateral spines on the furca; presence/absence of spines or setae on the

surface

Carapace outline: smooth surface or presence of humps/spines; covering cephalothorax or not;

lateral processes present/absent; presence/absence of posterior lobe; width of frontal region

Presence/absence; size; directed anteriorly or ventrally

Width; somites with posterolateral processes present/absent

Size and form

Size; presence of setae in the joints

General morphology

General morphology chelae

General outline; presence of spines in the posterior part

posterio-dorsal/

Carapace outline: e.g. rounded, suboval, polygonal; surface smooth or with humps/spines; lateral processes present/

absent; presence/absence of spines around the orbits

Form and size

General morphology

General morphology chelae

Cover of the dorsal surface e.g. spines, spinules. flattened granules

Patterns of arm plates and spines e.g. asymmetrical arms joints. regularly or irregularly fragmented dorsal arm plates

General appearance (long, slender, short, deep body); standard length; number of myomeres

Preflexion, flexion or postflexion transforming

No, light or heavily pigmented; size, position and number of melanophores

Straight, coiled or trailing

Number of rays in all fins; number of dorsal fins; position of pelvic fin (abdominal, thoracic or jugular); length of

pectoral fins;

Relative size and shape; presence/absent spines on surface; presence/absence of melanophores; presence/absent spines

on operculum; relative size and shape eye

Table 2. Higher taxa used in the data analysis (in bold) and themorphospecies identified herein (sp.: morphospecies; species:not further identified) with their stage considered (pi: postlarva;juv: juvenile; meg: megalopa). The third column indicates if themorphospecies are counted as holohyperbenthos (H) ormerohyperbenthos (M). The" " denotes an inefficientlysampled taxon that is not further used in the dataset

Taxon

Hydrozoa - superclass

Corynidae sp.

Siphonophora sp.

Anthozoa - superclass

Actiniaria sp.

Polychaeta - class

Palola sp.

Scolelepis sp.

Spionidae sp.

Magelona mirabilis

Gastropoda ~ class

Olivella semistriata

Mazatlania sp.

Bivalvia - class

Bivalvia sp.

Pycnogonida - class

Pycnogonida sp. 1-10

Copepoda - subclass

Calanoida species

Sapphirina sp.

Sapphiridae sp.

Caligus sp.

Stomatopoda~ordo

Stomatopoda sp.

Euphausiacea - ordo

Nyctiphanes simplex

Nyctiphanes simplex

Penaeidae ~ family

Penaeidae sp. 1~2

Acetes binghami

Acetes binghami

Caridea - infraordo

Alpheidae sp.

Caridea sp.

Caridea sp.

Anomura - infraordo

Pagurus sp.

Pagurus sp.

Emerita rathbunae

Stage Type

Medusa

Adult

H

H

Adult

Adult

Adult

Adult

Adult

H

H

H

H

Adult

Adult

Spat M

Adult H

Adult

Adult

Adult

Adult

H

H

H

Larva M

Larva

Adult

H

H

PI

Pi

M

H

HAdult

PI

Zoea

M

M

MPI

Meg

Juv

Juv

M

M

Table 2. (Continued)

Taxon

Brachyura - infraordo

Brachyura sp. 1-5

Brachyura sp. 1-20

Brachyura sp. I-II

Arenaeus mexican us

Arenaeus mexican us

Mysidacea ~ ordo

Bowmaniella sp.

Metamysidopsis sp.

Mysidopsis sp.

IsoJlOda - ordo

Gnathiidae sp.

Excirolana sp.

Cirolana sp.

Paracersis sp.

Amphipoda - ordo

Elasmopus sp.

. Haustorius sp.

Megaluropus sp.

Ericthonius sp.

Platyischnopidae sp.

Hyperoche sp.

Hyperia sp.

Echinodermata~phylum

Asteroidea sp.

Ophiuroidea sp. 1-2

Mellita longifissa

Chaetognatha -phylum

Sagitta sp.

Krohnitta sp.

Chaetognatha sp.

Pisces - superclass

Pisces sp. 1-9

Clupeidae sp.

Pleuronectiformes sp.

Bothidae sp.

Soleidae sp.

Stellijer sp. 1-2

Stellijer sp.

