Isognomon Bicolor Research Articles

Lake faro (Central Mediterranean): A potential short-term reservoir for Pinna nobilis

The noble fan shell, Pinna nobilis, is an endemic Mediterranean species included in the IUCN Red List because it is at risk of extinction after the global mass mortality event (MME) first detected in late 2016 in the Spanish waters. Throughout the whole Mediterranean Sea, measures to evaluate reproduction and recruitment in relict populations have been undertaken, in view of a wished species recovery. In this study we highlight the potential resilience of the Lake Faro P. nobilis population (north-eastern Sicily), which partially survived to the MME affection. Results of both monitoring and installation of larval collectors during a three-year period (from 2021 to 2023) are reported. Despite spawning events show that the population is reproductively active, a poor natural recruitment was detected. Each sign of potential resilience, moreover, contrasts with the failure of collectors in capturing P. nobilis larvae, while they were highly colonized by more competitive organisms, including non-native species, such as the ascidian Styela plicata and the bivalves Pinctada radiata, Isognomon bicolor and Anadara transversa.

New records of non-indigenous species from the eastern Mediterranean Sea (Crustacea, Mollusca), with a revision of genus Isognomon (Mollusca: Bivalvia).

We report new data on non-indigenous invertebrates from the Mediterranean Sea (four ostracods and 20 molluscs), including five new records for the basin: the ostracods Neomonoceratina iniqua, Neomonoceratina aff. mediterranea, Neomonoceratina cf. entomon, Loxoconcha cf. gisellae (Arthropoda: Crustacea)-the first records of non-indigenous ostracods in the Mediterranean-and the bivalve Striarca aff. symmetrica (Mollusca). Additionally, we report for the first time Electroma vexillum from Israel, and Euthymella colzumensis, Joculator problematicus, Hemiliostraca clandestina, Pyrgulina nana, Pyrgulina microtuber, Turbonilla cangeyrani, Musculus aff. viridulus and Isognomon bicolor from Cyprus. We also report the second record of Fossarus sp. and of Cerithiopsis sp. cf. pulvis in the Mediterranean Sea, the first live collected specimens of Oscilla galilae from Cyprus and the northernmost record of Gari pallida in Israel (and the Mediterranean). Moreover, we report the earliest records of Rugalucina angela, Ervilia scaliola and Alveinus miliaceus in the Mediterranean Sea, backdating their first occurrence in the basin by 3, 5 and 7 years, respectively. We provide new data on the presence of Spondylus nicobaricus and Nudiscintilla aff. glabra in Israel. Finally, yet importantly, we use both morphological and molecular approaches to revise the systematics of the non-indigenous genus Isognomon in the Mediterranean Sea, showing that two species currently co-occur in the basin: the Caribbean I. bicolor, distributed in the central and eastern Mediterranean, and the Indo-Pacific I. aff. legumen, at present reported only from the eastern Mediterranean and whose identity requires a more in-depth taxonomic study. Our work shows the need of taxonomic expertise and investigation, the necessity to avoid the unfounded sense of confidence given by names in closed nomenclature when the NIS belong to taxa that have not enjoyed ample taxonomic work, and the necessity to continue collecting samples-rather than relying on visual censuses and bio-blitzes-to enable accurate detection of non-indigenous species.

Influence of the invasive bivalve Isognomon bicolor on the native community found in northeast Brazilian coast

The Caribbean bivalve Isognomon bicolor (C. B. Adams, 1845) is currently among the main invasive species along the Brazilian coast. The present study evaluated the co-occurrence, influence, and relationship of the native macrobenthic community with I. bicolor. The study was performed on samples collected from two sandstone reefs located in Northeast Brazil. We observed that the macrobenthic community differed significantly across reefs, zones, and seasons. The higher density of I. bicolor in the lower intertidal zone (347.7 ind/m² ± 800.8) was one of the main differentiation factors of zonation. The results indicated that the evenness of the community and some gastropods had a negative effect on I. bicolor. We found a negative correlation between the co-occurrence of I. bicolor with the macroalgae Hypnea sp. and Gracilaria caudata J. Agardh 1852 and the microgastropod Eulithidium affine (C. B. Adams, 1850). This study provides data on the relationship between I. bicolor and the native community of sandstone reefs, which could be applied to monitor the expansion of I. bicolor to the Northeast region of Brazil.

