The community of mollusks at three rocky intertidal zone in Oaxaca, Mexico was analyzed. Two samplings per site were conducted. At each sampling the inspected area was 10 m 2. The sampling unit was 1 m 2. 5862 specimens were examined. 68 mollusks species were identified. The families better represented in species richness were: FISSURELLIDAE, MURICIDAE, LOTIIDAE, MYTILIDAE, CHAMIDAE, ISCHNOCHITONIDAE y CHITONIDAE. The species that had the greatest density were Lottia discors, Siphonaria palmata, Lottia acutapex, Chormoytilus palliopunctatus, Brachidontes adamsianus, Chton articulatus e Ischnochiton muscarius. The species with the widest distribution represent 11.76%. With irregular distribution was found in 58.82% of the species. The gastropod Crucibulummonticulus, the bivalve C. palliopunctatus and the polyplacophoran C. articulatus had the greatest size. The value of diversity index was H’ = 4.29 bits/ind. and J’ = 0.72. The mollusks community in the rocky intertidal zone study sites is characterized by small size, because they rarely exceed seventy millimeters. The values of H’ and J’ indicate that the mollusk community in the study area has a high diversity and high uniformity, corresponding to mature and stable communities in a tropical region.
The Commission for Environmental Cooperation of North America determined the existence of 24 marine eco- regions. Seven ecoregions are located in Mexico. The Mexican Pacific Transitional (MPT) forms part of these seven regions and is composed of the states of Jalisco, Colima, Michoacán, Guerrero and Oaxaca and the south- ern tip of Baja California Sur. It is characterized as a region of high productivity, as a result of warmer ocean temperatures; tropical marine fauna is very different to that found in areas influenced by the Humboldt and Cali- fornia currents.
The coasts of MPT are comprised of cliffs and have rocky and sandy bottoms. These sites are suitable for de- velopment of biotic communities. Mollusks are part of these communities and this group has pointed out that knowledge is scarce and we have a great ignorance of the status these organisms in the intertidal zone of the MPT [
For the State of Oaxaca the National Commission for the Knowledge and Use of Biodiversity (Comision Na- cional Para el Uso y Conocimiento de la Biodiversidad; CONABIO) stated that there are five marine priority areas for the conservation of coastal and ocean biodiversity; about these regions CONABIO has highlighted the lack of knowledge about the diversity of marine species [
There are reports of mollusks for different MPT sites that deal with biodiversity [
The lack of knowledge about mollusks in many places of the MPT, was the principal motivation for carrying out this research and focusing on the GASTROPODA, BIVALVIA and POLYPLACOPHORA Classes and ob- jectives were: 1) to determine species richness; 2) to analyze the composition of the community based on the most represented families; 3) to estimate the density; 4) to determine the distribution of the species in the study area; 5) to analyze the size composition of populations; and 6) to estimate the diversity index.
