Quantitative fidelity of recent freshwater mollusk assemblages from the Touro Passo River, Rio Grande do Sul, Brazil

Abstract

This study represents one of the first contributions to the knowledge on the quantitative fidelity of the recent freshwater molluscan assemblages in subtropical rivers. Thanatocoenoses and biocoenoses were studied in straight and meandering to braided sectors, in the middle course of the Touro Passo River, a fourth-order tributary of the Uruguay River, located in the westernmost part of the State of Rio Grande do Sul. Samplings were carried out through quadrats of 5 m², five in each sector. A total area of 50 m² was sampled. Samplings were also made in a lentic environment (abandoned meander), with intermittent communication with the Touro Passo River, aiming to record out-of-habitat shell transportation from the lentic communities to the main river channel. The results show that, despite the frequent oscillation of the water level, the biocoenosis of the Touro Passo River shows high ecological fidelity and undergoes little influence from the lentic vicinal environments. The taxonomic composition and some features of the structure of communities, especially the dominant species, also reflect some ecological differences between the two main sectors sampled, such as the complexity of habitats in the meandering-sector. Regarding the quantitative fidelity, 60% of the species found alive were also found dead and 47.3% of the species found dead were also found alive, at river-scale. However, 72% of the dead individuals belong to species also found alive. This value might be related with the good rank order correlation obtained for live/dead assemblages. Consequently, the dominant species of the thanatocoenoses could be used to infer the ecological attributes of the biocoenoses. The values of all the indexes analyzed were very variable in small-scale samplings (quadrat), but were more similar to others registered in previous studies, when they were analyzed in a station and river scale.

Diversity and distribution of mollusks along the Contas River in a tropical semiarid region (Caatinga), Northeastern Brazil

“…Thus, many of the specimens found in this study could have been carried in from lentic marginal environments (e.g., small açudes) or from terrestrial environments into the river, during the rainy period that preceded the sampling. This process has been reported for species of Biomphalaria and Pomacea in other parts of the country (Chieffi & Moretti 1979, Martello et al 2006. The accidental presence of terrestrial gastropods in the rivers studied supports this supposition.…”

Huesser Horizon: A Lake and a Marine Incursion in Northwestern South America During the Early Miocene

“…Deformation and fragmentation would have resulted from compaction of sediments under lithostatic forces (Martello et al, 2007), and most corrasion was caused by postburial dissolution or precipitation. Differential effects of deformation, fragmentation, and corrasion, however, are due to conditions that originated during the accumulation of assemblages.…”

Distribución y partición aditiva de la diversidad de las comunidades de moluscos de agua dulce en arroyos del Sur de Brasil.

“…Many freshwater mollusks are widely tolerant to environmental conditions, such as desiccation (Jokinen, 1978) and low water oxygen content (McMahon, 1983). In Southern Brazil, freshwater mollusk species are tolerant to variations in some important abiotic factors, such as grain size and presence of macrophytes (see review by Martello, Kotzian & Simões, 2006). In general, the microbasins, as well as many of the studied sites, showed similar values for abiotic factors such as pH and dissolved oxygen.…”