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Mollusc community from a rocky intertidal zone inAcapulco, MexicoRafael Flores-Garza a , Carmina Torreblanca-Ramírez a , Pedro Flores-Rodríguez a , SergioGarcía-Ibáñez a , Lizeth Galeana-Rebolledo a , Arcadio Valdés-González b & Agustín A. Rojas-Herrera aa Universidad Autónoma de Guerrero, Unidad Académica de Ecología Marina, Gran VíaTropical No. 20, Fraccionamiento Las Playas, Acapulco, Guerrero, 39390 Méxicob Universidad Autónoma de Nuevo León, Laboratorio de Acuacultura, Facultad de CienciasBiológicas, Ciudad Universitaria, San Nicolás de los Garza, Nuevo León, México

Available online: 16 Nov 2011

To cite this article: Rafael Flores-Garza, Carmina Torreblanca-Ramírez, Pedro Flores-Rodríguez, Sergio García-Ibáñez, LizethGaleana-Rebolledo, Arcadio Valdés-González & Agustín A. Rojas-Herrera (2011): Mollusc community from a rocky intertidalzone in Acapulco, Mexico, Biodiversity, 12:3, 144-153

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B I O D I V E R S I T YVol. 12, No. 3, September 2011, 144–153

Mollusc community from a rocky intertidal zone in Acapulco, Mexico

Rafael Flores-Garzaa*, Carmina Torreblanca-Ramıreza, Pedro Flores-Rodrıgueza, Sergio Garcıa-Ibaneza,Lizeth Galeana-Rebolledoa, Arcadio Valdes-Gonzalezb and Agustın A. Rojas-Herreraa

aUniversidad Autonoma de Guerrero, Unidad Academica de Ecologıa Marina, Gran Vıa Tropical No. 20,Fraccionamiento Las Playas, Acapulco, Guerrero, 39390 Mexico; bUniversidad Autonoma de Nuevo Leon,

Laboratorio de Acuacultura, Facultad de Ciencias Biologicas, Ciudad Universitaria, San Nicolas de los Garza,Nuevo Leon, Mexico

(Received 12 July 2011; final version received 2 September 2011)

The state of Guerrero, Mexico, has approximately 470 km of seashore but the marine fauna is not well known. Thecoastline has three marine areas for priority conservation of coastal and oceanic biodiversity, for which ComisionNacional para la Conservacion y Uso de la Biodiversidad (CONABIO) notes a distinct lack of knowledge in theseareas. This study was carried out in a rocky intertidal middle zone from Playa ‘Majahua’, Acapulco, located south ofBahia de Puerto Marques. The objectives were to study: the species richness for classes Gastropoda, Bivalvia andPolyplacophora; the community structure from the representation of classes, families and genera; estimate densityand species composition within a community; analyse size and structure of populations in the mollusc community;and estimate the diversity index. Three samplings were made in the intertidal middle zone in 2009. Ten square metreswere sampled at each visit. Ninety-nine mollusc species were found to be represented, corresponding to 36 families.From all of these species, no record in Acapulco was found for 21 Gastropoda, 5 Bivalvia and 8 Polyplacophoraspecies recorded. Gastropoda was the best represented; 1737 organisms were analysed with an estimated density of86.8 organisms/m2 and 31 species were dominant. Crucibullum umbrella was the largest sized species. The diversityand equity index estimate in Majahua was the highest found for the rocky coast of Guerrero, indicating amega-diverse area with great uniformity.

Keywords: Acapulco; molluscs; intertidal zone; diversity index

Introduction

The rocky intertidal zone is one of the most diverse

habitats in the marine environment. This area offers a

variety of micro-environmental conditions rich in

adapted species and a substrate considered to be

stable and safe enough that different organisms can

develop on it (Tait and Dipper 1998). Among these

organisms are molluscs, from those resistant to desic-

cation to varieties that remain submerged.Most of the information available on molluscs in

the Mexican Pacific is on topics such as taxonomy,

abundance, diversity and spatial and temporal distri-

bution (Stuardo and Villarroel 1976; Baqueiro and

Stuardo 1977; Baqueiro 1979; Reguero and Garcıa-

Cubas 1989; Holguın and Gonzalez 1989, 1994;

Roman, Cruz, and Ibanez 1991; Sevilla 1995;

Landa-Jaime and Arciniega-Flores 1998; Olabarrıa

1999; Esqueda et al. 2000; Villarroel et al. 2000;

Rıos-Jara et al. 2001; Flores-Campana et al. 2007;

Flores-Garza et al. 2007; Flores-Rodrıguez et al. 2007;

Garcıa Rıos and Alvarez Ruiz 2007; Landa-Jaime et al.