In Oaxaca the weather is subhumid tropical, with summer rains [
The rocks of the hydrological basins that drain into the sea are diverse in age and lithology [
Three sites were sampled, which are located in priority marine regions 34 and 35, each location was geo- graphically referenced and described according to the following criteria: type of substrate, type of rock, substrate stability and wave exposure. The sampling sites were described based on the report [
These sites vary in type, substrate stability and wave exposure. Substrate types were classified as: a) Massif rocks: fixed structures such as walls, cliffs, terraces, etc.; b) Blocks: loose rock larger than 50 cm in diameter, made of rocks submerged and immovable or that are difficult to move about by the impact of waves; c) Boulders: loose rock of size less than 50 and greater than 8 cm in diameter, rocks that can be easily moved by the impact of waves; d) Gravel: loose rock no more than 8 cm in diameter. The stability of the substrate was classified as: a) High: when the substrate remains virtually unchanged by the impact of waves; b) Middle: when the impact of the waves does not change the configuration of the substrate but there is rock movement; c) Low: when the site configuration changes due to the impact of waves, most of the rocks are moved. The wave exposure was classi- fied as: a) High: when the wave hits the substrate in a free manner, usually the sites that have this type of waves are outside of the protection of any barriers such as bays or hooks; b) Middle: when the impact of the wave on
Site | Coordinates | Length | Type of | Type of | Subtrate | Wave | |
---|---|---|---|---|---|---|---|
Latitud N | Longitud W | of thesite | substrate | rock | stability | exposure | |
Carrizalillo | 15˚51'35.19" | 97˚04'45.57" | 208 meters | Massifs and blocks. | Sedimentary rocks conglomerate Q (cg), formed in the Cenozoic and Quaternary [ | Middle | Middle |
Very roufh and abundant hollows | |||||||
Among the blocks are boulders and gravel on sand | |||||||
Coral | 15˚51'47.50" | 97˚05'14.34" | 147 meters | Massifs rocks alternating with sandy areas | Sedimentary rocks conglomerate Q (cg), formed in the Cenozoic and Quaternary [ | High | Middle |
The rocks massifs are large areas of smooth | |||||||
Surfaces, alternating with crevices and hollows | |||||||
Punta Cometa | 15˚51'47.50" | 97˚05'14.34" | 73 meters | Rocks massifs with large areas of smooth | Metamorphic rock, type Gneiss J (Gn) of Mesozoic and Jurassic period [ | High | High |
Surfaces and few grooves or channels |
the substrate is hindered by barriers or smoothing, as can occur at sites that are in front of the entrance of bays or at a distance from a wall of hooks, it also happens in places where subtidal rocky substrate merges or is shallow and reduces the direct impact of the waves to the substrate; c) Low: when the wave does not directly hit the sub- strate, since the sites are protected by different types of barriers [
Two samples were conducted in Carrizalillo and Coral and one in Punta Cometa between February and Novem- ber 2011. Sampling was performed during the hours of low tide at new moon days.
To carry on the quantification of organisms an area of 10 m2 was sampled per site. Sampling was systematic [
The starting point was randomly selected and then a nylon rope 30 m long was placed parallel to the shore on the intertidal zone using a PVC pipe square frame 1 m per side to delimit the sampling unit. Once the starting point was established, the PVC frame was placed at the selected point. All mollusks that were found alive in the quadrants were collected and placed into a plastic container filled with seawater and protected from exposure to direct sunlight. After completing the collection, a 2 m intersection along the rope was measured then the frame was again repositioned to define the following sampling unit. This procedure was repeated ten times along the nylon rope. Upon sample completion, the specimens’ preservation consisted of placing them in labeled jars containing 96% ethyl alcohol. They were then taken to the laboratory to be identified, quantified and meas- ured.
To complement the inventory of species searches were conducted to locate species that were not found within the quadrants in the quantitative samples.
The taxonomic identification required a confirmation stage in the laboratory. For the identification the cha- racteristics of the shell, the soft body parts and specialized literature [
Richness represents a based on the number of species found in the samples. The community composition was analyzed using the representation of families, which was evaluated based on species richness and abundance of organisms per Family. Density was measured by estimating the average number of specimens/m2.
To classify the species distribution, the following criteria were used: a) wide, the species was present at all three sites; b) regular, it was present in two; c) irregular, it was present at one.