New records of non-indigenous species at Lefkada Island (Greece)

During a malacological survey we conducted at the Ionian island of Lefkada (Greece) in September 2022, we found living specimens of the following non-indigenous molluscs not yet reported for the area: Viriola cf. bayani Jousseaume, 1884, Dendostrea frons (Linné, 1758), Isognomon aff. australicus (Reeve, 1858) and Isognomon bicolor (C. B. Adams, 1845). The presence of these species indicates the spread of non indigenous marine species to this area.

Mediterranean spreading of the bicolor purse oyster, Isognomon bicolor, and the chicken trigger, Malleus sp., vs. the Lessepsian prejudice

The introduction rate of alien species in the Mediterranean Sea is rapidly growing, and their taxonomical identification is increasingly challenging. This uncertain identification often leads to an incorrect estimation of the number of alien species, their route of introduction, and their potential negative effects. This is particularly true for some bivalves, which are characterized by high variation in their shells, resulting in uncertain morphological identification. This is the case for two alien bivalves, i.e., an Isognomonidae and a Malleidae species, both characterized by confused historical colonization records in the Mediterranean Sea, misidentifications, and controversial and changing nomenclatures that have insofar negatively affected our knowledge on their geographical distributions. In this respect, molecular approaches provide a strategy that is especially useful when traditional taxonomy fails, and DNA barcoding is a powerful and well-known tool to obtain reliable identifications through efficient molecular markers. In this work, we used the 16S rRNA marker to assess the preliminary identification of Isognomon sp. and Malleus sp. specimens from different localities in the Southern Mediterranean Sea. Bayesian inference (BI) and maximum likelihood (ML) methods were applied to test the monophyly of the phylogenetic linages and to clarify their taxonomic positions, allowing a complete overview of the colonization and spreading of these two alien bivalves in the Mediterranean Sea. In particular, the Isognomon sp. specimens were identified as the Atlantic I. bicolor, highlighting that previously suggested invasive migration patterns, (i.e., the Lessepsian migration), must be reconsidered with stronger critical attention in light of currently occurring global changes.

Reproduction and population dynamics of the invasive bivalves Mytilopsis sallei and Isognomon bicolor on the Northeast coast of Brazil

Knowing the reproductive biology and population dynamics of invasive species are essential for environmental conservation and protection of native species. The success of these invasive species is directly linked to their reproductive strategy. Therefore, this study aimed to describe the reproductive cycles and evaluate population parameters of the invasive bivalves Mytilopsis sallei and Isognomon bicolor, and to estimate if those characteristics would favor their population growths in the northeast coast of Brazil. The bivalves were sampled monthly from June 2016 to May 2017, respectively from the Sanhauá River estuary and Jacarapé beach, State of Paraíba, Northeast Brazil. Through histological analyses, reproductive parameters were determined in order to identify sex, gonadal development, minimum size at maturity, and mean gonadal index. The asymptotic growth (L∞) and growth rate (K) parameters were estimated using the von Bertalanffy growth curve, and recruitment patterns and cohorts were projected based on shell length frequency distributions. Mytilopsis sallei presented more than 50% spawning individuals in most months, while animals showing gametogenic gonads were predominant during the season of greatest precipitation. Isognomon bicolor had ripe gonads (about 30%) and spawning individuals (more than 40%) in all months of the year, but unlike M. sallei, it had the highest concentration of ripe individuals in the months of greatest precipitation. Both species showed equal and high growth rates (K = 1.1 yr-¹) and analysis of the cohorts indicated that these populations are established and expanding. The results confirmed the great invasive potential of the two species in their local environments (estuary and marine) in Northeast Brazil and, therefore, their harmful potential for the conservation of native species and the environment in the invaded areas.

Population structure of the invasive bivalve isognomon bicolor (C.B. Adams, 1845) on rocky beaches in northeastern Brazil

The invasive bivalve Isognomon bicolor is native to the Caribbean and had its first record for the Brazilian coast published in 2002. The objective of this study was to compare the population structure of I. bicolor in two rocky beaches of the coast of Paraíba and verify its temporal variation. Six samples (20 x 20 square cm) were collected on each beach, three in the dry season and three in the rainy season and at two levels of the mid-coastal zone (Bottom and High). Nine samples were obtained for each beach per month, totaling 108 samples. 2,196 specimens of I. bicolor were collected and measured. The highest densities occurred at Carapibus beach. Considering the size structure, there was a significant difference in the length of the nacreous layer between beaches, mid-littoral zones and seasons, with most recruits and smaller individuals occurring on Jacumã beach.