Diodon sp.

Pisces species

Stage

Zoea

Meg

Juv

Juv

Adult

Adult

Adult

Adult

Larva

Adult

Adult

Adult

Adult

Adult

Adult

Adult

Adult

Adult

Adult

Adult

Adult

Adult

Adult

Adult

Adult

PI

PI

PI

PI

PI

PI

Juv

PIEgg

211

Type

M

M

M

M

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

M

M

M

M

M

M

M

M

M

212

447 mgfl), from 36 mg/I in the flood sample ofBruja to 733 mg/I in the ebb sample of SanPedro. Less variation was observed in the POMmeasurements, with mean values between 3.0and 4.6% of the SPM concentrations. Chloro-phyll a and c showed mean values between 0.31and 0.60 p.g/I for chla, and 0.04 and 0.10 p.g/Ifor chic. A striking high local current velocitycould be found at the moment of the mid waterin the Bruja station (0.48 m S-I), while in theother sampling occasions the mean currentvelocity was found between 0 and 0.28 m S-I.The beach profiles and intertidal slopes of the 6transects are shown in Figure 2. The intertidalbeach width varied from 42 m (San Pedro) to109 m (Valdivia). The intertidal beach slopevaried between 1.9% (Casa and Valdivia) and4.0% (San Pedro). The spatial variation inenvironmental variables, evaluated with a Krus-kal-Wallis test, was only significant for salinity(p = 0.0045) and slope (p = 0.0045). No signifi-cant tidal effects could be demonstrated.

General hyperbenthos composition in Valdivia Bay

In the bay a total of 19 higher taxa and 103morpho species were recorded (Table 2). In eachsample between 16 and 35 morpho species werefound. The density of the total hyperbenthos andthe relevant organisms for each sample is shownin Figure 4. The average total density of all hy-perbenthic fauna in the bay was 6073 ::!::3590indo 100 m-2 and ranged between 80 and 62702indo 100 m-2. The mean holohyperbenthos den-sity along the bay was found between 68 and62510 indo 100 m-2. The merohyperbenthic ani-mals reached densities between 6 and 192 indo100 m-2. 97% of the total density was built up bythe mysid Metamysidopsis sp., a member of theholohyperbenthos. When Metamysidopsis sp. wasnot considered (Fig. 5), the holohyperbenthoswas further characterised by the mysids Mysid-opsis sp. and Bowmaniella sp. (> 61% of the ho-lohyperbenthos), calanoid copepods (14%),Chaetognatha (13%, mainly Sagitta sp.) andamphipods (5%; mainly Megaluropus sp.), whilethe merohyperbenthos was mainly represented byfish eggs and larvae (> 68% of the merohyper-benthos) and different brachyuran megalopa(22%).

Spatial variation of the hyperbenthos and relevanttaxa

In most of the stations an average of 2000-3000organisms per 100 m2 was caught, with theexception of Bruja where an extreme high meanabundance was encountered (22263 ::!::20 198 indo100 m-2), mainly due to the mid water sample(62205 indo 100 m-2). In all stations the mysidMetamysidopsis sp. dominated (> 90%). Its meandensities increased from the southern beaches ofthe bay towards the northern end, from1210 ::!:: 540 indo 100 m-2 to 21857 ::!::20140 indo100 m-2 (Fig. 6), although not significantly dem-onstrated by the Kruskal-Wa1\is test. Anextraordinary peak was observed in the mid-tidesample at the Bruja station (62091 indo 100 m-2).When this mysid was not considered, the holohy-perbenthos (Fig. 7A) of Casa and Bruja wasdominated by calanoid copepods, Chaetognatha(mainly Sagitta sp.) and the mysid Bowmaniellasp. (together resp. 86 and 78% of the holohyper-benthos), while in the remaining stations themysids Mysidopsis sp. and Bowmaniella sp. wereimportant (73-88%). The merohyperbenthos(Fig. 7B) of Casa and Bruja was dominated by fisheggs (80% of the merohyperbenthos). Punta wasdominated by fish larvae (60%; mainly Clupeidae),while in Cenaim Brachyura larva (71%; mainlyCallinectes sp.) were well represented. In SanPedro, the merohyperbenthos was mainly com-posed of Caridean larval stages and fish larvae(together 76%); in Valdivia larval stages ofBrachyura (44%) and fish eggs (37%) dominatedthe merohyperbenthos.