The analysis of structure of populations was considered by measuring the length, and obtained the statistical descriptive values such as maximum, minimum, mean and standard deviation expressed in millimeters was ob- tained using a digital vernier type caliper (accuracy 0.01 mm). The diversity was measured using the Shan- non-Weaver (H’) index and the evenness index of Pielou (J’) or equity [
5862 specimens were examined. 68 mollusks species were identified: 49 species of GASTROPODA Class, eight BIVALVIA and 11 POLYPLACO2
Families/Species | N. | De. | D. | Length(mm) | |||||
---|---|---|---|---|---|---|---|---|---|
1 | 2 | 3 | Org./m2 | Min. | Max. | Ave. | Sd. | ||
LOTTIIDAE Gray, 1840 | |||||||||
Lottia mesoleuca (Menke, 1851) | 2 | 34 | 20 | 1.12 | W | 4.52 | 23 | 10.09 | 3.79 |
Lottia mitella (Menke, 1847) | 20 | 43 | 213 | 5.52 | W | 4.8 | 19.7 | 8.48 | 2.99 |
Lottia acutapex (Berry, 1960) | 423 | 8.46 | I | 3.48 | 17.1 | 9.98 | 2.32 | ||
Lottia discors (Philippi, 1849) | 480 | 26 | 168 | 13.48 | W | 5.67 | 43.3 | 21.01 | 8.7 |
Lottia pediculus (Philippi, 1846) | 70 | 1 | 1.42 | R | 5.76 | 21.2 | 12.13 | 3.51 | |
Tectura fascicularis (Menke, 1851) | 10 | 7 | 0.034 | R | 5.05 | 27.2 | 15.86 | 6.71 | |
FISSURELLIDAE Fleming, CA, 1822 | |||||||||
Fissurella rubropicta Pilsbry, 1890 | 3 | 0.06 | I | 12.6 | 18.3 | 15.34 | 2.85 | ||
Fissurella (Cremides) microtrema Sowerby, 1835 | 1 | 0.02 | I | 15.3 | 15.3 | 15.26 | - | ||
Fissurella nigrocincta Carpenter, 1856 | 273 | 5.46 | I | 5.54 | 21 | 11.97 | 3.03 | ||
Fissurella gemmata Menke, 1847 | 27 | 31 | 48 | 2.12 | W | 8.22 | 36.4 | 18.36 | 6.36 |
Fissurella longifissa Sowerby, 1866 | 1 | 0.02 | I | 24.8 | 24.8 | 24.81 | |||
Fissurella morrisoni McLean, 1970 | 7 | 0.14 | I | 10.1 | 20.4 | 13.66 | 3.36 | ||
Fissurella spongiosa Carpenter, 1857 | 1 | 0.02 | I | 8.69 | 8.69 | 8.69 | |||
Fissurella asperella Sowerby, 1835 | 21 | 25 | 0.42 | R | 8.13 | 28.9 | 17.36 | 4.37 | |
Fissurella obscura Sowerby, 1835 | 2 | 0.04 | I | 14 | 18.1 | 16.07 | 2.91 | ||
TROCHIDAE Rafinesque, 1815 | |||||||||
Tegula globulus (Carpenter, 1857) | 35 | 0.7 | I | 4.14 | 29 | 9.08 | 3.91 | ||
NERITIDAE | |||||||||
Nerita scarbricosta Lamark, 1822 | 3 | 0.06 | I | 8.51 | 12.3 | 10.12 | 1.96 | ||
LITTORINIDAE Children, 1834 | |||||||||
Nodilittorina aspera (Philippi, 1846) | 60 | 231 | 5.82 | R | 1.56 | 12.1 | 4.03 | 1.34 | |
Nodilittorina modesta (Philippi, 1846) | 322 | 6.44 | I | 1.13 | 13.7 | 4.45 | 1.75 | ||
RISSOIDAE |
Rissoina stricta Menke, 1850 | 2 | 0.04 | I | 6.46 | 7.21 | 6.835 | 0.53 | ||
---|---|---|---|---|---|---|---|---|---|
VERMETIDAE | |||||||||
Petaloconchus complicatus Dall, 1908 | 12 | 1 | 0.26 | R | |||||
Serpulorbis margaritaceus (Chenu, 1844 ex Rousseau, MS) | 9 | 0.18 | I | ||||||
CERITHIDAE (Fleming, 1822) | |||||||||