Marine bioinvasions: bivalve molluscs introduced in northeast Brazil

ABSTRACT: Invasive alien species are those that, once introduced from other environments, adapt, starting to reproduce and proliferate in places they did not previously inhabit. The introduction of exotic marine species as a result of anthropic activity, whether intentionally or not, is a process that has been remote for centuries, which makes it difficult to assess the impact of these activities, making studies that address the status of knowledge about such organisms always important. Thus, this research aims to gather information about bivalve molluscs introduced into marine ecosystems in northeastern Brazil, in addition to discussing the knowledge of this invasive fauna for the Northeast, Southeast and South regions of Brazil. For that there was a search for bibliography in 5 databases - SciELO, Web of Science, Google Scholar, ScienceResearch.com and I3N Brazil Database of the Horus Institute for Environmental Conservation and Development. Three invasive bivalves for the northeastern region of Brazil were counted. When compared to the South and Southeast regions, the Northeast presents a significant amount of research on the ecology of the species Isognomon bicolor (C. B. Adams, 1845) and Mytilopsis leucophaeata (Conrad, 1831), which is very important, because with these results it is possible to track and understand the pathways that make bioinvasions possible. Regarding Perna Perna (Linnaeus, 1758), although there is a discussion about its supposed introduction in Brazilian waters, the species can be considered invasive in Northeastern Brazil.
 KEYWORDS: Invasive species, marine ecosystem, ecology.

MOLLUSKS ON RECRUITMENT PANELS PLACED IN AN OFFSHORE HARBOR IN TROPICAL NORTHEASTERN BRAZIL

Como o objetivo de contribuir para o conhecimento das comunidades marinhas incrustantes, o presente estudo analisou a variação temporal em comunidades de moluscos encontradas em placas de recrutamento trimestrais e anuais instaladas em uma região portuária no nordeste do Brasil. Um conjunto de 30 placas artificiais foi submerso entre os pilares do píer a uma profundidade aproximada de 6 m. A cada três meses, um subconjunto de 15 placas era removido para o exame da biota presente. O segundo subconjunto de 15 placas foi deixado submerso por um ano, e depois removido para análise. No mesmo dia em que as placas eram removidas, elas eram substituídas por novas placas. Doze remoções/reposições de placas foram realizadas de outubro de 2009 a novembro de 2012. Duas classes de Mollusca foram encontradas nos painéis de recrutamento: Gastropoda e Bivalvia. Trinta táxons foram encontrados nas placas trimestrais e 23 táxons nas placas anuais. Duas espécies nãonativas da costa brasileira foram encontradas: Isognomon bicolor e Eualetes tulipa. Nas placas trimestrais, a espécie mais comum e abundante foi a ostra Crassostrea brasiliana e a espécie mais abundante nas placas anuais foi o bivalve Musculus lateralis.

Complex food webs of tropical intertidal rocky shores (SE Brazil) – An isotopic perspective

Knowledge on food web structure, trophic links and energy pathways is essential for the understanding of complex and highly biodiverse tropical ecosystems. Emerging issues related to global change and species invasions call for an urgent advance on this topic. Isotopic analyses were applied to the tropical intertidal rocky shores of Southeastern Brazil, with the aim of 1) describing the general food web structure, 2) estimating food web length, 3) estimating the trophic level of the secondary consumers, and 4) their dependence on different energy pathways. An exceptionally high number of food web nodes (71) was analysed. The maximum trophic level (TL) was 3.3, similarly to what has been previously reported for temperate rocky intertidal ecosystems. Fish were the dominant top consumers (TL > 2.0), along with an important number of gastropods and crustaceans (both crabs and shrimp). Primary consumers were mostly crabs, gastropods and bivalves. Two invasive crustaceans were found among the top consumers, the Japanese peppermint shrimp, Lysmata lipkei (TL = 3.0), and the Indo-Pacific swimming crab, Charybdis hellerii (TL = 2.3). Among the primary consumers, one invasive bivalve was found, Isognomon bicolor. Mixing models showed that the top consumers depend mostly on the macroalgal and pelagic energy pathways. The food web currently established has low dependence on the benthic pathway. Given the important increase in precipitation predicted for this region and the increment in detritus it incurs, this food web is likely to suffer important alterations in the future.