2007; Ortız-Arellano and Flores-Campana 2008;

Flores-Rodrıguez et al. 2010; Reyes-Gomez et al.

2010).The State of Guerrero, Mexico, has approximately

470 km of seashore (Carranza-Edwards, Gutierrez-

Estrada and Rodrıguez-Torres 1975) and the marine

fauna is not well known. The coastline has three

marine areas prioritised for conservation of their

biodiversity. The Mexican National Commission for

Conservation and Use of the Biodiversity (Comision

Nacional para la Conservacion y Uso de la

Biodiversidad) (CONABIO) points out in its reports

that there is a lack of biodiversity knowledge in these

areas (Arriaga et al. 1998).Flores-Rodrıguez (2004) and Salcedo-Martınez

et al. (1988) presented a list of species of molluscs for

Zihuatanejo, in Guerrero‘s rocky intertidal zone,

contributing to the literature on mollusc ecology. For

Acapulco, there is information on species richness,

zonation, community structure and aspects of local

distribution (Villalpando 1986; Delgado 1989;

*Corresponding author. Email: rfloresgarza@yahoo.com

ISSN 1488–8386 print/ISSN 2160–0651 online

� 2011 Tropical Conservancy

http://dx.doi.org/10.1080/14888386.2011.625520

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Garcıa 1994; Flores-Rodrıguez et al. 2003;Valdez-Gonzalez et al. 2004; Barba-Marino et al.2010; Flores-Garza et al. 2010); however, the knowl-edge of molluscs from this region remains insufficient.

The current study was carried out on the rockyintertidal middle zone at Playa ‘Majahua’, Acapulco,Guerrero, Mexico. The objectives were to learn aboutthe species richness for classes Gastropoda, Bivalviaand Polyplacophora, the community structure repre-sented by classes, families and genera, as well asorganism density and species composition within thecommunity, to analyse the size and structure ofpopulations that make up the mollusc communityand to estimate their diversity index.

Materials and methods

Majahua is one of the most popular of the crowdedbeaches located south of Puerto Marques Bay inAcapulco, in the tourist zone Acapulco Diamante.Being the smallest beach in the bay, it is next to thevast main beach of Puerto Marques located at16�50058.2700 N and 99�54001.8500 W. Majahua isapproximately 600m in length and is an alluvialbeach characterised by large boulders, many smoothin structure with little presence of cracks and/orfissures and a soft, wavy surface.

Field methodology

The intertidal middle zone was visited on threeoccasions; one exploratory in January 2009, andformal visits in April and May. Ten square metreswere sampled at each visit. Sampling was realisedduring low tide hours and new moon days.

A systematic design was employed with a transectparallel to the shoreline. The sampling unit device wasa square shape PVC ½ inch tubular frame one metreper side. The starting point was chosen at random.Once the first sampling unit was done, a two-metrespace was left in between before the next collectiontook place.

Molluscs found within the sampling unit wereidentified and quantified. Once the sampling unit wasdone, the collected specimens were preserved in bottleswith 96% ethyl alcohol. Taxonomic identificationrequired a confirmation phase at the laboratory usingspecialised literature (Keen 1971; Reyes-Gomez 1999;Kaas and Van Belle 1985, 1994; Reyes-Gomez andSalcedo-Vargas 2002). Specimens were measured inlength (mm); nomenclature was updated according toSkoglund (2001, 2002). Subsequently the specimenswere placed in the mollusc collection of the Unidad

Academica de Ecologıa Marina at the UniversidadAutonoma de Guerrero.

Data analysis

Richness was calculated using the number of molluscspecies collected. Community structure was based onthe number of species in each of the genera andfamilies that characterised the malacological commu-nity under study, as well as on the relative abundancethat each class showed. Density was evaluated inorganisms/m2. Species composition within the com-munity was determined from its numerical abundanceand frequency through the method for Olmstead–Tukey correlation (Sokal and Rohlf 1969) consideringthe following criteria: (i) dominant, i.e. when abun-dance values and relative frequency exceeded thearithmetic average of both estimators; (ii) constant,i.e. relative abundance does not exceed average valueof abundance, but exceeds the estimated average valuefor the occurrence frequency; (iii) numerous littlefrequent, i.e. relative abundance is higher than averagevalue of abundance and occurrence frequency does notexceed the estimated average value for this variable;(iv) occasional, i.e. abundance values and occurrencefrequency does not exceed the arithmetic mean esti-mates for both variables. Size structure analyses ofmollusc populations in the community were realised inrelation to the maximum, minimum and average sizes,expressed in millimetres, using a digital calibrator.Diversity was measured by applying Pielou (J0) equityor uniformity index.