Over the entire bay the mysid Bowmaniella sp.showed average densities between 3 ::!::2 indo100 m-2 and 69 ::!::39 indo 100 m-2, showing theirhigher densities in the low water of Punta station(149 indo 100 m-2) and the mid water in Brujastation (137 indo 100 m-2) (Fig. 4). The othermysid Mysidopsis sp. showed densities along thebay between 3 ::!::2 indo 100 m-2 and 85 ::!::49 indo100 m-2, with the highest value in the low watersample at San Pedro station (204 indo 100 m-2)

(Fig. 4). The distribution of the fish eggs, fishlarvae and shrimp postlarvae, possibly importantfor the local fisheries, are depicted in Figure 4.Fish larvae showed densities between I ::!::I indo100 m-2 and 7 ::!::3 indo 100 m-2, grouping their

100

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200

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0.2

0.1

0

(ChIo)

0.12

0.1(ChIc)

0.08

~0.06:1

0.04

0.02

Punta Cenaim San Pedro Valdivia Casa Bruja

Figure 3. Average (:I: standard error) of the environmental variables measured in each sampling station.

higher densities in the southern part of the bay(Fig. 4), while fish eggs (densities between 2 ::!: Iindo 100 m-2 and 129 ::!:36 indo 100 m-2) hadtheir highest densities in the northern part (Fig. 4).Larvae of Penaeidea were not well represented inthe hyperbenthos with densities between I and3 ::!: 3 indo 100 m-2.

Hyperbenthic communities in Valdivia Bay

Multivariate analyses were used to look for spatialand/or tidal variations in the hyperbenthos of thebay using a database including the higher taxa thatwere represented by more than 0.002% of the totaldensity; i.e. 13 taxa. The TWINSPAN (not shown)grouped all samples of Casa and Bruja from theother samples. No tidal patterns could be distin-guished.

213

Punta Cenaim San Pedro Valdivia Casa Bruja

Furthermore, the PCA analysis spread thesamples along the first axis in a similar way as theTWINSPAN, with all samples of Casa and Brujaat the left part of the plot (Fig. 8). These sampleswere further referred to as the 'North'-group whilethe others as 'South'-community. The varianceexplained by the axes I and 2 was 35.9, respec-tively 14.8%. After performing a correlationanalysis, 7 environmental variables were retained(POM, chla, salinity, water temperature, localcurrent velocity, median grain size and elevationabove ML WS) and superimposed on the PCAbiplot (Fig. 8). The local current velocity explainedthe spread of the samples along the first axis, whiletemperature is related to the second axis.

Typical characteristics of the two communitiesare summarised in Table 3. The southern com-munity showed the lowest density (2160 ::!:787

214

fValdivia

iiSan Pedro

M elaln. vsidopsis sp.

Bowl11olJiella .rp.

~ ~ \,Bruja\ ,

I)) 1/::.// /1 :'Ccnaim

. ,/ ./

Mysidopsis sp.

Fish eggs

~ . ~ "Bruja

\ 1 ~' ,

Ca..\

, " \, '

\1 ) ;

/ t } :~:d~:~ro

I ) ) .'Ccnaim

/ / ./~ unta

----.---.-------.---P,sh Iorl'ae

\ \ \ .Bruja

\ "Casa

\ \ \j

I)

r t ;. ___,

.valdivi.

; ,. ..San Pedrn

/ '.

/ /~_~..ccnaim

/ / ,Punta

Penoeidoe

. ~\ \

\ \\ .\ \\ \

\

j)

.

;1

! fjValdi via

I t -,)0 San Pedro

///

1"

C"/ .;"enatm

/ ...",Punta

. > 20000 ind IOOm,2. 5000.1-20000 ind l00m,2...300.1-5000 ind 100m.2

100,1-300 ind IOOm.2

20.1-100 ind 100m.2

5,1-20 ind l00m.2

<5.1 ind IOOm,2

.

