Rev. bras. oceanogr.. 48(2):107-] 17.2000

Polychaete zonation on sandy beaches of São Sebastião Island,São Paulo State, Brazil

Margarete de O. Reis; Eloísa H. Morgado; Márcia R. Denadai & A. Cecília Z. Amaral

Instituto de Biologia, UNICAMPDepartamento de Zoologia

(Caixa Postal 6109, 13083-970 Campinas, SP, Brasil)

. Abstract: This study was performed in the intertidal zone of Barra Velha, Perequê, andEngenho d'Água beaches, located on São Sebastião lsland (São Paulo State, Brazil), to assessthe composition, abundance, and zonation of the polychaete community in the intertidal zone.Four structural1y different sectors were established, two on Barra Velha (I and lI), one onPerequê, and one on Engenho d'Água. Each sector was divided into 3 tidal levels (lower,middle, and upper), in which 5 or 6 random samples were taken seasonally using a corer of0.01m2 in area. Laeonereis acuta, Capitella capitata, and Heteromastusfiliformis dominated inthe upper tidal levels, and Scoloplos (Leodamas) sp. and Cirriformia tentaculata in the lowerlevels. The structural complexity of Engenho d'Água, caused by rocky fragments mixed withsand, supported the richest and most diverse polychaete fauna of all the sectors. The salinity ofthe interstitial water and the organic matter content were the principal factors related to thezonation patterns at these sites.

. Resumo: Este trabalho foi realizado na região entremarés das praias Barra Velha, Perequê eEngenho d'Água, situadas na Ilha de São Sebastião (Estado de São Paulo, Brasil), com oobjetivo de estudar a composição, abundância e zonação da taxocenose dos poliquetas. Quatrosetores estruturalmente diferentes foram delimitados, sendo dois na Barra Velha (I e lI), um noPerequê e um no Engenho d'Água. Cada setor foi dividido em 3 níveis entremarés (inferior,intermediário e superior), nos quais 5-6 amostras aleatórias foram tomadas sazonalmenteutilizando um delimitador com 0,01m2 de área. Laeonereis acuta, Capitella capitata eHeteromastus filiformis ocorreram predominantemente nos níveis superiores e Scoloplos(Leodamas) sp. e Cirriformia tentaculata nos inferiores. A complexidade estrutural do Engenhod' Água, caracterizado por fragmentos rochosos misturados ao sedimento, sustentou a fauna depoliquetas mais rica e diversificada dentre os setores. A salinidade da água intersticial e o teorde matéria orgânica foram os principais parâmetros determinantes da zonação nestes locais.

. Descriptors: Polychaetes, Sandy beaches, lntertidal, Zonation, Macrofauna.

. Descritores: Poliquetas, Praias arenosas, Entremarés, Zonação, Macrofauna.

Introduction

The intertidal zone of sandy beaches is arigorous environment, where the organisms areadapted to live in a gradient from marine toterrestrial conditions. This gradient, generated bytidal cycles, causes specific adaptations that result indifferent zones of distribution (Bal1y, 1983).

Some of the physical and biological factorsthat influence the faunal composition anddistribution in sandy beaches are: desiccation, wave

action, currents, sediment type, beach slope,temperature, sediment moistness, interstitial watersalinity, organic matter content, seasonal variation ofthe fauna, competition, and predation (Vohra, 1971;Brown & McLachlan, 1990; McLachlan & Jaramillo,1995). According to Dexter (1988), the factorsrelated to wave action are most relevant. The

opportunist species tend to occur in particular levelsof the beach, although their spatial and temporaldistribution can vary in response to environmentalinstability (VeIoso et a!., 1997).

108

Two universal patterns of zonation on sandybeaches are known. Oahl (1953) studied thecrustacean fauna and established 3 zones:supralittoral, midlittoral, and sublittoral. Thealternative model proposed by Salvat (1964)establishes 4 zones, defined on the basis of watercontent from high to low beach levels: dry sand zone;retention zone, where the sediment retains a smallamount of water and is well oxygenated; resurgencezone, where water circulates among the sand grains,however without reaching saturation; and saturationzone, where the sediment is constantly saturated bywater, with low circulation and oxygenation. Salvat'sdry sand zone corresponds to Oahl's supralittoral, theretention and resurgence zones to the midlittoral, andthe saturation zone to the sublittoral fringe(McLachlan et ai., 1981; Wendt & McLachlan,1985).