Rhinoclavis (O.) gemmata (Hinds, 1844) | 6 | 0.12 | I | 14.7 | 26.3 | 22.8 | 4.35 | ||
CALYPTRAEIDAE (Lamarck, 1809) | |||||||||
Crucibulum monticulus Berry, 1969 | 12 | 0.24 | I | 21.8 | 59.2 | 35.48 | 10.1 | ||
Crucibulumum brella (Deshayes, 1830) | 1 | 0.04 | I | 35 | 35 | 35 | |||
Crucibulum subacuatum Berry, 1963 | 3 | 0.06 | I | 3.33 | 6.26 | 4.98 | 1.5 | ||
Crucibulum scutellatum (Wood, 1828) | 1 | 0.02 | I | 17.9 | 17.9 | 17.94 | |||
MURICIDAE (Follows Vokes, 1996) | |||||||||
Mancinella speciosa (Valenciennes, 1832) | 10 | 0.02 | I | 10.2 | 25.6 | 19.66 | 5.38 | ||
Mancinella triangularis (Blaindville, 1832) | 138 | 17 | 3.1 | R | 4.94 | 17.8 | 10.61 | 2.2 | |
Stramonita biseralis (Blanville, 1832) | 40 | 29 | 1.38 | R | 3.91 | 31.4 | 12.86 | 5.02 | |
Vasula melones (Duclos, 1832) | 16 | 2 | 0.36 | R | 21.2 | 46.6 | 38.89 | 8.2 | |
Acanthais brevidentanta (Wood, 1828) | 17 | 0.34 | I | 18.1 | 28.2 | 21.53 | 2.96 | ||
Plicopurpura pansa (Gould, 1853) | 48 | 67 | 2.3 | R | 11.1 | 39.6 | 23.06 | 5.36 | |
Plicopurpura columellaris ( Lamarck, 1822) | 1 | 0.02 | I | 29.6 | 29.6 | 29.63 | |||
Trachypollia lugubris (C. B. Adams, 1852) | 2 | 2 | 0.08 | R | 11.4 | 23.3 | 18.26 | 5.75 | |
FASCIOLARIIDAE (McLean, 1996) | |||||||||
Leucozonia cerata (Wood, 1828) | 3 | 0.06 | I | 27.1 | 41.5 | 32.67 | 7.75 | ||
Opeatostoma pseudodon (Burrow, 1815) | 2 | 0.04 | I | 33.4 | 33.7 | 33.58 | 0.21 | ||
BUCCINIDAE | |||||||||
Engina tabogaensis Bartsch, 1931 | 3 | 0.06 | I | 12.8 | 22.5 | 16.09 | 5.54 | ||
Cantharus sanguinolentus (Duclos, 1833) | 2 | 0.04 | I | 22.8 | 23.7 | 23.24 | 0.57 | ||
COLUMBELLIDAE (Swainson, 1840) | |||||||||
Columbella fuscata Sowerby, 1832 | 84 | 1 | 1.7 | R | 8.32 | 21.2 | 14.07 | 3.26 | |
Mitrella xenia (Dall, 1919) | 39 | 0.78 | I | 1.89 | 13.6 | 6.18 | 2.19 | ||
Mitrella ocelata (Gmelin, 1791) | 73 | 3 | 0.04 | R | 4.23 | 11.7 | 9.78 | 1.41 | |
MITRIDAE (Swainsom, 1829) | |||||||||
Mitra tristis Broderip, 1836 | 6 | 1 | 0.014 | R | 9.82 | 14.3 | 12.31 | 1.61 | |
CONIDAE (Fleming, 1822) | |||||||||
Conus nux Broderip, 1833 | 2 | 0.04 | I | 17.6 | 23.8 | 20.66 | 4.36 | ||
Conus fergusoni Sowerby, 1873 | 1 | 0.02 | I | 25.1 | 25.1 | 25.14 | |||
ONCHIDIIDAE |
Hoffmanola hansi Marcus & Marcus, 1967 | 16 | 14 | 1 | 0.62 | W | ||||
---|---|---|---|---|---|---|---|---|---|
SIPHONARIDAE (Gray, 1827) | |||||||||
Siphonaria gigas Sowerby, 1825 | 7 | 0.14 | I | 10.5 | 16.9 | 13.82 | 2.69 | ||
Siphonaria maura Sowerby, 1835 | 85 | 73 | 3.16 | R | 1.14 | 18.1 | 10.05 | 3.04 | |
Siphonaria palmata Carpenter, 1857 | 137 | 379 | 16 | 10.64 | W | 2.92 | 18.1 | 8.78 | 2.36 |
N.: Number of test organism per site; 1: Carrizalillo; 2: Coral; 3: Punta Cometa; De.: Density; D.: Distribution; W.: Wide; R.: Regular; I.: Irregular; Min.: Minimum; Max.: Maximum; Ave.: Average; and Sd.: Standard deviation.