Intertidal vermetid reef as a shelter for invasive bivalves in a tropical bay

Vermetid reef building species play an important role as ecosystem engineers modifying the physical environment, creating microhabitats and affecting local hydro-sedimentary patterns. We explore the association of native vermetid reefs (Petaloconchus varians) with the invasive bivalves Isognomon bicolor and Leiosolenus aristatus. We also examined the different utilization of the reef habitat, since L. aristatus is a boring species, comparing their population structure on sheltered and exposed rocky shores. Ten sites (five sheltered, five exposed) were sampled at Ilha Grande Bay (Rio de Janeiro, Brazil). I. bicolor and L. aristatus were the most frequent with mean densities of 20,000 (±3400) and 2100 (±600) ind.m2, respectively. There were no significant differences (t = 1.41; p = 0.17) between sheltered and exposed sites in relation to the densities of I. bicolor. However, there were significant differences (t = 3.14; p = 0.03) in relation to the densities of L. aristatus, with higher values at exposed sites. Mean size of both species was significantly (p < 0.01) higher in sheltered areas where the vermetid weight was significantly higher (t = 2.36; p = 0.02). Although native vermetid reefs act as a shelter for both invasive bivalves on sheltered and exposed rocky shores, they prevent the growth of I. bicolor which reaches smaller sizes in relation to populations outside of the reefs. Our results indicate that the two invasive bivalves might be differently affected by hydrodynamic processes.

Survey of Bivalve Molluscs forBonamiaspp. and Other Parasitic Pathogens in Florida East Coast Lagoons

A 2007 study of Suminoe (Crassostrea ariakensis) and eastern (Crassostrea virginica) oysters exposed to Indian River Lagoon (IRL), Florida waters revealed the presence of Bonamia spp. in exposed oysters. In 2010, a survey of oysters and other bivalves (n = 721, 18 species) was conducted in the southern IRL (10 sites) and in the more southerly Lake Worth Lagoon (LWL, 3 sites). Polymerase chain reaction (PCR) was used to assess the prevalence of three oyster parasites, Bonamia spp., Perkinsus marinus, and Haplosporidium nelsoni, in collected samples. Histology, fluorescent in situ hybridization (FISH) and standard H&E staining, was used to confirm PCR-positive Bonamia results. Bonamia spp. was detected in eight species (Brachidontes exustus, Crassostrea virginica, Geukensia demissa, Ischadium recurvum, Isognomon alatus, Isognomon bicolor, Mercenaria campechiensis, and Ostrea stentina). The prevalence was 17.3% in the IRL and 9.9% in LWL with 66% of PCR-positive samples subsequently identified as either Bonamia exitiosa or Bonamia perspora. The presence of Bonamia spp. was confirmed by FISH in C. virginica, O. stentina, I. alatus, I. bicolor, and G. demissa, although only C. virginica and O. stentina showed evidence of infection. The presence of P. marinus was detected in eight species (Atrina rigida, B. exustus, C. virginica, G. demissa, I. recurvum, I. alatus, I. bicolor, and O. stentina). The prevalence was 12.4% in the IRL and 7.7% in LWL. The presence of MSX was not detected in any of the collected bivalves. This study confirms the presence of Bonamia spp. and P. marinus in Florida east coast waters and widens the described geographic range for Bonamia spp., and provides further evidence that MSX is unlikely to be found in Florida waters

Colonization record of Isognomon bicolor (Mollusca: Bivalvia) on pipeline monobuoys in the Brazilian south coast

The introduction of alien species in a system affecting native species due to competition for food and space. The purse oyster Isognomon bicolor (Bivalvia, Pteriidae), a potential exotic invader, presents gaps in its distribution and ecology knowledge in Brazilian coast. For this reason, our objective was to investigate the occurrence of this oyster on pipeline monobuoys in Rio Grande do Sul, southern Brazil. Specimens were collected monthly during surveys carried out from March 2010 to June 2011 at the Tramandai Beach, along two pipeline monobuoys, MN-601 and MN-602, randomly from the depths of three and 22 m. We found I. bicolor dwelling on artificial hard substrates present in the Rio Grande do Sul coast, Brazil. This Caribbean bivalve was accidentally introduced to the Brazilian coast by ballast water from ships and, until now; it had not been recorded on the coast of Rio Grande do Sul state, which is under subtropical conditions. The occurrence of I. bicolor in the faunistic surveys accomplished in the Rio Grande do Sul coast represents the first documented record for this species in this region. As this species is a potential exotic invader, with a high dispersal capacity, control measures must be employed to prevent its spread.