McLachlan (1983) stated that a zonationpattern with distinct edges has never been describedfor sandy beaches. Perhaps the only rigorous modelis that proposed by Brown & McLachlan (1990), whorecognized two zones: that composed of air-breathers, and that where ali organisms are water-breathers. There are several differences among thezonation patterns proposed for sandy beaches,probably because of their complexity, heterogeneity,and instability (Wendt & McLachlan, 1985; Velosoet ai., 1997).

Most zonation studies in exposed or partlysheltered sandy beaches have treated the crustaceansand molluscs, the most abundant groups in theseenvironments. The beaches selected for the presentstudy are located in sheltered areas in the SãoSebastião Channel, and support a rich polychaeteinfauna (Amaral et ai., 1995), a group commonlyreported in sheltered sand flats, where they aredistributed homogeneously (Gruet, 1974). Our studyprovides information about the polychaetecomposition, abundance, and zonation in fourintertidal sandy beach environments on SãoSebastião Island, considering the importance ofenvironmental factors for the community structure.

Area of study

Perequê, Barra Velha, and Engenho d'Águabeaches are located on São Sebastião Island, in thecentral region of the São Sebastião Channel(23°47'S; 45~7'W) on the northern coast of SãoPaulo State, Brazil (Fig. I). These are lowenergy sandy beaches subjected to semidiurnal tideswith 2 m maximum tidal range (Furtado &Mahiques, 1990). The morphodynamism of theseareas was not investigated due to the absence ofwaves, which occur only during sea storms.

Rev. bras. oceanogr.. 48(2). 2000

Four sectors were delimited, based onenvironmental characteristics: Barra Velha I, locatedin the southern end of the beach, has coarse sandgrains and a small rivulet, with typical mangrovevegetation; Barra Velha lI, in the central region ofthe beach, is a mudflat, composed of fine sediments;and Perequê and Engenho d'Água are characterizedby sand bars covered by the seagrass Halodule sp. inthe former, and coarse sand and rock fragments(about 50 to 300 mm in diameter) in the latter. Theintertidal zones of ali the sectors, as the adjacentareas, have gentle slopes.

Materiais and methods

The study sectors were divided into 3 tidallevels: lower, the nearest to the water line; upper,adjacent to the dry zone; and middle, between thelower and upper. The width of each tidal levei wasdetermined according to the intertidal distanceconsidering visual aspects, as the degree of watersaturation in the sediment and distribution of

known species. A cylindrical corer with 0.0 I m2 areaand 20 cm in depth was used for quantitativecollections. The samples were taken at low springtide, at four seasons in each sector: winter (August-September/92), spring (October-November/92),summer (March/93), and autumn (May/93). lnitially(winter), 5 random samples were taken in each leveI,and after analysis of the results, 6samples/level/period were taken, 3 of these fixed(selected among the 5 from the winter sample)and 3 randomly sorted. The total sampled area ineach sector was 0.69 m2 (69 samples). In thelaboratory, the sediment (biological material) waswashed with seawater over two superimposed sievesof 1.0 and 0.5 mm mesh. The polychaetes retainedwere preserved in 70% alcohol and identified tospecles.

Air and sediment temperature, interstitialwater salinity, sediment grain size [~= -log2 (meangrain size in mm)] (Suguio, 1973), and calciumcarbonate and organic matter content in the sediment(Amoureux, 1966) were obtained for each leveI.

Two-way analysis of variance (ANOVA)was performed to compare environmental variablesamong sectors and tidal levels. Oiversity (H:)(Shannon-Wiener index in IOg2)and evenness (J')(Krebs, 1989) were calculated for each sector andleveI. Canonical Correspondence Analysis [Hill's(1979) method, data standardized by "powertransform", given equal weight to each variable], wasused to establish relationships between polychaetedistribution and environmental variables.

