Mollusk Composition Research Articles

Mollusks as indicators of historical changes in an estuarine-lagoonal system (Cananéia-Iguape, SE Brazil)

Mollusks recovered from three cores taken from the Cananéia-Iguape estuarine-lagoonal system (São Paulo State, Brazil) were studied. The sampled sediments cover a period beginning approximately two centuries ago and end at the present, including a period when the system suffered significant changes of anthropogenic origin – that is, the construction of an artificial channel connecting the lagoon with a nearby river and with the resulting input of fresh water and contaminants generated from mining activity upstream. The mollusk composition reflects these changes. The more abrupt changes in this composition coincide with the opening of the Valo Grande artificial channel in 1852. Another significant but minor change event was verified for around 1977± one year in areas that were not previously affected, perhaps showing the effect of the closing and reopening of the channel.

Environmental significance of freshwater mollusks in the Southern Pampas, Argentina: to what detail can local environments be inferred from mollusk composition?

The aim of the present contribution is to assess whether the abundance of mollusk species in the Southern Pampas (Argentina), an environmentally homogeneous region, reflect the local conditions of water bodies. In order to test this hypothesis, a comprehensive study was conducted in 30 sites regularly distributed across the region. At each site, the abundance of mollusk species was determined, and a series of physico-chemical measurements taken. Principal Component Analysis (PCA) and Cluster Analysis (CA) were used for the ordination of sampling sites based on the measured environmental variables. In addition, Canonical Correspondence Analysis (CCA) was conducted to explore the relationships between environmental variables and mollusk abundances. Mollusk species were represented by the gastropods Biomphalaria peregrina, Chilina parchappii, Heleobia parchappii, Physa acuta, Pomacea canaliculata, Stenophysa marmorata, Uncancylus concentricus and the bivalve Musculium argentinum. Although aquatic vegetation cover, conductivity, and substrate were among the main parameters influencing mollusk distribution, their effect was insufficient to explain the spatial distribution pattern of the species in a regional scale. It is because the Southern Pampas is a very homogeneous area, and the ranges of these environmental conditions are within the range of ecological tolerance of most of the species represented. Yet, some species resulted good indicators of environmental conditions at local (microhabitat) scale, i.e., particular microhabitats that occur in different water bodies as well. In fact, even distributed in many different water bodies along the Southern Pampas C. parchappii is always linked to lotic environments, and U. concentricus is exclusively restricted to hard substrata. On the other hand, H. parchappii is the only species represented in mesohaline waters and P. acuta appeared to be a good indicator of pollution in the area.

Benthic mollusk composition of some facies in the upper-infralittoral zone of the southern Black Sea, Turkey

The aim of the present study was to describe the mollusk syntaxon associated with Cystoseira barbata and Mytilus galloprovincialis facies, which are widely distributed along the coasts of the Sinop Peninsula, Turkey. Four stations were chosen for each facies at depths of 0.5-5 m, and a total of 32 seasonal samplings were performed with 4 replicate groups between February 2006 and November 2006. As a result of the qualitative and quantitative analyses, the C. barbata facies was shown to be represented by 14 species and 5807 specimens, whereas that of M. galloprovincialis was represented by 11 species and 18,407 specimens. Dominant species of the C. barbata facies were Mytilaster lineatus (56%), Tricolia pullus (18%), Rissoa splendida (12%), and Gibbula adansonii (7%). Dominant species of the M. galloprovincialis facies were, however, Mytilaster lineatus (63%) and Mytilus galloprovincialis (36%). Seasonal water parameters were also measured at the stations. Seasonal and spatial variations in the mollusk fauna were observed and showed the highest values in station 3 and during the summer period.

Dominant benthic mollusks in closed atolls, French Polynesia

We investigated the mollusk fauna of 53 closed lagoons (atolls without passes) among the 83 French Polynesian atolls. These confined lagoons of closed atolls reveal a limited diversity of mollusks but with wide distribution of some species. A few species occur in these lagoons but each lagoon is unique with a particular qualitative mollusk composition related to only 5 species: Tridacna maxima, Pinctada margaritifera, Pinctada maculata, Chama iostoma and Arca ventricosa. Due to the absence or poor data on 14 closed lagoons, our detailed study was limited to 39. We characterised the mollusk fauna of each closed lagoon and attempted to identify group of lagoons with the same dominant mollusk composition. T. maxima, the giant clam, appeared to be the most characteristic species of these confined lagoons with large densities and populations in 32 of the 39 lagoons. P. margaritifera, the mother-of-pearl oyster, also occurs as large populations in 18 lagoons; these two species are of economic importance now as they were in the past. The three other species mentioned above occurred respectively in 25, 28 and 20 lagoons. There are 11 lagoons with original and unique characteristics (their assemblages of dominant species do not occur in any other lagoon), 28 are grouped in 7 categories of assemblages. The most numerous groups contain all 5 species or at least 4 of them. Research topics are suggested in order to understand the ability of each mollusk species to colonize and maintain its dominance in a confined lagoon.

Levantamento de Mollusca, Crustacea e Echinodermata associados a Sargassum spp. na Ilha da Queimada Pequena, Estação Ecológica dos Tupiniquins, litoral sul do Estado de São Paulo, Brasil

Neste trabalho foi realizado o primeiro levantamento da macrofauna de fital da ilha da Queimada Pequena, focalizando o registro das espécies de moluscos, crustáceos e equinodermos associados a Sargassum spp. Para a amostragem da macrofauna associada, foram coletadas aleatoriamente 6 frondes de Sargassum localizadas a 6 m de profundidade, usando-se equipamento de mergulho autônomo. As frondes foram envolvidas em sacos de tecido com malha de 200 mm, mraspadas do substrato, colocadas em recipientes com uma solução de formaldeído 10% e levadas ao laboratório para remoção e identificação da fauna. Quarenta e um táxons foram identificados, havendo dominância de crustáceos peracáridos. Em relação aos Mollusca, a composição específica foi diferente em relação àquela observada na costa norte do estado de São Paulo. Das 16 espécies de moluscos encontradas, apenas os gastrópodes dos gêneros Anachis e Odostomia e os bivalves dos gêneros Musculus e Modiolus são representantes da fauna associada à Sargassum comuns às duas regiões do estado de São Paulo, embora representantes do gênero Fissurela já tenham sido relatados na região de Santos em associação à alga Amphiroa fragilissima. A ocorrência do bivalve exótico Isognomon bicolor também foi confirmada. Os dados obtidos sugerem que a fauna de moluscos pode realmente ser distinta na região norte e sul do estado. No entanto, são necessários estudos mais extensos para confirmar esses resultados e para subsidiar futuras estratégias de manejo dessa unidade de conservação.