Figure 4. Schematic presentation of the densities of the total hyper benthos and the representative groups in each sample at low water(left), high water (right) and halfway the tidal cycle (middle).

100

- 80tIIIU

i 60'Cc:::Is:JftS

40.~(;

~20

0

215

. OthersI!:IAmphipoda

III Chaetognatha

. Copepoda[J Mysidacea

rn Penaeidae

iii Caridea

. Anomura0 Brachyura

IS!Pisces

Holohyperbenthos Merohyperbenthos

Figure 5. Relative abundance of the representative groups (taxa and species) in the holo- and merohyperbenthos of Valdivia bay (withthe dominant mysid Melamysidopsis sp. removed).

indo 100 m-2), but highest diversity (16 higher taxaand 78 morphospecies). The five samples formingthe northern community had an average density of15463 ::!: 11830 indo 100 m -2, 13 higher taxa and60 morphospecies.

The two communities were dominated by themysid Metamysidopsis sp. (79 and 81% on averagein the northern and southern community, respec-tively). When this species was not taken into ac-count (Fig. 9), the northern group mainly consistedof early life stages offish (37%), other mysids (21%),copepods (16%) and Chaetognatha (12%), while thesouthern group additionally contained other mysidspecies (64%) and to a lesser degree larvae andjuveniles of fish and Brachyura (each 9%).

The densities of Metamysidopsis sp. were al-most one order of magnitude higher in thenorthern community, although no significant dif-

50000

ference could be demonstrated by a t-test (Ta-ble 3). A multiple regression demonstrated thatcurrent was the only environmental variable sig-nificantly contributing to the distribution of thedensities of the mysid species. Mysidopsis sp.showed higher mean densities in the South com-munity, while Bowmaniella sp. was a species moretypical for the northern stations. However themean densities were not significantly different.Fish eggs had significantly higher densities in thenorthern community (p < 0.0001), while thedensities of fish larvae were too low to see anytrend within the bay. Although the penaeid larvaewere caught in low densities, their densities weresignificantly higher in the southern community(p = 0.019). Other groups present in significantlyhigher densities in the North community werecopepods, amphipods and chaetognatha, while

41XX)0

"'1IXXX)

E

8-ci 2()(XX).5

IIXXX)

0t .

Punta Ccnaim

Figure 6. Average (I standard error) densities of Melamysidopsis sp. measured in each sampling station.

Valdiviat +

+San Pedro Casa Bruja

(A)

100

80

60

40

~20

<IJUa

'"0 (8)c::I

.Dd 11M)<IJ.~

~80

"E

60

40

10

216

. Others

. Chaetognatha

. AnomuraIII Copepoda

III Mysidopsis sp.

. BowmanieUa sp.

Punta Cenaim San Pedro Valdivia

South

0 Fish larvae

. CarideaII Fish eggs

II Braehyura

mPenaeidea

. Others

Casa Rruja

North

Figure 7. Relative abundance of the representative groups of the holo- (A) and merohyperbenthos (8) in each station sampled (with

the dominant mysid Metamysidopsis sp. removed) with the north and south communities indicated below.

pycnogonids showed higher mean densities in thesouthern stations (Table 3).

The northern community was characterised bystrong currents parallel to the beach (p = 0.048).The southern community was characterised bysignificantly steeper intertidal beach slopes andrelatively higher SPM and chla values.

Discussion

Comparable studies, considering the whole surfzone hyperbenthic community, are scarce (see asummary in Table 4). With the exception of thepresented study in Valdivia Bay, informationabout tropical regions is lacking. Not always ex-actly the same organisms were considered withinthe hyperbenthic assemblage in the different stud-ies. However, general patterns can be compared.The average total density of the hyperbenthiccommunity in Valdivia Bay is high in relation toother studies. This is mainly due to the highnumber of one species of mysids that is dominant

over all stations and with an exeptionnaly highvalue in one sampling occasion. Even if this ex-treme value was not included, the mean total hy-perbenthic density remained high at 2539 :I: 676indo 100 m-2. Elsewhere, mysids are also domi-nating the hyperbenthic community, however to alesser extent, as they are probably the most typicalhyperbenthic taxon in coastal areas around theworld (Mauchline, 1980; Mees & Jones, 1997).They have been shown to be important for nutri-ent regeneration in the surf zone (Cockroft et aI.,1988) and as a food source to many fish species(Lasiak, 1983; Rossouw, 1983).