REIS et ai.: Polychaete zonation on sandy beaches 109

SÃO PAULOSTATE

Santos(:~r',"d?~~,~_/.;_J

ltanhaem

SÃOSEBASTIÃO

CHANNEL//

N

, ,--

SÀOSEBASTIÃO

ISLAND

Engenho d' Água

Perequê

Barra Velha

SÃOSEBASTIÃO

ISLAND

1830m

Fig. 1. Location ofthe sand beaches studied in the São Sebastião lsland (São Sebastião Channel, São Paulo State, Brazil).

Results

Air and sediment temperatures rangedfrom 20°C (winter) to 33°C (summer). The meanvalues (+1 ,SE) of salinity, grain size, sortingcoefficient, and calcium carbonate and organicmatter contents are shown in Figure 2, and the

results of two-way ANOVA for comparisons ofthe environmental variables among sectors andtidaI levels are presented in Table 1. Salinityranged from 6 to 35%0, the lowest values beingrecorded in Barra Velha I, followed by BarraVelha 11,Perequê, and Engenho d' Água

110 Rev. bras. oceanogr., 48(2), 2000

Fig. 2. Mean values (+1 Standard error) af salinity (%0),sediment grain size (phy), sorting coet1icient (phy), calciu111carbonatecontent (%), and organic 111attercontent (%) at the tidallevels and sampled sectors.

At Barra Velha I, the sediment ranged fromcOaJ'sesaríd to silt, with coarser grains dominating,while fine grains were more abundant in BarraVelha 11. Greater variations in grain size wereobserved at Perequê, where the coarser grainsoccurred inthe upper ticJal\tw~1and the fineI' ones inthe lower. At Engenho d'Água the sediment washeterogeneous, with cOaJ'sesand dOl11inatingin thelower and upper tidaI levels, and medium grains in

the middle. In general, ali the sectors had poorlysorted sediments.

Calcium carbonate varied less than organicmatter content. At Engenho d'Água the values ofcalcium carbonate in the lower tidal levei were

significantly higher than in the other levels. Thehighest organic matter content was observed in BarraVelha 11, where the mean values reached 8%.decreasing from the upper to lower tidal levels.

40[

3.5

35 3.0

2.5

1:111111111111-=<>

2.0N;;jC.; 1.5Oc

1.0lof____________ .,"::E

0.5

o 0.0L M U L M U L M U L M U L M U L M U L M U L M U

Barra Velha] Barra Velha 11 Perequê Engenho d'Água Barra Velha] Barra Velha 11 Perequê Engenho d'Água

2.01.6

1.4;; 1.6

'0 1.2 t,-..,... ""1.0 õio c 1.2u O

bJJ .D

"E0.8 a

uo 0.6 SVJ =

0.4 'G(;jU

0.2 .J0.0 0.01-_ _ _ _ - - - - - - -

Barra Velha Barra Velha Pereque Engenho L M U L M U L M U L M UBarraVelhaI Barra Velha 11 Perequê Engenhod'Água

2.5

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...E 1.5õi::Eu'c 1.0.,2!'O

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0.0L M LJ L M U L M U L M UBarra Velha I Barra Velha [] Perequê Engenho d'Água

REIS et ai.: Polychaete zonation on sandy beaches ] I]

Table 1. Two-way ANOV A for the effects of study sectors (Barra Velha 1, Barra Velha li, Perequêand Engenho d' Água) and tidallevels on salinity, sediment grain size, sorting coetticient.calcium carbonate content. and organic matter content. (dt~ degrees of treedom; MS. meansquare).

