Marine free-living nematodes in semiarid inland waters

Abstract

Aim This study reports the occurrence of five Nematoda genera previously considered as exclusively marine in inland waters. Methods Sediment samples were taken, weekly, during nine weeks, at a small spring at the Horto Florestal Olho D’Água da Bica, Cuité, PB, ca. 130 km away from the shoreline, between March and May 2016 and fixed in 4% formalin. Nematodes were sorted by manual elutriation through sieves with 0.5 and 0.045 mm and slides were prepared. Results The sediment was classified as coarse sand, with organic matter content ranging between 2.73 and 13.32%, temperature between 27-28°C and constant salinity of 6. From 315 nematodes were sampled among which 18 were from five genera previously thought to be exclusively marine were found. Bolbolaimus was the most common, found in 11.1% of the samples, followed by Gomphionema (3.7%), Rynchonema (7.4%), Prorynchonema (7.4%) e Sabatieria (3.7%), representing 5.7% from total of nematofauna. These genera are widely distributed worldwide, but had never been recorded from inland environments. Conclusions This study contributes with the distributional knowledge of free-living nematodes. From literature data, these genera are not restricted by low salinity, and can be found in estuarine and/or brackish water environments and body water with direct connection to the sea. In any case, the presence of marine genera in this region which is >130 km away from the nearest shoreline is noteworthy, highlighting the importance of studying nematodes from these poorly known semiarid water bodies. These new occurrences raise questionings about the dispersal mechanisms that certified the colonization of these nematodes in the semiarid.