The extreme high densities of the mysid Met-amysidopsis sp. in the northern part of ValdiviaBay can probably be explained by swarming, aphenomenon that has been described in differentpelagic invertebrates (Ritz, 1994). Since anotherspecies of the same genus (M. elongata Clutter,1966) was found to be swarming, it can beassumed that the Metamysidopsis species ofEcuador is also capable of forming aggregates.The notorious peak at the mid tide in Bruja

North

D

12

currentD

+13

station could be a response to the strong currentduring the sampling (0.48 m S-I) causing swarm-ing for position maintenance (O'Brien, 1988). Tominimise the influence of aggregations in thehyperbenthos sampling methodology, replicationmight have been a possible solution. In the past,however, it has been shown that this is notnecessary as long as the hauled distance is suffi-cient (Lock et aI., 1999).

In some other studies (Table 4) amphipods area representative part of the hyperbenthic commu-nity (> 5%). This is not the case in the presentstudy (0.1%), nor in similar studies done in thesame bay in a circadian and inter-annual samplingscheme (unpublished data). With the hyperbenthicsledge used in all of these studies the lowest 5 cmof the water column are not sampled. It is thuspossible that some actively swimming amphipodsare missed, an idea which is supported by the factthat the amphipod species found in the simulta-neously performed macrobenthos study in thebay (Aerts et aI., 2004) are not found in the hy-perbenthos, except for the haustoriid Haustoriussp.

In other studies where the whole hyperbenthiccommunity was investigated, no difference wasmade between the holo- and merohyperbenthos,except for Beyst (200 I) and Beyst et al. (200 I)studying the spatial and the seasonal variation in aNorth Sea surf zone. It can be noticed that in the

D

217

holohyperbenthos of Valdivia Bay less functionalspecies were found in comparison with the Belgiancoast (respectively 39 and 104). However, thepresent study was restricted in time. The interan-nual study done in Valdivia bay (unpublisheddata) makes notice of 181 holohyperbenthicmorphospecies.

In the merohyperbenthos of the Belgian coast,68 merohyperbenthic species have been found(Beyst et aI., 2001). In Valdivia Bay, 64 functionalspecies were found in the present study and even194 in the interannual study mentioned above.The diversity of the merohyperbenthos, whichmight use the surf zone as a nursery area, seemsto be higher in tropical areas than in temperateregions. The average total density of the holo-hyperbenthos in Valdivia Bay was two orders ofmagnitude higher than that of the merohyper-benthos (68-62510 indo 100 m-2 and 6-192 indo100 m-2 respectively), while along the Belgiancoast, holo- and merohyperbenthos representmore or less a same proportional part of the totalhyperbenthic community (710 and 940 indo100 m -2).

Taxonomic studies and species descriptions arelacking for many groups for the tropical southeastPacific coast. In the present study higher taxo-nomic groups were identified with keys that areapplicable worldwide and further determinationswere mainly done using keys for the Atlantic and

Figure 8. Biplot of the principal components analysis (PCA) on the transformed density data of the 13 higher taxonomic groupspresent with> 0.002% (eigenvalue axis I: 4.665; axis 2: 1.930); D: northern community (5 stations); 8: southern community (12stations); I: Isopoda; 2: Penaeidae; 3: Pycnogonida; 4: Caridea; 5: Anomura; 6: Hydrozoa; 7: Brachyura; 8: Amphipoda; 9: Pisces; 10:Mysidacea; II: Chaetognatha; 12: Copepoda and 13: Bivalvia. Environmental variables are superimposed on the plot afterwards.