Source of variation

Salinity (%0)SectorTidallevelSector *Tidallevel

Sediment grain size (phy)SectorTidallevelSector *Tidallevel

Sorting coetticient (phy)SectorTidal leve]Sector *Tidallevel

Calcium carbonate content (%)SectorTidal leveISector *Tidallevel

Organic matter content (%)SectorTidalleve]Sector *Tidallevel

A total of 36 species and 1822 individuais ofpolychaetes were taken in the study areas. Table 2shows the species composition, occurrence, anddensity in each sector. Laeonereis acuta, Capitellacapitata, and Heteromastus filiformis \vere abundantin Barra Velha I and 11,representing àpproximately88 and 51%, respectively, of the total number ofindividuais. Scoloplos (Leodamas) sp. was thedominant species in Barra Velha 11(35.2%) and inPerequê (42.9%). Cirriformia tentaculata showedgreater abundance (45.2%) in Engenho d'Água. Thehighest species richness was found in Engenhod' Água, followed by Perequê, Barra Velha 11, andBarra Velha I.

The spatial distribution of the moreabundant species in each sector is shown in Figs. 3-6.The species L. acuta, C. capitata, and H filiformisoccurred over the entire intertidal region of BarraVelha I, where the first two species reached higherdensities in the upper tidal levels. Heteromastusfiliformis was abundant in the lower leveI. Specieswith low densities, such as Marphysa sp. and Isoldapulchella, were ffequent over the entire intertidalarea. Both diversity and richness tended to increaseffom the upper to lower tidal levels of this sector(Tab. 3).

The middle tidallevel of Barra Velha II was

the richest (16 species) in comparison with thelower and upper (12 species in both). Capitella

capitata, H filiformis, and L. acuta had similardistribution patterns, decreasing in abundance fromupper to lower tidal levels. Contrariwise, Scoloplos(Leodamas) sp. had its highest density in the lowertidal leveI. A higher richness and lower number ofindividuais characterized Perequê Site. Marphysasp., Scoloplos (Leodamas) sp., Aricidea fragilis, C.tentaculata, and Armandia agilis were ffequentover the entire intertidal region, despite their lowdensity. Scoloplos (Leodamas) sp. was the mostabundant species in this sector, occurring mainly inthe middle tidai leveI. Diopatra cuprea and A.fragilis were relatively abundant in the upper andmiddle levels respectively. Engenho d'Água showedthe highest richness, but was characterized by thedominance of Cirriformia tentaculata, leading to areduction in diversity in the lower tidal leveI. Oweniafusiformis and Scolelepis squamata reached theirhighest. abundance in the upper tidal levels of thissector.

The diversity of the Barra Velha I and 11sectors was highest in the lower and middle tidallevels, respectively, while in the Perequê andEngenho d' Água sectors diversity was highest in theupper levei (Tab. 3). Evenness followed the diversity,increasing from the lower to upper tidal levei in thesectors on Barra Velha 11 and Engenho d'Água,inversely at Barra Velha I, and was uniform in thePerequê sector.

df MS F Q

3 364.004 31.671 <0.00]2 51.755 4.503 0.0126 ]9.966 1.737 0.113

3 48.164 ]31.04] <0.0012 6.726 18.299 <0.0016 2.907 7.910 <0.001

3 1.501 20.713 <0.0012 0.289 3.993 0.0206 0.668 9.226 <0.00]

3 3.653 35.420 <0.0012 0.323 3.135 0.0456 0.656 6.363 <0.001

3 16.966 138.611 <0.0012 0.308 2.517 0.0836 0.328 2.680 0.015

112 Rev. bras. oceanogr., 48(2), 2000

Table 2. Occurrence and density of species at the sectors studied (0.69m2/sector).

