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

Abstract

An inventory of macroinvertebrates conducted in the Contas River basin in Northeastern Brazil found 13 species of freshwater mollusks. Most of the community was represented by pulmonate gastropods, including Physa acuta, Drepanotrema anatinum, D. cimex, D. lucidum, Biomphalaria straminea?, Gundlachia radiata?, G. ticaga and Hebetancylus moricandi; the prosobranchs Pomacea archimedis?, Melanoides tuberculata and Littoridina sp. were also found. Bivalves were less diversified, represented only by Pisidium pulchellum? and Eupera simoni?. The taxonomic composition and the small size of many species reflect the intermittent condition of the basin. Additionally, the occurrence of shells of five terrestrial species (Helicina angulata, Gastrocopta pellucida hordeacella?, Beckianum beckianum, Succinea sp. and Systrophiidae gen. et sp. indet.) in the rivers reflects the occasional heavy rainfalls and floods in the region. The invasive gastropod M. tuberculata was the most abundant and widely distributed species. All 13 species were found in the lower course, in the Atlantic Forest region, and most, but not all, were recorded in the upper course, in the Caatinga region. The distribution and the occurrence of the bivalve species exclusively in the Atlantic Forest region indicate that the locally higher annual precipitation provides favorable conditions for the survival of these mollusks, such as a more stable hydroperiod. Resumo: Treze espécies de moluscos de água doce foram encontradas em um inventário de macroinvertebrados realizado ao longo da bacia do Rio de Contas, no Nordeste do Brasil. A maioria da comunidade foi representada por gastrópodes pulmonados, como Physa acuta, Drepanotrema anatinum, D. cimex, D. lucidum, Biomphalaria straminea?, Gundlachia radiata?, G. ticaga e Hebetancylus moricandi, embora prosobrânquios, como Pomacea archimedis?, Melanoides tuberculata e Littoridina sp. também tenham sido encontrados. Bivalves foram menos diversificados, e foram representados por Pisidium pulchellum? e Eupera simoni?. A composição taxonômica e o pequeno tamanho alcançado por muitas espécies refletem a condição intermitente da bacia. Além disso, a ocorrência de conchas de cinco espécies terrestres (Helicina angulata, Gastrocopta pellucida hordeacella?, Beckianum beckianum, Succinea sp. e Systrophiidae gen. et sp. indet.) dentro dos rios reflete as fortes chuvas e inundações que ocorrem ocasionalmente na região. O gastrópode invasor M. tuberculata foi a espécie mais abundante e bem distribuída. Todas as espécies foram encontradas no curso inferior, na região da Mata Atlântica, e a maioria, mas não todas, foram registradas no curso superior, na região da Caatinga. Esta distribuição e a ocorrência das espécies de bivalves exclusivamente na região da Mata Atlântica indicam que a maior precipitação anual desta região fornece condições favoráveis para a sobrevivência destes moluscos, como um hidroperíodo mais estável. Palavras-chave: Região Neotropical, Mata Atlântica, rios intermitentes, moluscos invasores, Bahia.

Malacofauna of lotic environments in the Northeast and Brazilian semiarid region: current knowledge and new records

“…Therefore, the conditions imposed by the drought in the semiarid can hinder their establishment. Different from gastropods, these bivalves commonly colonize deeper places with fine sediments and need more dissolved oxygen (Kotzian & Amaral 2013). This is the first record of P. dorbignyi to the state of Piauí.…”

“…In general, species of the genus Drepanotrema are drought-tolerant, often found in temporary water bodies, which are occasionally flooded (Pointier & David 2004, Kotzian & Amaral 2013. Considering its short life cycle, they can quickly reestablish populations with the return of rain (Pointier & David 2004).…”

“…Unlike pulmonary gastropods, Sphaeriidae bivalves are not well adapted to seasonally unfavorable environmental conditions, preferring more stable hydroperiods (Kotzian & Amaral 2013). Therefore, the conditions imposed by the drought in the semiarid can hinder their establishment.…”

“…Despite its great diversity and importance in freshwater ecosystems from the semiarid region, these animals are poorly studied. Studies on this group in Brazilian semiarid are still incipient and do not emphasize its importance to regional biodiversity (Abílio et al 2006, Kotzian & Amaral 2013, 2020b.…”

Freshwater mollusks from three reservoirs of Piauí, northeastern Brazil

“…Biomphalaria straminea is widely distributed in Brazil, as a result of their ability to adapt to different climates and ecological conditions (Paraense, 1986). According to Kotzian & Amaral (2013), B. straminea occurrence in water bodies of the semiarid region can be explained by their tolerance to dry periods, thus severe semi-arid conditions are not barriers to their survival. This species is the most important host of Schistosoma mansoni (Sambon, 1907) in Brazilian Northeastern.…”