218

Table 3. Average (:!: SE) characteristics of the Northern and Southern community and the significance level of the (-test distinguishing

for differences between the identified communities

North p-ValueSouth

General information

Higher taxaMorphospecies

Number of samples

Total density

13

60

5

15463 :!: 11830

Densities (ind/l 00 m2)

Hydrozoa

Polychaeta

Bivalvia

Pycnogonida

Copepoda

Stomatopoda

Euphausiacea

Penaeidea

Caridea

Anomura

0.05 :!: 0.05

0.21 :!: 0.14

2.93 :!: 2.50

49.36 :!: 20.56

1.71 :!: 1.46

0.07 :I: 0.07

0.79 :I: 0.29

19.71 :I: 8.25

15226 :I: 11795

15162 :I: 11777

44 :I: 27

21 :!: 190.Q7 :I: 0.07

14.07 :I: 9.23

37.07 :I: 14.19

110 :I: 28

109 :I: 27

2 :I: I

Brachyura

Mysidacea

Metamysidopsis sp.

Bowmaniella sp.

Mysidopsis sp.

Isopoda

Amphipoda

Chaetognatha

Pisces

Fish eggs

Fish larvae

Environmental variables

Temperature (°C)

Salinity (p.s.u.)

Local current (m/s)

Suspended Particulate Matter(mg/L)

Particulate Organic Matter (%)

Chlorophyll a (Jlg/L)

Chlorophyll C (Jlg/L)

Median grain size (Jlm)

Intertidal slope (%)

24.2 :I: 0.2

34.0 :I: 0.0

0.264 :I: 0.064

70 :I: 19

4.5 :I: 0.27

0.36 :I: 0.09

0.05 :I: 0.01

246 :I: 20

2.1 :!: 0.1

16

78

12

2160 :I: 787 0.060

1.04 :!: 0.46

0.06 :!: 0.04

0.36 :!: 0.22

1.19 :I: 0.26

1.34 :I: 0.82

0.03 :!: 0.03

0.06 :I: 0.04

2.35 :I: 0.50

2.86 :I: 2.79

2.29 :I: 1.03

9.43 :I: 3.89

2121 :I: 788

2050 :I: 787

19 :I: 12

52 :!: 18

0.39 :I: 0.20

2.65 :I: 0.48

5.24 :I: 1.64

10 :I: 3

4 :I: 2

6:1: 1

0.447

0.282

0.136

<0.0001

< 0.0001

0.536

0.362

0.019

0.616

0.439

0.109

0.095

0.087

0.341

0.336

0.249

0.047

0.007

<0001

<0001

0.062

24.6 :!: 0.3

33.8 :I: 0.2

0.088 :!: 0.019

293 :!: 56

4.05 :I: 0.29

0.48 :I: 0.03

0.06 :I: 0.01

238 :I: 17

3.0 :I: 0.2

0.347

0.244

0.048

0.007

0.358

0.042

0.216

0.949

0.024

North Sea. To preliminary describe the biodiver-sity of the surf zone hyperbenthos in the region, weused a morphospecies concept that was based onmorphological difference between organismswithin a taxonomic group (Table I). Taxonomic

studies, although time consuming, must be one ofthe next steps in future tropical southeast Pacifichyperbenthic research. The three mysid species arecurrently being described (Deprez et aI., in prep-aration).

100

~ 80t...u5; 60

'gC:JJ:ICD

40.~iiGi~ 20

0South

219

.OthersiiiCaridearn Penaeidae

~Amphipoda

0 Brachyura

fillChaetognatha

. CopepodaIS!PiscesCJMysidacea

Figure 9. Relative abundance of the representative higher taxa in the identified communities (not taken into account Meramysidopsissp.)

North

For multivariate analyses, higher taxa wereused. These were not all from the same taxonomiclevel and varied from phylum to family. Using thehighest common level (i.e. phylum) would hide a lotof the patterns within the data set. For example, thephylum Arthropoda, which represents 99% of thetotal hyperbenthos density in the bay and 70% ofthe total number of distinguished morphospecies, ishighly diverse, structurally as well as functionally(especially within the Decapoda). The taxonomicsubdivisions within the Arthropoda differ withinthe different orders and hamper the use of only onecommon level. Nevertheless, we assumed that theorganisms within the selected higher taxa, do havean approximately comparable life style.

Along the 8 km wide bay of Valdivia, twomain geographically distinct hyperbenthic associ-ations could be distinguished. Both communitiesare dominated by Metamysidopsis sp., but differin the other groups present (Fig. 9). The envi-ronmental variables that explain the devisionbetween the southern and northern communityare chla, current velocity, intertidal slope andSPM.