Species Barra Barra Perequê EngenhoVelha 1 Velha II d'Água-

Sthenelais boa (Johnston, 1839) 4

Eurythoe complanata (Palias, 1766) 4

Sigambra grubei Müller, 1858 1 2

Parandalia americana (Hartman, 1947) 14 3

Langerhansia cornuta (Rathke, 1843) 27

Laeonereis acuta Treadwell, 1923 223 93

Neanthes sp. 6

Glycinde multidens Müller. 1858 3 2 6

Goniada littorea Hartman, 1950 1 3 3

Goniada brunnea Treadwell. 1906 1

Diopatra cuprea (Box, 1802) 1 4 29 4

Lysidice ninetta A. & M. Edwards, 1833 2

Marphysa sp. 11 25 6 37

Nematonereis hebes Verril, 1900 1 3

Lumbrineris tetraura (Schmarda, 1861) 5 1 1

Naineris setosa (Verril, 1900) 2 16

Scoloplos (Leodamas) sp. 4 251 85 2

Aricideafragilis Webster, 1879 1 24 2

Polydora websteri Hartman, 1943

Prionospio steenstrupi Malmgren, 1867 12

Scolelepis squamata (Müller, 1806) 12 1 23

Magelona sp. 1

Magelona variolamellata Bolivar & Lana, 1986 2 1 4

Cirriformia tentaculata (Montagu, 1808) 16 5 214

Armandia agilis Andrews. 1891 1 7 1

Sternaspis capillata Nonato, 1966 10 1

Capitella capitata (Fabricius, 1780) 135 147 2

Heteromastus filiformis (Claparede, 1869) 42 123 6 3

Mediomastus californiensis Hartman, 1944 1 1

Notomastus sp. 2 2 37

Oweniafusiformis Claparede. 1870 6 54

Isolda pulchella Müller. 1858 16 14 2 6

Terebellides anguicomus Müller. 1858 1 1

Branchiomma cflucullana (delle Chiaje. 1828)

Branchiomma nigromaculata (Baird. 1865) I 1 2 2

Megalomma bioculatum (Ehlers. 1867) 4

TOTAL 453 713 198 473

REIS et. aI.: Polyehaete wnation on sandy beaches 113

11 a 10 inds./O,23m' 11 a 10 inds./0,2Jm'

Díopofra cupreal

Morphysa sp.

Morphysa sp.

Aricidea fragills

Scolopios [Leodamas) sp.

Cirrlformla tentaculata

Clrríformia tentocu/ato

Armandia aglils

I

Heteromastus tilltormísI

'I

Owenla fusítormís

I

Megalomma biocu/atum

Iso/da pulChella

75m UPPER 45 m MIDDlE 20 m LOWEROm(MLW)

Fig. 3. Zonation of the most abundant species inthe intertidal region of the Sector BarraVelha I.

I 1 a 10 inds./O,23m'

ób---LUPPER 40m

20m

IJOm

(MLW)

Fig. 5. Zonation of the most abundant species inthe intertidal region of the SectorPerequê.

11 a 10 Inds./O,23m'

MIDDLE LOWER

Parondalla americana

80 m UPPER 40 m MIDDLE20m Om

LOWER

[MLW)

I EurythoecomLangerhanslacomuto

Neanfhe~~.

Sthene/ais boa

ív1crphy.$O sp.~

50mUPPER MIDDLE LOWER

Fig. 4. Zonation of the most abundant species inthe intertidaI region of the Sector BarraVelha 11.

Fig. 6. Zonation of the most abundant species inthe intertidal region of the SectorEngenho d'Água.

114 Rev. bras. oceanogr., 48(2), 2000

Canonical correspondence analyses orderedthe species according to their distribution in theintertidal region, ranking the environmentalvariables in importance (Fig. 7). Laeonereis acuta,H filiformis, and C. capitata were strongly related tothe sectors of Barra Velha Beach, where salinity waslow and organic matter content high. In contrast,Owenia fusiformis occurred mainly in Engenhod' Água. Scoloplos (Leodamas) sp. and D. cupreashowed a strong positive relationship with finer,welI-sorted sediments. Cirriformia tentaculata andNotomastus sp. tended to occur in environmentscomposed of coarse sediment with low organicmatter content.

SCL..

NUJ

~

OrganicMatter

NOTCIR ..

..

Sorting Coefficient.