Results

Ninety-nine mollusc species were collected correspond-ing to 36 families (21 Gastropoda, 9 Bivalvia and 6Polyplacophora) and 62 genera (42 Gastropoda, 11Bivalvia and 9 Polyplacophora). No previous recordwas found in Acapulco for 21 of the Gastropoda(Figure 1), 5 Bivalvia and 8 Polyplacophora (Figure 2).Of these, Stenoplax (S.) regulata (Dall 1919 ex BartschMS) and Lepidochitona hartewii (Carpenter 1855) haveno records in the tropical Mexican Pacific.

Class Gastropoda (Table 1) was the best repre-sented, comprising 67.67% of the species, with Bivalvia15.15% (Table 2) and Polyplacophora 17.17%(Table 3). With regards to distribution by classes andfamilies, the best represented families in Gastropodawere Collumbellidae (11 species), Muricidae (7 spe-cies), Calyptraeidae (6 species), Fissureliidae (6 species)and Lottiidae (6 species) (see Table 1), in Bivalvia,family Chamidae with (3 species) (see Table 2), and in

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Polyplacophora, family Tonicellidae (5 species)(see Table 3).

Gastropoda was determined to be the class with

greater relative abundance, 64.54% of specimenssampled, followed by Bivalvia with 18.82% and

Polyplacophora with 16.63% of abundance.A total of 1737 organisms were registered, with a

density of 86.8 specimens/m2. Estimating from this

density, 56.05 organisms/m2 belonged to Gastropoda,16.35 organisms/m2 to Bivalvia and 14.45 organisms/

m2 to Polyplacophora. The species that showed greater

density in Gastropoda were Crucibullum umbrella

(Deshayes 1830) at 6.95 organisms/m2 and Macinellatriangularis (Blainville 1832) at 6.65 organisms/m2. ForBivalvia, higher density species included Crassostreaprismatica (Gray 1825) at 4.65 organisms/m2)followedby Crassostrea palmula (Carpenter 1857) at 4.20

organisms/m2, and in Polyplacophora, Chaetopleuralurida (Sowerby in Broderip and Sowerby 1832) had adensity of 4.35 organisms/m2, followed by Isnochitonmuscarius (Broderip & Sowerby 1829) at 2.1organisms/m2.

Regarding the community composition, of the total

number of species collected, 31 were dominant

Figure 1. Species with no record found in Acapulco: Gastropoda.

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(17 Gastropoda, 6 Bivalvia and 8 Polyplacophora),9 species were constant (7 Gastropoda and 2Polyplacophora), 7 species were less frequent(4 Gastropoda, 2 Bivalvia and 1 Polyplacophora),and 52 species were occasional (39 Gastropoda, 7Bivalvia and 6 Polyplacophora). For each of the threeanalysed classes, 47.05% of species fromPolyplacophora were dominant, making this the classwith the highest percentage of dominant species,followed by Bivalvia in which 40% of species were

dominant, and lastly Gastropoda with 26.86% ofspecies dominant (Figure 3).

With regards to size of species in class Gastropoda,Crucibullum umbrella registered the largest specimenwith 56.06mm (minimum¼ 17.58mm, average¼ 38.63and s.d.¼ 7.63) and Natica grayi (Philippi 1852)registered the smallest size at 2.00mm. In Bivalvia,the largest species was Chama corallina (Olsson 1971)at 57.82mm (minimum¼ 13.20mm, average¼ 27.64and s.d.¼ 10.77) and the smallest was Lithophaga

Figure 2. Species with no record found in Acapulco: Bivalvia and Polyplacophora.

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Table 1. Richness, density (organisms/m2), size (length in mm) and gastropod species composition present in rocky intertidalmiddle zone of Playa Majahua, Acapulco, Guerrero, Mexico.