In others studies, the chlorophyll concentrationhas also been found as structuring hyperbenthiccommunities. Nevertheless, such studies have beendone within a seasonal sampling frame (Beystet aI., 2001) or in an extended subtidal area whereclear spatial variations in chlorophyll concentra-tions exist due to differences in nutrient input(Dewicke et aI., 2003). In the surf zone, high dia-tom concentrations forming dark brown patcheshave been described (Lewin & Schaefer, 1983;

Odebrecht et aI., 1995) and the response of mysidsto those accumulations were demonstrated byWooldridge (1989). In the present study, the use ofchlorophyll content as a structuring factor of thecommunities should be considered with care asrelatively low chlorophyll concentrations weremeasured (Table 3). Variations in the chlorophyllconcentrations within each sampling day are reg-istered (standard error amounts 7--49% of themean value) since the samples are taken within aperiod of 6 h. In a 24-h sampling performed in thesame bay, a circadian chlorophyll a variation wasobserved with a peak around noon (unpub-lished data). No dark brown patches wereobserved within the surf zone on the moment ofsampling.

The beaches in Valdivia bay are charactarisedas exposed, low tide terrace - rip beaches (Aertset aI., 2004). The variables associated to thehydrodynamics were significantly different be-tween the communities, i.e. the current velocity,slope and SPM. The northern beaches are lesssteep than the ones in the south but haveapproximately the same sediment type, althoughthe former have less particulate matter suspendedin the water column. SPM in the surf zone is re-lated to wave action and hydrodynamics in gen-eral. The current velocities are one order ofmagnitude stronger in the north. Exposition andhydrodynamics along the Valdivia bay are prob-ably the most important structuring factors for thehyperbenthic communities, as is demonstratedelsewhere by Munilla & Corrales (1995) and Mu-nilla et al. (1998).

Author(s) and year

Table 4. Summary of studies of hyperbenthic communities in the surf zone of sandy beaches

North Sea - Atlantic

Colman & Segrove (1955)

Lock (1996)

Lock et a!. (1999)

Lock & Mees (1999)

Beyst (2001) - Chapter

Beyst et al. (200 I)

San Vicente & Sorbe (2001)

Mediterranean

San Vicente & Sorbe (1999)

Munilla & Corrales (1995)

Munilla et al. (1998)

Pacific

Unpublished study

(Dominguez Granda, 2001)

Unpublished study

(Ruiz , 2002)

This study

Study area

North Sea,

Great-Britain

North Sea,

Sampling period

8 days, within

two weeks

Summer & winter

France, Belgium,

The Netherlands

North Sea, Belgium Bi-hourly, 24 h,

One occasion

One occasionAtlantic, Portugal

North Sea, One occasion

Belgium and France

North Sea, Belgium Monthly, I year

Atlantic, Spain

Mediterranean,

Spain

Mediterranean,

Spain

Mediterranean,

Spain

Valdivia Bay,

Ecuador

Valdivia Bay,

Ecuador

Valdivia Bay,

Ecuador

Monthly, I year

Monthly, I year

One occasion

Spring -summer,

one occasion

Bi-hourly, 24 h,

One occasion

Bi-weekly, I year

tidally, one

occasion,

within 6 days

Mesh size Average total density Average relative composition( indo per 100 m2)

IVIV0

I mm

30 mesh silk 9-222

< 100-7417

1 mm

I mm

I mm

I mm

0.5 mm

0.5 mm

0.5 mm

0.5 mm

I mm

I mm

I mm

100-425

192

1470-2140

100-225

500-9760

408-3610

574

510-10400

63-1621

840-2690

837-19256 without

Metamysidopsis

spec.: 103-322

Mysidacea > Amphipoda > Decapoda > Others

Mysidacea (59%), Annelida larva (II %),

Amphipoda (10%), Decapoda (5%), Cnidaria (6%)

Mysidacea (38%), Cnidaria (26%), Isopoda(10%), Decapoda (9%), Cumacea (8%)

Mysidacea (44%), Fish eggs (42%), Amphipoda(10%), others (45%)

Mysidacea (50%), early life stages of fish (38%),

Decapoda (5%), Copepoda and Ctenophora (each 2%)