EAlow

AXIS1

Fig. 7. Canonical Correspondence Analysis (CCA) of themost abundant species and of the levels/sectorsin relation to environmental variables (totalvariation explained by axis 1= 64.0 %, and by axis2= 19.8 %). CAP = Capitella capitata; CIR =Cirriformia tentaculata; DlO = Diopatra cuprea;HET = Heteromastus filiformis; ISO = Isoldapulchella; LAE = Laeonereis acuta; MAR =Marphysa sp.; NOT = Notomastus sp.; OWE =Owenia fusiformis; SCS = Scolelepis squamata;SCL = Scoloplos (Leodamas) sp. The studysectors: BVI and BVII (Barra Velha I and lI); PQ(Perequê) and EA (Engenho d'Água) at thedifferent tidai levels: lower (low), middle (mid)and upper (upp).

Discussion

Some species established an obviouszonation pattem in abundance, making it possibleto infer their preferences for intertidal zoneoccupation. Laeonereis acuta showed a widedistribution, but reached its highest populationdensities in the upper levels of Barra Velha Beach(Sectors I and II), where the salinity oscilIatedstrongly. Although recorded in alI types ofsediment, this species tended to occur in coarsegrains. These results were similar to those obtainedby Amaral (1979) and Corbisier (1991) in Ubatubaand Santos (São Paulo State), respectively, and byElias (1992), who related its occurrence to adjacentfreshwater runofE The presence of a smalI rivuletmay have caused the salinity fluctuations (6%0inthe spring to 32%0in the summer) that we observedin the upper leveI of this area, enabling thedominance of euryhaline species such as L. acuta(Amaral et a!., 1995). Morgado et a!. (1994) foundthis species in organicalIy enriched medium and finesediments in sandy beaches of São SebastiãoChannel.

Capitella capitata was also frequent in theupper tidal levels of the beach, as observed earlier(Dauer & Simon, 1975; Amaral, 1979; Shackley,1981; Read, 1984; Amaral et aI., 1990; Corbisier,1991). The occurrence of this species is related tofine and medium sediments (Fauchald & Jumars,1979; Shackley, 1981) or with mud flats (Butman &Grassle, 1992), which agrees with the resultsobtained in this study, on species dominance infine and poorly sorted sand. Capitella capitata hasalso been reported from sheltered environments(Dauer & Simon, 1975) and organicalIy enrichedones (Cognetti, 1972; Bamett, 1984; Mora et aI.,1989; Butman & Grassle, 1992; Amaral et aI.,1998). Certainly, high organic matter content andlow salinity are factors influencing the distribution ofthis species.

Heteromastus filiformis also showeddominance in the upper tidallevels. However, Read(1984) found H filiformis exdusively dose to thewater line, and considered it as a subtidal species that

Table 3. Abundance, diversity, evenness and richness for the different levels (0.23 mZ) at each study sector

Barra Velha I Barra Velha II Perequê Engenhod'Água

UPP MIDD. LOW. UPP MIDD. LOW. UPP MIDD. LOW. UPP MIDD. LOW.

ABUNDANCE 174 156 123 334 214 165 83 69 46 103 179 191

DIVERSITY 0,498 0.415 0.720 0,752 0.823 0.423 0,861 0.709 0.839 0.971 0.861 0.670

EVENNESS 0,579 0.594 0.720 0,697 0.683 0.392 0,700 0.619 0.777 0,789 0.686 0.570

RlCHNESS 7 5 10 12 16 12 17 14 12 17 18 15

REIS et ai.: Polychaete zonation on sandy beaches 115

extends into the intertidal region. The species cantolerate wide oscillations of salinity and differentsediment types (Read, 1984), occurring :fi:equentlyinorganically enriched locations (Dauer & Conner,1980; Beukema, 1991; Morgado et aI., 1994; Amaralet ai., 1998). This species attained a high populationlevei in the Barra Velha Beach, a known pollutedenvironment, where it occurred predominantly infiner sediments.

The previously mentioned species L. acuta,C. capitata, and H filiformis maintained a stabledistribution pattem in these study sites. In studiesdone in 1990 in the same areas, these species showedhigh :fi:equenciesin the upper levels of the intertidalregion (Amaral et ai., 1995), where there was strongevidence of organic enrichment, and were thereforeconsidered bioindicators of pollution (Amaral et ai.,1998). .