Length (mm)

Families/species n Co De Min Max Ave Sd

FissurellidaeHemitoma (H.) natlandi (Durham 1950)* 1 O 0.15 15.17 15.17 15.17Diodora inaequalis (Sowerby 1835) 3 O 0.05 8.79 10.60 9.92 0.98Diodora diguenti (Mabille 1895)* 1 O 0.2 10.46 10.46 10.46Fissurella (C.) desemcostata (McLean 1970) 4 O 0.15 16.38 20.80 18.12 1.88Fissurella (C.) microtrema (Sowerby 1835) 3 O 0.05 12.92 27.08 21.60 7.35Fissurella sp. (Sowerby 1834) 1 O 0.05 21.60 21.60 21.60

LottiidaeLotiia pediculus (Philippi 1846) 2 O 0.1 11.83 14.68 13.25 2.01Lottia sp. 1 O 0.15 20.60 20.60 20.60Tectura fasicularis (Menke 1851) 28 D 1.4 11.78 30.72 21.09 5.19Patellioida semirubida (Dall 1914)* 3 O 0.05 9.40 12.24 10.61 1.46Patelloida sp (Quoy & Gaimard 1834) 7 NLF 0.35 7.61 13.80 10.56 2.18Scurria mesoleuca (Menke 1851) 14 NLF 0.7 13.92 29.11 20.91 4.73

TroquidaeCallistoma aequisculptum (Carpenter 1865) 2 O 0.05 16.41 17.35 16.88 0.66Tegula (A.) globulus (Carpenter 1857)* 64 D 3.2 3.06 9.64 6.50 1.39Tegula (A.) panamensis (Phylippi 1849) 1 O 0.05 15.28 15.28 15.28Molinea patricia (Philippi 1851)* 1 O 0.1 10.08 10.08 10.08

TurbinidaeAstraea (U.) buschii (Philippi 1844) 11 NLF 0.55 9.89 32.07 18.86 6.36

NeritidaeNerita (C.) scabricosta (Lamarck 1822) 2 O 0.1 8.18 9.13 8.65 0.67Nerita (T.) funiculata (Menkey 1851) 24 D 1.2 5.45 11.01 8.00 0.36

EpitoniidaeOpalia (N.) infrequens (C.B. Adams 1852)* 1 O 0.05 6.73 6.73 6.73

HipponicidaeHipponix a. panamensis (C.B. Adams 1852) 1 O 0.05 12.03 12.03 12.03Hipponix delicatus (Dall 1908)* 14 D 0.7 6.31 14.60 10.61 1.90

CalyptraeidaeCrepidula acueleata (Gmelin 1791) 26 D 1.3 4.78 19.06 14.67 3.27Crepidula excavata (Broderip 1834) 2 C 0.1 14.02 17.57 15.79 2.51Crepidula incurva (Broderip 1834)* 9 NLF 0.45 6.01 16.53 9.07 3.37Crepidula striolata (Menke 1851)* 1 O 0.05 23.70 23.70 23.70Crucibulum (C.) scutellatum (Wood 1928) 15 D 0.75 4.15 21.83 13.08 5.67Cucibulum (C.) umbrella (Deshayes 1830) 139 D 6.95 17.58 56.06 38.63 7.63

NaticidaeNatica (N.) grayi (Philippi 1852)* 2 O 0.1 2.00 2.91 2.45 0.64

TriviidaeTrivia pacifica (Sowerby 1832, ex Gray MS) 2 O 0.1 8.82 8.91 8.86 0.06

CypraeidaeMaurita arabicula (Lamarck 1811) 5 C 0.25 11.58 14.57 13.15 1.12Jenneria pustulata (Lightfoot 1786) 4 O 0.2 10.87 12.73 11.67 0.77

CymatiidaeCymatium (S.) vestitum (Hinds, 1844) 1 O 0.05 49.63 49.63 49.63

MuricidaeTrachypollia lugubris (C.B. Adams 1852)* 18 D 0.9 7.77 24.24 17.22 4.03Muricopsis (M.) zeteki (Hertlein & Strong 1951) 6 O 0.3 12.77 19.19 16.82 2.23Mancinella speciosa (Valenciennes 1832) 6 C 0.3 6.54 21.71 11.91 5.45Mancinella triangularis (Blainville 1832) 133 D 6.65 6.06 16.49 12.19 2.20Stramonita biserialis (Blainville 1832) 65 D 3.25 5.83 50.62 11.76 6.80Acanthais brevidentata (Wood 1828) 1 O 0.05 21.60 21.60 21.60Vitularia salebrosa (King & Broderip 1832) 3 O 0.15 15.65 19.99 18.53 2.49

(continued )

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aristata (Dillwyn 1817) at 3.86mm. In Polyplacophora,Chiton articulatus (Sowerby 1832) registered the largestsize at 42.06mm (minimum¼ 11.53mm, aver-age¼ 25.19 and s.d.¼ 8.05) and Chaetopleura hansel-mani (Ferreira 1932) the smallest size at 3.17mm.