Mysidacea (51 %), Osteichthyes (38%), Decapoda (5%),

Copepoda (2%), Ctenophora (2%), Others (2%)

Mysidacea (73%), Cumacea (18%), Amphipoda,

Decapoda & Isopoda (each 3%)

Mysidacea (73%), Amphipoda (13%), Cumacea (9%),

Decapoda (2%), Isopods & Pycnogonida (each 1%)

Mysidacea (27%), Amphipoda (23%) , Copepoda

(16%), postlarval Osteichthyes (12%), Isopoda (7%)

Mysidacea (60%), Amphipoda (29%), Others (II %)

Brachyura (61%), Anomura (5%), Penaeidae (4%),

Mysidacea, Isopoda & Chaetognatha (3%), Others

(27%)

Mysidacea (92%), Decapoda (3%), Bivalvia (1%),

Osteichthyes (I %), Copepoda, Isopoda and

Amphipoda « I %), Others « 1%)

Mysidacea (97%), Others (3%) without Meramysidopsis

sp.: Mysidacea (41%), Fish eggs and larvae (21%),

Decapoda (11%), Copepoda (9%), Chaetognatha (9%),

No tidal patterns could be distinguished in thepresent study. Lock et al. (1999) described thecircadian patterns in the intertidal hyperbenthosfor a sandy beach in the North Sea. The density,species composition and diversity differed betweenthe ebb and flood situation both during daytimeand at night. Similar work has been done in Val-divia bay by Dominguez Granda (unpublisheddata), where mysids showed a strong recruitmentaround ebb tide.

The importance of inshore waters, and morespecificaIly the surf zone, as a nursery area formarine teleosts is weIl documented (Lasiak, 1981;Robertson & Lenanton, 1984; Cornejo et aI, 1993;Beyst et aI., 1999). In the present study the densi-ties of fish larvae are low « 15 indo 100 m-2) andrepresent maximaIly 19% of all animals caught(without including Metamysidopsis sp.). On theother hand, passively distributed fish eggs showedhigher densities in the turbulent northern part (109indo 100 m-2; 30% without Metamysidopsis sp.).Unfortunately, the identification of the fish eggscould not be done to species level. It was thus notpossible to determine if the eggs originated fromintertidal or off-shore spawning fishes. The densityof Penaeids larvae does show significant differ-ences between both communities, and is low in thecold dry season (only 1% of all animals caughtwith Metamysidopsis sp. removed). No artisanalfishermen were working in the area at the momentof sampling, probably reflecting the low andcommerciaIly not interesting density.

The present study demonstrated the relativehigh hyperbenthic densities in tropical sandy beachsurf zones, where Mysidacea showed to be thedominant taxonomic group. Hydrodynamic fac-tors such as local current velocity, intertidal beachslope and suspended particulate matter, werefound to structure hyperbenthic communities. Al-though limited in time and performed with a lim-ited taxonomic resolution, the results indicate ahigh contribution of early life stages of inverte-brate and fish species to the biodiversity of theintertidal community in comparison with temper-ate areas. Future taxonomical research is neces-sary to describe the surf zone hyperbenthos of thetropical eastern Pacific, while more detailed - bothstructural and functional - ecological studies areneeded to elucidate the role of specific specieswithin the system.

221

Acknowledgements

The authors thank Katrien Aerts, Bart Bulckaenand Jan Wittoeck for their help during the field-work. Ann Dewicke, Kris Hostens and VeroniqueVanquickelberghe helped with identification. Sedi-ment and chlorophyIl analyses were performed bythe technical staff of the Marine Biology Section ofthe Ghent University. We are grateful to AnnVanreusel, Steven Degraer, Thomas Vanagt, DavidMatamoros and the anonymous referees for theiradvice on the data analyses and valuable commentson the manuscript. Financial support for the pro-ject is given by the Science Foundation of Flanders(FWO-Vlaanderen) with the project G.0086.96'Causal factors of biodiversity: community struc-ture, phylogeny and biogeography' and by the IUC-programme between The Flemish InteruniversityCouncil (VLIR) and the Escuela Superior Politec-nica del Litoral (ESPOL) in Guayaquil, Ecuador.

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