DETERMINACION DE METALES PESADOS EN Isognomon bicolor EN LA BAHIA DE SANTA MARTA, COLOMBIA

In order to determine the concentrations of cadmium, copper and lead, four collections of the bivalve Isognomon bicolor were made in two stations in the Bahía de Santa Marta between May 1982 and March 1985. Wide variations in the concentrations both temporally and spatially were observed.

The Impact of Trampling on Reef Macrobenthos in Northeastern Brazil: How Effective are Current Conservation Strategies?

Tropical reefs are used for intensive tourism in various parts of the world. However, few studies have investigated the effect of regular trampling on these fragile ecosystems. The aim of this study was to assess the effect of different conservation strategies (open access, partial protection, and total long-term closure) on intertidal reef tops in Porto de Galinhas and Tamandaré, Pernambuco State, Brazil. Analysis of the macrobenthic community was performed with photo transects and image analysis (CPCe). Twenty-seven transects were surveyed from January to August 2012, in intensively impacted (I) open-access sites, in partially protected (P) sites with occasional, illegal trampling, and in a permanently closed (C) site. In I sites, total live cover was half the cover found in adjacent P sites. The area of bare rock averaged 53.6 and 25.0% in I and P sites, respectively. In the C site, the area of bare rock was only 19.8%. In I and P sites, macroalgae (Palisada perforata) were dominating, while in the C site, the zoanthid Zoanthus sociatus was most abundant. Shell-bearing vermetids (Petaloconchus varians) and bivalves (Isognomon bicolor) were more abundant at the C site, being possible bioindicators for areas with zero or little trampling. Twelve years of total closure produced near-pristine communities in the C site, dominated by zoanthids and fragile mollusks. This study showed that trampling has severe and long-lasting consequences for the structure of these ecosystems.

Temporal Variation of Population Structure of the Invasive <i>Isognomon bicolor</i> (Mollusca, Bivalvia), <i>Brachidontes solisianus</i> (Mollusca, Bivalvia) and <i>Ulva</i> spp. (Chlorophyta, Ulvales) Biomass, Pernambuco - Brazil

Specifically in Piedade reef, where we performed the present study, Isognomon bicolor invasive bivalve showed greater abundance in the mid intertidal band before dominated by the bivalve Brachidontes solisianus and the barnacle Tetraclita stalactifera. However, the abundance and size structure of Isognomon bicolor and Brachidontes solisianus are variable in the local collection related to desiccation and the presence of Ulva spp.. In this context, this study aims to evaluate the population structure of Isognomon bicolor and Brachidontes solisianus from density and shell length data. For that, were randomly collected 3 quadrats of 20 X 20 cm in February and May 2012, dry and rainy seasons respectively. The animals were scraped, and placed in labeled plastic bags, and frozen for later sorting. After sorting the length of the bivalve shells were measured with the aid of caliper, the seaweed Ulva spp. was also screened, dried and weighed. The Chi-Square test was used to assess the difference between the frequency distribution of the different size classes. The bivalves were divided into 10 size classes. The chi-square test detected a significant difference between the population structure of bivalves. Isognomon bicolor had lower density in May 2012 during the drought, while more individuals Brachidontes solisianus were found in May. However the largest proportion of individuals was always between 13-16 mm in both months of collection for Isognomon bicolor and 3 mm for Brachidontes solisianus presenting both bivalve unimodal distribution these sizes could be more resistant to desiccation and predation stress. The Mann-Whitney test showed a lower density for Ulva spp. in May 2012.

Structure of intertidal sessile communities before and after the invasion of Isognomon bicolor (C.B. Adams, 1845) (Bivalvia, Isognomonidae) in southeastern Brazil

Scientists recognize the importance of ecological data prior to invasion by non-native species in order to evaluate changes in the recipient community. Here we assess the potential impact of the invasion of the bivalve Isognomon bicolor (C.B. Adams, 1845) on Brazilian rocky shores through the use of surveys both before and after the arrival of this non–native species. The invader was mostly distributed across the mid and low shore levels of the intertidal zone with relative abundance ranging from 9.0 to 36.7 percent cover. The mid shore, previously dominated by the native barnacle Tetraclita stalactifera (Lamarck, 1818), was co-dominated by this barnacle species and I. bicolor after invasion. The relative abundance of these species, and presumably the interaction strength between them, differed between sites. At the site where I. bicolor reached the highest abundance (around 30% on average), the abundance of T. stalactifera decreased on average 70% compared to baseline values obtained before the I. bicolor invasion. Finally, conspicuous and extensive I. bicolor beds such as those observed in this study have not been reported in its original distribution range. Beds of I. bicolor may create a much more intricate biogenic matrix than the extents of bare rock and barnacle clumps it replaced. This bivalve may act as an ecosystem engineer and, thus a functionally different component of the intertidal community in its invaded range compared to its native distribution.