Families/Species | N. | De | D. | Length (mm) | |||||
---|---|---|---|---|---|---|---|---|---|
1 | 2 | 3 | Org./m2 | Min. | Max. | Ave. | Sd. | ||
BIVALVIA | |||||||||
MYTILIDAE (Rafinesque, 1815) | |||||||||
Brachidontes adamsianus (Dunker, 1857) | 24 | 650 | 4 | 13.56 | W | 2.16 | 13.8 | 5.87 | 1.26 |
Brachidontes semilaevis (Menke, 1849) | 2 | 0.04 | I | 5.32 | 6.1 | 5.71 | 0.55 | ||
Choromytilus palliopunctatus (Carpenter, 1857) | 725 | 14.5 | I | 4.9 | 56 | 17.2 | 7.7 | ||
ISOGNOMONIDAE (Woodring, 1925 (1828)) | |||||||||
Isognomon janus Carpenter, 1857 | 92 | 1.84 | I | 5.6 | 30.9 | 15.7 | 5.4 | ||
OSTREIDAE (Rafinesque, 1815) | |||||||||
Crassostrea palmula (Carpenter, 1857) | 1 | 0.02 | I | 24.4 | 24.4 | 24.4 | - | ||
Crassostrea prismatica (Gray, 1825) | 1 | 0.02 | I | 48.9 | 48.9 | 48.9 | - | ||
CHAMIDAE (Lamarck, 1809) | |||||||||
Chama (chama) coraloides Revee, 1846 | 21 | 41 | 1.24 | R | 6.89 | 46.6 | 21.5 | 8.85 | |
Chama mexicana Carpenter 1857 | 38 | 2 | 0.8 | R | 5 | 38.1 | 16.3 | 8.05 | |
POLYPLACOPHORA | |||||||||
ISCHNOCHITONIDAE (Dall, 1889) | |||||||||
Ischnochiton (I.) muscarius (Reeve, 1847) | 108 | 4 | 2.24 | R | 3.71 | 21.1 | 11.5 | 3.73 | |
Stenoplax (S.) limaciformis (Sowerby & Broderip 1832) | 3 | 0.06 | I | 8.53 | 29.9 | 16 | 6.3 | ||
Stenoplax (S.) regulata (Sowerby, 1832)) | 1 | 0.02 | I | 5.33 | 5.33 | 5.33 | |||
CALLISTOPLACIDAE (Pilsbry, 1893) | |||||||||
Callistochiton elenensis (Sowerby, 1832) | 4 | 0.08 | I | 4.79 | 6.3 | 5.29 | 0.87 | ||
Callistoplax retusa (Sowerby in Broderip & Sowerby, 1832) | 1 | 0.02 | I | 7.12 | 7.12 | 7.12 | |||
CHAETOPLEURIDAE (Plate, 1899) | |||||||||
Chaetopleura (C.) hanselmani (Ferreira, 1982) | 1 | 1 | 0.04 | R | 8.58 | 8.58 | 8.58 | ||
Chaetopleura (C.) lurida Sowerby in Broderip & Sowerby, 1832) | 1 | 0.02 | I | 6.8 | 6.8 | 6.8 |
CHITONIDAE (Rafinesque, 1815) | |||||||||
---|---|---|---|---|---|---|---|---|---|
Chiton (C.) articulatus Sowerby, 1832 | 42 | 29 | 48 | 2.38 | W | 5.71 | 57.7 | 27.6 | 13.1 |
Chiton (C.) albolineatus Broderip & Sowerby, 1829 | 47 | 2 | 0.98 | R | 7.33 | 48.4 | 22.3 | 8.58 | |
Tonicia (T.) forbesii forbesii (Carpenter, 1857) | 1 | 0.02 | I | 13.1 | 13.1 | 13.1 | |||
TONICELLIDAE (Simroth, 1894) | |||||||||
Lepidochitona sp1 | 2 | 0.04 | I | 3.19 | 3.19 | 3.19 |
N.: Number of test organism per site; 1: Carrizalillo; 2: Coral; 3: Punta Cometa; De.: Density; D.: Distribution; W.: Wide; R.: Regular; I.: Irregular; Min.: Minimum; Max.: Maximum; Ave.: Average; and Sd.: standard deviation.
