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Avoidance and recolonization responses of the gastropod Olivella semistriata exposed to coastal sediments

Abstract:

The spatial distribution of the snail Olivella semistriata along the Ecuadorian coast near the city of Manta seems to be influenced by urban discharges. This observation leads us to hypothesize that contamination might determine inhabitable areas for the snails. Therefore, the ability of the snails to detect the local contamination and react by moving away from contaminated sediment has been assessed. In addition, the ability of the snails to recolonize contaminated sediment under recovery was also studied. Six sediment samples (El Murciélago beach - reference point, El Puerto, La Poza, Río Burro, Los Esteros, and Río Muerto) were taken and tested in two different assays: avoidance and recolonization. Assays were performed in a non-forced exposure system in which a contamination gradient was formed by mixing the test sample and the reference sediment. Avoidance was more intense in the samples from Río Burro and Río Muerto. In the recolonization assays, the reference sample was always preferred regarding all test samples. As there is no physical barrier to prevent the displacement of the organisms among the studied areas, the absence (visual field observation) of snails in the sediment from Rio Burro and Rio Muerto is suggested to be due to the ability of the organisms to avoid these areas. The present data indicate that contaminants can affect the spatial distribution of the snails by triggering avoidance or even preventing the colonization of contaminated areas, acting as a chemical barrier that might isolate populations.