The value of calculated the Pielou (J0) equity oruniformity index for the study area was J0 ¼ 0.795.

Discussion and conclusions

Reports from research with similar methodology byGarcıa 1994, Flores-Rodrıguez et al. 2003, Valdez-Gonzalez et al. 2004, Flores-Rodrıguez et al. 2007,

Flores-Garza et al. 2007 and Barba-Marino et al. 2010,had richness values for sampled beaches lower thanwhat was found for Playa Majahua.

The high species richness found in Majahua is thehighest that has ever been registered for any rockyintertidal beach of the state. The difference found inrichness is believed to be due to its structure and giventhat it is formed by alluvial accumulation. Also it islocated in a protected area with slow waves andtherefore it has minimal abrasion. The difference inspecies richness from the reports mentioned above isprobably due to the structure and complexity of PlayaMajahua, with a heterogeneous substrate leading to awide variety of habitats. We assume that the soft gentle

Table 1. Continued.

Length (mm)

Families/species n Co De Min Max Ave Sd

BuccinidaeCantharus (P.) sanguinolentus (Duclos 1833) 6 O 0.3 18.60 24.01 21.50 1.93Engina tabogaensis (Bartsch 1931) 62 D 3.1 5.55 14.86 10.76 2.28

ColumbellidaeColumbella fuscata (Sowerby 1832) 91 D 4.55 5.14 20.66 15.44 3.42Columbella major (Sowerby 1832) 2 O 0.1Columbella sonsonatensis (Morch 1860) 2 O 0.1 8.11 9.36 8.73 0.88Columbella auromexicana (Howard 1963)* 1 O 0.05 14.67 14.67 14.67Costanachis nigrofusca (Carpenter 1844) 47 D 2.35 3.01 8.30 6.19 1.26Parvanachis dalli (Bartsch 1931)* 64 D 3.2 3.21 6.71 5.28 0.74Parvanachis pygmaea (Sowerby 1832)* 1 O 0.05 5.17 5.17 5.17Parvanachis guerreorensis (Strong & Hertlein 1937) 3 O 0.15 9.21 9.97 9.61 0.38Mitrella ocellata (Gemelin 1791) 3 O 0.3 8.65 11.06 9.99 1.07Mitrella santabarbarensis (Gould & Carpenter 1857)* 3 O 0.15 8.20 9.62 8.99 0.72Decipifus lyrta (Baker, Hanna & Strong 1938)* 1 O 0.05 7.35 7.35 7.35

FasciolariidaeLeucozonia cerata (Wood 1828) 19 D 0.95 16.99 39.79 24.75 7.40Opeatostoma pseudodon (Burrow 1815) 1 O 0.05 15.01 15.01 15.01

MitridaeMitra (S.) tristis (Broderip 1836) 5 C 0.25 6.45 8.65 7.55 0.82Mitra lignaria (Reeve 1844)* 4 O 0.2 8.40 10.20 9.27 1.01

CancellariidaeCancellaria (S.) buccinoides (Sowerby 1832)* 1 O 0.05

ConidaeConus (P.) fergusoni (Sowerby 1873)* 3 C 0.15 4.82 7.46 6.55 1.49Conus (S) nux (Broderip 1833) 5 C 0.25 10.14 21.23 17.11 4.68Conus(C) princeps (Linnaeus 1758) 1 O 0.05 14.02 14.02 14.02Conus(C) purpurascens (Sowerby 1833) 1 O 0.05 31.04 31.04 31.04

TurridaePilsbryspira (P) garciacubasi (Shasky 1971) 2 O 0.1 4.66 4.81 4.73 0.10Crassispira (D.) cerithoidea (Carpenter 1857)* 1 O 0.05 9.26 9.26 9.26

SiphonariidaeSiphonaria (H.) maura (Sowerby 1835) 56 D 2.8 7.12 19.06 10.46 2.16Siphonaria (H.) palmata (Carpenter 1857) 105 D 5.25 6.11 13.31 8.91 1.28Williamia peltoides (Carpenter 1864)* 1 O 0.05 5.51 5.51 5.51

*¼ Species not found for Acapulco; n¼ number of analysed organisms; Co¼ composition; D¼ dominant; C¼ common;NLF¼ numerous little frequent; O¼ occasional; De¼ density; Min¼minimum; Max¼maximum; Ave¼ average;Sd¼ standard deviation.