Scoloplos (Leodamas) sp. was also abundantin environrnents composed of organically enriched,finer sediments, but with slight changes in interstitialsalinity, as in the lower and middle tidai levels ofBarra Velha 11. These results are similar to thoseobtained by Lopez-Cotelo et ai. (1982) for S.armiger, which was recorded in the middle levels ofsheltered and organically enriched beaches, and byShackley (1981), who related it to moderatelyselected fine sediments. Species of the genusScoloplos are dominant in polluted estuaries andorganically enriched mixohaline waters (Fauchald &Jumars, 1979). The dominance of Scoloplos(Leodamas) sp. caused the decrease in diversity andevenness in the lower tidal leveI of Barra Velha 11.The species was also well represented in the middletidal levei of Perequê, where the sediment is coarserand the organic matter content lower than in BarraVelha 11.

Diopatra cuprea is commonly found inthe lower intertidal levei on the sandy beaches ofsoutheastem Brazil. However, it tended to occur inthe upper levels of Perequê. This was probablybecause of the presence of sandbars covered by theseagrass Halodule sp. in the lower tidal levei,causing a onger period of emersion in this leveIcompared to the middle and upper levels.

In Engenho d'Água, the species distributionwas more heterogeneous, probably because of theslight variation in environmental factors along theintertidal region. Scolelepis squamata occurredpredominantly in the upper tidal leveI, togetherwith o. fusiformis, which maintained the samedensity in the intermediate leveI. More than 50% ofindividuaIs of the cirratulid C. tentaculata occurredin the lower tidal leveI, where the sediment wascoarser. Gruet (1974) considered this species astypical of the subtidal leveI, and abundant under

stones such as in Engenho d'Água. Bestwick et aI.(1989) reported that it occurred mainly in theintermediate levels ofthe intertidal region.

In general, the areas near the waterline insandy beaches are little influenced by changes inthe environment, decreasing physiological stresson the inhabitants. Nevertheless, the number ofspecies tended to decrease :fi:omupper to lowertidal levels in the sites studied (except in BarraVelha I), in opposition to the general tendencyreported in the literature (Day & Morgans, 1956;McLachlan, 1977; Amaral, 1979; Dexter, 1983;Haynes & Quinn, 1995). In Barra Velha I, thelower tidal leveI showed high diversity, as wellas in the three levels of Perequê where no singlespecies dominated. The marked dominance ofScoloplos (Leodamas) sp. and C. tentaculata,respectively, caused a decrease in diversity in thelower tidal levels of Barra Velha 11 and Engenhod' Água.

The sandy beaches in the central andnorthem part of São Sebastião Channel havesediments composed of a mixture of different sandtypes, which support the existence of a large numberof species. Other variables, as salinity, organic mattercontent, sediment moistness, slope, andenvironmental heterogeneity also can contribute toor regulate the species presence in a particularleveI. The principal factors affecting the occurrenceand intertidal distribution of species were: atBarra Velha I, wide oscillations in salinity; atBarra Velha 11,organic enrichment; at Perequê, thepresence of sandbars covered by the seagrassHalodule sp. and the gentle slope, which allowthe lower tidal levei to remain more exposedthan other levels during low tide; and at Engenhod' Água, the presence of rock :fi:agmentsassociatedwith the gentle slope, creating small tide pools andmoist microhabitats.

Acknowledgements

To the Conselho de Amparo à Pesquisa(CAPES) and the Fundo de Apoio à Pesquisa(FAEP-UNICAMP) for their grants for thisstudy. To the Centro de Biologia Marinha(CEBIMar-USP) for logistics support. To Mr. ÉlcioSoares Marinho (IB - UNlCAMP), and thetechnicians of CEBIMar-USP, who assisted in thefieldwork. To biologist Alexander Turra for hiscollaboration in the statistical analysis andmanuscript revision. To Dr. Janet W. Reid forrevision of the English text.

116 Rev. bras. oceanogr., 48(2), 2000

References

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(Manuscript received 18 April 2000; revised 03July 2000; accepted 16 October 2000)