On tours conducted outside of the quadrants, they found four species of OPISTHOBRANCHIA Subclass: Berthelina chloris (Dall, 1918), Elysia sp1, Glossodoris sedna (Marcus y Marcus, 1967) and Mexichromis tura (Marcus y Marcus, 1967).
The GASTROPODA Class, showed the highest relative abundance (67.66%), followed by BIVALVIA (27.31%) and POLYPLACOPHORA (5.03%).
26 Families were identified, of which 17 are of the GASTROPODA Class, four are from the BIVALVIA Class and five are of the POLYPLACOPHORA Class.
The Families of the GASTROPODA Class better represented in species richness were FISSURELLIDAE (nine species), MURICIDAE (eight species), LOTTIIDAE (six species) (
The best represented in relative abundance was MYTILIDAE with 87.75%. In the POLYPLACOPHORA Class, the best represented families in species richness were ISCHNOCHITONIDAE and CHITONIDAE with 3 species each. The best represented Family in relative abundance was CHITONIDAE with 57.28%.
The estimated density was 117.84 organisms/m2, which is divided into 79.32 gastropods/m2, 32.02 bivalves/m2 and 5.9 polyplacophorans/m2.
The species of the GASTROPODA Class that showed the highest density were Lottia discors (Philippi, 1849) (13.48 organisms/m2), Siphonaria palmata Carpenter, 1857 (10.64 organisms/m2), Lottia acutapex (Berry, 1960) (8.46 organisms/m2), and Nodilittorina modesta (Philippi, 1846) (6.44 organisms/m2). In BIVALVIA Class, spe- cies that showed the highest density were Chormoytilus pallopunctatus (Carpenter, 1857) (14.5 organisms/m2), Brachidontes adamsianus (Dunker, 1857) (13.56 organisms/m2), Isognomon janus Carpenter, 1857 (1.84 organ- isms/m2), and species POLYPLACOPHORA Class showing the highest density were Chiton articulatus Sower- by, 1832 (2.38 organisms/m2) and Ischnochiton muscarius Reeve, 1847 (2.24 organisms/m2) (
The species with the widest distribution (
In GASTROPODA Class Crucibulum monticulus had the greatest size with 59.20 mm (minimum = 21.84 mm, mean = 35.48 mm and standard deviation = 10.08). In GASTROPODA Class Crucibulum monticulus had the greatest size, and Nodilittorina modesta the smallest size, with 1.13 mm (maximum = 13.72 mm, mean = 4.45 mm and standard deviation = 1.74). In BIVALVIA Class Choromytilus palliopunctatus showed the greatest size, 55.99 mm (minimum = 4.90 mm, mean = 17.19 mm and standard deviation = 7.70 mm) and B. adamsianus the smallest size and was 2.16 mm (maximum = 13.81 mm, mean = 5.87 mm and standard deviation = 1.26 mm), (
In POLYPLACOPHORA Class, Chiton articulatus showed the greatest size and was 57.69 mm (minimum = 5.71 mm, mean = 27.56 mm and standard deviation = 13.09 mm) and showed the smallest size Lepidochitona sp1 and was 3.19 mm (maximum = 3.19 mm, mean = 3.19 mm).