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waves of this area also support a higher speciesrichness. The area at the sampling unit was carefullychecked, which was possible because of both theamount of the area sampled and the ease of accessfor researchers.

There were 34 identified species not previouslyreported in the literature for Acapulco, and in addi-tion, two species not previously reported for theMexican Pacific. This indicates that the availableinformation on marine fauna for the State ofGuerrero is lacking and shows the importance andneed for this type of study. Moreover, in agreementwith previous studies in Guerrero and in other states ofMexico, the most abundant and best represented classof molluscs is Gastropoda. Nevertheless, there isdisagreement with previous studies in recorded abun-dance of classes Bivalvia and Polyplacophora. InMajahua, Bivalvia is more abundant thanPolyoplacophora which, in contrast, has a greaternumber of species.

For Gastropoda, this study reports for the firsttime that family Collumbellidae has the highest repre-sentation when compared to other mollusc families inthe state of Guerrero. It is in fact the family thatpresented the highest number of species. Reports in theliterature on studies that included classPolyplacophora in the state of Guerrero, indicatedthat the Chitonidae family was best represented inrelation to species richness and abundance. This resultis different from that found in this investigationbecause the family Tonicellidae was recorded as thebest represented in relation to species richness, and thisis the first time that this family is reported as the bestrepresented for Polyplacophora.

The estimated density value is the highest reportedfor rocky beaches in Acapulco, and it was foundamong the highest ever reported for Guerrero.Flores-Rodrıguez (2004) reports a highest density of117 organisms/m2, corresponding to the average ofnine sites sampled along the rocky coast of Guerrero.

Table 2. Richness, density (organisms/m2), size (length in mm) and bivalve species composition present in rocky intertidal middlezone of Playa Majahua, Acapulco, Guerrero, Mexico.

Families/species n Co De

Length (mm)

Min Max Ave Sd

ArcidaeBarbatia (B.) lurida (Sowerby 1833)* 3 O 0.15 13.38 25.45 18.04 6.48Acar rostae (Berry, 1954) 7 NLF 0.35 5.15 8.84 7.18 1.35

IsogmonidaeIsognomon janus (Carpenter 1857) 17 D 0.85 5.27 16.80 10.23 2.98

MytilidaeBrachidontes adamsianus (Dunker 1857)* 1 O 0.05 6.16 6.16 6.16Lithophaga (M.) aristata (Dillwyn 1817) 1 O 0.05 3.86 3.86 3.86

LimidaeLimaria pacifica (de‘Orbigny 1846) 4 O 0.2 8.22 22.33 16.43 6.32

OstreidaeCrassostrea prismatica (Gray 1825) 93 D 4.65 10.09 56.07 28.76 11.41Crassostrea palmula (Carpenter 1857) 84 D 4.2 13.14 50.33 28.95 7.28

PlicatulidaePlicatula penicillata (Carpenter 1857) 6 O 0.3 9.72 18.33 14.18 3.16Plicatula anomioides (Keen 1958)* 8 NLF 0.4 16.05 38.76 26.55 8.09

AnomiidaeAnomia (A.) peruviana (d’Orbigny) 2 O 0.1 26.52 31.06 28.79 3.21

CarditidaeCardites grayi (Dall 1903) 6 O 0.3 16.06 42.31 26.28 8.99

ChamidaeChama corallina (Olsson 1971)* 47 D 2.35 13.20 57.82 27.64 10.77Chama mexicana (Carpenter 1857) 41 D 2.05 14.23 45.77 24.52 6.39Chama sordida (Broderip 1835)* 7 D 0.35 9.60 48.03 21.58 12.64

*¼ Species not found for Acapulco; n¼ number of analysed organisms; Co¼ composition; D¼ dominant; C¼ common,NLF¼ numerous little frequent; O¼ occasional; De¼ density; Min¼minimum; Max¼maximum; Ave¼ average;Sd¼ standard deviation.

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With reference to community species composition,

the quantity of dominant species found in the present

study is the highest that has ever been reported for the

Guerrero state, and it is the first occasion where this

many members from class Polyplacophora have been

reported within the set of dominant species.