First records of the non-native bivalve Isognomon bicolor (C. B. Adams, 1845) rafting to the Uruguayan coast

In the southwestern Atlantic Ocean, Isognomon bicolor is an invasive bivalve on rocky shores along the coast of Brazil. We report here records of this species rafting on floating debris in Uruguay (ca. 34° S). Rafting may be an important mechanism for the dispersal of I. bicolor on the coast of Uruguay and elsewhere in the Southernmost Atlantic Ocean and the presence of this invasive species on rocky shores should be monitored.

Proximate composition of marine invertebrates from tropical coastal waters, with emphasis on the relationship between nitrogen and protein contents

The chemical profiles of Desmapsamma anchorata, Hymeniacidon heliophila (Porifera), Bunodosoma caissarum, Renilla muelleri (Cnidaria), Aplysia brasiliana, Eledone massyae, Isognomon bicolor (Mollusca), Echinaster brasiliensis, Echinometra lucunter, Holothuria grisea, Lytechinus variegatus (Echinodermata), and Phallusia nigra (Chordata) were determined. Hydrosoluble protein was the most abundant class of substances for all species, except for the ascidian Phallusia nigra, in which the carbohydrate content was higher. The percentages of hydrosoluble protein (dry weight, dw) varied widely among the invertebrates, ranging from 5.88% (R. muelleri) to 47.6% (Eledone massyae) of the dw .The carbohydrate content fluctuated from 1.3% (R. muelleri) to 18.4% (Aplysia brasiliana) of the dw. For most of the species, lipid was the second most abundant class of substances, varying from 2.8% (R. muelleri) to 25.3% (Echinaster brasiliensis) of the dw. Wide variations were also found for the invertebrates nitrogen content, with the lowest value recorded in the cnidarian R. muelleri (2.02% of the dw) and the highest in the molluscan E. massyae (12.7% of the dw). The phosphorus content of the dw varyed from 0.24% (R. muelleri) to 1.16% (E. massyae). The amino acid composition varied largely among the species, but for most of the species glycine, arginine, glutamic acid, and aspartic acid were the most abundant amino acids, with histidine and tyrosine among the less abundant amino acids. The actual content of total protein in the samples was calculated by the sum of amino acid residues, establishing dw values that fluctuated from 11.1% (R. muelleri) to 66.7% (E. massyae). The proteinaceous nitrogen content was high in all species, with an average value of 97.3% of the total nitrogen. From data of total amino acid residues and total nitrogen, specific nitrogen-to-protein conversion factors were calculated for each species. The nitrogen-to-protein conversion factors ranged from 5.10 to 6.15, with an overall average of 5.45. The use of the specific nitrogen-to-protein conversion factors established here is recommended, since it would yield more accurate determinations of total protein in the species tested in this study.

Estructura comunitaria de bivalvos y gasterópodos en raíces del mangle rojo Rhizophora mangle (Rhizophoraceae) en isla Larga, bahía de Mochima, Venezuela

The Rhizophora mangle roots form a complex ecosystem where a wide range of organisms are permanently established, reproduce, and find refuge. In this study, we assessed the diversity of bivalves and gastropods that inhabit red mangrove roots, in isla Larga, Mochima, Venezuela Sucre state. Bimonthly collections were made from January 2007 to May 2008, in four study areas denominated: South, North, East and West. In each area, five mangrove roots were sampled, and the specimens were obtained. We analyzed a total of 180 roots and a total of 35 bivalve species and 25 gastropod species were found. The most abundant bivalves were: Isognomon alatus, Isognomon bicolor, Ostrea equestris, Crassostrea rhizophorae and Brachidontes exustus; among gastropods, the most common where: Littorina angulifera, (Cymatium pileare and Diodora cayenensis. The months with the highest abundances and number of individuals for both groups were January and July 2007, and March 2008. The mangrove ecosystem in isla Larga, presented a number of individuals and species higher than those reported for other regions in Venezuela and the Caribbean.