The value of diversity index (H’) calculated for the study area was H’ = 4.29 bits/ind and value Pielou index (J’) was J’ = 0.72. By study site: Carrizalillo H’ = 3.70 bits/ind. and J’= 0.0.68; Coral H’ = 3.57 bits/ind. and J’= 0.68; Punta Cometa H’ = 2.68 bits/ind. and J’ = 0.62.
In research conducted in one sampling site in the rocky intertidal zone of Oaxaca [
The greater number of species recorded in this study is attributed to sampling that was conducted at three sites that vary in type of substrate, stability and wave exposure, so the composition of the microhabitat is considera- bly varied and thus, a greater number of species is supported.
Reference [
In composition classes, all research was conducted at the respective sites in the rocky intertidal zone in the State of Oaxaca agree that the GASTROPODA Class has the highest species richness, a result that was also re- ported in the present investigation.
The BIVALVIA Class has been reported with higher species richness after GASTROPODA Class [
In the GASTROPODA Class, the families best represented in species richness were FISSURELLIDAE and MURICIDAE, [
In the BIVALVIA Class, MYTILIDAE and CHAMIDAE Families were better represented in species richness, as was reported for Acapulco by Galeana-Rebolledo et al. (2012). The CHAMIDAE Family was also reported by [
In POLYPLACOPHORA Class families who turned out to be better represented in species richness were ISCHNOCHITONIDAE and CHITONIDAE, as was reported for Acapulco by [
The Families with higher abundance in the GASTROPODA Class were LOTTIDAE and SIPHONARIDAE, in BIVALVIA Class was the MYTILIDAE Family and POLYPLACOPHORA Class had the highest abundance CHITONIDAE Family. For the GASTROPODA Class, this research does not agree with what has been reported in research conducted on other sites in the Mexican Pacific Transitional, as occurs with [
The density values estimated for the study area are high. Other studies have also reported high densities in the region such as [
Reference [
The GASTROPODA Class has the largest number of species with irregular distribution.
Regarding the size of the species, is coincides with reports from [
The results of this investigation indicate that mollusk species associated with the rocky intertidal zone, the maximum size rarely exceeds seventy millimeters in length. The same was reported for other sites that are lo- cated in the Mexican Pacific Transitional.
In the Mexican Transitional Pacific for mollusks associated with the rocky intertidal zone, have had high val- ues reported for the diversity index of Shannon-Weaver [
The value of diversity index found by this research is high and corresponds to that expected in the rocky sites where this research was conducted.
With regard to uniformity for Transitional Mexican Pacific reports values were found around J’ > 0.60 [
Species richness found in the study sites corresponds to that expected for rocky intertidal zones located in the Mexican Pacific Transitional. The GASTROPODA Class provides a greater number of species followed by the POLYPLACOPHORA Class.
Families considered as representative in species richness on the rocky intertidal zone of the study sites were FISSURELLIDAE and MURICIDAE (GASTROPODA), CHAMIDAE and MYTILIDAE (BIVALVIA) and CHITONIDAE (POLYPLACOPHORA).
Families considered as representative in abundance on rocky intertidal zones of the study sites were TRO- CHIDAE and COLUMBELLIDAE (GASTROPODA), MYTILIDAE (BIVALVIA) and CHITONIDAE (POLY- PLACOPHORA).
The density found is high and corresponds to that expected in sites that are located in the Mexican Pacific transitional.
Species considered representative by high density values recorded in the study area were, C. pallopuntatus, B. semilaevis and L. discors.
The mollusks community in the rocky intertidal study sites is characterized by small size, because they rarely exceed seventy millimeters. Among the species with larger size are Cruibullum monticulus; Ch. palliopunctatus and C. articulatus.
The values of H’ and J’ indicate that the mollusk community in the study area has a high diversity and high uniformity, corresponding to mature and stable communities in a tropical region.