Polyplacophora, in terms of percentage, has most of

the dominant species. Members of this class have a

design (plane, oval, articulated valves, with girdle and

a great muscular foot) efficient enough to survive theenvironmental conditions of the rocky intertidal zone.

Bivalvia was second in percentage of dominantspecies, largely sessile organisms. Gastropoda as wellhave a design that allows them to endure the rockyintertidal conditions. In the literature, there are noreports with analysis of the size structure of popula-tions that make up the community of Polyplacophora.For this reason, it was not possible to compare ourresults with the Polyplacophora communities fromother sites in the Mexican Pacific.

In the literature for the Mexican Pacific, no reportwas found with a Pielou index (J0) greater or equal tothat found for the Playa Majahua. The value of J0

found in Playa Majahua, indicates a highly diversearea and this result corresponds to that expected for atropical beach.

Acknowledgements

This work was partly funded by CONACYT (ConsejoNacional de Ciencia y Tecnologıa – National council ofScience and Technology) and the state government of

Table 3. Richness, density (organisms/m2), size (length in mm) and Polyplacophora species composition present in rockyintertidal middle zone of Playa Majahua, Acapulco, Guerrero, Mexico.

Families/species n Co De

Length (mm)

Min Max Ave Sd

IschnochitonidaeIschnochiton (I.) muscarius (Reeve 1847)* 42 D 2.1 6.88 27.71 16.23 4.98Stenoplax (S.) regulata (Dall 1919, ex Bartsch MS) 2 O 0.1 7.20 12.19 10.05 4.03Stenoplax (S.) limaciformis (Sowerby 1832) 4 C 0.2 5.33 29.54 17.05 6.15Lepidozona (L.) serrata (Carpenter 1864) 19 D 0.95 4.96 10.17 6.51 1.94

AcanthochitonidaeAcanthochitona arragonites (Carpenter 1857) 1 O 0.05 9.29 9.29 9.29

ChitonidaeChiton (C.) albolineatus (Broderip & Sowerby 1829) 27 D 1.35 4.43 39.58 19.60 6.18Chiton (C.) articulatus (Sowerby in Borderip & Sowerby 1832) 19 D 0.95 11.53 42.06 25.19 8.05Tonicia forbesii forbesii (Carpenter 1857) 16 D 0.8 13.08 31.84 23.19 6.43

ChaetopleuridaeChaetopleura (C.) lurida (Sowerby 1832) 87 D 4.35 5.11 32.39 18.89 4.95Chaetopleura (C.) hanselmani (Ferreira 1932) 1 O 0.05 8.37 8.37 8.37Chaetopleura (C.) unilineata (Leloup 1954) 15 NLF 0.75 3.17 7.03 5.37 0.1.92

CallistoplacidaeCallistoplax retusa (Sowerby in Broderip & Sowerby 1832) 41 D 2.05 5.04 24.07 13.97 4.86

TonicellidaeLepidochitona (L.) beanii (Carpenter 1857) 3 C 0.15 6.12 6.28 6.20 0.11Lepidochitona (L.) salvadorensis (Garcıa-Rıos 2006) 7 D 0.35 6.01 13.77 9.42 2.65Lepidochitona hartewii 1 O 0.05 8.95 8.95Lepidochitona sp 1 2 O 0.1 6.92 9.65 8.28 1.93Lepidochitona sp 2 2 O 0.1 4.21 8.46 5.74 1.71

*¼ Species not found for Acapulco; n¼ number of analysed organisms; Co¼ composition; D¼ dominant; C¼ common;NLF¼ numerous little frequent; O¼ occasional; De¼ density; Min¼minimum; Max¼maximum; Ave¼ average;Sd¼ standard deviation.

0

10

20

30

40

50

60

BIVALVIAPOLYPLACOPHORA

GASTROPODA

Per

cent

age

CLASS

Dominant

Constant

Numerous little frequent

Occasional

Figure 3. Intertidal mollusc community species compositionfrom Playa Majahua, Acapulco, Guerrero.

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Guerrero through the research project No. 91624 ‘Ecologicalstudy of the Acapulco Bay’ FOMIX 2008-C01 and theresearch project No. 91724 ‘Diversity and abundance ofmarine cockroach off the coast of Guerrero state’ FOMIX2008-C01. Thanks to M. Diaz Santana for editing thisEnglish language text.

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